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. 2023 Jun 1;42(12):1411–1424. doi: 10.1021/acs.organomet.3c00056

Expanding the Utility of β-Diketiminate Ligands in Heavy Group VI Chemistry of Molybdenum and Tungsten

Daniel Leitner †, Benjamin Wittwer †, Florian R Neururer †, Michael Seidl †, Klaus Wurst †, Frank Tambornino ‡, Stephan Hohloch †,*
PMCID: PMC10302891  PMID: 37388273

Abstract

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We report the synthesis of 17 molybdenum and tungsten complexes supported by the ubiquitous BDI ligand framework (BDI = β-diketiminate). The focal entry point is the synthesis of four molybdenum and tungsten(V) BDI complexes of the general formula [MO(BDIR)Cl2] [M = Mo, R = Dipp (1); M = W, R = Dipp (2); M = Mo, R = Mes (3); M = W, R = Mes (4)] synthesized by the reaction between MoOCl3(THF)2 or WOCl3(THF)2 and LiBDIR. Reactivity studies show that the BDIDipp complexes are excellent precursors toward adduct formation, reacting smoothly with dimethylaminopyridine (DMAP) and triethylphosphine oxide (OPEt3). No reaction with small phosphines has been observed, strongly contrasting the chemistry of previously reported rhenium(V) complexes. Additionally, the complexes 1 and 2 are good precursors for salt metathesis reactions. While 1 can be chemically reduced to the first stable example of a Mo(IV) BDI complex 15, reduction of 2 resulted in degradation of the BDI ligand via a nitrene transfer reaction, leading to MAD (4-((2,6-diisopropylphenyl)imino)pent-2-enide) supported tungsten(V) and tungsten(VI) complexes 16 and 17. All reported complexes have been thoroughly studied by VT-NMR and (heteronuclear) NMR spectroscopy, as well as UV–vis and EPR spectroscopy, IR spectroscopy, and X-ray diffraction analysis.

Introduction

β-Diketiminate (BDI) ligands are among the most explored ligands in modern organometallic and coordination chemistry.1−3 Due to their unique combination of simple synthetic accessibility, following a facile but highly modular condensation protocol, and their steric and electronic tunability,4,5 these ligands have played a vital role in the isolation of long-sought intermediates and highly reactive species. Thus, these ligands have found widespread applications all over the periodic table spanning from main group chemistry, covering both s-6−11 and p-block12−14 elements, to d-block transition metal chemistry,15−23 culminating in f-block chemistry.24−28 Focusing on their chemistry with the early transition metals,29 these breakthroughs included the isolation of a plethora of reactive metal–ligand multiple bonds. Mindiola and co-workers for example reported the isolation of titanium nitrido30,31 and phosphinidene32,33 complexes or a vanadium phosphinidene complex,34 while Arnold and co-workers recently explored the versatile chemistry of niobium35−43 and rhenium BDI complexes.44−48 The latter included a rare example of a noncarbonyl stabilized rhenium(I) cyclopentadiene complex,49,50 which has also been proven to be a potent candidate for the formation of new metal–metal bonds, e.g., a Re–Zn–Zn–Re complex,51 or Cp bridged tetranuclear actinide complexes.52 Apart from that, a plethora of catalytic reactions have been elucidated using BDI supported early transition metal complexes, e.g., nitrene transfer reactions to yield carbodiimides40 or hydrodefluorinations39,41,53 both catalyzed via low-valent niobium(III)39−41 or titanium(III)53 complexes. However, looking at the numerous explorations of the BDI ligand framework in group IV,30−33,54−58 group V,29,34,37,42,43,59−61 and group VII44−49,51,52,62−69 metal chemistry, group VI metals (except for chromium70−83) have been mostly neglected in this research. Hitherto, there are only three literature reports on BDI supported molybdenum complexes: two on imido alkylidene complexes by Schrock84,85 (Figure 1 A–C) and one covering the synthesis of dioxo and bis-imido complexes (Figure 1D–F) by Mösch-Zanetti.86 Turning to tungsten, only two β-diiminato complexes (Figure 1G,H) have been reported so far by Filippou and co-workers.87 However, these do not form via the direct installation of a BDI ligand on a tungsten complex, but by the addition of an organic nitrile onto a Cp-supported aza-allyl tungsten(II) complex. Given the fundamental meaning of molybdenum and tungsten in catalysis88−98 and small molecule activation,99,100 especially nitrogen,101−105 the use of BDI ligands might be interesting to develop new paths in the chemistry of these elements.

Figure 1.

Figure 1

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Overview of previously reported BDI complexes of molybdenum by Mösch-Zanetti (A–C)86 and Schrock (D–F)84,85 and the sole tungsten complex (G and H) by Filippou et al.87

Our group has recently started to explore the chemistry of redox-active dipyrrin ligands in high-valent molybdenum bis-imido chemistry.106 Simultaneously, Betley and co-workers reported high-valent chromium (bis-)imido complexes,107 generated through the redox-versatility of low-valent chromium dipyrrin complexes. In both these reports it becomes obvious that dipyrrin ligands seem to mimic the coordination chemistry of BDI ligands very well108 but offer larger potential for further applications of these systems, e.g., in photo- and redox-chemistry and suppressing catalyst deactivation pathways. However, given the lack of BDI reference complexes discussed above, we aim to expand our investigations toward the scope and limitations of BDI ligands to be able to further explore the differences and similarities between these two important ligand types in early transition metal chemistry.

Results and Discussion

Given the observed preference of the +V oxidation state over +VI in molybdenum BDI complexes,86 we investigated the less Lewis-acidic molybdenum(V) and tungsten(V) mono-oxo complexes. Synthesis was achieved by mixing LiBDIR (R = Dipp, Mes) and the oxo trichloride precursors MOCl3(THF)2 (M = Mo, W) in THF at −40 °C and let proceed at RT overnight. This procedure gave access to complexes 1–4 (Scheme 1) in yields of 58–88% and is scalable to up to 10 g for 1 and 2. Due to the inherent paramagnetism of the complexes, no characteristic NMR signals could be observed (Figure S1–S4). The Evans method revealed magnetic moments of 1.75, 1.30, 1.61, and 1.37 μB for 1–4 respectively, which is in line with a d1 configuration. Furthermore, the EPR spectra of all complexes agree with metal centered S = 1/2 spin systems (Figure 2, bottom) and revealed giso-values of 1.963 (aiso = 130 MHz), 1.844 (aiso = 244 MHz), 1.962 (aiso = 130 MHz), and 1.841 (aiso = 249 MHz) for 1–4, respectively. X-ray quality crystals were grown from concentrated diethyl ether solutions for all four complexes. The complexes 1 and 2, as well as the complexes 3 and 4 crystallize isostructurally in the orthorhombic space group Pnma with half a molecule in the asymmetric unit (for 1 and 2) or the triclinic space group P1̅ with a full molecule in the asymmetric unit (for 3 and 4). In all complexes, the metal center exhibits a square pyramidal coordination geometry, displaying τ5 values of 0.00 for 1 and 2 and 0.13/0.12 for 3 and 4 respectively. The BDI ligand is symmetrically bound to the metal center, displaying similar metal nitrogen distances of 2.090(3) and 2.100(3) Å in complex 1 and 2 and 2.097(2)/2.089(2) and 2.084(2)/2.088(3) Å in complex 3 and 4. This similarity in bond lengths between the molybdenum and the tungsten complexes can also be found in the M1–O10 distances lying at 1.640(4), 1.693(4), 1.657(2), and 1.681(2) Å in 1–4 and is a direct result of the lanthanide contraction and similar ionic radii of MoV and WV. Overall, the structural parameters are also comparable to the recently studied BDI complexes of niobium(V) and rhenium(V).29,39,44,60 For further structural parameters, please refer to the Supporting Information, Table S1–S3.

Scheme 1. Synthesis of Molybdenum(V) and Tungsten(V) BDI Complexes with Variable Steric Demand.

Scheme 1

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Figure 2.

Figure 2

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Molecular structures of the monometallic molybdenum(V) and tungsten(V) complexes 1–4. Solvent molecules and hydrogen atoms have been omitted for clarity. Ellipsoids are shown at a probability level of 50% (top). EPR spectra of all complexes measured at 298 K (black line) and simulated (red line) (bottom).

Considering the fact that the BDIDipp complexes 1 and 2 can be accessed more conveniently and in higher yields, we examined their further reactivity. Initial focus was laid on their reactivity toward neutral donor systems such as DMAP, triethylphosphine oxide (OPEt3), isocyanides, and small phosphines (PEt3 or PMe3). Upon mixing solutions of 1 or 2 with DMAP or OPEt3 in diethyl ether an instant color change of the solution was observed (see Experimental Section) concomitant with the formation of a reddish precipitate. The precipitate was filtered off, but unfortunately due to its low solubility no further characterization of this material was possible. The remaining solutions were evaporated and gave access to the DMAP (5 and 6) and OPEt3 adducts (7 and 8) in yields between 33% and 60% (Scheme 2). As expected, all complexes are paramagnetic (Figure S5–S8) displaying effective magnetic moments ranging from 1.51 to 1.82 μB indicative for a d1 configured metal center. Room temperature EPR spectra also showed the expected signals for an unpaired electron located at the respective molybdenum and tungsten centers (Figure S52–S55). X-ray quality crystals of the adducts 5–8 were grown from concentrated diethyl ether solutions at room temperature over 2 days. The corresponding molybdenum and tungsten adducts crystallize isostructurally in the monoclinic space groups P21/n for 5 and 6 and C2/c for 7 and 8 with one molecule of the respective complex in the asymmetric unit. All complexes display a distorted octahedral environment around the metal center with the trans O10–M1–Cl1 angles being 165.62(7)°, 167.43(14)°, 171.97(6)°, and 172.95(12)° in 5, 6, 7, and 8 (Figure 3). Notably, Cl1 oriented trans to the oxo ligand experiences a strong trans-influence, as its distance to the metal center increases by 0.06–0.1 Å to 2.453(3), 2.4594(16), 2.4945(6) and 2.4946(13) Å compared to 2.383(2), 2.3753(14), 2.3946(6), 2.3935(13) Å for M1–Cl2 for 5, 6, 7 and 8 respectively. The additional donor ligands are located trans to a BDI nitrogen donor and cis to the oxo ligand (Figure 3) and display distances of 2.256(3) and 2.237(5) Å for M1–N30 in the DMAP adducts 5 and 6, and M1–O40 distances of 2.1117(15) and 2.104(3) Å in the triethylphosphine oxide adducts 7 and 8. The substantially contracted M1–O40 distances (shorter by ca. 0.1 Å) in 7 and 8 compared to the M1–N30 distances in 5 and 6 is in line with OPEt3 being the stronger donor, as it would be expected for oxophilic transition metals. Similar conformations have also been reported for rhenium oxo BDI adducts.44

Scheme 2. Reactivity between Complexes 1 and 2 and Neutral Lewis Bases.

Scheme 2

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Ar = Dipp.

Figure 3.

Figure 3

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Molecular structures of the molybdenum and tungsten DMAP and OPEt3 adducts 5–8. Hydrogen atoms and lattice solvent molecules have been omitted for clarity. Ellipsoids are shown at a probability level of 50%.

In contrast, no defined reaction took place between complexes 1 and 2 and xylyl or tert-butyl isocyanides. Instead, complex reaction mixtures were observed employing different reaction conditions. Also, with triethylphosphine (PEt3) no reaction was observed. Both are surprising, since the corresponding niobium38,109 and rhenium44,110 adducts both have been reported. Furthermore, heating samples containing PEt3 to 100 °C did not facilitate any visible amount of OAT (oxygen atom transfer) reactivity in these systems (see Figure S24 for NMR monitoring of the reaction between 1 and PEt3), contrasting the rhenium case.44 The inertness of complexes 1 and 2 toward small phosphines is further surprising, since other molybdenum complexes can be easily deoxygenated under similar conditions.95,111 A possible explanation for this could be, that the deoxygenation of 1 and 2 would result in a corresponding M(III) oxidation state, which is highly reducing for both, molybdenum and tungsten. Thus, it is possible that stronger reductants (stronger oxygen atom acceptors) are needed to promote this reaction.

Next, salt metathesis reactions, with complexes 1 and 2 were investigated, aiming toward the formation of more complex and reactive structures (Scheme 3). Independent from the equivalents used (1 or 2), the reaction between 1 or 2 with lithium mesitolate (LiOMes) resulted in the formation of the monomesitolate complexes 9 and 10 (Scheme 3). Even under forcing conditions (50 °C overnight), it was not possible to replace the second chloride ion by an additional phenolate ligand. We assume that this is related to steric crowding caused by the BDIDipp supporting ligand. To support this hypothesis, we also performed the reaction with the BDIMes complex 3 (vide infra) and two equivalents of LiOMes. As expected, this led to the clean and direct isolation of the bis-mesitolate complex 11. All mesitolate complexes display the expected features of a paramagnetic d1 configured metal center with magnetic moments of 1.57, 1.26, and 1.63 μB for 9, 10, and 11 (Figure S9–S11) as well as the expected metal centered EPR signals (Figure S56–S58). Unambiguous proof for the identity of the mesitolate complexes was provided by X-ray structure analysis. X-ray quality crystals of all complexes were grown from concentrated diethyl ether solutions over several days. Complex 8 crystallizes in the orthorhombic space group Pbca, complex 10 in the triclinic space group P1̅ and complex 11 in the monoclinic space group P21/n, all with one molecule in the asymmetric unit. In all complexes, the metal center is penta-coordinated by the BDI ligand, the oxo ligand and the anionic mesitolate/chloride ligands. Notably, with a τ5 value of 0.30 and 0.24 for 9 and 10, compared to 0.03 in 11 the monosubstituted complexes show a more distorted square-pyramidal environment around the metal center. However, this might not only be related to the monosubstitution but also to the higher steric congestion caused by the Dipp group in 9 and 10 compared to the Mes-substituents in 11. At the same time, this “asymmetry” causes a minor distortion in the bond lengths toward the BDI ligands. While in the previous cases (1–8), the BDI-metal distances were symmetric (deviating only by 0.02 Å in average), for 9 and 10 differences up to 0.08 Å between M1–N1 and M1–N2 can be observed. The metal mesitolate distances are 1.932(4) in 9, 1.938(3) in 10, and 1.9390(16)/1.9356(16) in 11 and are thus in the range of previously reported molybdenum mesitolate complexes (Figure 4).94

Scheme 3. Salt Metathesis Reactivity between Complexes 1, 2, and 3 with Mesitolate, Tolyl-amide, and Bis-tolyl-amide.

Scheme 3

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Figure 4.

Figure 4

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Molecular structures of the mesitolate complexes 9–11 and the bis-p-tolyl-amide complex 12. Hydrogen atoms and solvent lattice molecules have been omitted for clarity. Ellipsoids are shown at a probability level of 50%.

Since mesitolate is sterically too crowded to be installed twice on the sterically more demanding complex 1 with the BDIDipp supporting ligand, we turned our focus to smaller nucleophiles. Indeed, when reducing the steric bulk of the coligands from mesityl to p-tolyl as in p-tolylamide, the clean formation of the corresponding bis-p-tolylamide complex 12 is observed. Similar to the mesitolate complexes discussed before, the complex exhibits a d1 configuration displaying an effective magnetic moment of 1.52 μB and a g-value of 1.962 (see Figure S12 and S59 for NMR and EPR). The EPR spectrum shows hyperfine coupling (aiso(H) = 17.2 MHz) to two NH protons, further supporting a successful salt metathesis reaction. Unambiguous proof for the formation of 12 was obtained by X-ray diffraction analysis from single crystals grown from concentrated pentane solutions within 10 min at room temperature. Similar to the other complexes the molybdenum center is penta-coordinated but due to the steric repulsion between the ligands, its geometry is in between of square pyramidal and trigonal bipyramidal displaying a τ5 value of 0.45. The molybdenum amido distances are 1.984(2) and 2.006(2) Å for Mo1–N40 and Mo1–N50. Thus, these are substantially shortened compared to the BDI nitrogen distances at 2.118(3) and 2.2098(19) Å for Mo1–N1 and Mo1–N2 respectively.

In all complexes described so far, the geometry around the metal center is square-pyramidal (except for 12), with the oxo ligand O10 taking up the apical position of the coordination polyhedron. This situation changes if sterically more encumbering groups are introduced. Both 1 and 2 react smoothly with lithium di-p-tolyl-amide (LiN(Tol)2) giving access to dark green and purple colored complexes for molybdenum (13) and tungsten (14) (Figure 5). Both 13 and 14 show the expected d1 electronic structure by Evans method and EPR spectroscopy (see Experimental Section and Figure S13–S14 and S60, S61 for more information). It should be emphasized at this point, that the salt metathesis reactions leading to 13 and 14 give higher yields and cleaner conversions if the reaction is performed in toluene instead of diethyl ether. X-ray quality crystals grown from concentrated diethyl ether solutions and subsequent diffraction analysis, however, revealed that the metal centers are now coordinated in a trigonal-bipyramidal fashion displaying τ5 values of 0.89 (13) and 0.74 (14). Strikingly, the oxygen atom O10 is not in the apical position anymore, but has moved into the equatorial position of the trigonal bipyramid while the di-p-tolyl amide ligand occupies the expected position of O10. Overall, the di-p-tolyl amide, one BDI nitrogen and the oxo ligand occupy the equatorial position, while the other BDI nitrogen donor and the remaining chloride form the axial ligands. The change in conformation has no influence on the M1–O10 distances which are 1.662(2) and 1.669(9) Å in 13 and 14, compared to 1.640(4) and 1.693(3) Å in 1 and 2. We assume that the square pyramidal ligand arrangement is caused by the strong steric repulsion between the BDI and the p-tolylamide ligand. However, with M1–N40 distances of 1.995(4) and 1.984(14) Å these are slightly shorter compared to other molybdenum/tungsten–secondary amide interactions reported in the literature (2.00–2.12 Å).112−122 Further studies on the influence of this rearrangement on the reactivity of the oxo ligand (e.g. towards small phosphines)44 are currently ongoing.

Figure 5.

Figure 5

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Molecular structures of the di-p-tolyl-amide complexes 13 and 14. Hydrogen atoms and solvent lattice molecules have been omitted for clarity. Ellipsoids are shown at a probability level of 50%.

We have also tried other nucleophiles (thiomesitolate, mesitylphosphanide) but these reactions resulted in the formation of complex (paramagnetic) mixtures, from which no defined material was isolated. Also, the synthesis of a dimethyl analogue employing methyl lithium or methyl magnesium halides have failed so far.

Finally, we examined the electrochemical properties of complexes 1 and 2 with emphasis on the question: Can low-valent molybdenum(IV) and tungsten(IV) complexes be accessed? The isolation of such a species is of major interest for future applications of the BDI complexes in small molecule activation and catalysis. Cyclic voltammograms of 1 and 2 were recorded in MeCN (0.001 M analyte; 0.2 M NBu4PF6 electrolyte) and showed that both complexes can indeed be reduced but at very different potentials (Figure 6). The molybdenum complex 1 shows a reductive process at −0.95 V vs. Fc/[Fc]+ and a second one at −2.35 V vs. Fc/[Fc]+. Upon reoxidation, we found the second reduction to be irreversible. However, for the first reduction, reoxidation at −0.27 V vs Fc/[Fc]+ is observed. Although at 680 mV the peak-to-peak separation is relatively large, the Randles–Sevcik plot (Figure S49 and S50) is indicative of a reversible process. For complex 2 only one irreversible process is observed at −1.27 V vs. Fc/[Fc]+. Turning to the oxidative side, both complexes can be irreversibly oxidized at +0.79 V for 1 and +0.46 V vs. Fc/[Fc]+ for 2.

Figure 6.

Figure 6

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Cyclic voltammogram of complex 1 (top) and complex 2 (bottom), recorded in 0.2 M NBu4PF6 solution in MeCN at 298 K. Analyte concentration: 0.001 M. Scan Rate: 100 mV s–1.

Consequently, we attempted the chemical facilitation of these redox-processes. Even though the cyclic voltammograms indicate that high-valent molybdenum(VI) and tungsten(VI) complexes might be accessible we have not yet been able to isolate any useful products from the oxidation of 1 and 2 using various oxidizing reagents such as silver(I) salts, trityl chloride, tribromide salts, or PhICl2. This is in line with the results by Mösch-Zanetti and co-workers, showing that the combination of oxo-ligands in molybdenum(VI) ions and BDI ligands make a nonideal fit.86 Reductions of the complexes proved to be more successful. Mixing complex 1 with 1.5 equiv of potassium graphite (KC8) in THF and subsequent stirring overnight, results in a color change from dark green to light green/yellow and large orange/yellow blocks can be isolated after crystallization from pentane. 1H NMR studies revealed the presence of two diamagnetic species in solution in a 1:0.7 ratio (determined via the characteristic BDI backbone proton; Figure S15). The presence of a diamagnetic complex would be expected for a d2 configured molybdenum(IV) center and is in line with related d2-configured rhenium complexes.44 VT-NMR between 25 and 70 °C show that the ratio between the signals changes from 1:0.7 to 1:0.88, pointing to the presence of two isomers of the same species (Figure S16 and S22). The formulation of two isomers is also consistent with the fact, that 1H-DOSY measurements indicated the same diffusion coefficient for these two species (Figure S17). Given the structural information on two C2-symmetric species by 1H NMR spectroscopy we assume that the two possible isomers are the dimeric complexes 15-cis and 15-trans, whereby cis and trans refers to the orientation of the terminal metal oxo function (Scheme 4). The presence of two isomers is also supported by elemental analysis fitting perfectly for the molecular formula of complex 15. X-ray diffraction analysis revealed the presence of a chloride bridged dimer showing the proposed cis–trans isomers with respect to the oxo orientation in a 95:5 ratio with the cis isomer being the minor one. Please note that even though the isomeric ratio in the crystal differs from the one determined in solution, this might also be related to crystal packing and picking effects. We have not checked all crystals obtained for their isomeric ratios. Complex 15 crystallizes in the monoclinic space group P21/n with half a molecule in the asymmetric unit (Figure 7). The molybdenum–molybdenum distance was found to be 3.869(1) Å ruling out any direct interaction between the two molybdenum centers. The chloride bridge is almost symmetric displaying Mo–Cl distances of 2.4648(5) and 2.4841(5) Å. In line with the reduction of the metal center, i.e., an increase of its ionic radius, the molybdenum BDI-nitrogen distances increase from 2.090(3) Å in complex 1 to 2.1110(16) and 2.1184(16) in complex 15. Similarly, the Mo1–O10 oxo distance slightly increases from 1.640(4) in 1 to 1.6585(14) Å in 15. This is also in line with other molybdenum(IV) oxo complexes reported so far.123−132

Scheme 4. Synthesis and Attempt to Synthesize Low-Valent Molybdenum and Tungsten(IV) Complexes Supported by BDI Ligand Frameworks Using Potassium Graphite as a Reductant.

Scheme 4

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Ar = Dipp.

Figure 7.

Figure 7

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Molecular structures of the complexes 15, 16, and 17 (left to right) isolated after reduction of complexes 1 and 2 by KC8. Please note that for complex 15, only the trans isomer is shown. Hydrogen atoms, additional lattice solvent molecules, and iPr groups of the Dipp substituents have been omitted for clarity. All ellipsoids are shown at a probability level of 50%.

Turning to the tungsten complex 2 reduction under the same conditions applied for the reduction of complex 1 to 15 resulted in the formation of a complex product mixture (Figure S23), which could not be further separated. However, we were able to grow minor quantities of two different compounds (inseparable from each other) from the reaction mixture, giving some insight into its outcome (Figure 7). The first crystal (complex 16) consisted of a dinuclear, oxo-bridged tungsten oxo and tungsten imido unit, on which the BDI ligand remained intact on the tungsten oxo-fragment, but has decomposed to a MAD ligand (MAD = 4-((2,6-diisopropylphenyl)imino)pent-2-enide) via a nitrene transfer reaction on the tungsten imido side. We believe that at least one of the additional oxo ligand, bridging the two tungsten centers comes from residual water in the crystallization solvent. Overall, counting the anionic charges present in complex 16, the two tungsten centers have the formal +V oxidation state. This is in line with the W–W distance of 2.663(3) Å, indicating a weak bond between the two tungsten centers and a d1–d1 interaction. The bond lengths within the tungsten oxo bridges range from 1.916(4)–1.976(4) Å being substantially longer than the terminal oxo distance, 1.704(4) Å in 2. These values are in accordance with the literature for other diamond-core μ-O,O bridged tungsten(V) complexes.133−140 The tungsten imido distance was found to be 1.750(5) Å, which is also in line with previously reported tungsten Dipp-imido complexes.141−150 While the exact mechanism of the formation of complex 16 is unclear, the formation of the other crystallized reaction product can be rationalized more easily. Complex 17 is a dimeric diamond-core μ-O,O complex. However, contrasting complex 16, both BDI ligands have been degraded to the MAD ligand framework by nitrene transfer reaction, resulting in the formation of two oxo-imido tungsten units, which are bridged via the oxygen atoms. In addition, one chloride ion remains on each tungsten atom. Overall, both tungsten atoms are in the +VI oxidation state and we propose the following reaction: Initial reduction of WV to a transient WIV complex takes place. This WIV complex is not stable and undergoes a two-electron oxidative nitrene transfer reaction, thus degrading the BDI ligand and forming the MAD ligand (Scheme 5).

Scheme 5. Proposed Reaction Sequence to the Formation of Complex 17 by One-Electron Reduction of Complex 2.

Scheme 5

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Nitrene transfer reactions are commonly observed with BDI ligands, especially with low-valent early transition metals,3 e.g., titanium,151−156 niobium,35,36,109 and rhenium.44 Complex 17 crystallizes in the triclinic space group P1̅ with half a molecule in the asymmetric unit. A W1–W1 distances of 3.1742(14) Å clearly rules out any direct bonding between the two tungsten centers. Each tungsten center is hexacoordinated in a distorted octahedral coordination environment by the MAD ligand, the two bridging oxides, the new imido ligand and the chloride ligand. The tungsten imido distance of 1.764(12) Å for W1–N40 is substantially longer as in the terminal oxo complexes reported here (between 1.65–1.69 Å) but matches well with previously reported Dipp-imido tungsten complexes (1.73–1.77 Å in average).141,143,148,149,157,158 The oxo bridge is asymmetric with W1–O10 distances of 1.801(10) and 2.220(11) Å. These distances are slightly longer compared to the tungsten(V) dimer 16, which is expected considering the lack of a d1–d1 WV–WV interaction.

Conclusion

We have presented a series of 17 new molybdenum and tungsten complexes supported by the BDI ligand framework (or its degradation products). Both the molybdenum(V) and tungsten(V) complexes 1 and 2 are excellent precursors for the coordination of neutral and anionic donor ligands such as DMAP, OPEt3, mesitolates, and primary or secondary amides. Interestingly, the complexes do not react (neither via adduct formation, nor OAT) with small phosphines (PEt3), contrasting the otherwise well-examined OAT reactivity of high-valent molybdenum(VI) and tungsten(VI) complexes.129−132 Cyclic voltammetry revealed both complexes to be reducible with one electron processes. Chemical reduction of complex 1 forged the first molybdenum(IV) complex 15 supported by the BDI ligand framework. In contrast, reduction of the tungsten complex 2 gave access to intractable mixtures, from which single crystals of the tungsten(VI) complex 17 supported by a MAD ligand were isolated. Complex 17 forms most likely by a nitrene transfer degradation of the BDI ligand,3 via an intermediate tungsten(IV) complex. In summary, this study not only shows the subtle difference in the stability of the +IV oxidation states of molybdenum and tungsten, but also gives access to an interesting new starting material, complex 15, whose reactivity and propensity to engage in small molecule activation will be further explored by our group.

Experimental Section

General Remarks

If not stated otherwise, all transformations were conducted in an argon filled glovebox under inert conditions. Solvents were dried by an MBraun SPS system and stored over activated molecular sieves (3 Å) for at least 1 day prior to use. C6D6 was dried over sodium/benzophenone followed by vacuum transfer and three freeze–pump–thaw cycles. H[BDI], Li[BDI],159 KC8,160,161 MoOCl3(THF)2,162 and WOCl3(THF)2163 were synthesized according to the literature; LiOMes, LiNHTol, and LiNTol2 were obtained by deprotonating the corresponding phenol or aniline in pentane using 1.2 equiv of n-BuLi and filtering off the white products. DMAP and OPEt3 were used as commercially received, without any additional purification or drying steps. NMR spectra were collected at ambient temperature on an Ascent 400 or Ascent 700 spectrometer; 1H and 13C NMR chemical shifts (δ) are reported in ppm and were calibrated to residual solvent peaks. IR spectra were collected using a Bruker Alpha IR spectrometer using an ATR detector setup. UV–vis spectra were collected on a PerkinElmer Lambda XLS+ spectrometer in 10 mm fused silica cuvettes. Cyclic voltammetry was recorded using a BioLogic potentiostat and a three-electrode array (working electrode: glassy carbon, counter electrode: platinum, reference electrode: silver). Solvents for cyclic voltammetry (THF and DCM, electrochemical grade) have been dried over activated molecular sieves for at least 48 h prior to use. The supporting electrolyte NBu4PF6 (electrochemical grade) was recrystallized three times from absolute ethanol and dried under a high vacuum (1 × 10–3 mbar) at 80 °C for 48 h and was stored in an argon-filled glovebox. All experiments have been performed in 0.2 M solutions of NBu4PF6 in the corresponding solvent at 0.001 M solutions of the analyte under strictly inert conditions in an argon-filled glovebox. Purity of the electrolyte solutions was confirmed by back-ground scans prior to addition of the analyte, showing no redox-events. Electron paramagnetic spectroscopy was conducted on a Magnettech 5000 X-Band spectrometer equipped with a variable temperature unit in 3 mm o.d. J-Young style fused silica tubes. Simulations were performed using the garlic and pepper functions of the EasySpin package for MatLab and parameters obtained with least-squares fitting.164

Synthetic Procedures

General Procedure for the Synthesis of 1–4

Metal precursors MOCl3(THF)2 and ligand LiBDIR(Et2O) were dissolved separately 5 mL THF each and cooled to −40 °C. The ligand was added dropwise under stirring while the mixture was allowed to warm to room temperature. After 24 (Mo) or 48 (W) hours the solvent was removed in vacuo and the residue dissolved in diethyl ether. After filtration the solution was concentrated and crystals of compounds 1–4 were obtained within 24 h.

BDIDippMoOCl2 (1)

From MoOCl3(THF)2 (1 equiv, 0.500 mmol, 181 mg) and LiBDIDipp(Et2O) (1 equiv, 0.525 mmol, 257 mg). 238 mg (79%) of a dark green solid. 1H NMR (C6D6, 298 K) δ (ppm) 8.60, 6.57, 2.11, 1.83, −1.61. Elemental analysis (%) calc’d for C29H41N2O1Cl2Mo1: C, 58.00; H, 6.88; N, 4.67. Found C, 57.64; H, 6.77; N, 4.78. μeff (Evans Method, C6D6): 1.75 μB. IR (cm–1) 2961, 2928, 2869, 1619, 1541, 1464, 1441, 1384, 1354, 1313, 1284, 1245, 1227, 1178, 1098, 1058, 1041, 1023, 988, 935, 861, 849, 798, 788, 763, 704, 533, 463. UV–vis λmax 320 nm (ε = 7000 L mol–1 cm–1), 393 nm (ε = 5800 L mol–1 cm–1), 583 nm (ε = 950 L mol–1 cm–1).

BDIDippWOCl2 (2)

From WOCl3(THF)2 (1 equiv, 0.385 mmol, 173 mg) and LiBDIDipp(Et2O) (1.05 equiv, 0.404 mmol, 190 mg). 199 mg (75%) of a gray solid. 1H NMR (C6D6, 298 K) δ (ppm) 8.14, 7.53, 1.83, 1.41, 0.99, 0.40. Elemental analysis (%) calc’d for C29H41N2O1Cl2W1: C, 50.60; H, 6.00; N, 4.07. Found C, 50.80; H, 5.72; N, 3.81. μeff (Evans Method, C6D6): 1.30 μB. IR (cm–1) 2965, 2930, 2871, 1633, 1590, 1544, 1515, 1460, 1441, 1384, 1364, 1315, 1290, 1245, 1182, 1147, 1098, 1058, 1023, 994, 960, 935, 866, 849, 798, 759, 706, 535, 453, 422. UV–vis λmax 336 nm (ε = 10400 L mol–1 cm–1), 369 nm (ε = 13300 L mol–1 cm–1).

BDIMesMoOCl2 (3)

From MoOCl3(THF)2 (1 equiv, 0.500 mmol, 181 mg) and LiBDIMes(Et2O) (1.05 equiv, 0.525 mmol, 218 mg). To ensure all lithium chloride to precipitate, the ether extract is stirred for 6 h at room temperature prior to filtration. 162 mg (62%) of a brown to green solid. 1H NMR (C6D6, 298 K) δ (ppm) 5.81, 3.75, 1.71, 1.54, 1.49, 1.41, 1.37, −3.16. Elemental analysis (%) calc’d for C23H29N2O1Cl2Mo1: C, 53.50; H, 5.68; N, 5.43. Found C, 50.44; H, 5.60; N, 4.93. The low carbon value can be explained by metal carbide formation which is a common problem in group VI chemistry. μeff (Evans Method, C6D6): 1.61 μB. IR (cm–1) 2969, 2920, 2856, 1609, 1562, 1535, 1509, 1476, 1423, 1370, 1341, 1282, 1233, 1209, 1192, 1141, 1023, 986, 964, 937, 896, 859, 817, 735, 702, 657, 629, 569, 506, 416. UV–vis λmax 323 (ε = 7900 L mol–1 cm–1), 376 (ε = 5600 L mol–1 cm–1), 560 nm (ε = 1000 L mol–1 cm–1).

BDIMesWOCl2 (4)

From WOCl3(THF)2 (1 equiv, 0.300 mmol, 135 mg) and LiBDIMes(Et2O) (1.05 equiv, 0.315 mmol, 131 mg). To ensure all lithium chloride to precipitate, the ether extract is stirred for 6 h at room temperature prior to filtration. 89 mg (50%) of a brown solid. 1H NMR (C6D6, 298 K) δ (ppm) 6.44, 3.86, 3.32, 1.70, 1.43. Elemental analysis (%) calc’d for C23H29N2O1Cl2W1: C, 45.72; H, 4.84; N, 4.64. Found C, 45.93; H, 5.06; N, 4.20. μeff (Evans Method, C6D6): 1.37 μB. IR (cm–1) 2918, 2856, 1609, 1517, 1476, 1431, 1362, 1343, 1313, 1288, 1243, 1229, 1211, 1194, 1143, 1113, 1025, 994, 964, 853, 829, 817, 731, 657, 639, 629, 596, 572, 543, 500, 425. UV–vis λmax 257 nm (ε = 7700 L mol–1 cm–1), 324 nm (ε = 9800 L mol–1 cm–1).

General Procedure for the Synthesis of 5–8

The corresponding base complex was dissolved in 5 mL of diethyl ether, and a solution of the reactant (OPEt3, DMAP) in 2 mL diethyl ether was added in one portion. After stirring for 2 h, the reaction mixture was filtrated and evaporated to dryness. The crude samples were then recrystallized from concentrated pentane solutions (0.5 mL) at room temperature.

BDIDippMoOCl2(DMAP) (5)

From BDIDippMoOCl2 (1 equiv, 0.167 mmol, 100 mg) and DMAP (1 equiv, 0.167 mmol, 20 mg). 63 mg (52%) of a bright green solid. 1H NMR (C6D6, 298 K) δ (ppm) 8.43, 6.10, 2.09. Elemental analysis (%) calc’d for C36H51N4O1Cl2Mo1: C, 59.83; H, 7.11; N, 7.75. Found C, 59.22; H, 7.53; N, 7.00. μeff (Evans Method, C6D6): 1.51 μB. IR (cm–1) 2965, 2926, 2867, 1623, 1544, 1517, 1462, 1439, 1366, 1317, 1247, 1233, 1166, 1100, 1062, 1013, 978, 937, 855, 798, 761, 735, 696, 529, 457. UV–vis λmax 257 nm (ε = 11700 L mol–1 cm–1), 294 nm (ε = 13000 L mol–1 cm–1), 583 nm (ε = 800 L mol–1 cm–1).

BDIDippWOCl2(DMAP) (6)

From BDIDippWOCl2 (1 equiv, 0.102 mmol, 70 mg) and DMAP (1 equiv, 0.102 mmol, 12 mg). 42 mg (51%) of a dark green - brown solid. 1H NMR (C6D6, 298 K) δ (ppm) 8.45, 7.69, 6.88, 6.09, 5.42, 2.81, 2.22, 1.97, 1.67, 1.34, 0.60. Elemental analysis (%) calc’d for C36H51N4O1Cl2W1 · 1.5 Et2O:: C, 54.73; H, 7.22; N, 6.08. Found C, 54.98; H, 7.47; N, 5.81. μeff (Evans Method, C6D6): 1.54 μB. IR (cm–1) 2969, 2928, 2869, 1646, 1623, 1544, 1521, 1462, 1439, 1382, 1366, 1317, 1286, 1233, 1168, 1107, 1060, 1015, 949, 857, 800, 761, 729, 704, 631, 610, 553, 529, 459, 414, 404. UV–vis λmax 258 nm (ε = 19900 L mol–1 cm–1), 270 nm (ε = 19800 L mol–1 cm–1), 342 nm (ε = 14200 L mol–1 cm–1), 559 nm (ε = 1700 L mol–1 cm–1).

BDIDippMoOCl2(OPEt3) (7)

From BDIDippMoOCl2 (1 equiv, 0.167 mmol, 100 mg) and OPEt3 (1 equiv, 0.167 mmol, 22 mg). 73 mg (60%) of a dark green solid. 1H NMR (C6D6, 298 K) δ (ppm) 8.57, 6.56, 3.8, 2.40, 1.33. Elemental analysis (%) calc’d for C35H56N2O2P1Cl2Mo1: C, 57.22; H, 7.68; N, 3.81. Found C, 57.66; H, 7.29; N, 4.10. μeff (Evans Method, C6D6): 1.82 μB. IR (cm–1) 2963, 2928, 2871, 1535, 1462, 1439, 1384, 1354, 1315, 1282, 1247, 1098, 1058, 1023, 984, 937, 859, 796, 761, 704, 527, 455. UV–vis λmax 313 nm (ε = 8900 L mol–1 cm–1), 391 nm (ε = 6000 L mol–1 cm–1), 599 nm (ε = 960 L mol–1 cm–1).

BDIDippWOCl2(OPEt3) (8)

From BDIDippWOCl2 (1 equiv, 0.145 mmol, 0.100 mg) and OPEt3 (1 equiv, 0.145 mmol, 20 mg). 40 mg (33%) of an orange solid. 1H NMR (C6D6, 298 K) δ (ppm) 7.95, 7.36, 4.00, 2.48, 1.67, 1.60, 1.51, 1.46 0.39. Elemental analysis (%) calc’d for C35H56N2O2P1Cl2W1: C, 57.22; H, 7.68; N, 3.81. Found C, 56.89; H, 7.66; N, 3.43. μeff (Evans Method, C6D6): 1.76 μB. IR (cm–1) 2967, 2940, 2867, 1533, 1462, 1437, 1407, 1382, 1364, 1315, 1284, 1254, 1166, 1102, 1066, 1051, 1035, 1017, 986, 957, 857, 798, 786, 766, 729, 706, 680, 635, 608, 525, 478, 453, 431. UV–vis λmax 258 nm (ε = 12700 L mol–1 cm–1), 322 nm (ε = 5600 L mol–1 cm–1), 373 nm (ε = 6500 L mol–1 cm–1), 407 nm (ε = 4900 L mol–1cm–1).

General Procedure for the Synthesis of 9–14

The corresponding base complex was dissolved in 5 mL of diethyl ether and cooled to −40 °C. A solution of the reactant in 5 mL diethyl ether was added dropwise with continuous cooling. After the addition the reaction mixture was allowed to warm slowly to room temperature and stirred for 16 h. The solvent was removed in vacuo and the solids suspended in pentane. After filtration the solution was evaporated to dryness to give the title compound.

BDIDippMoOCl(OMes) (9)

From BDIDippMoOCl2 (1 equiv, 0.117 mmol, 70 mg) and LiOMes (2.1 equiv, 0.246 mmol, 35 mg). 53 mg (65%) of a dark blue to purple solid. 1H NMR (C6D6, 298 K) δ (ppm) 7.84, 6.60, 2.16, 2.09, 1.53. Elemental analysis (%) calc’d for C38H52N2O2Cl1Mo1 · 0.55 C5H12: C, 66.15; H, 7.98; N, 3.79. Found C, 66.02; H, 7.62; N, 3.44. μeff (Evans Method, C6D6): 1.57 μB. IR (cm–1) 2963, 2930, 2869, 1537, 1511, 1476, 1462, 1439, 1358, 1313, 1276, 1247, 1219, 1180, 1151, 1100, 1055, 1021, 974, 957, 935, 855, 827, 798, 784, 761, 735, 706, 594, 547, 531, 453, 431. UV–vis λmax 308 nm (ε = 14700 L mol–1 cm–1), 366 nm (ε = 13300 L mol–1 cm–1), 549 nm (ε = 3600 L mol–1 cm–1).

BDIDippWOCl(OMes) (10)

From BDIDippWOCl2 (1 equiv, 0.102 mmol, 70 mg) and LiOMes (2.1 equiv, 0.214 mmol, 31 mg). 65 mg (81%) of a dark red solid. 1H NMR (C6D6, 298 K) δ (ppm) 7.85, 7.49, 2.76, 1.75, 1.59. Elemental analysis (%) calc’d for C38H52N2O2Cl1W1 · 0.5 C5H12: C, 59.02; H, 7.09; N, 3.40. Found C, 59.01; H, 6.83; N, 2.91. μeff (Evans Method, C6D6): 1.26 μB. IR (cm–1) 2963, 2926, 2869, 1619, 1593, 1541, 1476, 1464, 1439, 1374, 1356, 1311, 1258, 1241, 1213, 1151, 1100, 1055, 1019, 978, 957, 935, 851, 835, 796, 759, 725, 706, 680, 651, 576, 547, 533, 500, 459. UV–vis λmax 258 nm (ε = 12600 L mol–1 cm–1), 343 nm (ε = 11600 L mol–1 cm–1).

BDIMesMoO(OMes)2 (11)

From BDIMesMoOCl2 (1 equiv, 0.116 mmol, 60 mg) and LiOMes (2.2 equiv, 0.256 mmol, 36 mg). 60 mg (72%) of a dark blue to purple solid. 1H NMR (C6D6, 298 K) δ (ppm) 7.85, 7.49, 3.49, 2.80, 1.77, 1.58, 1.36, −0.11. Elemental analysis (%) calc’d for C41H51N2O3Mo1: C, 68.80; H, 7.18; N, 3.91. Found C, 69.12; H, 7.42; N, 3.64. μeff (Evans Method, C6D6): 1.63 μB. IR (cm–1) 2963, 2926, 2869, 1623, 1588, 1537, 1511, 1476, 1464, 1437, 1360, 1309, 1276, 1247, 1219, 1151, 1100, 1055, 1021, 974, 957, 935, 894, 884, 853, 827, 798, 784, 761, 735, 725, 706, 649, 627, 594, 580, 541, 531, 453, 429. UV–vis λmax 265 nm (ε = 12400 L mol–1 cm–1), 365 nm (ε = 9000 L mol–1 cm–1), 549 nm (ε = 2300 L mol–1 cm–1).

BDIDippMoO(NHTol)2 (12)

From BDIDippMoOCl2 (1 equiv, 0.117 mmol, 70 mg) and LiNHTol (2.1 equiv, 0245 mmol, 28 mg). To ensure all lithium chloride to precipitate, the pentane extract is stirred for 6 h at room temperature prior to filtration. 76 mg (88%) of an intense dark green solid. 1H NMR (C6D6, 298 K) δ (ppm) 7.40, 6.44, 2.11. Elemental analysis (%) calc’d for C43H57N4O1Mo1: C, 67.05; H, 7.74; N, 7.55. Found C, 67.05; H, 7.63; N, 7.29. The low carbon value can be explained by metal carbide formation which is a common problem in group VI chemistry. μeff (Evans Method, C6D6): 1.52 μB. IR (cm–1) 3326, 3304, 2961, 2926, 2867, 1621, 1588, 1548, 1517, 1503, 1462, 1435, 1376, 1315, 1256, 1174, 1098, 1058, 1021, 970, 939, 868, 855, 808, 794, 761, 702, 637, 596, 525, 506, 490, 455, 414, 404. UV–vis λmax 275 nm (ε = 18000 L mol–1 cm–1), 295 nm (ε = 19300 L mol–1 cm–1), 369 nm (ε = 11400 L mol–1 cm–1), 549 nm (ε = 2100 L mol–1 cm–1).

BDIDippMoOCl(N(Tol)2) (13)

Equivalent to the general procedure in toluene. From BDIDippMoOCl2 (1 equiv, 0.262 mmol, 157 mg) and LiN(Tol)2 (1.1 equiv, 0.289 mmol, 59 mg). To ensure all lithium chloride to precipitate, the pentane extract is stirred for 6 h at room temperature prior to filtration. 105 mg (52%) of a dark green solid. 1H NMR (C6D6, 298 K) δ (ppm) 6.57, 1.35. Elemental analysis (%) calc’d for C43H55Cl1N3O1Mo1: C, 67.84; H, 7.28; N, 7.29. Found C, 64.29; H, 7.31; N, 4.97. The low carbon value can be explained by metal carbide formation which is a common problem in group VI chemistry. μeff (Evans Method, C6D6): 1.59 μB. IR (cm–1) 2961, 2926, 2869, 1609, 1507, 1460, 1437, 1366, 1315, 1298, 1252, 1209, 1178, 1102, 1055, 1021, 984, 955, 937, 892, 855, 806, 796, 759, 704, 582, 549, 529, 500, 455. UV–vis λmax 258 nm (ε = 19500 L mol–1 cm–1), 286 nm (ε = 18700 L mol–1 cm–1), 384 nm (ε = 8100 L mol–1 cm–1).

BDIDippWOCl(N(Tol)2) (14)

From BDIDippWOCl2 (1 equiv, 0.236 mmol, 162 mg) and LiN(Tol)2 (1.1 equiv, 0.259 mmol, 53 mg). 104 mg (52%) of a dark brown solid. 1H NMR (C6D6, 298 K) δ (ppm) 8.59, −1.96 Elemental analysis (%) calc’d for C43H55Cl1N3O1W1: C, 60.82; H, 6.53; N, 4.95. Found C, 60.48; H, 6.77; N, 4.75. μeff (Evans Method, C6D6): 1.45 μB. IR (cm–1) 3024, 2963, 2922, 2867, 1609, 1590, 1515, 1460, 1439, 1382, 1362, 1315, 1243, 1178, 1107, 1055, 1039, 1019, 992, 966, 937, 906, 866, 806, 759, 704, 680, 639, 592, 502. UV–vis λmax 258 nm (ε = 12100 L mol–1 cm–1), 295 nm (ε = 13600 L mol–1 cm–1), 639 nm (ε = 1700 L mol–1 cm–1).

[BDIDippMoOCl]2 (15)

Solid BDIDippMoOCl2 (1 equiv, 0.266 mol, 160 mg) and KC8 (1.5 equiv, 0.400 mmol, 54 mg) were mixed and cooled to −40 °C. Seven milliliters of cold THF was added in one portion, and the mixture was slowly warmed to room temperature over 16 h. After filtration, the solvent was removed and the residue suspended in 10 mL pentane. The mixture was filtrated again and concentrated to 5 mL. After 1 h a light green solid started to precipitate. The solid was filtered after 24 h and washed with a minimal amount of pentane to give clean [BDIDippMoOCl]2. 65 mg (43%) of a light green solid. 1H NMR (C6D6, 298 K, 700 MHz): Isomer A δ 7.00 (t, J = 7.7 Hz, 2H, Aryl para-H), 6.92 (d, J = 7.7 Hz, 4H, Aryl meta-H), 4.88 (s, 1H, BDI α-H), 3.39 (hept, J = 6.8 Hz, 2H, iPr–CH), 2.63 (hept, J = 6.8 Hz, 2H, iPr–CH), 1.49 (s, 6H, BDI-CH3), 1.45 (d, J = 6.8 Hz, 6H, iPr–CH3), 1.24 (d, J = 6.8 Hz, 6H, iPr–CH3), 1.23 (d, J = 6.8 Hz, 6H, iPr–CH3), 1.04 (d, J = 6.8 Hz, 6H, iPr–CH3), Isomer B δ 7.03 (t, J = 7.7 Hz, 2H, Aryl para-H), 6.94 (d, J = 7.7 Hz, 4H, Aryl meta-H), 4.81 (s, 1H, BDI α-H), 3.29 (hept, J = 6.8 Hz, 2H, iPr–CH), 2.72 (hept, J = 6.8 Hz, 2H, iPr–CH), 1.43 (s, 6H, BDI-CH3), 1.38 (d, J = 6.8 Hz, 6H, iPr–CH3), 1.20 (d, J = 6.8 Hz, 6H, iPr–CH3), 1.06 (d, J = 6.8 Hz, 12H, iPr–CH3). 13C{1H} NMR (C6D6, 298 K, 176 MHz) Isomer A δ 167.30 (BDI β-C), 149.07 (Aryl C), 141.23 (Aryl-C-iPr), 141.12 (Aryl-C-iPr), 126.20 (Aryl-CH), 124.46 (Aryl-CH), 123.16 (Aryl-C), 104.04 (BDI-CH), 29.03 (iPr-CH), 26.96 (iPr-CH), 25.49 (CH3), 24.65 (CH3), 24.58 (CH3), 24.41 (CH3), 24.33 (CH3). Isomer B δ 167.12 (BDI β-C), 149.26 (Aryl C), 141.61 (Aryl-C-iPr), 140.54 (Aryl-C-iPr), 125.88 (Aryl-CH), 125.11 (Aryl-CH), 122.68 (Aryl-CH), 103.85 (BDI-CH), 29.23 (iPr-CH), 26.84 (iPr-CH), 25.11 (CH3), 24.92 (CH3), 24.74 (CH3), 24.63 (CH3), 24.48 (CH3). Elemental analysis (%) calc’d for C58H82N4O2Cl2Mo2: C, 61.64; H, 7.31; N, 4.96. Found C, 61.44; H, 7.04; N, 4.75. IR (cm–1) 2963, 2928, 2867, 1529, 1460, 1437, 1366, 1317, 1284, 1252, 1176, 1100, 1058, 1019, 980, 937, 853, 796, 770, 757, 704, 635, 543, 527, 451. UV–vis λmax 228 nm (ε = 7200 L mol–1 cm–1), 258 nm (ε = 10200 L mol–1 cm–1), 381 nm (ε = 9000 L mol–1 cm–1).

Reduction of 2

Solid BDIDippWOCl2 (1 equiv, 0.232 mmol, 160 mg) and KC8 (1.5 equiv, 0.349 mmol, 47 mg) were mixed and cooled to −40 °C. Seven milliliters of cold THF was added in one portion, and the mixture was slowly warmed to room temperature over 16 h. After filtration, the solvent was removed and the residue suspended in 10 mL pentane. The mixture was filtrated again and the solvent was evaporated. Few single crystals of 16 and 17 were obtained by stopping the evaporation of the pentane extract at 1 mL volume of pentane and leaving the solution overnight at room temperature. The crude NMR can be seen in Figure S23.

X-ray Crystallography

X-ray diffraction experiments were performed at the analytical facility of the University of Innsbruck. Data collection was performed using the ApexIV software package on a Bruker D8 Quest instrument. Data refinement and reduction were performed using the Bruker ApexIV suite 2022. Using the OLEX2 software package,165 all structures were solved with SHELXT166 and refined with SHELXL.167 Strongly disordered solvent molecules have been removed using the SQUEEZE operation.168 All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were included at the geometrically calculated positions and refined using a riding model. For further crystallographic details, see Tables S1 and S2 in the Supporting Information.

Acknowledgments

We are grateful to the University of Innsbruck and the Austrian Science Fund (FWF, Grant No. P-34626-N) for funding of this work.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.organomet.3c00056.

  • NMR and EPR spectra, IR spectra, crystallographic details, cyclic voltammograms, and UV–vis spectra (PDF)

Author Contributions

The project was designed and created by S.H. Experimental work was carried out by D.L. (lead), B.W., and S.H. X-ray structure analysis was performed by F.T., K.W., M.S., and S.H. Cyclic voltammetry was recorded by F.R.N. and EPR measurements were performed and simulated by D.L. The manuscript was written by S.H. (lead) and D.L. and proofread by all authors prior to publication.

Open Access is funded by the Austrian Science Fund (FWF).

The authors declare no competing financial interest.

Supplementary Material

om3c00056_si_001.pdf (3.4MB, pdf)

References

  1. Bourget-Merle L.; Lappert M. F.; Severn J. R. The Chemistry of β-Diketiminatometal Complexes. Chem. Rev. 2002, 102 (9), 3031–3066. 10.1021/cr010424r. [DOI] [PubMed] [Google Scholar]
  2. Webster R. L. β-Diketiminate complexes of the first row transition metals: applications in catalysis. Dalton Trans. 2017, 46 (14), 4483–4498. 10.1039/C7DT00319F. [DOI] [PubMed] [Google Scholar]
  3. Camp C.; Arnold J. On the non-innocence of ″Nacnacs″: ligand-based reactivity in β-diketiminate supported coordination compounds. Dalton Trans. 2016, 45 (37), 14462–14498. 10.1039/C6DT02013E. [DOI] [PubMed] [Google Scholar]
  4. Chen C.; Bellows S. M.; Holland P. L. Tuning steric and electronic effects in transition-metal β-diketiminate complexes. Dalton Trans. 2015, 44 (38), 16654–16670. 10.1039/C5DT02215K. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Do D. C. H.; Keyser A.; Protchenko A. V.; Maitland B.; Pernik I.; Niu H.; Kolychev E. L.; Rit A.; Vidovic D.; Stasch A.; Jones C.; Aldridge S. Highly Electron-Rich β-Diketiminato Systems: Synthesis and Coordination Chemistry of Amino-Functionalized ″N-nacnac″ Ligands. Chem. Eur. J. 2017, 23 (24), 5830–5841. 10.1002/chem.201700757. [DOI] [PubMed] [Google Scholar]
  6. Dove A. P.; Gibson V. C.; Marshall E. L.; White A. J. P.; Williams D. J. Magnesium and zinc complexes of a potentially tridentate beta-diketiminate ligand. Dalton Trans. 2004, (4), 570–578. 10.1039/B314760F. [DOI] [PubMed] [Google Scholar]
  7. Friedrich A.; Pahl J.; Elsen H.; Harder S. Bulky cationic β-diketiminate magnesium complexes. Dalton Trans. 2019, 48 (17), 5560–5568. 10.1039/C8DT03576H. [DOI] [PubMed] [Google Scholar]
  8. Rösch B.; Gentner T. X.; Langer J.; Färber C.; Eyselein J.; Zhao L.; Ding C.; Frenking G.; Harder S. Dinitrogen complexation and reduction at low-valent calcium. Science 2021, 371 (6534), 1125–1128. 10.1126/science.abf2374. [DOI] [PubMed] [Google Scholar]
  9. Bonyhady S. J.; Jones C.; Nembenna S.; Stasch A.; Edwards A. J.; McIntyre G. J. Beta-diketiminate-stabilized magnesium(I) dimers and magnesium(II) hydride complexes: synthesis, characterization, adduct formation, and reactivity studies. Chem. Eur. J. 2010, 16 (3), 938–955. 10.1002/chem.200902425. [DOI] [PubMed] [Google Scholar]
  10. Green S. P.; Jones C.; Stasch A. Stable magnesium(I) compounds with Mg-Mg bonds. Science 2007, 318 (5857), 1754–1757. 10.1126/science.1150856. [DOI] [PubMed] [Google Scholar]
  11. Gentner T. X.; Rösch B.; Ballmann G.; Langer J.; Elsen H.; Harder S. Low Valent Magnesium Chemistry with a Super Bulky β-Diketiminate Ligand. Angew. Chem., Int. Ed. 2019, 58 (2), 607–611. 10.1002/anie.201812051. [DOI] [PubMed] [Google Scholar]
  12. Zhong M.; Sinhababu S.; Roesky H. W. The unique β-diketiminate ligand in aluminum(i) and gallium(i) chemistry. Dalton Trans. 2020, 49 (5), 1351–1364. 10.1039/C9DT04763H. [DOI] [PubMed] [Google Scholar]
  13. Tuscher L.; Ganesamoorthy C.; Bläser D.; Wölper C.; Schulz S. A Gallium-Substituted Distibene and an Antimony-Analogue Bicyclo1.1.0butane: Synthesis and Solid-State Structures. Angew. Chem., Int. Ed. 2015, 54 (36), 10657–10661. 10.1002/anie.201502827. [DOI] [PubMed] [Google Scholar]
  14. Schoeller W. W.; Frey G. D. White phosphorus degradation with a NacNac aluminum carbene analogue: the biradical reaction mechanism. Inorg. Chem. 2014, 53 (10), 4840–4846. 10.1021/ic402649b. [DOI] [PubMed] [Google Scholar]
  15. Mindiola D. J. Nacnac ... Are You Still There? The Evolution of β-Diketiminate Complexes of Nickel. Angew. Chem., Int. Ed. 2009, 48 (34), 6198–6200. 10.1002/anie.200901400. [DOI] [PubMed] [Google Scholar]
  16. Hartmann N. J.; Wu G.; Hayton T. W. Synthesis of a ″Masked″ Terminal Nickel(II) Sulfide by Reductive Deprotection and its Reaction with Nitrous Oxide. Angew. Chem., Int. Ed. 2015, 54 (49), 14956–14959. 10.1002/anie.201508232. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Baeza Cinco M. Á.; Wu G.; Kaltsoyannis N.; Hayton T. W. Synthesis of a ″Masked″ Terminal Zinc Sulfide and Its Reactivity with Brønsted and Lewis Acids. Angew. Chem., Int. Ed. 2020, 59 (23), 8947–8951. 10.1002/anie.202002364. [DOI] [PubMed] [Google Scholar]
  18. Spitzer F.; Graßl C.; Balázs G.; Zolnhofer E. M.; Meyer K.; Scheer M. Influence of the nacnac Ligand in Iron(I)-Mediated P4 Transformations. Angew. Chem., Int. Ed. 2016, 55 (13), 4340–4344. 10.1002/anie.201510716. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Hein N. M.; Suzuki T.; Ogawa T.; Fryzuk M. D. Low coordinate iron derivatives stabilized by a β-diketiminate mimic. Synthesis and coordination chemistry of enamidophosphinimine scaffolds to generate diiron dinitrogen complexes. Dalton Trans. 2016, 45 (37), 14697–14708. 10.1039/C6DT01673A. [DOI] [PubMed] [Google Scholar]
  20. Spitzer F.; Graßl C.; Balázs G.; Mädl E.; Keilwerth M.; Zolnhofer E. M.; Meyer K.; Scheer M. Nacnac-Cobalt-Mediated P4 Transformations. Chem. Eur. J. 2017, 23 (11), 2716–2721. 10.1002/chem.201605451. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. McWilliams S. F.; Broere D. L. J.; Halliday C. J. V.; Bhutto S. M.; Mercado B. Q.; Holland P. L. Coupling dinitrogen and hydrocarbons through aryl migration. Nature 2020, 584 (7820), 221–226. 10.1038/s41586-020-2565-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. DeRosha D. E.; Chilkuri V. G.; van Stappen C.; Bill E.; Mercado B. Q.; DeBeer S.; Neese F.; Holland P. L. Planar three-coordinate iron sulfide in a synthetic 4Fe-3S cluster with biomimetic reactivity. Nat. Chem. 2019, 11 (11), 1019–1025. 10.1038/s41557-019-0341-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Rodriguez M. M.; Bill E.; Brennessel W. W.; Holland P. L. N2 reduction and hydrogenation to ammonia by a molecular iron-potassium complex. Science 2011, 334 (6057), 780–783. 10.1126/science.1211906. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Boreen M. A.; Gould C. A.; Booth C. H.; Hohloch S.; Arnold J. Structure and magnetism of a tetrahedral uranium(iii) β-diketiminate complex. Dalton Trans. 2020, 49 (23), 7938–7944. 10.1039/D0DT01599G. [DOI] [PubMed] [Google Scholar]
  25. Yao Y.; Zhang Y.; Zhang Z.; Shen Q.; Yu K. Synthesis and Structural Characterization of Divalent Ytterbium Complexes Supported by β -Diketiminate Ligands and Their Catalytic Activity for the Polymerization of Methyl Methacrylate. Organometallics 2003, 22 (14), 2876–2882. 10.1021/om030136g. [DOI] [Google Scholar]
  26. Zhang J.; Zhang Z.; Chen Z.; Zhou X. Oxidation and coupling of β-diketiminate ligand in lanthanide complexes: novel eight-nuclear lanthanide clusters with μ-, μ3-Cl, and μ4-O bridge. Dalton Trans. 2012, 41 (2), 357–359. 10.1039/C1DT11383F. [DOI] [PubMed] [Google Scholar]
  27. Wooles A. J.; Lewis W.; Blake A. J.; Liddle S. T. β-Diketiminate Derivatives of Alkali Metals and Uranium. Organometallics 2013, 32 (18), 5058–5070. 10.1021/om400435b. [DOI] [Google Scholar]
  28. Klementyeva S. V.; Afonin M. Y.; Bogomyakov A. S.; Gamer M. T.; Roesky P. W.; Konchenko S. N. Mono- and Dinuclear Rare-Earth Chlorides Ligated by a Mesityl-Substituted β-Diketiminate. Eur. J. Inorg. Chem. 2016, 2016 (22), 3666–3672. 10.1002/ejic.201600488. [DOI] [Google Scholar]
  29. Hohloch S.; Kriegel B. M.; Bergman R. G.; Arnold J. Group 5 chemistry supported by β-diketiminate ligands. Dalton Trans. 2016, 45 (40), 15725–15745. 10.1039/C6DT01770C. [DOI] [PubMed] [Google Scholar]
  30. Tran B. L.; Washington M. P.; Henckel D. A.; Gao X.; Park H.; Pink M.; Mindiola D. J. A four coordinate parent imide via a titanium nitridyl. Chem. Commun. 2012, 48 (10), 1529–1531. 10.1039/C1CC14574F. [DOI] [PubMed] [Google Scholar]
  31. Thompson R.; Chen C.-H.; Pink M.; Wu G.; Mindiola D. J. A nitrido salt reagent of titanium. J. Am. Chem. Soc. 2014, 136 (23), 8197–8200. 10.1021/ja504020t. [DOI] [PubMed] [Google Scholar]
  32. Basuli F.; Tomaszewski J.; Huffman J. C.; Mindiola D. J. Four-coordinate phosphinidene complexes of titanium prepared by alpha-H-migration: phospha-Staudinger and phosphaalkene-insertion reactions. J. Am. Chem. Soc. 2003, 125 (34), 10170–10171. 10.1021/ja036559r. [DOI] [PubMed] [Google Scholar]
  33. Zhao G.; Basuli F.; Kilgore U. J.; Fan H.; Aneetha H.; Huffman J. C.; Wu G.; Mindiola D. J. Neutral and zwitterionic low-coordinate titanium complexes bearing the terminal phosphinidene functionality. Structural, spectroscopic, theoretical, and catalytic studies addressing the Ti-P multiple bond. J. Am. Chem. Soc. 2006, 128 (41), 13575–13585. 10.1021/ja064853o. [DOI] [PubMed] [Google Scholar]
  34. Basuli F.; Bailey B. C.; Huffman J. C.; Baik M.-H.; Mindiola D. J. Terminal and four-coordinate vanadium(IV) phosphinidene complexes. A pseudo Jahn-Teller effect of second order stabilizing the V-P multiple bond. J. Am. Chem. Soc. 2004, 126 (7), 1924–1925. 10.1021/ja0392216. [DOI] [PubMed] [Google Scholar]
  35. Obenhuber A. H.; Gianetti T. L.; Berrebi X.; Bergman R. G.; Arnold J. Reaction of (bisimido)niobium(V) complexes with organic azides: 3 + 2 cycloaddition and reversible cleavage of β-diketiminato ligands involving nitrene transfer. J. Am. Chem. Soc. 2014, 136 (8), 2994–2997. 10.1021/ja413194z. [DOI] [PubMed] [Google Scholar]
  36. Obenhuber A. H.; Gianetti T. L.; Bergman R. G.; Arnold J. Regioselective 2 + 2 and 4 + 2 cycloaddition reactivity in an asymmetric niobium(bisimido) moiety towards unsaturated organic molecules. Chem. Commun. 2015, 51 (7), 1278–1281. 10.1039/C4CC07851A. [DOI] [PubMed] [Google Scholar]
  37. Tomson N. C.; Arnold J.; Bergman R. G. Halo, Alkyl, Aryl, and Bis(imido) Complexes of Niobium Supported by the beta-Diketiminato Ligand. Organometallics 2010, 29 (13), 2926–2942. 10.1021/om1001827. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Tomson N. C.; Arnold J.; Bergman R. G. Synthesis and reactivity of cationic niobium and tantalum methyl complexes supported by imido and β-diketiminato ligands. Dalton Trans. 2011, 40 (30), 7718–7729. 10.1039/c1dt10202h. [DOI] [PubMed] [Google Scholar]
  39. Nechayev M.; Gianetti T. L.; Bergman R. G.; Arnold J. C-F sp(2) bond functionalization mediated by niobium complexes. Dalton Trans. 2015, 44 (45), 19494–19500. 10.1039/C5DT02082D. [DOI] [PubMed] [Google Scholar]
  40. Kriegel B. M.; Bergman R. G.; Arnold J. Nitrene Metathesis and Catalytic Nitrene Transfer Promoted by Niobium Bis(imido) Complexes. J. Am. Chem. Soc. 2016, 138 (1), 52–55. 10.1021/jacs.5b11287. [DOI] [PubMed] [Google Scholar]
  41. Gianetti T. L.; Bergman R. G.; Arnold J. Carbon-fluorine bond cleavage in fluoroarenes via a niobium(iii) imido complex: from stoichiometric to catalytic hydrodefluorination. Chem. Sci. 2014, 5 (6), 2517. 10.1039/c4sc00006d. [DOI] [Google Scholar]
  42. Fostvedt J. I.; Grant L. N.; Kriegel B. M.; Obenhuber A. H.; Lohrey T. D.; Bergman R. G.; Arnold J. 1,2-Addition and cycloaddition reactions of niobium bis(imido) and oxo imido complexes. Chem. Sci. 2020, 11 (42), 11613–11632. 10.1039/D0SC03489D. [DOI] [PMC free article] [PubMed] [Google Scholar]
  43. Camp C.; Grant L. N.; Bergman R. G.; Arnold J. Photo-activation of d(0) niobium imido azides: en route to nitrido complexes. Chem. Commun. 2016, 52 (32), 5538–5541. 10.1039/C6CC02081J. [DOI] [PubMed] [Google Scholar]
  44. Lohrey T. D.; Bergman R. G.; Arnold J. Oxygen Atom Transfer and Intramolecular Nitrene Transfer in a Rhenium β-Diketiminate Complex. Inorg. Chem. 2016, 55 (22), 11993–12000. 10.1021/acs.inorgchem.6b02122. [DOI] [PubMed] [Google Scholar]
  45. Lohrey T. D.; Cortes E. A.; Fostvedt J. I.; Oanta A. K.; Jain A.; Bergman R. G.; Arnold J. Diverse Reactivity of a Rhenium(V) Oxo Imido Complex: 2 + 2 Cycloadditions, Chalcogen Metathesis, Oxygen Atom Transfer, and Protic and Hydridic 1,2-Additions. Inorg. Chem. 2020, 59 (15), 11096–11107. 10.1021/acs.inorgchem.0c01589. [DOI] [PubMed] [Google Scholar]
  46. Lohrey T. D.; Rao G.; Britt R. D.; Bergman R. G.; Arnold J. H2 Activation and Direct Access to Terminal Nitride and cyclo-P3 Complexes by an Acceptor-Free Rhenium(II) β-Diketiminate. Inorg. Chem. 2019, 58 (19), 13492–13501. 10.1021/acs.inorgchem.9b02556. [DOI] [PubMed] [Google Scholar]
  47. Lohrey T. D.; Bergman R. G.; Arnold J. Olefin-Supported Rhenium(III) Terminal Oxo Complexes Generated by Nucleophilic Addition to a Cyclopentadienyl Ligand. Angew. Chem., Int. Ed. 2017, 56 (45), 14241–14245. 10.1002/anie.201707957. [DOI] [PubMed] [Google Scholar]
  48. Ouellette E. T.; Carpentier A.; Joseph Brackbill I.; Lohrey T. D.; Douair I.; Maron L.; Bergman R. G.; Arnold J. σ or π? Bonding interactions in a series of rhenium metallotetrylenes. Dalton Trans. 2021, 50 (6), 2083–2092. 10.1039/D1DT00129A. [DOI] [PubMed] [Google Scholar]
  49. Lohrey T. D.; Rao G.; Small D. W.; Ouellette E. T.; Bergman R. G.; Britt R. D.; Arnold J. Electronic Structures of Rhenium(II) β-Diketiminates Probed by EPR Spectroscopy: Direct Comparison of an Acceptor-Free Complex to Its Dinitrogen, Isocyanide, and Carbon Monoxide Adducts. J. Am. Chem. Soc. 2020, 142 (32), 13805–13813. 10.1021/jacs.0c04719. [DOI] [PubMed] [Google Scholar]
  50. Ouellette E. T.; Magdalenski J. S.; Bergman R. G.; Arnold J. Applications of Low-Valent Transition Metalates: Development of a Reactive Noncarbonyl Rhenium(I) Anion. Acc. Chem. Res. 2022, 55 (5), 783–793. 10.1021/acs.accounts.2c00013. [DOI] [PubMed] [Google Scholar]
  51. Lohrey T. D.; Maron L.; Bergman R. G.; Arnold J. Heterotetrametallic Re-Zn-Zn-Re Complex Generated by an Anionic Rhenium(I) β-Diketiminate. J. Am. Chem. Soc. 2019, 141 (2), 800–804. 10.1021/jacs.8b12494. [DOI] [PubMed] [Google Scholar]
  52. Boreen M. A.; Lohrey T. D.; Rao G.; Britt R. D.; Maron L.; Arnold J. A Uranium Tri-Rhenium Triple Inverse Sandwich Compound. J. Am. Chem. Soc. 2019, 141 (13), 5144–5148. 10.1021/jacs.9b01331. [DOI] [PubMed] [Google Scholar]
  53. Kühnel M. F.; Lentz D. Titanium-catalyzed C-F activation of fluoroalkenes. Angew. Chem., Int. Ed. 2010, 49 (16), 2933–2936. 10.1002/anie.200907162. [DOI] [PubMed] [Google Scholar]
  54. Basuli F.; Bailey B. C.; Huffman J. C.; Mindiola D. J. Intramolecular C–H Activation Reactions Derived from a Terminal Titanium Neopentylidene Functionality. Redox-Controlled 1,2-Addition and α-Hydrogen Abstraction Reactions. Organometallics 2005, 24 (13), 3321–3334. 10.1021/om049318g. [DOI] [Google Scholar]
  55. Basuli F.; Bailey B. C.; Tomaszewski J.; Huffman J. C.; Mindiola D. J. A terminal and four-coordinate titanium alkylidene prepared by oxidatively induced alpha-hydrogen abstraction. J. Am. Chem. Soc. 2003, 125 (20), 6052–6053. 10.1021/ja034786n. [DOI] [PubMed] [Google Scholar]
  56. Basuli F.; Clark R. L.; Bailey B. C.; Brown D.; Huffman J. C.; Mindiola D. J. Latent low-coordinate titanium imides supported by a sterically encumbering beta-diketiminate ligand. Chem. Commun. 2005, (17), 2250–2252. 10.1039/b500350d. [DOI] [PubMed] [Google Scholar]
  57. Adhikari D.; Basuli F.; Orlando J. H.; Gao X.; Huffman J. C.; Pink M.; Mindiola D. J. Zwitterionic and Cationic Titanium and Vanadium Complexes Having Terminal M–C Multiple Bonds. The Role of the β-Diketiminate Ligand in Formation of Charge-Separated Species. Organometallics 2009, 28 (14), 4115–4125. 10.1021/om900115v. [DOI] [Google Scholar]
  58. Gong S.; Ma H.; Huang J. Zirconium and hafnium complexes supported by linked bis(beta-diketiminate) ligands: synthesis, characterization and catalytic application in ethylene polymerization. Dalton Trans. 2009, (39), 8237–8247. 10.1039/b905392a. [DOI] [PubMed] [Google Scholar]
  59. Basuli F.; Bailey B. C.; Brown D.; Tomaszewski J.; Huffman J. C.; Baik M.-H.; Mindiola D. J. Terminal vanadium-neopentylidyne complexes and intramolecular cross-metathesis reactions to generate azametalacyclohexatrienes. J. Am. Chem. Soc. 2004, 126 (34), 10506–10507. 10.1021/ja0472376. [DOI] [PubMed] [Google Scholar]
  60. Kriegel B. M.; Kaltsoyannis N.; Chatterjee R.; Bergman R. G.; Arnold J. Synthesis and Redox Chemistry of a Tantalum Alkylidene Complex Bearing a Metallaimidazole Ring. Organometallics 2017, 36 (18), 3520–3529. 10.1021/acs.organomet.7b00448. [DOI] [Google Scholar]
  61. Tran B. L.; Singhal M.; Park H.; Lam O. P.; Pink M.; Krzystek J.; Ozarowski A.; Telser J.; Meyer K.; Mindiola D. J. Reactivity Studies of a Masked Three-Coordinate Vanadium(II) Complex. Angew. Chem., Int. Ed. 2010, 122 (51), 10067–10071. 10.1002/ange.201005029. [DOI] [PubMed] [Google Scholar]
  62. Panda A.; Stender M.; Wright R. J.; Olmstead M. M.; Klavins P.; Power P. P. Synthesis and characterization of three-coordinate and related beta-diketiminate derivatives of manganese, iron, and cobalt. Inorg. Chem. 2002, 41 (15), 3909–3916. 10.1021/ic025552s. [DOI] [PubMed] [Google Scholar]
  63. Chai J.; Zhu H.; Fan H.; Roesky H. W.; Magull J. Structurally Characterized Neutral Monoalkyl and -aryl Complexes of Manganese(II). Organometallics 2004, 23 (6), 1177–1179. 10.1021/om030645i. [DOI] [Google Scholar]
  64. Chai J.; Zhu H.; Most K.; Roesky H. W.; Vidovic D.; Schmidt H.-G.; Noltemeyer M. Synthesis and Reaction of Mn II Iodides Bearing the β-Diketiminate Ligand: the First Divalent Manganese N-Heterocyclic Carbene Complexes [{HC(CMeNAr) 2}MnI{C[N(i Pr)CMe] 2}] and [{HC(CMeNAr) 2}MnNHAr{C[N(i Pr)CMe] 2}] (Ar = 2,6- i Pr 2 C 6 H 3). Eur. J. Inorg. Chem. 2003, 2003 (24), 4332–4337. 10.1002/ejic.200300289. [DOI] [Google Scholar]
  65. Chai J.; Zhu H.; Roesky H. W.; He C.; Schmidt H.-G.; Noltemeyer M. Synthesis, Structure, and Reactivity of β -Diketiminate Complexes of Manganese(II). Organometallics 2004, 23 (13), 3284–3289. 10.1021/om049857l. [DOI] [Google Scholar]
  66. Chai J.; Zhu H.; Roesky H. W.; Yang Z.; Jancik V.; Herbst-Irmer R.; Schmidt H.-G.; Noltemeyer M. Synthesis and Structure of Allyl and Alkynyl Complexes of Manganese(II) Supported by a Bulky β -Diketiminate Ligand. Organometallics 2004, 23 (21), 5003–5006. 10.1021/om049605k. [DOI] [Google Scholar]
  67. Chai J.; Zhu H.; Stückl A. C.; Roesky H. W.; Magull J.; Bencini A.; Caneschi A.; Gatteschi D. Synthesis and reaction of HC(CMeNAr)2Mn2 (Ar = 2,6-iPr2C6H3): the complex containing three-coordinate manganese(I) with a Mn-Mn bond exhibiting unusual magnetic properties and electronic structure. J. Am. Chem. Soc. 2005, 127 (25), 9201–9206. 10.1021/ja042269e. [DOI] [PubMed] [Google Scholar]
  68. Oh C.; Siewe J.; Nguyen T. T.; Kawamura A.; Flores M.; Groy T. L.; Anderson J. S.; Trovitch R. J.; Baik M.-H. The electronic structure of a β-diketiminate manganese hydride dimer. Dalton Trans. 2020, 49 (41), 14463–14474. 10.1039/D0DT02842H. [DOI] [PubMed] [Google Scholar]
  69. Nguyen T. T.; Mukhopadhyay T. K.; MacMillan S. N.; Janicke M. T.; Trovitch R. J. Synthesis of Aminosilane Chemical Vapor Deposition Precursors and Polycarbosilazanes through Manganese-Catalyzed Si-N Dehydrocoupling. ACS Sustainable Chem. Eng. 2022, 10 (13), 4218–4226. 10.1021/acssuschemeng.2c00008. [DOI] [Google Scholar]
  70. Latreche S.; Schaper F. Chromium(III) Bis(diketiminate) Complexes. Organometallics 2010, 29 (9), 2180–2185. 10.1021/om100144y. [DOI] [Google Scholar]
  71. Monillas W. H.; Bazzoli T. C.; Yap G. P. A.; Theopold K. H. Synthesis and Structure of bis(β-Diketiminate) Chromium(II) Complexes. J. Chem. Crystallogr. 2010, 40 (1), 67–71. 10.1007/s10870-009-9627-8. [DOI] [Google Scholar]
  72. Monillas W. H.; Yap G. P. A.; Theopold K. H. Synthesis and Structure of Chromium(II) Complexes Supported by Both a β-Diketiminate and an Amidinate Ligand. J. Chem. Crystallogr. 2009, 39 (11), 849–852. 10.1007/s10870-009-9621-1. [DOI] [Google Scholar]
  73. Tsai Y.-C.; Wang P.-Y.; Chen S.-A.; Chen J.-M. Inverted-sandwich dichromium(I) complexes supported by two beta-diketiminates: a multielectron reductant and syntheses of chromium dioxo and imido. J. Am. Chem. Soc. 2007, 129 (26), 8066–8067. 10.1021/ja072003i. [DOI] [PubMed] [Google Scholar]
  74. Fan H.; Adhikari D.; Saleh A. A.; Clark R. L.; Zuno-Cruz F. J.; Sanchez Cabrera G.; Huffman J. C.; Pink M.; Mindiola D. J.; Baik M.-H. Understanding and predicting distorted T- versus Y-geometries for neutral chromous complexes supported by a sterically encumbering beta-diketiminate ligand. J. Am. Chem. Soc. 2008, 130 (51), 17351–17361. 10.1021/ja803798b. [DOI] [PubMed] [Google Scholar]
  75. Monillas W. H.; Yap G. P. A.; MacAdams L. A.; Theopold K. H. Binding and activation of small molecules by three-coordinate Cr(I). J. Am. Chem. Soc. 2007, 129 (26), 8090–8091. 10.1021/ja0725549. [DOI] [PubMed] [Google Scholar]
  76. Champouret Y.; MacLeod K. C.; Baisch U.; Patrick B. O.; Smith K. M.; Poli R. Cyclopentadienyl Chromium β-Diketiminate Complexes: Initiators, Ligand Steric Effects, and Deactivation Processes in the Controlled Radical Polymerization of Vinyl Acetate. Organometallics 2010, 29 (1), 167–176. 10.1021/om900869p. [DOI] [Google Scholar]
  77. Monillas W. H.; Yap G. P.; Theopold K. H. Reactivity of a low-valent chromium dinitrogen complex. Inorg. Chim. Acta 2011, 369 (1), 103–119. 10.1016/j.ica.2010.11.024. [DOI] [Google Scholar]
  78. Lin K.-M.; Wang P.-Y.; Shieh Y.-J.; Chen H.-Z.; Kuo T.-S.; Tsai Y.-C. Reductive N-N bond cleavage and coupling of organic azides mediated by chromium(i) and vanadium(i) β-diketiminate. New J. Chem. 2010, 34 (8), 1737. 10.1039/c0nj00114g. [DOI] [Google Scholar]
  79. Monillas W. H.; Yap G. P. A.; Theopold K. H. A tale of two isomers: a stable phenyl hydride and a high-spin (S = 3) benzene complex of chromium. Angew. Chem., Int. Ed. 2007, 46 (35), 6692–6694. 10.1002/anie.200701933. [DOI] [PubMed] [Google Scholar]
  80. Dai F.; Yap G. P. A.; Theopold K. H. The direct oxidative addition of O2 to a mononuclear Cr(I) complex is spin forbidden. J. Am. Chem. Soc. 2013, 135 (45), 16774–16776. 10.1021/ja408357x. [DOI] [PubMed] [Google Scholar]
  81. MacLeod K. C.; Patrick B. O.; Smith K. M. Reactivity of Cr(III) μ-oxo compounds: catalyst regeneration and atom transfer processes. Inorg. Chem. 2012, 51 (1), 688–700. 10.1021/ic202233f. [DOI] [PubMed] [Google Scholar]
  82. Monillas W. H.; Yap G. P. A.; Theopold K. H. Synthesis and Structural Comparison for a Series of Cr(II) (iodo) NacNac Complexes. J. Chem. Crystallogr. 2009, 39 (1), 73–77. 10.1007/s10870-008-9492-x. [DOI] [Google Scholar]
  83. Nakagaki M.; Sakaki S. CASPT2 study of inverse sandwich-type dinuclear Cr(I) and Fe(I) complexes of the dinitrogen molecule: significant differences in spin multiplicity and coordination structure between these two complexes. J. Phys. Chem. A 2014, 118 (7), 1247–1257. 10.1021/jp410410j. [DOI] [PubMed] [Google Scholar]
  84. Tonzetich Z. J.; Jiang A. J.; Schrock R. R.; Müller P. Cationic Imido Alkylidene Complexes of Molybdenum Supported by β-Diketonate and β-Diketiminate Ligands. Organometallics 2006, 25 (20), 4725–4727. 10.1021/om060518x. [DOI] [Google Scholar]
  85. Tonzetich Z. J.; Jiang A. J.; Schrock R. R.; Müller P. Molybdenum Imido Alkylidene Complexes that Contain a β-Diketiminate Ligand. Organometallics 2007, 26 (15), 3771–3783. 10.1021/om7003207. [DOI] [Google Scholar]
  86. Lyashenko G.; Herbst-Irmer R.; Jancik V.; Pal A.; Mösch-Zanetti N. C. Molybdenum oxo and imido complexes of beta-diketiminate ligands: synthesis and structural aspects. Inorg. Chem. 2008, 47 (1), 113–120. 10.1021/ic701534a. [DOI] [PubMed] [Google Scholar]
  87. Filippou A. C.; Völkl C.; Rogers R. D. Metal-centred C—C coupling of nitriles with 1-azaallyl ligands; synthesis and structure of β-diiminato complexes of tungsten. J. Organomet. Chem. 1993, 463 (1–2), 135–142. 10.1016/0022-328X(93)83410-W. [DOI] [Google Scholar]
  88. Hierlmeier G.; Tosatti P.; Puentener K.; Chirik P. J. Identification of Cyclohexadienyl Hydrides as Intermediates in Molybdenum-Catalyzed Arene Hydrogenation. Angew. Chem., Int. Ed. 2023, 62, e202216026 10.1002/anie.202216026. [DOI] [PubMed] [Google Scholar]
  89. Viereck P.; Hierlmeier G.; Tosatti P.; Pabst T. P.; Puentener K.; Chirik P. J. Molybdenum-Catalyzed Asymmetric Hydrogenation of Fused Arenes and Heteroarenes. J. Am. Chem. Soc. 2022, 144 (25), 11203–11214. 10.1021/jacs.2c02007. [DOI] [PubMed] [Google Scholar]
  90. Benedikter M. J.; Ziegler F.; Groos J.; Hauser P. M.; Schowner R.; Buchmeiser M. R. Group 6 metal alkylidene and alkylidyne N-heterocyclic carbene complexes for olefin and alkyne metathesis. Coord. Chem. Rev. 2020, 415, 213315. 10.1016/j.ccr.2020.213315. [DOI] [Google Scholar]
  91. Buchmeiser M. R. Homogeneous Metathesis Polymerization by Well-Defined Group VI and Group VIII Transition-Metal Alkylidenes: Fundamentals and Applications in the Preparation of Advanced Materials. Chem. Rev. 2000, 100 (4), 1565–1604. 10.1021/cr990248a. [DOI] [PubMed] [Google Scholar]
  92. Buchmeiser M. R. Molybdenum Imido, Tungsten Imido and Tungsten Oxo Alkylidene N-Heterocyclic Carbene Olefin Metathesis Catalysts. Chem. Eur. J. 2018, 24 (54), 14295–14301. 10.1002/chem.201802497. [DOI] [PubMed] [Google Scholar]
  93. Buchmeiser M. R.; Sen S.; Unold J.; Frey W. N-heterocyclic carbene, high oxidation state molybdenum alkylidene complexes: functional-group-tolerant cationic metathesis catalysts. Angew. Chem., Int. Ed. 2014, 53 (35), 9384–9388. 10.1002/anie.201404655. [DOI] [PubMed] [Google Scholar]
  94. Baltrun M.; Watt F. A.; Schoch R.; Hohloch S. Dioxo-, Oxo-imido-, and Bis-imido-Molybdenum(VI) Complexes with a Bis-phenolate-NHC Ligand. Organometallics 2019, 38 (19), 3719–3729. 10.1021/acs.organomet.9b00472. [DOI] [Google Scholar]
  95. Liu S.; Amaro-Estrada J. I.; Baltrun M.; Douair I.; Schoch R.; Maron L.; Hohloch S. Catalytic Deoxygenation of Nitroarenes Mediated by High-Valent Molybdenum(VI)-NHC Complexes. Organometallics 2021, 40 (2), 107–118. 10.1021/acs.organomet.0c00352. [DOI] [Google Scholar]
  96. Jiang H.; Lu R.; Luo X.; Si X.; Xu J.; Lu F. Molybdenum-Catalyzed Deoxygenation Coupling of Lignin-Derived Alcohols for Functionalized Bibenzyl Chemicals. Chem. Eur. J. 2021, 27 (4), 1292–1296. 10.1002/chem.202003776. [DOI] [PubMed] [Google Scholar]
  97. Suárez-Pantiga S.; Hernández-Ruiz R.; Virumbrales C.; Pedrosa M. R.; Sanz R. Reductive Molybdenum-Catalyzed Direct Amination of Boronic Acids with Nitro Compounds. Angew. Chem., Int. Ed. 2019, 58 (7), 2129–2133. 10.1002/anie.201812806. [DOI] [PubMed] [Google Scholar]
  98. Baltrun M.; Watt F. A.; Schoch R.; Wölper C.; Neuba A. G.; Hohloch S. A new bis-phenolate mesoionic carbene ligand for early transition metal chemistry. Dalton Trans. 2019, 48 (39), 14611–14625. 10.1039/C9DT03099A. [DOI] [PubMed] [Google Scholar]
  99. Bezdek M. J.; Pelczer I.; Chirik P. J. Coordination-Induced N-H Bond Weakening in a Molybdenum Pyrrolidine Complex: Isotopic Labeling Provides Insight into the Pathway for H 2 Evolution. Organometallics 2020, 39 (16), 3050–3059. 10.1021/acs.organomet.0c00471. [DOI] [Google Scholar]
  100. Margulieux G. W.; Kim S.; Chirik P. J. Determination of the N-H Bond Dissociation Free Energy in a Pyridine(diimine)molybdenum Complex Prepared by Proton-Coupled Electron Transfer. Inorg. Chem. 2020, 59 (20), 15394–15401. 10.1021/acs.inorgchem.0c02382. [DOI] [PubMed] [Google Scholar]
  101. Kim S.; Park Y.; Kim J.; Pabst T. P.; Chirik P. J. Ammonia synthesis by photocatalytic hydrogenation of a N2-derived molybdenum nitride. Nat. Synth. 2022, 1 (4), 297–303. 10.1038/s44160-022-00044-1. [DOI] [Google Scholar]
  102. Ashida Y.; Arashiba K.; Nakajima K.; Nishibayashi Y. Molybdenum-catalysed ammonia production with samarium diiodide and alcohols or water. Nature 2019, 568 (7753), 536–540. 10.1038/s41586-019-1134-2. [DOI] [PubMed] [Google Scholar]
  103. Eizawa A.; Arashiba K.; Tanaka H.; Kuriyama S.; Matsuo Y.; Nakajima K.; Yoshizawa K.; Nishibayashi Y. Remarkable catalytic activity of dinitrogen-bridged dimolybdenum complexes bearing NHC-based PCP-pincer ligands toward nitrogen fixation. Nat. Commun. 2017, 8, 14874. 10.1038/ncomms14874. [DOI] [PMC free article] [PubMed] [Google Scholar]
  104. Arashiba K.; Miyake Y.; Nishibayashi Y. A molybdenum complex bearing PNP-type pincer ligands leads to the catalytic reduction of dinitrogen into ammonia. Nat. Chem. 2011, 3 (2), 120–125. 10.1038/nchem.906. [DOI] [PubMed] [Google Scholar]
  105. Tanaka H.; Arashiba K.; Kuriyama S.; Sasada A.; Nakajima K.; Yoshizawa K.; Nishibayashi Y. Unique behaviour of dinitrogen-bridged dimolybdenum complexes bearing pincer ligand towards catalytic formation of ammonia. Nat. Commun. 2014, 5, 3737. 10.1038/ncomms4737. [DOI] [PMC free article] [PubMed] [Google Scholar]
  106. Locher J.; Watt F. A.; Neuba A. G.; Schoch R.; Munz D.; Hohloch S. Molybdenum(VI) bis-imido Complexes of Dipyrromethene Ligands. Inorg. Chem. 2020, 59 (14), 9847–9856. 10.1021/acs.inorgchem.0c01051. [DOI] [PubMed] [Google Scholar]
  107. Dong Y.; Clarke R. M.; Zheng S.-L.; Betley T. A. Synthesis and electronic structure studies of a Cr-imido redox series. Chem. Commun. 2020, 56 (21), 3163–3166. 10.1039/D0CC00108B. [DOI] [PMC free article] [PubMed] [Google Scholar]
  108. Ballmann G.; Grams S.; Elsen H.; Harder S. Dipyrromethene and β-Diketiminate Zinc Hydride Complexes: Resemblances and Differences. Organometallics 2019, 38 (14), 2824–2833. 10.1021/acs.organomet.9b00334. [DOI] [Google Scholar]
  109. Tomson N. C.; Arnold J.; Bergman R. G. Synthesis, Characterization, and Reactions of Isolable (β-Diketiminato)Nb(III) Imido Complexes. Organometallics 2010, 29 (21), 5010–5025. 10.1021/om1002528. [DOI] [PMC free article] [PubMed] [Google Scholar]
  110. Lohrey T. D.; Bergman R. G.; Arnold J. Reductions of a Rhenium(III) Terminal Oxo Complex by Isocyanides and Carbon Monoxide. Organometallics 2018, 37 (20), 3552–3557. 10.1021/acs.organomet.8b00238. [DOI] [Google Scholar]
  111. Schindler T.; Sauer A.; Spaniol T. P.; Okuda J. Oxygen Atom Transfer Reactions with Molybdenum Cofactor Model Complexes That Contain a Tetradentate OSSO-Type Bis(phenolato) Ligand. Organometallics 2018, 37 (23), 4336–4340. 10.1021/acs.organomet.8b00386. [DOI] [Google Scholar]
  112. Chakraborty J.; Mandal U.; Ghiviriga I.; Abboud K. A.; Veige A. S. Ammonia Synthesis through Hydrolysis of a Trianionic Pincer Ligand-Supported Molybdenum-Nitride Complex. Chem. Eur. J. 2019, 25 (62), 14059–14063. 10.1002/chem.201903740. [DOI] [PubMed] [Google Scholar]
  113. Gonsales S. A.; Ghiviriga I.; Abboud K. A.; Veige A. S. Carbon dioxide cleavage across a tungsten-alkylidyne bearing a trianionic pincer-type ligand. Dalton Trans. 2016, 45 (40), 15783–15785. 10.1039/C6DT01049K. [DOI] [PubMed] [Google Scholar]
  114. Jakhar V.; Pal D.; Ghiviriga I.; Abboud K. A.; Lester D. W.; Sumerlin B. S.; Veige A. S. Tethered Tungsten-Alkylidenes for the Synthesis of Cyclic Polynorbornene via Ring Expansion Metathesis: Unprecedented Stereoselectivity and Trapping of Key Catalytic Intermediates. J. Am. Chem. Soc. 2021, 143 (2), 1235–1246. 10.1021/jacs.0c12248. [DOI] [PubMed] [Google Scholar]
  115. Mandal U.; VenkatRamani S.; Ghiviriga I.; Abboud K. A.; Veige A. S. Synthesis and Characterization of Tungsten Alkylidene and Alkylidyne Complexes Featuring a New Carbazole-Based Rigid Trianionic ONO 3- Pincer-Type Ligand. Organometallics 2020, 39 (12), 2207–2213. 10.1021/acs.organomet.0c00150. [DOI] [Google Scholar]
  116. Morales D.; Pérez J.; Riera L.; Riera V.; Miguel D. Formation of a 1-azaallenylidene ligand by reaction of an amido complex with tetracyanoethylene. Inorg. Chem. 2002, 41 (16), 4111–4113. 10.1021/ic025665b. [DOI] [PubMed] [Google Scholar]
  117. O’Reilly M. E.; Ghiviriga I.; Abboud K. A.; Veige A. S. A new ONO3- trianionic pincer-type ligand for generating highly nucleophilic metal-carbon multiple bonds. J. Am. Chem. Soc. 2012, 134 (27), 11185–11195. 10.1021/ja302222s. [DOI] [PubMed] [Google Scholar]
  118. O’Reilly M. E.; Ghiviriga I.; Abboud K. A.; Veige A. S. Unusually stable tungstenacyclobutadienes featuring an ONO trianionic pincer-type ligand. Dalton Trans. 2013, 42 (10), 3326–3336. 10.1039/c2dt32653a. [DOI] [PubMed] [Google Scholar]
  119. Rosenkoetter K. E.; Ziller J. W.; Heyduk A. F. A Heterobimetallic W-Ni Complex Containing a Redox-Active WSNS2Metalloligand. Inorg. Chem. 2016, 55 (13), 6794–6798. 10.1021/acs.inorgchem.6b01164. [DOI] [PubMed] [Google Scholar]
  120. Rosenkoetter K. E.; Ziller J. W.; Heyduk A. F. Heterobimetallic complexes of palladium and platinum containing a redox-active WSNS2 metalloligand. Dalton Trans. 2017, 46 (17), 5503–5507. 10.1039/C6DT04451D. [DOI] [PubMed] [Google Scholar]
  121. Shaffer D. W.; Szigethy G.; Ziller J. W.; Heyduk A. F. Synthesis and characterization of a redox-active bis(thiophenolato)amide ligand, SNS3-, and the homoleptic tungsten complexes, WSNS2 and WONO2. Inorg. Chem. 2013, 52 (4), 2110–2118. 10.1021/ic302506e. [DOI] [PubMed] [Google Scholar]
  122. Wojnar M. K.; Ziller J. W.; Heyduk A. F. Heterobimetallic and Heterotrimetallic Clusters Containing a Redox-Active Metalloligand. Eur. J. Inorg. Chem. 2017, 2017 (47), 5571–5575. 10.1002/ejic.201701222. [DOI] [Google Scholar]
  123. de Aguiar S. R. M. M.; Öztopcu Ö.; Troiani A.; de Petris G.; Weil M.; Stöger B.; Pittenauer E.; Allmaier G.; Veiros L. F.; Kirchner K. Formation of Mono Oxo Molybdenum(IV) PNP Pincer Complexes: Interplay between Water and Molecular Oxygen. Eur. J. Inorg. Chem. 2018, 2018 (7), 876–884. 10.1002/ejic.201701413. [DOI] [PMC free article] [PubMed] [Google Scholar]
  124. Boyd I. W.; Spence J. T. Molybdenum(IV)-oxo complexes with oxygen, nitrogen and sulfur ligands. Syntheses and electrochemical studies. Inorg. Chem. 1982, 21 (4), 1602–1606. 10.1021/ic00134a066. [DOI] [Google Scholar]
  125. Carmona E.; Galindo A.; Guille-Photin C.; Sanchez L. Oxo-molybdenum(IV) and tungsten(IV) complexes with phosphine and isocyanide ligands. Polyhedron 1988, 7 (18), 1767–1771. 10.1016/S0277-5387(00)80409-X. [DOI] [Google Scholar]
  126. Carmona E.; Galindo A.; Sanchez L.; Nielson A. J.; Wilkinson G. Mononuclear and dinuclear tertiary phosphine molybdenum complexes. oxo-molybdenum(IV), dinuclear Mo2Cl4L4 and related derivatives. Polyhedron 1984, 3 (3), 347–352. 10.1016/S0277-5387(00)88119-X. [DOI] [Google Scholar]
  127. Carmona E.; Sánchez L.; Poveda M. L.; Jones R. A.; Hefner J. G. Some trimethyl phosphine and trimethyl phosphite complexes of tungsten(IV). Polyhedron 1983, 2 (8), 797–801. 10.1016/S0277-5387(00)87209-5. [DOI] [Google Scholar]
  128. Tran B. L.; Carrano C. J. Oxo-molybdenum(VI,V,IV) complexes of the facially coordinating tris(mercaptoimidazolyl)borate ligand: synthesis, characterization, and oxygen atom transfer reactivity. Inorg. Chem. 2007, 46 (13), 5429–5438. 10.1021/ic7005259. [DOI] [PubMed] [Google Scholar]
  129. Heinze K. Bioinspired functional analogs of the active site of molybdenum enzymes: Intermediates and mechanisms. Coord. Chem. Rev. 2015, 300, 121–141. 10.1016/j.ccr.2015.04.010. [DOI] [Google Scholar]
  130. Leppin J.; Förster C.; Heinze K. Molybdenum complex with bulky chelates as a functional model for molybdenum oxidases. Inorg. Chem. 2014, 53 (23), 12416–12427. 10.1021/ic501751p. [DOI] [PubMed] [Google Scholar]
  131. Dupé A.; Judmaier M. E.; Belaj F.; Zangger K.; Mösch-Zanetti N. C. Activation of molecular oxygen by a molybdenum complex for catalytic oxidation. Dalton Trans. 2015, 44 (47), 20514–20522. 10.1039/C5DT02931G. [DOI] [PubMed] [Google Scholar]
  132. Lyashenko G.; Saischek G.; Judmaier M. E.; Volpe M.; Baumgartner J.; Belaj F.; Jancik V.; Herbst-Irmer R.; Mösch-Zanetti N. C. Oxo-molybdenum and oxo-tungsten complexes of Schiff bases relevant to molybdoenzymes. Dalton Trans. 2009, (29), 5655–5665. 10.1039/b820629e. [DOI] [PubMed] [Google Scholar]
  133. Chen G.-X.; Datta A.; Hsiao H.-C.; Lin C.-H.; Huang J.-H. Structural elucidation of tungsten compounds containing arylamine, piperazine and morpholine fragments of pyrrole and keto-amine ligands. Polyhedron 2015, 101, 299–305. 10.1016/j.poly.2015.09.035. [DOI] [Google Scholar]
  134. Clough C. R.; Cummins C. C.. CCDC 823810: Experimental Crystal Structure Determination, 2011, 10.5517/ccwn7j8. [DOI]
  135. Cremer C.; Burger P. Tuning the redox potentials of dinuclear tungsten oxo complexes (Cp*W(4,4’-R,R-2,2’-bpy)(mu-O))2PF62 toward photochemical water splitting. Chem. Eur. J. 2003, 9 (15), 3583–3596. 10.1002/chem.200204330. [DOI] [PubMed] [Google Scholar]
  136. Cremer C.; Burger P. Tuning the redox potentials of dinuclear tungsten oxo complexes (Cp*W(4,4’-R,R-2,2’-bpy)(mu-O))2PF62 toward photochemical water splitting. Chem. Eur. J. 2003, 9 (15), 3583–3596. 10.1002/chem.200204330. [DOI] [PubMed] [Google Scholar]
  137. Hazama R.; Umakoshi K.; Ichimura A.; Ikari S.; Sasaki Y.; Ito T. Dinuclear Oxomolybdenum(V) and Oxotungsten(V) Complexes of the Hexadentate Ligands N, N, N ′, N ′-Tetrakis(2-pyridylmethyl)ethylenediamine and Its Propylenediamine Analog. Bull. Chem. Soc. Jpn. 1995, 68 (2), 456–468. 10.1246/bcsj.68.456. [DOI] [Google Scholar]
  138. Mouat A. R.; Mane A. U.; Elam J. W.; Delferro M.; Marks T. J.; Stair P. C. Volatile Hexavalent Oxo-amidinate Complexes: Molybdenum and Tungsten Precursors for Atomic Layer Deposition. Chem. Mater. 2016, 28 (6), 1907–1919. 10.1021/acs.chemmater.6b00248. [DOI] [Google Scholar]
  139. Schreiber P.; Wieghardt K.; Floerke U.; Haupt H. J. Acid-catalyzed anti.fwdarw. syn isomerization of the {WV2O4}2+ core. Crystal structures of anti-tetraoxobis(1,4,7-triazacyclononane)ditungsten(2+) diiodide and syn-bis[tetraoxobis(1,4,7-triazacyclononane)ditungsten(2+)] dithionate diiodide dihydrate. Inorg. Chem. 1988, 27 (12), 2111–2115. 10.1021/ic00285a020. [DOI] [Google Scholar]
  140. Yan T.; VenkatRamani S.; Schrock R. R.; Müller P. Synthesis of Tungsten Oxo Alkylidene Biphenolate Complexes and Ring-Opening Metathesis Polymerization of Norbornenes and Norbornadienes. Organometallics 2019, 38 (16), 3144–3150. 10.1021/acs.organomet.9b00377. [DOI] [Google Scholar]
  141. Benedikter M. J.; Musso J. V.; Frey W.; Schowner R.; Buchmeiser M. R. Cationic Group VI Metal Imido Alkylidene N-Heterocyclic Carbene Nitrile Complexes: Bench-Stable, Functional-Group-Tolerant Olefin Metathesis Catalysts. Angew. Chem., Int. Ed. 2021, 60 (3), 1374–1382. 10.1002/anie.202011666. [DOI] [PMC free article] [PubMed] [Google Scholar]
  142. Chao Y. W.; Rodgers P. M.; Wigley D. E.; Alexander S. J.; Rheingold A. L. Tris(phenylimido) complexes of tungsten: preparation and properties of the d0 W(:NR)3 functional group. J. Am. Chem. Soc. 1991, 113 (16), 6326–6328. 10.1021/ja00016a090. [DOI] [Google Scholar]
  143. Duhacek J. C.; Siddiquee T. A.; Bennett D. W.; Duncan D. C. The Synthesis, Crystal, and Molecular Structure of Two Mononuclear Arylimido Tungsten Tetrachloride Complexes, [WCl4(NC6H4I-p)(CH3CN)] and [WCl4(NC6H3–2,6-i-Pr 2)(CH3CN)]. J. Chem. Crystallogr. 2008, 38 (6), 431–435. 10.1007/s10870-008-9334-x. [DOI] [Google Scholar]
  144. Grubba R.; Ordyszewska A.; Ponikiewski L.; Gudat D.; Pikies J. An investigation on the chemistry of the R2P = P ligand: reactions of a phosphanylphosphinidene complex of tungsten(VI) with electrophilic reagents. Dalton Trans. 2016, 45 (5), 2172–2179. 10.1039/C5DT03085D. [DOI] [PubMed] [Google Scholar]
  145. Imbrich D. A.; Frey W.; Buchmeiser M. R. N-Heterocyclic carbene-induced transmethylation in tungsten imido alkylidene bistriflates: unexpected formation of an N-heterocyclic olefin complex. Chem. Commun. 2017, 53 (88), 12036–12039. 10.1039/C7CC07471A. [DOI] [PubMed] [Google Scholar]
  146. Lokare K. S.; Ciszewski J. T.; Odom A. L. Group-6 Imido Activation by a Ring-Strained Alkyne. Organometallics 2004, 23 (23), 5386–5388. 10.1021/om049262q. [DOI] [Google Scholar]
  147. Lopez L. P. H.; Schrock R. R.; Müller P. Dimers that Contain Unbridged W(IV)/W(IV) Double Bonds. Organometallics 2006, 25 (8), 1978–1986. 10.1021/om050961s. [DOI] [Google Scholar]
  148. Mougel V.; Copéret C. Magnitude and consequences of OR ligand σ-donation on alkene metathesis activity in d 0 silica supported (SiO)W(NAr)(CHtBu)(OR) catalysts. Chem. Sci. 2014, 5 (6), 2475–2481. 10.1039/C4SC00230J. [DOI] [Google Scholar]
  149. Tanahashi H.; Ikeda H.; Tsurugi H.; Mashima K. Synthesis and Characterization of Paramagnetic Tungsten Imido Complexes Bearing α-Diimine Ligands. Inorg. Chem. 2016, 55 (4), 1446–1452. 10.1021/acs.inorgchem.5b02145. [DOI] [PubMed] [Google Scholar]
  150. Williams D. S.; Schofield M. H.; Schrock R. R. Synthesis of d2 complexes that contain tungsten [W(NAr)2] and rhenium [Re(NAr)2] cores, SCF-X.alpha.-SW calculations, and a discussion of the MCp2/M’(NR)2 isolobal relationship. Organometallics 1993, 12 (11), 4560–4571. 10.1021/om00035a047. [DOI] [Google Scholar]
  151. Bai G.; Wei P.; Stephan D. W. Reductions of β-Diketiminato–Titanium(III) Complexes. Organometallics 2006, 25 (10), 2649–2655. 10.1021/om060076p. [DOI] [Google Scholar]
  152. Basuli F.; Huffman J. C.; Mindiola D. J. Reductive C-N bond cleavage of the NCCCN β-diketiminate backbone: A direct approach to azabutadienyl and alkylidene-anilide scaffolds. Inorg. Chim. Acta 2007, 360 (1), 246–254. 10.1016/j.ica.2006.07.045. [DOI] [Google Scholar]
  153. Hamaki H.; Takeda N.; Tokitoh N. Reduction of Tetravalent Group 4 Metal Complexes Supported by an Extremely Bulky, Unsymmetrically Substituted β-Diketiminato Ligand Leading to the Regioselective CN Bond Cleavage Giving Ring-Contracted Metal-Imido Complexes. Organometallics 2006, 25 (10), 2457–2464. 10.1021/om0509948. [DOI] [Google Scholar]
  154. Hamaki H.; Takeda N.; Tokitoh N. Nucleophilic Attack toward Group 4 Metal Complexes Bearing Reactive 1-Aza-1,3-butadienyl and Imido Moieties. Inorg. Chem. 2007, 46 (5), 1795–1802. 10.1021/ic0620844. [DOI] [PubMed] [Google Scholar]
  155. Ponikiewski L.; Ziółkowska A.; Pikies J. Reactions of Lithiated Diphosphanes R2P-P(SiMe3)Li (R = tBu and iPr) with MeNacnacTiCl2·THF and MeNacnacTiCl3. Formation and Structure of TitaniumIII and TitaniumIV β-Diketiminato Complexes Bearing the Side-on Phosphanylphosphido and Phosphanylphosphinidene Functionalities. Inorg. Chem. 2017, 56 (3), 1094–1103. 10.1021/acs.inorgchem.6b01929. [DOI] [PubMed] [Google Scholar]
  156. Ziółkowska A.; Szynkiewicz N.; Pikies J.; Ponikiewski L. Solvent Impact on the Diversity of Products in the Reaction of Lithium Diphenylphosphide and a Ti(III) Complex Supported by a tBu2P-P(SiMe3) Ligand. Inorg. Chem. 2020, 59 (16), 11305–11315. 10.1021/acs.inorgchem.0c00824. [DOI] [PMC free article] [PubMed] [Google Scholar]
  157. Ignatov S. K.; Khalimon A. Y.; Rees N. H.; Razuvaev A. G.; Mountford P.; Nikonov G. I. Beta-agostic silylamido and silyl-hydrido compounds of molybdenum and tungsten. Inorg. Chem. 2009, 48 (20), 9605–9622. 10.1021/ic900591e. [DOI] [PubMed] [Google Scholar]
  158. Ordyszewska A.; Szynkiewicz N.; Ponikiewski L.; Scheer M.; Pikies J.; Grubba R. Syntheses and Structures of Transition Metal Complexes with Phosphanylphosphinidene Chalcogenide Ligands. Inorg. Chem. 2019, 58 (12), 7905–7914. 10.1021/acs.inorgchem.9b00594. [DOI] [PubMed] [Google Scholar]
  159. Complexes of Bulky β-Diketiminate Ligands. In Inorganic Syntheses; Rauchfuss T. B., Ed.; John Wiley & Sons, Inc., 2010; pp 1–55. 10.1002/9780470651568.ch1. [DOI] [Google Scholar]
  160. Lalancette J.-M.; Rollin G.; Dumas P. Metals Intercalated in Graphite. I. Reduction and Oxidation. Can. J. Chem. 1972, 50 (18), 3058–3062. 10.1139/v72-485. [DOI] [Google Scholar]
  161. Bergbreiter D. E.; Killough J. M. Reactions of potassium-graphite. J. Am. Chem. Soc. 1978, 100 (7), 2126–2134. 10.1021/ja00475a025. [DOI] [Google Scholar]
  162. Rice C. A.; Benson C. G.; McAuliffe C. A.; Hill W. E. The coordination chemistry of molybdenum and tungsten. Part XVI. Oxomolybdenum(V) and oxotungsten(V) complexes containing neutral monodentate and anionic bidentate Schiff base ligands. Inorg. Chim. Acta 1982, 59, 33–39. 10.1016/S0020-1693(00)87304-1. [DOI] [Google Scholar]
  163. Persson C.; Andersson C. Reduction of tungsten(VI) and molybdenum(V) by allyltrimethylsilane and cyclopentene. Simple high yield syntheses of MoCl4(OEt2)2, MoCl4(dme), WCl4(thf)2, WCl4(dme) and WOCl3(thf)2. Inorg. Chim. Acta 1993, 203 (2), 235–238. 10.1016/S0020-1693(00)81663-1. [DOI] [Google Scholar]
  164. Stoll S.; Schweiger A. EasySpin, a comprehensive software package for spectral simulation and analysis in EPR. Journal of magnetic resonance (San Diego, Calif.: 1997) 2006, 178 (1), 42–55. 10.1016/j.jmr.2005.08.013. [DOI] [PubMed] [Google Scholar]
  165. Dolomanov O. V.; Bourhis L. J.; Gildea R. J.; Howard J. A. K.; Puschmann H. OLEX2: a complete structure solution, refinement and analysis program. J. Appl. Crystallogr. 2009, 42 (2), 339–341. 10.1107/S0021889808042726. [DOI] [Google Scholar]
  166. Sheldrick G. M. SHELXT - integrated space-group and crystal-structure determination. Acta Cryst. A 2015, 71 (1), 3–8. 10.1107/S2053273314026370. [DOI] [PMC free article] [PubMed] [Google Scholar]
  167. Sheldrick G. M. Crystal structure refinement with SHELXL. Acta Cryst. C 2015, 71 (1), 3–8. 10.1107/S2053229614024218. [DOI] [PMC free article] [PubMed] [Google Scholar]
  168. van der Sluis P.; Spek A. L. BYPASS: an effective method for the refinement of crystal structures containing disordered solvent regions. Acta Cryst. A 1990, 46 (3), 194–201. 10.1107/S0108767389011189. [DOI] [Google Scholar]

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