Skip to main content
NCBI home page
Chemical Science logoLink to Chemical Science
. 2026 Sep 21. Online ahead of print. doi: 10.1039/d6sc05592c

Comparison of MgYb and Mg–Ca bonding: structures, electronic analyses and reactivities

Sandeep Kumar Thakur a, Tanuja Tewari a, Nil Roig b, Jens Langer a, Mercedes Alonso c, Sjoerd Harder a,✉
PMCID: PMC13636282  PMID: 42835594

Abstract

Reaction of [(BDI*)MgNa]2 with (Am*YbI)2 in methylcyclohexane led to the precipitation of NaI and quantitative formation of (BDI*)Mg–Yb(Am*) (1-Yb); BDI* = HC[C(tBu)N(DIPeP)]2, DIPeP = 2,6-Et2CH-phenyl; Am* = tBuC(N-DIPP)2, DIPP = 2,6-iPr-phenyl. Complex 1-Yb features a long unsupported 2c–2e Mg–Yb bond of 3.302 Å and crystallizes isomorphous to (BDI*)Mg–Ca(Am*) (1-Ca). The formal Mg0–YbII oxidation states in 1-Yb are confirmed by effective-oxidation-state analysis but the low reliability index of 68.0% indicates that this description is not fully representative of the electron distribution. Analysis of the electron density shows significant Mg0 → YbII electron transfer and therefore the complex has partial MgI–YbI character. EDA-NOCV analysis suggests that bonding in 1-Yb is best pictured as a combination of neutral open-shell radicals (BDI*)Mg˙/(Am*)Yb˙. Accordingly, (BDI*)Mg acts as an X-type ligand for Yb(Am*). The long, polarized Mgδ−–Ybδ+ bond in 1-Yb is highly reactive. The thermal decomposition and reactivity of 1-Yb with N2O, NH3, 1,1-diphenylethylene, trans-stilbene and anthracene have been studied. Comparison with the reactivity of 1-Ca shows strong similarities, but also important differences. Most reactants oxidize the Mg0 centre in 1-Yb and 1-Ca and produce similar complexes that generally crystallize isomorphous. However, N2O can also oxidize the YbII centre, resulting in paramagnetic YbIII products. In all cases, the Mg–Yb and Mg–Ca bonds in 1-Yb and 1-Ca are considerably more reactive than the unpolarized Mg–Mg bond in complexes of type (BDI)Mg–Mg(BDI).

A complex featuring an unsupported 2c–2e Mg–Yb bond and formal oxidation states Mg0–YbII was isolated. The properties and very high reactivity of the polarized Mgδ−–Ybδ+ bond are compared with those of a related Mg–Ca complex.graphic file with name d6sc05592c-ga.webp

Introduction

Cotton's first examples of metal–metal bonding are now more than half a century old.1 What began as investigations of homometallic multiple bonding between transition metals has developed into a large research field covering homo- and heterometallic bonding in all varieties throughout the periodic table.2 The vast majority of these bonds involve p- and d-block metals whereas f- and especially s-block metal–metal bonding remain clearly underrepresented. This is undoubtedly due to their highly electropositive character, which results in facile loss of the electrons required for metal–metal bonding. There are rare examples of unusual, supported metal–metal interactions between f-block elements.3–6 Stable complexes with bonding between group 1 metals are unknown although long, weak M+⋯M− or M−⋯M− metal–metal interactions in alkalides have been discussed.7,8 The only homometallic metal–metal bonds established in the s-block involve the most electronegative metals, Be and Mg. Whereas stable (BDI)Mg–Mg(BDI), (Gua)Mg–Mg(Gua) or CpBe–BeCp complexes have been reported (BDI = β-diketiminate ligand, Gua = guanidinate ligand, and Cp = cyclopentadienyl ligand),9,10 attempts to isolate similar complexes for the larger, more electropositive alkaline-earth (Ae) metals Ca and Sr resulted in electron loss and reduction of either the solvent or N2 used as a protecting gas.11–13

Aiming to further develop the rapidly growing field of low-oxidation-state group 2 metal chemistry,14–17 we recently isolated a Mg0/NaI complex: [(BDI*)Mg−Na+]2 (I, Scheme 1, BDI* = HC[C(tBu)N(DIPeP)]2, DIPeP = 2,6-Et2CH-phenyl).18 This unusual magnesyl sodium dimer, for which a second example has been recently reported,19 displays unique Mg–Na bonding that is best described as an electrostatic interaction between a magnesyl anion, (BDI*)Mg−, and a Na+ cation. However, charge distribution calculations show slight electron transfer from the electron rich (BDI*)Mg− anion to Na+, indicating that this is a simplified bonding model.

Scheme 1. The magnesyl sodium complex [(BDI*)Mg−Na+]2 (I) as a key precursor to create new Mg–metal bonds either by ligand–metal exchange (left) or salt-metathesis (right) (Ar = 2,6-Et2CH-phenyl).

Scheme 1

Open in a new tab

Mixing dimeric I with (AeN″2)2 (N″ = N(SiMe3)2) gave access to a range of mixed aggregates with unique Mg–Ae bonds (II-Ae, Ae = Mg, Ca, Sr, Ba).20 These aggregates could be regarded as (BDI*)Mg–AeN″ complexes stabilized by aggregation with NaN″. Also, these complexes feature slight electron transfer from the electron rich (BDI*)Mg− anion to Ae2+ and Na+. Charge distributions show that (BDI*)Mg− → Ae2+ electron transfer increases with increasing Lewis acidity of the Ae2+ cation (Ba2+ < Sr2+ < Ca2+ < Mg2+). The large, electropositive Ae2+ cations form very long and rather labile Mg–Ae bonds, whereas the small, more electronegative Mg2+ cation forms the strongest bond. The Mg–Mg bond in II-Mg is so strong that NaN″ elimination to give (BDI*)Mg–MgN″ is facile. However, in the heavier complexes of type II-Ae (Ae = Ca, Sr, Ba) the Mg–Ae bond is weak. Therefore, they are in dynamic equilibrium with (BDI*)Mg−Na+ and AeN″2. This allows facile exchange of Ae for another metal M by simple addition of MN″2.

Based on the close similarity between CaII and YbII complexes,21 we could also isolate II-Yb which shows the same structure and properties as II-Ca.22 The Mg–Ca and Mg–Yb bonds in II-Ca and II-Yb are supported by interaction with a Na–N″ moiety. According to Green's MLX covalent-bond-classification,23,24 the (BDI*)Mg− anion in II-Ca or II-Yb could be considered as a L-type ligand, i.e. an anionic 2e− Lewis base coordinating to AeN″2 or YbN″2 in a similar manner to neutral Cp*Ga or THF coordinating to AeCp2*.25–27

In a different approach, the magnesyl sodium complex I has been used as a reactant in salt-metathesis reactions (Scheme 1). Thus, we have been able to prepare complexes in which (BDI*)Mg is an X-type ligand for BeCp* (III),28 MgCp* (IV)29 or Ca(Am*) (1-Ca);30 Am* = tBuC(N-DIPP)2 and DIPP = 2,6-iPr-phenyl. These complexes feature unsupported Mg–Ae bonds in which both metals contribute one electron each. Based on the decreasing electronegativities descending group 2 (Be: 1.56, Mg: 1.31, and Ca: 1.00),31 the formal oxidation state assignments in these types of complexes are MgII/Be0 (III), MgI/MgI (IV) and Mg0/CaII (1-Ca). Although formal oxidation states are not equivalent to metal charges, the calculated NPA charges (III: Mg +1.21/Be +0.62; 1-Ca: Mg +0.66/Ca +1.28) rationalize the observed switch in metal–metal bond polarization from Mgδ+–Beδ− to Mgδ−–Caδ+. Indeed, the Mg centre in (BDI*)Mg-Ca(Am*) (1-Ca) was shown to react as a nucleophile, whereas Ca functions as an electrophile.30 Despite these roles and formal oxidation states Mg0/CaII, there is considerable transfer of electron density from Mg0 to CaII. This is evident from the NPA charge of +1.28 on Ca which is significantly lower than typical values calculated for CaII (ca. +1.75). It is also considerably lower than the +1.52 charge on Ca in II-Ca in which (BDI*)Mg− is an L-type ligand. In fact, the +1.28 charge on Ca in 1-Ca is the lowest calculated charge for any reported Ca complex. Hence, this complex could be considered to have partial MgI/CaI character.

As there are striking similarities, but also important differences in Ca+II and Yb+II chemistry,21 we extended this chemistry through the isolation and full characterization of (BDI*)Mg–Yb(Am*) (1-Yb). This complex represents the first lanthanide complex with an unsupported s-block metal–Yb bond. In addition, we expect an unusually low charge on Yb and a significant contribution of MgI/YbI character.

Results and discussion

Synthesis

The synthesis of (BDI*)Mg–Yb(Am*) (1-Yb) was achieved following a similar protocol to that reported for (BDI*)Mg–Ca(Am*) (1-Ca, Scheme 2). Salt-metathesis between Am*K and YbI2 gave the precursor (Am*YbI)2 (2-Yb) in the form of an orange powder in 70% yield. It crystallized from pentane solution as an ether-free dimer (Fig. S57). 1H NMR analysis (Fig. S1) revealed two different DIPP-substituents indicating that the N-aryl-chelation of the Am* ligand is maintained in solution.

Scheme 2. Synthesis of (BDI*)Mg–Yb(Am*) (1-Yb), and reactivity of 1-Yb and the previously reported 1-Ca complex.

Scheme 2

Open in a new tab

Reaction of (Am*YbI)2 (2-Yb) with the magnesyl sodium dimer (I) in methylcyclohexane led to immediate precipitation of NaI and quantitative formation of the expected (BDI*)Mg–Yb(Am*) complex (1-Yb). The crude product obtained after solvent removal is essentially pure, but can also be crystalized overnight from a concentrated pentane solution at −35 °C in 94% yield. Like 1-Ca, it crystallized in the triclinic space group P1̄ with very similar cell parameters (Fig. 1a).30 There are two independent molecules in the asymmetric unit with nearly equal Mg–Yb bond lengths (3.299(2) Å and 3.305(2) Å). The average Mg–Yb distance of 3.302 Å is close to the sum of the covalent radii of 3.28 Å (Mg 1.41 and Yb 1.87)32 and very similar to the Mg–Ca bond length in 1-Ca (3.298 Å). However, it is considerably shorter than the Mg–Yb bond in II-Yb (3.466(1) Å).22 Fitting the structure of 1-Yb on that of 1-Ca shows their close similarity (Fig. 1b).

Fig. 1. (a) Crystal structure of 1-Yb. (b) Superimposed structures of 1-Yb (dark-green) and 1-Ca (pink). (c) Crystal structure of 3-Ca. (d) Crystal structure of 7-Ca. All H atoms (except OH and NH hydrogen) are omitted for clarity. In 3-Ca and 7-Ca, the Et and Me groups from BDI* and Am*, respectively, have also been omitted for clarity.

Fig. 1

Open in a new tab

The Mg–N bond lengths in 1-Yb range from 2.086(4) to 2.107(5) Å. The average Mg–N bond (2.094 Å) is longer as expected for BDI*–MgII coordination. For example, the average Mg–N bond distance in (BDI*)MgI, which features a similar tricoordinate Mg centre, is only 1.998 Å.33 As we noticed earlier, the Mg–N bond distances are very sensitive to the oxidation state of the Mg centre. Complex 1-Yb is formally a Mg0/YbII complex and the electron rich Mg0 centre results in Mg–N bond elongation. However, the average Mg–N bond distance in 1-Yb (2.094 Å) is smaller than the Mg0–N bond in I (2.117 Å)18 but larger than the MgI–N bond in (BDI*)Mg–Mg(BDI*)33 (2.064 Å). This is a strong indication for partial transfer of electron density from the electron rich Mg0 centre to YbII. Such transfer of electron density to Yb is also in agreement with the rather long Yb–N bonds in 1-Yb (2.392(4)–2.421(5) Å, average 2.407 Å) when compared to that in precursor 2-Yb (2.369 Å). Also, the Yb⋯C(Ar) contacts in 1-Yb (average: 2.485 Å) are longer than in 2-Yb (average: 2.429 Å). Charge calculations confirm the electron-rich nature of both, Mg and Yb (vide infra).

Complexes 1-Ca and 1-Yb are not stable in benzene solution and immediately lose their intense dark-brown colour. 1H NMR analyses suggest reductive cleavage of the benzene C–H bond and formation of previously reported (BDI*)MgPh18 and (Am*)MH complexes (M = Ca, Yb)34,35 (Fig. S43). The 1H NMR spectrum of 1-Yb in C6D12 (Fig. S6) shows close similarities to that of 1-Ca, revealing sharp resonances with clear spin coupling. This confirms its diamagnetic nature and the YbII oxidation state. The only broadened signals are assigned to the DIPP-substituents of the Am* ligand. Two sets of resonances are observed showing that the Am* ligand in 1-Yb is also N-aryl-chelating in solution. Broadening is due to slow exchange, but because of thermal instability of 1-Yb, we were unable to reach coalescence by heating. In C6D12, 1-Yb decomposes over time (Fig. S37; 24 h: 50% decomposition and 4 days: full decomposition). The complex is significantly less stable than 1-Ca, which required 10 days for full decomposition. Its decomposition is also less selective and at least 3–4 different products are formed. Although we could not crystallize the major decomposition product, we propose a similar decomposition route to that for 1-Ca. This involves insertion of Mg0 in a benzylic C–H bond and formation of a complex with a bridging hydride ligand (Scheme 2). Strong evidence for this complex is provided by comparison of the 1H NMR data of the decomposition products of 1-Yb with those reported for 1-Ca. These spectra show close similarities except for the resonance of the bridging hydride (Fig. S38). This is a singlet at 2.57 ppm for the Mg–H–Ca unit but is considerably downfield shifted for Mg–H–Yb (5.16 ppm). A similar shift of the hydride resonance to higher ppm values has previously been observed for Yb hydride complexes and is due to the close vicinity of the heavy metal Yb nucleus.36 As the 171Yb nucleus (14% abundance, I = 1/2) is NMR active, the hydride signal also shows weak satellites with 1JYb–H coupling of 252 Hz (Fig. S37). However, we have not been able to detect the 171Yb NMR signal which is often a problem for ytterbium hydride complexes.36,37

Computational analysis

Complex 1-Yb was optimized at the same level of theory as previously reported for 1-Ca (B3PW91-D3BJ/def2-TZVP//B3PW91-D3BJ/def2-SVP), using a Stuttgart–Dresden (SDD) effective core potential for the heavy Yb atom. The calculated bond distances are generally in good agreement with the experimental values (Fig. S66), except for the Mg–Yb bond, which is calculated to be somewhat shorter (3.241 Å versus 3.302 Å). Such discrepancies of 0.05–0.10 Å are commonly observed for metal–metal bonds.38

Atoms-In-Molecules (AIM) analysis of 1-Yb (Fig. 2a) shows a weak Mg–Yb bond path with a bond-critical-point (bcp). Similar to 1-Ca, a Non-Nuclear-Attractor (NNA) could not be located and the electron density in the Mg–Yb bond is polarized towards the Mg centre. The electron density and Laplacian in the bcp are similar to that calculated for the Mg–Ca complex (1-Yb: ρ(r) = 0.023, ∇2ρ(r) = −0.002; 1-Ca: ρ(r) = 0.022, ∇2ρ(r) = −0.001; values in a.u.). These low values indicate weak covalent interactions.

Fig. 2. (a) Atoms-In-Molecules (AIM) analysis. Laplacian distribution for 1-Yb. Light-blue dots: bond-critical-points (bcps). (b) HOMO, LUMO and LUMO+1 in 1-Yb. (c) EDA-NOCV analysis for a truncated version of (BDI*)Mg–Yb(Am*) (1-Yb) using either charged closed-shell fragments or neutral open-shell fragments. The direction of the charge flow is red → blue. For charged fragments, the major NOCV deformation densities are characterized by a flow of electron density from Mg0 to YbII (ΔEorb = −21.8 kcal mol−1, |v1| = 0.694). For neutral fragments, electron density flows primarily from YbI to MgI (ΔEorb = −20.1 kcal mol−1, |v1| = 0.517) and there is a smaller flow from MgI to YbI (ΔEorb = −8.9 kcal mol−1, |v2| = 0.294).

Fig. 2

Open in a new tab

As pointed out previously,22,39 NPA charge analysis for the metal in YbII complexes consistently shows considerably smaller values than for analogous CaII complexes. This is also the case for 1-Ca and 1-Yb (Table S4). This deficiency is likely related to the use of relativistic effective core potentials in the calculations of Yb complexes. The atomic charges calculated using AIM, which are based on a partitioning of the electron density, provide a much better comparison between 1-Yb (Mg +0.59 and Yb +1.31) and 1-Ca (Mg +0.49 and Ca +1.41). The AIM charge of +1.31 on Yb in 1-Yb is the lowest value calculated for any existing YbII complex. For comparison, the AIM charges in II-Yb are Mg +0.47 and Yb +1.46. This indicates that the transfer of electron density from the electron-rich Mg0 centre to YbII in 1-Yb is even larger than in II-Yb. Although 1-Yb is formally a Mg0/YbII complex, its electron density suggests partial MgI/YbI character. This is in agreement with the experimentally observed geometry (vide supra).

The HOMO in 1-Yb (Fig. 2b) corresponds to a σ-bond along the Mg–Yb axis with a major contribution from s-orbitals on Mg and Yb (Mg: 3s 33%, 3p 20%; Yb: s 19%, p 11%, d 5%). The HOMO−1 to HOMO−7 are mainly represented by the seven f-orbitals located on Yb (Yb: f > 95%). The LUMO and LUMO+1 are represented by a combination of a Yb d-orbital, contributing 12% and 13%, respectively, and the π*-system of the coordinating aryl ring (45% and 57%, respectively), with additional minor contributions from a Mg p-orbital in the LUMO (5%) and from a Yb s-orbital in the LUMO+1 (6%).

Effective-Oxidation-State (EOS) analysis derives oxidation states from first principles.40 This method indicates that 1-Yb can be best described as a Mg0/YbII complex, in agreement with the formal oxidation states (Table S6 and Fig. S67). However, a low reliability index of 68.0% indicates that these assigned oxidation states are not fully representative of the electron distribution described by the wavefunction. This is consistent with the previously discussed transfer of electron density from Mg0 to YbII and closely resembles the EOS analysis on 1-Ca.30

Energy Decomposition Analysis combined with Natural Orbitals for Chemical Valence (EDA-NOCV) calculations (Fig. 2c) on a truncated model system for 1-Yb showed similar results to those for 1-Ca. Two different fragmentations were evaluated: charged closed-shell fragments (BDI*)Mg−/(Am*)Yb+ and neutral open-shell radical ions (BDI*)Mg˙/(Am*)Yb˙ (Table S8). The total interaction energy is significantly larger for the charged fragments (ΔEint = −155.5 kcal mol−1) than for the neutral fragments (ΔEint = −61.6 kcal mol−1). This is mainly due to a larger electrostatic contribution for the charged fragments (ΔEelstat = −178.9 kcal mol−1) versus that for neutral fragments (ΔEelstat = −79.1 kcal mol−1). The orbital interaction energy is also considerably larger for the charged fragments (ΔEorb = −53.7 kcal mol−1) than for the neutral fragments (ΔEorb = −32.8 kcal mol−1). According to EDA convention, the partitioning giving the smallest absolute ΔEorb represents the most realistic description for the bonding interaction. This means that bonding in 1-Yb is best pictured as a combination of neutral open-shell radicals (BDI*)Mg˙/(Am*)Yb˙. However, as there are exceptions to this rule,41 this conclusion should be treated with caution. A similar situation was found in the EDA-NOCV analysis for the Ca analogue 1-Ca.30

Reactivity

We recently reported preliminary results on the reactivity of 1-Ca.30 Herein, we extend these reactivity studies and provide a direct comparison with the reactivity of 1-Yb (Scheme 2).

Solutions of both complexes in methylcyclohexane-d14 react rapidly with H2 already at −80 °C, underscoring the extreme reactivity of these mixed-metal low-valent complexes. For comparison, the well-known (BDI)Mg–Mg(BDI) complexes only react with H2 at increased temperatures.9 Unfortunately, the reactions of 1-Yb and 1-Ca with H2 are fully unselective and even at low temperatures we could not isolate any defined products.

Both complexes 1-Yb and 1-Ca also reacted fast, but unselectively, with CO and CO2 to yield a complex mixture of products. In contrast, MgI complexes reacted selectively with CO and CO2.42,43 Similarly, (BDI)CaI synthons also reacted selectively with CO2 at low temperatures, yielding well-defined carbonates as the major product.44

While reaction of 1-Ca with I2 selectively produced a mixture of BDI*MgI and Am*CaI,30 the oxidation of 1-Yb with I2 was unselective. The formation of paramagnetic species showed that complex 1-Yb was overoxidized to undefined YbIII species. The possibility of additional oxidation of the lanthanide metal complicates reactivity studies of this Mg0/YbII complex. This represents the most significant difference in the reactivity of 1-Yb and 1-Ca.

Stasch and coworkers showed that (BDI)Mg–Mg(BDI) complexes can be selectively oxidized with N2O to give a soluble form magnesium oxide: (BDI)Mg–O–Mg(BDI).45 The ability to deprotonate H2 supports the very high reactivity of such molecular oxide complexes.45 We showed that a similar isolation of a molecular Ca oxide complex could only be achieved by the solid-state conversion of a CaI synthon with N2O gas.46 This afforded a powder of a (BDI)Ca–O–Ca(BDI) complex which despite rapid decomposition in solution could be crystallized fast in a low yield of 27%. The relative stability of a (BDI)Mg–O–Mg(BDI) complex compared with the instability of an analogous (BDI)Ca–O–Ca(BDI) complex, motivated us to attempt the synthesis of the mixed metal (BDI*)Mg–O–Ca(Am*) complex.

Reaction of a solution of 1-Ca in methylcyclohexane with excess N2O at −70 °C led to an immediate change of colour from dark-brown to yellow. 1H NMR of the reaction mixture indicated the formation of several products (Fig. S51). Also, the reaction of solid crystalline 1-Ca with excess N2O gas gave a similar mixture of products. Cooling the crude mixture of products to −35 °C led to formation of a few colourless crystals (circa 5%) suitable for X-ray diffraction. This showed the formation of 3-Ca (Scheme 2) in which one of the terminal CH3 substituents in the BDI* ligand has been deprotonated by the oxide dianion (Fig. 1c), demonstrating the very high reactivity of soluble complexes with low-coordinate O2− anions. A similar reaction of 1-Yb with excess N2O led to further oxidation of YbII and formation of multiple unidentified paramagnetic YbIII products (Fig. S52). Reaction with exactly one equivalent of N2O gas led to partial conversion of 1-Yb and formation of the same paramagnetic product(s). This shows that the oxidations of YbII and Mg0 by N2O are of similar rates.

It was found that the Yb metal in 1-Yb can be replaced with Ca by the reaction of 1-Yb with 0.5 equivalents of (Am*CaI)2 (2-Ca). However, the reaction gave an equilibrium mixture of 1-Yb, 1-Ca, 2-Yb and 2-Ca (Fig. S50). This underscores the weak nature of the Mg–Ca and Mg–Yb bonds.

As reported for 1-Ca,30 a solution of 1-Yb in methylcyclohexane reacted at room temperature quantitatively within two hours with 1,1-diphenylethylene (DPE) giving essentially pure (BDI*)Mg(CH2CPh2)Yb (Am*) in 94% isolated yield. Single crystals of 4-Yb were grown from a mixture of pentane and THF. The crystal structure of 4-Yb (Fig. 3a) shows the formation of a product with a (BDI*)Mg–CH2CPh2 bond. This confirms the nucleophilic nature of Mg. The (Am*)Yb fragment is not bound to carbon but instead coordinates to one of the phenyl rings in CH2CPh22− (Yb–C: range = 2.712(4)–2.480(4) Å; shortest contact is Yb–Cpara = 2.712(4) Å). The C–C bond in CH2CPh22− is elongated to 1.514(5) Å and shows a single-bond character whereas one of the C–Ph bonds is very short (1.393(5) Å) and displays a double-bond character. The phenyl ring connected to Yb shows characteristics similar to a “Meisenheimer anion” in which the negative charge is delocalized over Cortho and Cpara positions. The 1H NMR spectrum of 4-Yb in cyclohexane-d12 shows three very broad signals in a 2 : 2 : 1 ratio (5.15–5.85 ppm) which are assigned to the phenyl rings (Fig. S11). This pronounced high-field shift is indicative of loss of aromaticity. As both phenyl rings give one set of signals, there is fast exchange between the coordinating (non-aromatic) Ph ring and the non-coordinated (aromatic) Ph ring. It should also be noted that the presence of THF has a pronounced effect on the coordination mode of the Am* ligand. Without THF the ligand binds N-aryl-chelating, e.g. in 1-Yb or in the recently reported THF-free Ca analogue of 4-Yb.30 With two additional THF ligands, the Am* ligand switches to N,N-coordination, e.g. in 4-Yb. Note that the reaction of a (BDI)Mg–Mg(BDI) complex with DPE led to formation of (BDI)Mg–H2CC(Ph2)–Mg(BDI) in which both Mg atoms form Mg–C single bonds.47 Preference of the larger Ca2+ or Yb2+ cations for Ph-coordination can be explained by the hard–soft acid–base (HSAB) principle.48

Fig. 3. (a) Crystal structure of 4-Yb and selected bond distances in the Mg–CH2CPh2–Yb unit. (b) Crystal structure of 5-Yb and selected bond distances in the Mg–CH(Ph)C(H)Ph–Yb unit. (c) Crystal structure of 6-Yb and selected bond distances in the Mg–(anthracene)–Yb unit. All H atoms, Et groups on BDI* and Me groups on Am* have been omitted for clarity.

Fig. 3

Open in a new tab

Reaction of 1-Yb with trans-stilbene afforded a similar product (5-Yb) but with slightly different connectivity (Fig. 3b). Again, the smaller and harder Mg2+ prefers Mg–CH(Ph)CHPh coordination, whereas the softer Yb2+ shows (η6)Ph⋯Yb coordination (Yb–Phcentroid = 2.304(1) Å). The analogous complex 5-Ca could also be isolated and crystallized isostructural with Mg–C and (η6)Ph⋯Ca coordination (Ca–Phcentroid = 2.312(1) Å). The contact between a formally negatively charged Ph ring and Yb2+ (or Ca2+) in 5-Yb/Ca (Yb–Phcentroid = 2.304(1) Å; Ca–Phcentroid = 2.312(1) Å) is considerably shorter than the Yb⋯Arcentroid contact in 2-Yb (average: 2.429 Å) which involves a neutral aryl ring.

The bridging mode of the trans-stilbene2− dianion in 5-Yb/Ca differs from that in (BDI)Mg–(stilbene)–Mg(BDI),49 (Am*)Ca–(stilbene)–Ca(Am*)50 or (Am*)Yb–(stilbene)–Yb(Am*).34 As pointed out previously,50 the bridging mode in the M–(stilbene)–M moiety depends on the nature of the metal (Scheme 3). Electropositive metals (Li, Na, K, and Ca) produce highly ionic M–stilbene bonds which prefer a planar delocalized Ph(H)CC(H)Ph2− dianion with short C Created by potrace 1.16, written by Peter Selinger 2001-2019 C and Ph–C bonds and sp2-hybridization of the central C atoms. The negative charge is mainly on the Ph rings which also coordinate to the metals. Less electropositive metals (Mg, Be, and Al) results in the formation of more covalent M–stilbene bonds which prefer a Ph(H)C–C(H)Ph fragment with long C–C and Ph–C bonds and sp3-hybridization of the central C atoms. Due to significant covalency, there is only a small negative charge on the stilbene unit which is mainly on the central C atoms that are bound to the metals. The bonding situation in the heterobimetallic complexes 5-Yb/Ca is new and represents a hybrid of these two situations (Fig. 3b).

Scheme 3. Metal complexes with a bridging stilbene2− dianion. Dependence of geometry and hybridization on the nature of the metal.

Scheme 3

Open in a new tab

The 1H NMR spectra of 5-Yb and 5-Ca show very similar features, but slightly different dynamics for exchange of the phenyl rings in the stilbene2− dianion (Fig. S16 and S22). The 1H NMR signals for the Ph groups are in both cases broadened. Heating a solution of 5-Yb in methylcyclohexane-d14 to +80 °C results in fast exchange and appearance of three signals in a 2 : 2 : 1 ratio between 4.81 and 5.67 ppm (Fig. S21). This also confirms the remarkable thermodynamic stability of 5-Yb up to 80 °C without any decomposition or reversible formation of starting materials 1-Yb and trans-stilbene. Such a reductive elimination process was observed for (BDI)Mg–(stilbene)–Mg(BDI).49 This underscores the very high reducing power of heterobimetallic Mg–Ca/Yb complexes.

Cyclohexane solutions of 1-Yb and 1-Ca also reacted smoothly with anthracene and overnight selectively afforded 6-Yb and 6-Ca, respectively. The isostructural crystal structures show that the small Mg2+ cation is connected covalently with the C in the anthracene 9-position whereas the larger, more electropositive Yb2+/Ca2+ cations bind ionically to one of the terminal C6-rings via (η6)ring-Yb/Ca interactions (Fig. 3c and S63). This binding mode of reduced anthracene is somewhat similar to that in a (BDI*)Mg–(anthracene)–Ca(BDI) complex in which Mg bridges the 9,10-positions and Ca binds to one of the terminal C6-rings.51 The 1H NMR spectra of 6-Yb and 6-Ca are quite similar and show one broadened signal for the bridgehead 9,10-anthracene positions and one set of two broadened signals (1 : 1 ratio) for the two flanking C6-rings (Fig. S27–S32). This indicates that there is in solution fast exchange between the 9, 10-positions and the flanking rings.

Ammonia activation is well known with transition metal and p-block metal complexes,52–56 but not explored for low-oxidation-state s-block metal complexes. A dark-red solution of 1-Ca in methylcyclohexane reacts at −80 °C rapidly with NH3(g) to give a light-yellow solution from which the heterobimetallic Mg–Ca amide complex 7-Ca was crystallized in 43% yield. The presence of two bridging NH2− anions in the crystal structure (Fig. 1d) is consistent with activation of two equivalents of NH3. We assume a mechanism in which Mg0 inserts in the N–H bond, a formal oxidative addition which forms the intermediate complex (BDI*)Mg–(µ2-H)(µ2-NH2)–Ca(Am*). Similar intermediates with M–(µ2-H)(µ2-NH2)–M cores (M = Ca, Al, Ru, Ir) have been reported.56–58 The reactive hydride ligand in this intermediate deprotonates a second NH3 molecule, resulting in H2 release and formation of 7-Ca. Following the reaction at low temperatures indeed suggests the intermediate formation of (BDI*)Mg–(µ2-H)(µ2-NH2)–Ca(Am*) (Fig. S45).

The Mg–N and Ca–N bond lengths in 7-Ca are in the normal range for MgII–N and CaII–N bond distances. N-aryl-coordination of the amidinate ligand is maintained in solution. The two bridging NH2− anions show 1H NMR signals at high field (−1.90 ppm, Fig. S44). This is in accordance with previously reported polar Al–NH2 (−1.79 ppm)56 and Ca–NH2 (−1.73 ppm)57 amide complexes.

A solution of complex 1-Yb in methylcyclohexane also reacted rapidly with NH3(g) at −80 °C. The immediate colour change from dark-brown to pale yellow indicated the oxidation of 1-Yb. This was confirmed by 1H NMR (Fig. S53–S56) which showed full consumption of 1-Yb. However, all signals are considerably broadened suggesting further conversion to YbIII species. This was followed by rapid precipitation of an off-white product that is fully insoluble in THF but can be quenched with methanol under release of ammonia. Since the precipitate does not contain BDI* or Am* ligands, we propose the formation of insoluble Yb(NH2)3. As the synthesis of YbI2 can be carried out in liquid NH3,59 the oxidation of 1-Yb to an YbIII product by reaction with NH3 may be unexpected. However, there is precedence for such redox reactivity60 and it is also known that Yb metal can react in liquid ammonia to Yb(NH2)3.61

Conclusion

It was recently demonstrated that the magnesyl anion (BDI*)Mg− in [(BDI*)Mg−Na+]2 can function as an electron-donating L-type ligand for Yb (II-Yb). In the present work, a salt-metathesis procedure involving the reaction of the sodium salt [(BDI*)Mg−Na+]2 and (Am*YbI)2 resulted in formation of (BDI*)Mg–Yb(Am*) (1-Yb) and NaI. Complex 1-Yb, in which (BDI*)Mg˙ acts as an X-type ligand for Yb (Am*), crystallizes isomorphous to (BDI*)Mg–Ca(Am*) (1-Ca). The crystal structures of 1-Yb and 1-Ca fit quite well on each other.

The formal oxidation states in 1-Yb are Mg0–YbII. This is confirmed by effective-oxidation-state analysis. However, a low reliability index of 68.0% indicates that this assignment is not fully representative of the electron distribution. Charge analysis shows significant transfer of electron density from the electron rich Mg0 centre to YbII. Therefore, the complex has partial MgI–YbI character. According to energy decomposition analysis, bonding in 1-Yb is best understood as a combination of neutral open-shell radicals (BDI*)Mg˙/(Am*)Yb˙.

Due to electronegativity differences, the metal–metal bond in 1-Yb is polarized: Mgδ−–Ybδ+. AIM charges for the metal atoms in 1-Yb (Mg +0.59 and Yb +1.31) compare well to those in 1-Ca (Mg +0.49 and Ca +1.41). This bond polarization makes the complexes highly reactive and unstable. In solution, 1-Yb slowly decomposes by insertion of the Mg0 centre into a benzylic C–H bond of one of the Et2CH-substituents. Such C–H bond activation by oxidative addition is normally associated with transition metals, but is now also well established for main group elements in low oxidation states. In comparison to unpolarized Mg–Mg bonds, the polarized Mgδ−–Ybδ+ bond is highly reactive.

Whereas the structures of 1-Yb and 1-Ca and their electron distributions are comparable, their reactivities partially differ. Oxidation of 1-Ca with N2O gave an unstable Mg–O–Ca complex which decomposed by deprotonation of the terminal CH3 group in the Et2CH-substituent by the O2− dianion (3-Ca). In contrast, the same reaction with 1-Yb led to overoxidation and formation of an unknown paramagnetic YbIII species. This highlights an important difference between the Mg–Ca and Mg–Yb systems: the additional redox accessibility of the lanthanide centre can complicate the reactivity of 1-Yb.

This is also the case for reactions of 1-Yb with gaseous NH3. Whereas 1-Ca reacted already at −80 °C to form a dimeric complex with bridging NH2− anions (7-Ca), the reaction of 1-Yb under similar conditions resulted in overoxidation to YbIII species and precipitation of an insoluble salt which is likely Yb(NH2)3.

Reactions of 1-Ca and 1-Yb with extended π-systems (1,1-diphenylethylene, trans-stilbene or anthracene) gave the expected products with dianionic bridging ligands [Ph2CCH22−], [Ph(H)CC(H)Ph2−] and [anthracene2−], respectively, which have been fully characterized by X-ray diffraction. In these complexes, the small and hard Mg2+ generally forms covalent Mg–C σ-bonds, whereas the larger and softer Ca2+ (or Yb2+) cations preferentially bind to the softer π-system of one of the six-membered rings. Overall, these studies show that unsupported and polarized Mg–Ca and Mg–Yb bonds are exceptionally reactive platforms for small-molecule activation and reduction of unsaturated organic substrates.

Although challenging, we continue our research with attempts to isolate complexes with even more labile and reactive Mg–Sr or Mg–Ba bonds.

Author contributions

S. K. Thakur: conceptualization, investigation, validation, formal analysis, writing – original draft, visualization. T. Tewari: investigation, validation, formal analysis. N. Roig: investigation, validation, formal analysis. J. Langer: formal analysis, validation. M. Alonso: investigation, validation, formal analysis, supervision, project administration. S. Harder: conceptualization, writing – original draft – review and editing, visualization, validation, supervision, project administration.

Conflicts of interest

There are no conflicts to declare.

Supplementary Material

SC-OLF-D6SC05592C-s001
SC-OLF-D6SC05592C-s002

Acknowledgments

We thank Mrs A. Roth for CHN analyses, and Dr C. Färber and Mr J. Schmidt for assistance with NMR analyses. The Deutsche Forschungsgemeinschaft is acknowledged for funding (HA 3218/12-1). M. A. thanks the VUB for the Strategic Research Program awarded to the ALGC research group. The computational resources and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation–Flanders (FWO) and the Flemish Government.

Data availability

CCDC 2566191–2566199 contain the supplementary crystallographic data for the complexes.62a–i

Supplementary information (SI): synthetic procedures, selected NMR spectra, details of crystal structure determination, details of computational work, experimental details of reactivity studies, 1H and 13C NMR spectra, crystallographic details including ORTEP presentations, and details of the DFT calculations including XYZ-files. See DOI: https://doi.org/10.1039/d6sc05592c.

References

  1. Multiple Bonds Between Metal Atoms, ed. F. A. Cotton, C. A. Murillo and R. A. Walton, Springer US, Boston, MA, 2005 [Google Scholar]
  2. Molecular Metal-Metal Bonds: Compounds, Synthesis, Properties, ed. S. T. Liddle, Wiley, 1st edn, 2015 [Google Scholar]
  3. Liu F. Spree L. Krylov D. S. Velkos G. Avdoshenko S. M. Popov A. A. Acc. Chem. Res. 2019;52:2981–2993. doi: 10.1021/acs.accounts.9b00373. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Gould C. A. McClain K. R. Reta D. Kragskow J. G. C. Marchiori D. A. Lachman E. Choi E.-S. Analytis J. G. Britt R. D. Chilton N. F. Harvey B. G. Long J. R. Science. 2022;375:198–202. doi: 10.1126/science.abl5470. [DOI] [PubMed] [Google Scholar]
  5. Kwon H. McClain K. R. Kragskow J. G. C. Staab J. K. Ozerov M. Meihaus K. R. Harvey B. G. Choi E. S. Chilton N. F. Long J. R. J. Am. Chem. Soc. 2024;146:18714–18721. doi: 10.1021/jacs.4c06250. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Boronski J. T. Seed J. A. Hunger D. Woodward A. W. Van Slageren J. Wooles A. J. Natrajan L. S. Kaltsoyannis N. Liddle S. T. Nature. 2021;598:72–75. doi: 10.1038/s41586-021-03888-3. [DOI] [PubMed] [Google Scholar]
  7. Wagner M. J. Dye J. L. Annu. Rev. Mater. Sci. 1993;23:223–253. doi: 10.1146/annurev.ms.23.080193.001255. [DOI] [Google Scholar]
  8. Riedel R. Seel A. G. Malko D. Miller D. P. Sperling B. T. Choi H. Headen T. F. Zurek E. Porch A. Kucernak A. Pyper N. C. Edwards P. P. Barrett A. G. M. J. Am. Chem. Soc. 2021;143:3934–3943. doi: 10.1021/jacs.1c00115. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Green S. P. Jones C. Stasch A. Science. 2007;318:1754–1757. doi: 10.1126/science.1150856. [DOI] [PubMed] [Google Scholar]
  10. Boronski J. T. Crumpton A. E. Wales L. L. Aldridge S. Science. 2023;380:1147–1149. doi: 10.1126/science.adh4419. [DOI] [PubMed] [Google Scholar]
  11. Rösch B. Gentner T. X. Langer J. Färber C. Eyselein J. Zhao L. Ding C. Frenking G. Harder S. Science. 2021;371:1125–1128. doi: 10.1126/science.abf2374. [DOI] [PubMed] [Google Scholar]
  12. Mondal R. Yuvaraj K. Rajeshkumar T. Maron L. Jones C. Chem. Commun. 2022;58:12665–12668. doi: 10.1039/D2CC04841H. [DOI] [PubMed] [Google Scholar]
  13. Morasch M. Vilpas T. Patel N. Maurer J. Thum S. Schmidt M. A. Langer J. Harder S. Angew. Chem., Int. Ed. 2025;64:e202506989. doi: 10.1002/anie.202506989. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Jones C. Nat. Rev. Chem. 2017;1:0059. doi: 10.1038/s41570-017-0059. [DOI] [Google Scholar]
  15. Rösch B. Harder S. Chem. Commun. 2021;57:9354–9365. doi: 10.1039/D1CC04147A. [DOI] [PubMed] [Google Scholar]
  16. Freeman L. A. Walley J. E. Gilliard R. J. Nat. Synth. 2022;1:439–448. doi: 10.1038/s44160-022-00077-6. [DOI] [Google Scholar]
  17. Schulz S., in Comprehensive Coordination Chemistry III, Elsevier, 2021, pp. 66–105 [Google Scholar]
  18. Rösch B. Gentner T. X. Eyselein J. Langer J. Elsen H. Harder S. Nature. 2021;592:717–721. doi: 10.1038/s41586-021-03401-w. [DOI] [PubMed] [Google Scholar]
  19. Jiang Y. Niksefat M. Unsworth S. G. Parr J. M. Evans M. J. Jones C. Chem. Sci. 2026;17:10917–10926. doi: 10.1039/D6SC01992G. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Mai J. Maurer J. Langer J. Harder S. Nat. Synth. 2023;3:368–377. doi: 10.1038/s44160-023-00451-y. [DOI] [Google Scholar]
  21. Harder S. Angew. Chem., Int. Ed. 2004;43:2714–2718. doi: 10.1002/anie.200353557. [DOI] [PubMed] [Google Scholar]
  22. Thakur S. K. Roig N. Maurer J. Langer J. Alonso M. Harder S. J. Am. Chem. Soc. 2025;147:12555–12561. doi: 10.1021/jacs.4c17853. [DOI] [PubMed] [Google Scholar]
  23. Green M. L. H. J. Organomet. Chem. 1995;500:127–148. doi: 10.1016/0022-328X(95)00508-N. [DOI] [Google Scholar]
  24. Green M. L. H. Parkin G. J. Chem. Educ. 2014;91:807–816. doi: 10.1021/ed400504f. [DOI] [Google Scholar]
  25. Wiecko M. Roesky P. W. Nava P. Ahlrichs R. Konchenko S. N. Chem. Commun. 2007:927–929. doi: 10.1039/B614165J. [DOI] [PubMed] [Google Scholar]
  26. Ihanus J. Hänninen T. Hatanpää T. Aaltonen T. Mutikainen I. Sajavaara T. Keinonen J. Ritala M. Leskelä M. Chem. Mater. 2002;14:1937–1944. doi: 10.1021/cm0111130. [DOI] [Google Scholar]
  27. Schüler P. Sengupta S. Koch A. Görls H. Krieck S. Westerhausen M. Chem.–Eur. J. 2022;28:e202201897. doi: 10.1002/chem.202201897. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Berthold C. Maurer J. Klerner L. Harder S. Buchner M. R. Angew. Chem., Int. Ed. 2024;63:e202408422. doi: 10.1002/anie.202408422. [DOI] [PubMed] [Google Scholar]
  29. Stecher H. Thum S. Maurer J. Mai J. Schmidt M. A. Langer J. Harder S. Angew. Chem., Int. Ed. 2025;64:e202518538. doi: 10.1002/anie.202518538. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Thakur S. K. Langer J. Roig N. Patro A. G. Schmidt M. A. Alonso M. Harder S. Angew. Chem., Int. Ed. 2026;65:e25777. doi: 10.1002/anie.202525777. [DOI] [PubMed] [Google Scholar]
  31. Murphy L. R. Meek T. L. Allred A. L. Allen L. C. J. Phys. Chem. A. 2000;104:5867–5871. doi: 10.1021/jp000288e. [DOI] [Google Scholar]
  32. Cordero B. Gómez V. Platero-Prats A. E. Revés M. Echeverría J. Cremades E. Barragán F. Alvarez S. Dalton Trans. 2008:2832. doi: 10.1039/B801115J. [DOI] [PubMed] [Google Scholar]
  33. Rösch B. Gentner T. X. Eyselein J. Friedrich A. Langer J. Harder S. Chem. Commun. 2020;56:11402–11405. doi: 10.1039/D0CC05200K. [DOI] [PubMed] [Google Scholar]
  34. Basalov I. V. Lyubov D. M. Fukin G. K. Shavyrin A. S. Trifonov A. A. Angew. Chem., Int. Ed. 2012;51:3444–3447. doi: 10.1002/anie.201108662. [DOI] [PubMed] [Google Scholar]
  35. Causero A. Ballmann G. Pahl J. Zijlstra H. Färber C. Harder S. Organometallics. 2016;35:3350–3360. doi: 10.1021/acs.organomet.6b00566. [DOI] [Google Scholar]
  36. Ruspic C. Spielmann J. Harder S. Inorg. Chem. 2007;46:5320–5326. doi: 10.1021/ic700403d. [DOI] [PubMed] [Google Scholar]
  37. Richardson G. M. Douair I. Cameron S. A. Bracegirdle J. Keyzers R. A. Hill M. S. Maron L. Anker M. D. Nat. Commun. 2021;12:3147. doi: 10.1038/s41467-021-23444-x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Friedrich A. Eyselein J. Langer J. Färber C. Harder S. Angew. Chem., Int. Ed. 2021;60:16492–16499. doi: 10.1002/anie.202103250. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Thakur S. K. Roig N. Monreal-Corona R. Langer J. Alonso M. Harder S. Angew. Chem., Int. Ed. 2024;63:e202405229. doi: 10.1002/anie.202405229. [DOI] [PubMed] [Google Scholar]
  40. Postils V. Delgado-Alonso C. Luis J. M. Salvador P. Angew. Chem., Int. Ed. 2018;57:10525–10529. doi: 10.1002/anie.201802745. [DOI] [PubMed] [Google Scholar]
  41. Gimferrer M. Danés S. Vos E. Yildiz C. B. Corral I. Jana A. Salvador P. Andrada D. M. Chem. Sci. 2023;14:384–392. doi: 10.1039/D2SC05769G. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Yuvaraj K. Douair I. Paparo A. Maron L. Jones C. J. Am. Chem. Soc. 2019;141:8764–8768. doi: 10.1021/jacs.9b04085. [DOI] [PubMed] [Google Scholar]
  43. Lalrempuia R. Stasch A. Jones C. Chem. Sci. 2013;4:4383. doi: 10.1039/C3SC52242C. [DOI] [Google Scholar]
  44. Thum S. Mai J. Patel N. Langer J. Harder S. ChemistryEurope. 2025;3:e202500080. doi: 10.1002/ceur.202500080. [DOI] [Google Scholar]
  45. Thompson S. Burnett S. Ferns R. Van Mourik T. McKay A. P. Slawin A. M. Z. Cordes D. B. Stasch A. J. Am. Chem. Soc. 2025;147:5247–5257. doi: 10.1021/jacs.4c16041. [DOI] [PMC free article] [PubMed] [Google Scholar]
  46. Thum S. Schmidt M. A. Langer J. Harder S. Chem. Commun. 2025;61:12127–12130. doi: 10.1039/D5CC03340C. [DOI] [PubMed] [Google Scholar]
  47. Boutland A. J. Carroll A. Alvarez Lamsfus C. Stasch A. Maron L. Jones C. J. Am. Chem. Soc. 2017;139:18190–18193. doi: 10.1021/jacs.7b11368. [DOI] [PubMed] [Google Scholar]
  48. Pearson R. G. J. Am. Chem. Soc. 1963;85:3533–3539. doi: 10.1021/ja00905a001. [DOI] [Google Scholar]
  49. Dange D. Gair A. R. Jones D. D. L. Juckel M. Aldridge S. Jones C. Chem. Sci. 2019;10:3208–3216. doi: 10.1039/C9SC00200F. [DOI] [PMC free article] [PubMed] [Google Scholar]
  50. Causero A. Elsen H. Ballmann G. Escalona A. Harder S. Chem. Commun. 2017;53:10386–10389. doi: 10.1039/C7CC05792J. [DOI] [PubMed] [Google Scholar]
  51. Mai J. Rösch B. Patel N. Langer J. Harder S. Chem. Sci. 2023;14:4724–4734. doi: 10.1039/D3SC00909B. [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Hanna T. E. Lobkovsky E. Chirik P. J. Eur. J. Inorg. Chem. 2007;2007:2677–2685. doi: 10.1002/ejic.200601134. [DOI] [Google Scholar]
  53. Fafard C. M. Adhikari D. Foxman B. M. Mindiola D. J. Ozerov O. V. J. Am. Chem. Soc. 2007;129:10318–10319. doi: 10.1021/ja0731571. [DOI] [PubMed] [Google Scholar]
  54. Zhao J. Goldman A. S. Hartwig J. F. Science. 2005;307:1080–1082. doi: 10.1126/science.1109389. [DOI] [PubMed] [Google Scholar]
  55. Yadav S. Saha S. Sen S. S. ChemCatChem. 2016;8:486–501. doi: 10.1002/cctc.201501015. [DOI] [Google Scholar]
  56. Sarkar D. Vasko P. Ying L. Struijs J. J. C. Griffin L. P. Aldridge S. Angew. Chem., Int. Ed. 2025;64:e202502326. doi: 10.1002/anie.202502326. [DOI] [PubMed] [Google Scholar]
  57. Ruspic C. Harder S. Inorg. Chem. 2007;46:10426–10433. doi: 10.1021/ic701479r. [DOI] [PubMed] [Google Scholar]
  58. Kimura T. Arita H. Ishiwata K. Kuwata S. Ikariya T. Dalton Trans. 2009:2912. doi: 10.1039/B902810M. [DOI] [PubMed] [Google Scholar]
  59. Tilley T. D., Boncella J. M., Berg D. J., Burns C. J., Andersen R. A., Lawless G. A., Edelman M. A. and Lappert M. F., in Inorganic Syntheses, ed. A. P. Ginsberg, Wiley, 1st edn, 1990, vol. 27, pp. 146–150 [Google Scholar]
  60. Imamura H. Sakata Y. Tsuruwaka Y. Mise S. J. Alloys Compd. 2006;408–412:1113–1117. doi: 10.1016/j.jallcom.2004.12.126. [DOI] [Google Scholar]
  61. Görne A. L. George J. Van Leusen J. Dück G. Jacobs P. Chogondahalli Muniraju N. K. Dronskowski R. Inorg. Chem. 2016;55:6161–6168. doi: 10.1021/acs.inorgchem.6b00736. [DOI] [PubMed] [Google Scholar]
  62. (a) CCDC 2566191: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bcn. [DOI]; (b) CCDC 2566192: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bdp [DOI]; (c) CCDC 2566193: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bfq [DOI]; (d) CCDC 2566194: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bgr [DOI]; (e) CCDC 2566195: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bhs [DOI]; (f) CCDC 2566196: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bjt [DOI]; (g) CCDC 2566197: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bkv [DOI]; (h) CCDC 2566198: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4blw [DOI]; (i) CCDC 2566199: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bmx [DOI]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Citations

  1. (a) CCDC 2566191: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bcn. [DOI]
  2. (b) CCDC 2566192: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bdp [DOI]
  3. (c) CCDC 2566193: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bfq [DOI]
  4. (d) CCDC 2566194: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bgr [DOI]
  5. (e) CCDC 2566195: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bhs [DOI]
  6. (f) CCDC 2566196: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bjt [DOI]
  7. (g) CCDC 2566197: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bkv [DOI]
  8. (h) CCDC 2566198: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4blw [DOI]
  9. (i) CCDC 2566199: Experimental Crystal Structure Determination, 2026, 10.5517/ccdc.csd.cc2s4bmx [DOI]

Supplementary Materials

SC-OLF-D6SC05592C-s001
SC-OLF-D6SC05592C-s001.pdf (7.1MB, pdf)
SC-OLF-D6SC05592C-s002
SC-OLF-D6SC05592C-s002.cif (2.2MB, cif)

Data Availability Statement

CCDC 2566191–2566199 contain the supplementary crystallographic data for the complexes.62a–i

Supplementary information (SI): synthetic procedures, selected NMR spectra, details of crystal structure determination, details of computational work, experimental details of reactivity studies, 1H and 13C NMR spectra, crystallographic details including ORTEP presentations, and details of the DFT calculations including XYZ-files. See DOI: https://doi.org/10.1039/d6sc05592c.

Articles from Chemical Science are provided here courtesy of Royal Society of Chemistry

RESOURCES