Skip to main content
NCBI home page
ACS AuthorChoice logoLink to ACS AuthorChoice
. 2023 Aug 9;42(16):2304–2311. doi: 10.1021/acs.organomet.3c00291

Group IV Complexes with Sterically Congested N-Aryl-adamantylcarbamidate Ligands

Bahareh Rezaei Kheirkhah †, Wimonsiri Huadsai †,‡, Phil Liebing †, Sébastien Bontemps ‡,*, Matthias Westerhausen †,*
PMCID: PMC10467577  PMID: 37654652

Abstract

graphic file with name om3c00291_0008.jpg

Metalation of N-(2,6-dibenzhydryl-4-tolyl)adamantane-1-carboxamide (1, Ar*N(H)–C(O)–Ad) with M(NMe2)4 (M = Ti, Zr, Hf) yields amidate complexes Ar*N=C(Ad)–O–Ti(NMe2)3 (2) as well as bis(amidate) compounds (Ar*N=C(Ad)–O)2M(NMe2)2 (M = Zr (3), Hf (4)). In 2, the amidate ligand acts as a monodentate base via the oxygen atom with the Ti center in a slightly distorted tetrahedral environment. The steric requirement of the amidate ligand stabilizes the small coordination number of four of the Ti atom. In congeners 3 and 4, two bidentate amidate ligands exist in the coordination spheres, leading to hexacoordinate group IV metal atoms. The small bite angles of the Zr- and Hf-bound amidate ligands lead to severe distortion of the octahedral environments of the Zr and Hf centers. Titanium compound 2 is an unsuitable choice to catalyze hydrofunctionalization of alkynes with amines and phosphane oxides and despite the significantly smaller pKa value of the carboxylic amide, formation of carboxamide 1 is the dominant reaction upon addition of amines or phosphane oxides to release intramolecular steric strain introduced by the very bulky adamantylamidato ligand.

Introduction

The complexes of the group IV elements are of tremendous relevance in catalysis with polymerization of alkenes probably being the standard example in many textbooks.1 Beyond that the coordination compounds of these metals play an important role in hydrofunctionalization processes such as hydroamination reactions of unsaturated compounds.2 The radii of the group IV metals gradually differ in size (tetra-/hexacoordinate Ti4+ 56/74.5 pm, tetra-/hexacoordinate Zr4+ 73/86 pm, and tetra-/hexacoordinate Hf4+ 72/85 pm)3a and Allred–Rochow electronegativity (Ti 1.32, Zr 1.22, Hf 1.23)3b with very similar values for Zr and Hf. These highly charged electropositive metal ions are very hard Lewis acids, attracting electron-rich ligands such as alkenes, alkynes, and their heteroatom-substituted congeners. This behavior enables manifold applications in catalysis such as polymerization of alkenes as well as hydrofunctionalization of alkenes and alkynes,1,2,4 leading to an extensive research on coordination compounds of group IV elements.

Advantageous starting materials for metalation reactions and syntheses of precatalysts are the easily accessible tetrakis(dialkylamido) compounds M(NR2)4. Thus, the reaction of these group IV amides with tetradentate Jacobsen-type Schiff base ligands with a biphenyl backbone leads to the formation of 2,2′-bis[(2-oxido-3,5-di(tert-butyl)phenyl)-dimethylaminomethylamino]-1,1′-biphenyl titanium(IV) with a distorted octahedrally coordinated titanium center as depicted in Scheme 1.5 The Ti(IV) atom is effectively shielded by this hexadentate ligand and, hence, catalytically inactive in hydroamination processes.

Scheme 1. Two-Fold Metalation of the Schiff Base 2,2′-Bis[2-hydroxy-3,5-di(tert-butyl)benzylideneamino]-1,1′-biphenyl with Ti(NMe2)4 Followed by an Intramolecular Addition of the Dimethylamido ligands onto the Imine Functionalities.

Scheme 1

Open in a new tab

Stereocenters are marked with asterisks.

Therefore, another ligand class with the opportunity to easily vary bulkiness to tune the reactivity has attracted our attention. Generally, deprotonation of carboxylic acid amides with Ti(NR2)4 yields complexes of the type (R2N)2Ti[OC(NR′)-R″]2 with bidentate N,O-donating iminocarboxy ligands. In these complexes, the titanium atoms have also the coordination number six, but two dimethylamido groups enable intermolecular hydroamination of unsaturated compounds.6 The substituents R′ and R″ allow to influence of steric as well as electronic properties of the amidates. Very often, R″ is an aryl group such as phenyl,7 pentafluorophenyl,8 or ortho-substituted aryl groups9,10 but alkyl substituents have also been used in this ligand.10,11 The addition of the metal-bound dialkylamido group onto the C=N double bond has not been observed, but occasionally, the dimethylamido ligands show a peculiar reactivity, leading to metallaaziridines via liberation of an amine.12 The amidate ligands commonly act as bidentate Lewis bases with very few exceptions leading to pentacoordinate group IV transition metal centers,7e,9,13 coordination numbers smaller than five have not been observed for this compound class up to now.

We became interested in complexes of the group IV metals containing heavily congested amidate ligands with bulky substituents R′ and R″ to elucidate the influence of overcrowding on the molecular structures of group IV complexes also containing dimethylamido anions.

Results and Discussion

The sterically crowded 2,6-dibenzhydrylphenylamine and adamantoyl chloride were combined in dichloromethane at room temperature, and then, trimethylamine was added dropwise as depicted in Scheme 2. During stirring overnight, a white solid precipitated which was redissolved in dichloromethane. After the addition of aqueous NaHCO3, colorless 1 was isolated from the organic phase and could be recrystallized from toluene.

Scheme 2. Synthesis of the Group IV Complexes Containing the Bulky Adamantylamidate Ligand via Metalation of N-(2,6-Dibenzhydryl-4-tolyl)adamantane-1-carboxamide (1) with M(NMe2)4 (M = Ti, Zr, Hf) Yielding Amidate Complexes 2, 3, and 4.

Scheme 2

Open in a new tab

A solution of M(NMe2)4 in n-hexane was added to a suspension of equimolar amounts of 1 in the same solvent. The Ti compound reacted according to the stoichiometric ratio of the substrates, yielding yellow complex 2, whereas the heavier homologous metalation reagents formed colorless bis(amidate) complexes 3 and 4 regardless of the applied stoichiometry, and despite the molar 1:1 ratio, the metalation reagents of the heavier metals Zr and Hf reacted with 2 equiv of 1. Compound 2 was highly soluble in toluene, 3 and 4 were sparingly soluble in toluene, but all complexes were insoluble in aliphatic hydrocarbons.

All new compounds were authenticated by X-ray structure determinations, allowing structural comparisons depending on the binding partner of the amidate. For comparison reasons, the molecular structure of 1 has also been determined. Molecular structure and atom labeling scheme of 1 are depicted in Figure 1. Intramolecular steric strain is minimized by a trans arrangement of the bulky adamantyl and dibenzhydryl-4-tolyl substituents. Despite the valence of three for N1, the 1-aza-3-oxaallylic system shows a significantly shorter N1–C1 bond of 136.8(3) pm than the N1–C12 distance of 143.3(3) pm to the ipso-carbon atom of the aryl group (Table 1). The angle of 67.7° between the planes of the O1–C1–N1 unit and the crowded aryl group shows a twisting of these substructures, precluding an effective interaction between their π-systems. Due to an efficient shielding of the CO–NH moiety by the bulky aryl group, no intermolecular hydrogen bonds exist in the crystal structure of 1.

Figure 1.

Figure 1

Open in a new tab

Molecular structure and atom labeling scheme of N-(2,6-dibenzhydryl-4-tolyl)adamantane-1-carboxamide (1). Displacement ellipsoids represent a probability of 50%, C-bound H atoms are omitted for clarity reasons. Selected structural parameters are given in Table 1.

Table 1. Selected Structural Parameters (Bond Lengths (pm) and Angles (deg)) of N-(2,6-Dibenzhydryl-4-tolyl)adamantane-1-carboxamide (1) and Its Amidate Complexes 2–4 of the Group IV Metals.

  1 2 3 4
M1–O1   187.31(9) 214.0(3) 219.9(2)
M1–O2     221.1(3) 222.0(1)
M1–N1     234.6(3) 225.7(2)
M1–N2   188.0(1) 237.3(3) 225.8(2)
M1–N3   188.6(1) 203.1(3) 203.7(2)
M1–N4   188.9(1) 208.4(3) 204.7(2)
C1–O1 122.7(3) 133.0(1) 132.0(4) 129.7(2)
C1–N1 136.8(3) 127.4(1) 131.0(5) 132.2(3)
C1–C2 152.6(3) 151.8(1) 152.0(5) 152.0(3)
N1–C12 143.3(3) 141.1(1) 144.0(5) 143.3(2)
C45–O2     129.0(5) 129.4(2)
C45–N2     132.7(5) 132.9(2)
C45–C46     152.9(5) 152.3(3)
N2–C56     143.5(5) 143.7(2)
O1–C1–N1 121.3(2) 124.5(1) 113.3(3) 113.2(2)
O2–C45–N2     114.0(3) 113.1(2)
C1–N1–C12 121.7(2) 121.31(9) 128.6(3) 129.9(2)
C45–N2–C56     127.0(3) 129.8(2)
M1–O1–C1   173.67(8) 98.6(2) 95.3(1)
M1–O2–C45     98.4(2) 95.3(1)
Open in a new tab

As depicted in Scheme 2, titanium complex 2 contains three dimethylamido ligands and one monodentate amidate-κO group. The molecular structure and atom labeling scheme are depicted in Figure 2. The Ti1 atom shows an unusually small coordination number of four with a slightly distorted tetrahedral environment of the Ti1 atom. The O1–Ti1–N bond angles (average value 112.6(4)°) are larger than the N–Ti1–N values with an average of 106.1(5)° due to the much larger steric demand of the O-bound amidate ligand.

Figure 2.

Figure 2

Open in a new tab

Molecular structure and atom labeling scheme of titanium complex 2. Displacement ellipsoids represent a probability of 50%, H atoms are omitted for clarity reasons. Selected structural parameters are given in Table 1. Environment of Ti1: O1–Ti1–N2 113.81(4), O1–Ti1–N3 112.56(4), O1–Ti1–N4 111.54(5), N2–Ti1–N3 105.93(5), N2–Ti1–N4 105.33(5), and N3–Ti1–N4 107.14(5).

As in the starting material 1, the organic adamantyl and aryl groups of 2 are trans-arranged to each other, and the O1–C1–N1 plane and the aryl group are nearly perpendicular to each other (84.8°), excluding an interaction between these two π-systems. The Ti(NMe2)3 fragment binds to the O1 atom, and intramolecular restraints lead to a nearly linear Ti1–O1–C1 moiety of 173.67(8)° and a slightly widened O1–C1–N1 bond angle of 124.5(1)°.

The molecular structure of 2 is the only example of an amidate complex with a tetracoordinate titanium atom. A monodentate O-bound amidate has been observed earlier when bulky N-bound 2,6-diisopropylphenyl groups are present.7e,10 In these complexes with penta-coordinate Ti atoms, κ1O- and κ2O,N-bound amidate ligands coexist, allowing the comparison of Ti–O bond lengths depending on the binding mode. Thus, monodentate κ1O-coordination leads to a shortening of the Ti–O bond by approximately 20 pm and values of 190.2(1) (O–C(Ph)=N-Dipp ligand)7e and 185.8 pm (O–C(tBu)=N-Dipp ligand)10 are observed. In 2, the Ti–O bond length lies in the same range, despite the smaller coordination number of the Ti center due to the enormous bulkiness of the amidate ligand.

The molecular structures of Zr and Hf compounds 3 and 4 are very similar. Hf congener 4 is depicted in Figure 3, and the Zr derivative is shown in Figure S17. Hf complex 4 has been recrystallized from toluene to isolate single crystals in which five toluene molecules are intercalated between the complex molecules. Therefore, the crystal structures are not isotypic, despite rather similar binding parameters and very similar radii of the metal ions. The bidentate binding mode of the amidate ligands leads to Δ- and Λ-isomers. The bulky organic groups stabilize again a nearly perpendicular arrangement of the 1-aza-3-oxaallyl plane versus the phenyl ring (3: 84.6° and 89.3°, 4: 87.8° and 87.3°).

Figure 3.

Figure 3

Open in a new tab

Molecular structure and atom labeling scheme of hafnium complex 4·5MePh. Displacement ellipsoids represent a probability of 50%, H atoms and intercalated toluene molecules are omitted for clarity reasons. Selected structural parameters are given in Table 1. Environment of Hf1 (values for Zr1 in 3 are given in square brackets): O1–Hf1–O2 86.59(5) [94.4(1)], O1–Hf1–N1 58.77(5) [58.4(1)], O1–Hf1–N2 88.03(6) [88.6(1)], O1–Hf1–N3 160.04(6) [147.8(1)], O1–Hf1–N4 90.95(6) [92.3(1)], O2–Hf1–N1 89.51(5) [90.4(1)], O2–Hf1–N2 58.49(5) [57.1(1)], O2–Hf1–N3 90.10(6) [91.0(1)], O2–Hf1–N4 162.26(6) [158.2(1)], N1–Hf1–N2 136.27(6) [132.9(1)], N1–Hf1–N3 101.57(7) [89.9(1)], N1–Hf1–N4 104.21(6) [110.7(1)], N2–Hf1–N3 106.94(7) [120.5(1)], N2–Hf1–N4 103.89(6) [102.5(1)], N3–Hf1–N4 97.93(7) [94.2(1)].

The small bite angles of the O1–M1–N1 (Zr: 58.4(1)°, Hf: 58.77(5)°) and the O2–M1–N2 (Zr: 57.1(1)°, Hf 58.49(5)°) axes enforce distortion of the octahedral environment of the metal centers. The dimethylamido ligands are cis-arranged with N3–M1–N4 bond angles of 94.2(1)° and 97.93(7)° for 3 and 4, respectively. Despite the bulky adamantyl and dibenzhydrylphenyl substituents, both amidato-κ2O,N ligands act as bidentate Lewis bases. Monodentate coordination behavior of an amidate group via the oxygen atom has been observed earlier for a Zr complex leading to a pentacoordinate zirconium atom only when the two amidate functionalities are interconnected by a rather stiff biphenyl backbone.13 In addition, in [Zr(NMe2)(κ1O-OC(tBu)=NtBu)(κ2O,N-OC(tBu)=NtBu)2] mono- and bidentate amidate ligands are present side by side stabilizing a distorted octahedral environment of the Zr center,14 whereas [Zr(NMe2)(κ2O,N-OC(Naph)=N-Dipp)3] contains a hepta-coordinate metal atom.7c

In compound 3, one amidato ligand is slightly pushed out of the coordination sphere, leading to elongated Zr1–O2 and Zr1–N2 bonds compared to the other ligand with the O1 and N1 donor atoms. This asymmetry can also be observed for the dimethylamido groups with a difference of more than 5 pm between Zr1–N3 and Zr1–N4. On the contrary, in the hafnium congener similar Hf1–O1/O2, Hf1–N1/N2 as well as Hf1–N3/N4 values are observed. It is noteworthy, that the bond length difference of 18.4 pm between av. Zr1–O1/O2 (217.6 pm) and av. Zr1–N1/N2 (236.0 pm) is much more expressed than the corresponding difference of 4.8 pm between av. Hf1–O1/O2 (221.0 pm) and av. Hf1–N1/N2 (225.8 pm) values. This finding hints toward an increasing oxophilicity for the lighter metals of this titanium group favoring the bonding to the oxygen rather than to the nitrogen base. Steric reasons play a minor role due to the very same radii of Zr and Hf ions.3 In Table 2 selected bond lengths in compounds of the type [M(NR2)2(κ2O,N–O–C(R′)=NR″)2] with hexa-coordinate group IV metal atoms are compared. Complexes with additional ring strain by bridging benzo15 and biaryl9a,16 fragments are omitted in this table. Hafnium congeners attract much less attention and only very few derivatives have been authenticated by solid-state structures.17 Contrary to the adamantylamidate in 2, 3, and 4, even rather bulky amidate ligands form isostructural compounds for titanium and zirconium (entries 1/10, 6/11, 7/12, 8/13, and 9/14). In complexes with hexa-coordinate group IV metals, the M–O bond lengths are smaller than the M–N distances due to the oxophilic character of the metal ions. Exceptions have been observed if outer Lewis bases such as methoxy or dimethylamino substituents are able to bind to the metals, which enhances their coordination number and pushes the oxygen-base out of the vicinity of the metal centers (entries 6–8 as well as 12 and 13).

Table 2. Comparison of M–O and M–N Bond Lengths (pm, average values for M–NNR2) of Complexes of the Type [M(NR2)2(κ2O,N–O–C(R′)=NR″)2] with Hexa-Coordinate Group IV Metal Atomsa.

entry M R R′ R″ M–Oamidate M–Namidate M–NNR2 ref
1 Ti Et Ph tBu 203.5(4) 223.4(5) 190.7(6) (7b)
2 Ti Et Ph C6H3-2,6-Me2 207.6(1), 200.4(1) 221.1(1), 237.5(1) 189.8(1) (7b)
3 Ti Et Ph Dipp 214.6(1) 215.6(1) 189.9(2) (7a, 7b)
4 Ti Et C6F5 tBu 204.4(6) 235.6(7) 188.7(7) (8)
5 Ti Et C6F5 Dipp 217.0(1) 220.1(1) 190.3(1) (18)
6 Ti Me Mes C6H3-3-Me-2-Aryl-OMe 213.1(1) 212.5(1), 214.3(1) 190.8(1) (9b)
7 Ti Me Mes C6H3-3-Me-2-Aryl-NMe2 211.9(1) 202.9(2) 190.5(2) (9a)
8 Ti Me Mes Naph–Naph′-NMe2 214.7(3) 202.9(4) 190.7(4) (9a)
9 Ti Me tBu C6H3-2,6-Me2 211.8(2), 214.2(2) 211.2(3), 210.9(3) 190.6(3) (10)
10 Zr Et Ph tBu 218.7(3) 231.8(3) 204.3(3) (7b)
11 Zr Me Mes C6H3-3-Me-2-Aryl-OMe 222.4(2) 227.8(2), 228.3(2) 204.8(2) (9b)
12 Zr Me Mes C6H3-3-Me-2-Aryl-NMe2 222.2(3) 217.1(3) 203.4(3) (9a)
13 Zr Me Mes Naph–Naph′-NMe2 224.3(3) 218.1(4) 204.1(4) (9a)
14 Zr Me tBu C6H3-2,6-Me2 215.0, 220.3 240.1, 230.5 204.5 (10)
15 Zr Me Ad C6H2-4-Me-2,6-(CHPh2)2 214.0(3), 221.1(3) 234.6(3), 237.3(3) 205.8(3) Here
16 Hf Me Ad C6H2-4-Me-2,6-(CHPh2)2 219.9(2), 222.0(1) 225.7(2), 225.8(2) 204.2(2) Here
Open in a new tab
a

Ad, 1-adamantyl; Bu, butyl; Dipp, 2,6-diisopropylphenyl; Et, ethyl; Me, methyl; Mes, 2,4,6-trimethylphenyl (mesityl); Naph, naphthyl; Ph, phenyl.

In principle, five diastereomers exist for octahedral complexes of the type [M(NR2)2(κ2O,N–O–C(R′)=NR″)2] as depicted in Scheme 3 which are distorted due to the small bites of the amidate ligands. In the solid state, the dimethylamido substituents show a cisoid arrangement and the nitrogen atoms of the amidate ions (carrying the bulky aryl groups) are trans-arranged due to steric reasons. The asymmetric binding mode of the amidate ligands could hint toward dissociation and intermediate formation of a penta-coordinate metal center easing isomerization processes in solution. Alternatively, the isomers can be interconverted into each other via rotation of two opposite triangular faces of the octahedral coordination polyhedron. In isomers A and D, the bulky N–Ar* fragments are in the favored trans positions.

Scheme 3. Possible Diastereomeric Isomerism in Complexes of the Type [M(NR2)2(κ2O,N–O–C(R′)=NR″)2] (M = Zr, Hf) with Hexa-Coordinate Group IV Metal Atoms.

Scheme 3

Open in a new tab

In diastereomers A, B, and C, the NMe2 ligands are cis-arranged; in D and E, these ligands are in trans positions.

Due to the enormous steric demand of the adamantylamidato ligands in group IV complexes 3 and 4, hindered rotation of substituents can abrogate the chemical and magnetic equivalence of the ortho-CHPh2 substituents which leads to broad and overlapping signals in the NMR spectra. Both phenomena enhance the complexity of the NMR spectra which showed temperature-dependent appearance; however, concrete rotational barriers could not be determined due to overlapping signals. In addition, complexes 3 and 4 are only sparingly soluble exacerbating the interpretation of 13C{1H} NMR experiments at diluted solutions.

The crowding adamantylamidato ligands ensure a small coordination number of the titanium cation in compound 2, and we expected that this fact should ease the hydrofunctionalization processes. Therefore, we studied the hydroamination of alkynes following a published procedure.19 In a typical protocol, 1 mmol of alkyne, 1 mmol of primary amine, and 5 mol % compound 2 were stirred in 2 mL of toluene at 80 °C for 4 h. The progress of the reaction was monitored by 1H NMR spectroscopy. Contrary to our expectation, which was based on the highly different pKa values of amines (approximately 35) and carboxylic amides (approximately 18), significant amounts of N-(2,6-dibenzhydryl-4-tolyl)adamantane-1-carboxamide (1) formed during this reaction (see Figures S13–S16). We interpret this finding that preferably steric pressure was released by competing reactions of the amines with the amido substituents on the one hand and preferentially with the adamantylamidato ligands on the other. Furthermore, hydrophosphorylation, i.e., the addition of diarylphosphane oxides across alkynes, failed as well because compound 1 formed again predominantly. The nature of the titanium-containing compounds remained unknown, but the 31P{1H} NMR spectrum verified the formation of phosphinites with Ti–O–PAr2 moieties. Again, the release of intramolecular strain and hence the preferred formation of carboxylic amide 1 seemed to be the driving force in these reactions. In summary, the accessibility of the two-coordinate O- and N-bases of the amidato ligand by weak Brønsted acids such as amines and phosphane oxides is much more important than the higher basicity of the amido groups with three-coordinate N-donor atoms.

Conclusion

In this investigation, we elucidate the influence of extremely bulky amidato ligands on the structures of group IV metal complexes deprotonated with M(NMe2)4 (M = Ti, Zr, Hf) in hydrocarbons. N-(2,6-Dibenzhydryl-4-tolyl)adamantane-1-carboxamide (1) crystallizes with a sterically favored trans-arrangement of the adamantyl and 2,6-dibenzhydryl-4-tolyl substituents in the 1-aza-3-oxaallyl system. Metalation with Ti(NMe2)4 yields yellow tris(dimethylamido)titanium N-(2,6-dibenzhydryl-4-tolyl)adamantane-1-carbamidate (2) with maintenance of the trans-arrangement of the bulky adamantyl and tolyl groups. The amidate ion acts as a monodentate ligand and binds via the oxygen atom to the tetracoordinate titanium atom, an unusually small coordination number for derivatives of this compound class.

Deprotonation of 1 with M(NMe2)4 (M = Zr and Hf) yields colorless bis(dimethylamido)zirconium bis[N-(2,6-dibenzhydryl-4-tolyl)adamantane-1-carbamidate] (3) and isostructural hafnium congener 4 regardless of the applied stoichiometry. In these compounds, the amidato ligands act as bidentate bases with cis-arranged adamantyl and tolyl substituents, leading to complexes with common hexacoordinate metal centers. Steric strain induced by the bulky dibenzhydryl groups and ring strain due to the small bite of the ligands leads to severe distortion of the octahedral environment of the metal atoms.

Most commonly, Ti and Zr derivatives show very similar solid-state structures. Here, a rare example is observed where the bulky amidate ligand enforces a low coordination number of four at titanium, whereas the distorted octahedral coordination sphere of zirconium follows the expectation. Very few hafnium derivatives have been structurally authenticated, and it is not surprising that the Zr and Hf congeners are isostructural based on very similar radii of these metal ions.

In all these group IV metal complexes with N-(2,6-dibenzhydryl-4-tolyl)adamantane-1-carbamidate ligands, the intramolecular transfer of a dimethylamido ligand onto the 1-aza-3-oxaallyl moiety has not been observed. This finding makes these compounds possible candidates for metal-mediated intermolecular hydrofunctionalization reactions. However, compound 2, having a weakly shielded titanium center with the coordination number of four due to the monodentate binding mode of the amidato ligand, decomposes during intermolecular hydroamination and hydrophosphorylation of alkynes via preferred protonation of the adamantylamidato ligand and hence formation of N-(2,6-dibenzhydryl-4-tolyl)adamantane-1-carboxamide (1), the obvious reason being the release of intramolecular steric strain introduced by this bulky adamantylamidato ligand. The titanium complexes, which are summarized in Table 2, contain bidentate amidato ligands and catalytically enable hydroamination reactions, supposing that the monodentate binding mode and excessive bulkiness of the amidato ligand in compound 2 are disadvantageous for the use of this Ti compound as catalyst in hydrofunctionalization processes.

Experimental Section

General

All manipulations were carried out under anaerobic conditions in an argon atmosphere using standard Schlenk techniques. The solvents were dried according to common procedures and distilled in an argon atmosphere; deuterated solvents were dried over sodium, degassed, and saturated with argon. The yields given are not optimized. 1H and 13C NMR spectra were recorded on Bruker AC 400, AC 500, and AC 600 spectrometers. Chemical shifts are reported in parts per million (ppm, δ scale) relative to the residual signal of the solvent. Samples for MS were measured on a Finnigan MAT SSQ710 mass spectrometer operating with an EI ionization source operating at 70 eV. Samples were measured using a direct ionization probe (DIP) by placing a minute amount on the rhenium wire of the probe and heating the wire up during measurement. Mass spectra were averaged from the maximum of the thermogram. 2,6-Dibenzhydryl-4-tolylamine was prepared according to a literature procedure.20 Complexes 3 and 4 are only sparingly soluble, and we were unable to elucidate reliable 13C{1H} NMR parameters. Due to the sensitivity of the metal complexes toward moisture and air and due to loss of intercalated solvent molecules, no reliable C,H,N analyses could be performed for 3 and 4.

Synthesis of 1

2,6-Dibenzhydryl-4-tolylamine (11.26 g, 25.61 mmol) and Ad–C(O)Cl (5.95 g, 29.97 mmol) were added to 125 mL of dichloromethane. Then distilled trimethylamine (4.64 mL, 33.30 mmol) was added dropwise to this solution at room temperature. The reaction mixture was stirred overnight to give a white solid. This precipitate was dissolved in dichloromethane, quenched with 1 M aqueous solution of NaHCO3 and washed twice with 50 mL of distilled water. The organic layer was separated and dried over anhydrous MgSO4. Volatiles were removed from the filtrate in vacuo yielding the product 1 as a white powder (yield: 14.6 g, 24.26 mmol, 95%). Recrystallization from toluene gave single crystals suitable for X-ray diffraction studies.

Physical data of 1. 1H NMR (toluene-d8): δ = 1.51 (m, 6H, Ad-Hc), 1.64 (m, 6H, Ad-Ha), 1.77 (m, 3H, Ad-Hb), 1.84 (s, 3H, CH3e), 5.82 (s, 2H, CHd-Ph2), 5.97 (s, 1H, NH), 6.75 (s, 2H, Ar–Hf), 6.97–7.16 (m, overlapping phenyl protons with toluene-d7). 13C{1H} NMR (toluene-d8): δ = 21.3 (CH3e) 28.6 (Ad-CHb), 36.7 (Ad-CHc), 39.1 (Ad-CHa), 41.2, 52.9 (CHd-Ph2), 126.6, 129.1, 130 (Ar–CHf), 132.6, 136.9, 142.7, 144.1, 175.4 (C=O). The assignment of the signals is marked with superscripts and depicted in Scheme 4. Elemental analysis (C44H43NO, 601.83): calcd.: C 87.81, H 7.20, N 2.33; found: C 87.86, H 7.16, N 2.31. MS (APCI+, m/z): 601 (36) [M+], 167 (100). MS (APCI+, m/z): 602 (76) [M + 1]+, 601 (31) [M+], 434 (14) [M+ – CHPh2], 167 (100) [CHPh2]+. IR (ATR, cm–1): 3425 (w, ν(N–H)), 3058 (w), 3023 (w), 2920 (w), 2851 (w), 1957 (vw), 1889 (vw), 1815 (vw), 1764 (vw), 1659 (m, υ(C=O)), 1597 (w), 1580 (w), 1494 (m), 1471 (m), 1445 (m), 1368 (vw), 1346 (vw), 1319 (vw), 1252 (w), 1247 (w), 1228 (w), 1183 (w), 1156 (vw), 1132 (vw), 1102 (vw), 1076 (m), 1032 (m), 979 (vw), 942 (vw), 921 (vw), 882 (w), 858 (w), 828 (w), 766 (m), 746 (s), 703 (vs), 688 (vw), 666 (vw), 650 (w), 641 (w), 629 (w), 621 (w), 605 (w).

Scheme 4. Assignment of the Signals in the NMR Spectra with the Red Letters a–f as Superscripts.

Scheme 4

Open in a new tab

Synthesis of Ti Complex 2

Compound 1 (0.255 g, 0.423 mmol) was suspended in 20 mL of n-hexane. Then Ti(NM2)4 (0.1 mL, 0.947g/mL, 0.423 mmol) was added to this suspension. The cloudy reaction mixture was stirred overnight at room temperature. Afterward, the solution was stirred at 70 °C for 3 h, and 10 mL of n-hexane and 2 mL of toluene were added to obtain a clear reaction solution. Yellow crystals began to form when the mixture slowly cooled to ambient temperature (yield: 250 mg, 0.32 mmol, 76%).

Physical data of 2. 1H NMR (toluene-d8): δ = 1.66 (m, 6H, Ad-Hc), 1.83 (m, 6H, Ad-Ha), 1.94 (overlapping, 6H, Hb and He), 2.95 (s, 18H, NMe2), 5.81 (s, 2H, CHd-Ph2), 6.77 (s, 2H, Ar-Hf), 6.98–7.27 (m, overlapping phenyl protons with toluene-d7). 13C{1H} NMR (toluene-d8): δ = 21.2 (CH3e) 29.1 (Ad-CHb), 37.4 (Ad-CHc), 40.4 (Ad-CHa), 44.5 (NMe2), 52.6 (CHd-Ph2), 126.03, 126.07, 128.4, 129.2, 129.4 (Ar–CHf), 129.9, 130.5, 133.9, 144.9, 145.7, 166.7 (C=N). Elemental analysis (C50H60N4OTi, 780.92): calcd.: C 76.90, H 7.74, N 7.17; found: C 76.96, H 7.68, N 7.26. MS (ESI+, m/z): 648 (45) [M+ – 3(NMe2)], 647 (100) [M+ – 3(NMe2) – H]. IR (ATR, cm–1): 2846 (m); 2771 (m); 1633 (m); 1599 (m); 1493 (m); 1465 (m); 1446 (m); 1418 (m); 1323 (m); 1273 (m); 1245 (s); 1183 (w); 1148 (m); 1118 (w); 1103 (m);1075 (m); 1053 (m); 1031 (m); 986 (w); 939 (s); 854 (m); 839 (w); 829 (m); 814 (w); 800 (w); 764 (m); 745 (s); 721 (m); 699 (s); 665 (m).

Synthesis of Zr Complex 3

Carboxamide 1 (0.862 g, 1.43 mmol) was suspended in 15 mL of n-hexane. A solution of Zr(NMe2)4 (0.383 g, 1.43 mmol) dissolved in 10 mL of n-hexane was added. After 45 min of stirring at room temperature, the reaction solution became clear. Overnight stirring at room temperature led to formation of a white solid. This precipitate was collected by filtration and washed with cold n-pentane (yield: 661 mg, 0.48 mmol, 67%). Crystallization succeeded via diffusion of n-pentane into a saturated toluene solution, yielding colorless crystals of 3.

Physical data of 3. 1H NMR ([D6]benzene): δ = 1.23, 1.35, 1.38, 1.40, 1.46, 1.59, 1.69, 1.90, 1.92, 2.18, 2.19, 2.85, 2.96 (s, NMe2), 3.25, 6.01 (s, CHd-Ph2), 7.06, 7.19, 7.21, 7.27, 7.34, 7.44, 7.59, 7.71. 13C{1H} NMR (benzene-d6): δ = 14.4, 21.3, 23.1, 27.2, 28.1, 32.0, 36.3, 38.3, 42.4 (NMe2), 44.0, 52.4 (CHd-Ph2), 126.2, 126.6, 126.8, 128.7, 128.8, 130.0, 130.1, 130.5, 133.0, 136.9, 141.6, 143.3, 145.2, 188.3 (OCN). MS (APCI+, m/z): decomposition, 601 (36) [1+], 167 (100) [CHPh2+]. IR (ATR, cm–1): 3416 (w), 3057 (w), 3023 (m), 2902 (m), 2847 (m), 1672 (w), 1642 (m), 1631 (m), 1621 (m), 1613 (m), 1597 (m), 1493 (m), 1470 (m), 1448 (m), 1328 (m), 1279 (m), 1256 (m), 1183 (w), 1077 (m), 1030 (m), 764 (m), 744 (s), 699 (vs), 665 (m), 642 (m), 622 (m), 605 (s), 532 (s), 522 (s), 477 (s), 438 (s), 412 (s), 405 (s).

Synthesis of Hf Complex 4

Carboxamide 1 (0.602 g, 1.00 mmol) was suspended in 15 mL of toluene. A 1 M solution of Hf(NMe2)4 in toluene (1.1 mL, 0.328 g/mL, 1.01 mmol) was added to this suspension. Immediately, the reaction mixture became clear. The reaction solution was stirred overnight at room temperature. Reduction of the volume of the solution under reduced pressure and cooling of the solution to +5 °C led to precipitation of colorless crystals of 4·5 toluene (yield: 770 mg, 0.40 mmol, 80%). Recrystallization from toluene gave single crystals with the same composition.

Physical data of 4. 1H NMR (toluene-d8): δ = 0.95, 1.13, 1.16, 1.30, 1.33, 1.39, 1.53, 1.58, 1.71, 1.92, 2.11, 2.22, 2.99 (s, NMe2), 3.05, 3.29, 5.97 (s, CHd-Ph2), 6.17, 6.56, 7.04, 7.07, 7.12, 7.14, 7.16, 7.18, 7.27, 7.29, 7.37, 7.39, 7.49, 7.73. 13C{1H} NMR (toluene-d8): δ = 21.4, 28.0, 36.0, 36.2, 37.9, 38.1, 42.2 (NMe2), 43.7, 44.6, 52.3 (CHd-Ph2), 125.6, 125.6, 126.1, 126.6, 126.7, 127.4, 128.1, 128.3, 128.5, 128.8, 129.3, 130.1, 130.2, 130.5, 131.0, 137.2, 137.2, 137.7, 140.9, 143.2, 145.1, 188.6 (OCN). MS (EI, m/z): decomposition, 601 (46) [1+], 167 (100) [CHPh2+]. IR (ATR, cm–1): 3418 (w), 3082 (w), 3057 (w), 3025 (w), 2902 (m), 2847 (m), 2776 (w), 1666 (w), 1640 (w), 1629 (w), 1619 (w), 1597 (m), 1564 (w), 1548 (w), 1527 (w), 1511 (w), 1493 (m), 1448 (m), 1407 (w), 1381 (m), 1364 (m), 1342 (w), 1330 (w), 1313 (w), 1279 (w), 1258 (m), 1215 (w), 1185 (m), 1154 (w), 1103 (m), 1077 (m), 1030 (m), 985 (m), 958 (w), 932 (m), 883 (w), 864 (m), 844 (w), 797 (m), 764 (m), 744 (s), 732 (m), 699 (vs), 665 (m), 644 (m), 622 (m), 605 (s), 560 (m), 530 (m), 503 (s),475 (s), 465 (s), 450 (s), 436 (s), 403 (s).

X-ray Structure Determinations

The single-crystal X-ray intensity data for the reported compounds were collected on a Bruker-Nonius Kappa-CCD diffractometer, equipped with a Mo Kα IμS microfocus source and an Apex2 CCD detector, at T = 120(2) K. The crystal structures were solved with SHELXT-2018/321 and refined by full matrix least-squares methods on F2 with SHELXL-2018/3,22 using the OLEX 1.2 environment.23 Multiscan absorption correction was applied to the intensity data.24 CCDC 2220636–2220639 contain the supplementary crystallographic data for this paper (cf. Table S1). These data can be obtained free of charge from The Cambridge Crystallographic Data Centre (CCDC; http://www.ccdc.cam.ac.uk).

Acknowledgments

This research has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 860322. B.R.K. is grateful to the German Academic Exchange Service (DAAD, Bonn, Germany; grant no. 57440921) for a generous Ph.D. stipend. We acknowledge the valuable support of the NMR service platform (www.nmr.uni-jena.de) and of the mass spectrometry platform (www.ms.uni-jena.de) of the Faculty of Chemistry and Earth Sciences of the Friedrich Schiller University Jena, Germany.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.organomet.3c00291.

  • NMR spectra of all new compounds, table with crystallographic and refinement details, representation of the molecular structure of zirconium complex 3 (PDF)

The authors declare no competing financial interest.

Supplementary Material

om3c00291_si_005.pdf (1.1MB, pdf)

References

  1. Selected textbooks:; a Omae I.Applications of Organometallic Compounds; Wiley: Chichester, 1998. [Google Scholar]; b Cornils B.; Herrmann W. A.. Applied Homogeneous Catalysis with Organometallic Compounds: A Comprehensive Handbook; Wiley-VCH: Weinheim, Germany, 2000. [Google Scholar]; c Hartwig J.Organotransition Metal Chemistry: From Bonding to Catalysis; University Science Books: Sausalito, CA, 2010. [Google Scholar]; d Behr A.; Neubert P.. Applied Homogeneous Catalysis; Wiley-VCH: Weinheim, Germany, 2012. [Google Scholar]; e Beller M.; Renken A.; van Santen R. A.. Catalysis: From Principles to Applications; Wiley-VCH: Weinheim, Germany, 2012. [Google Scholar]; f Steinborn D.Fundamentals of Organometallic Catalysis; Wiley-VCH: Weinheim, Germany, 2012. [Google Scholar]; g Bochmann M.Organometallics and Catalysis: An Introduction; Oxford University Press: New York, 2015. [Google Scholar]
  2. Selected reviews:; a Nobis M.; Drießen-Hölscher B. Recent Developments in Transition Metal Catalyzed Intermolecular Hydroamination Reactions – A Breakthrough?. Angew. Chem., Int. Ed. 2001, 40, 3983–3985. . [DOI] [PubMed] [Google Scholar]; b Pohlki F.; Doye S. The Catalytic Hydroamination of Alkynes. Chem. Soc. Rev. 2003, 32, 104–114. 10.1039/b200386b. [DOI] [PubMed] [Google Scholar]; c Hultzsch K. C. Catalytic Asymmetric Hydroamination of Non-Activated Olefins. Org. Biomol. Chem. 2005, 3, 1819–1824. 10.1039/b418521h. [DOI] [PubMed] [Google Scholar]; d Severin R.; Doye S. The Catalytic Hydroamination of Alkynes. Chem. Soc. Rev. 2007, 36, 1407–1420. 10.1039/b600981f. [DOI] [PubMed] [Google Scholar]; e Aillaud I.; Collin J.; Hannedouche J.; Schulz E. Asymmetric Hydroamination of Non-Activated Carbon-Carbon Multiple Bonds. Dalton Trans. 2007, 5105–5118. 10.1039/b711126f. [DOI] [PubMed] [Google Scholar]; f Müller T. E.; Hultzsch K. C.; Yus M.; Foubelo F.; Tada M. Hydroamination: Direct Addition of Amines to Alkenes and Alkynes. Chem. Rev. 2008, 108, 3795–3892. 10.1021/cr0306788. [DOI] [PubMed] [Google Scholar]; g Chemler S. R. The Enantioselective Intramolecular Aminative Functionalization of Unactivated Alkenes, Dienes, Allenes and Alkynes for the Synthesis of Chiral Nitrogen Heterocycles. Org. Biomol. Chem. 2009, 7, 3009–3019. 10.1039/b907743j. [DOI] [PMC free article] [PubMed] [Google Scholar]; h Roesky P. W. Catalytic Hydroaminoalkylation. Angew. Chem., Int. Ed. 2009, 48, 4892–4894. 10.1002/anie.200900735. [DOI] [PubMed] [Google Scholar]; i Yadav J. S.; Antony A.; Rao T. S.; Subba Reddy B. V. Recent Progress in Transition Metal Catalysed Hydrofunctionalisation of Less Activated Olefins. J. Organomet. Chem. 2011, 696, 16–36. 10.1016/j.jorganchem.2010.09.052. [DOI] [Google Scholar]; j Zi G. Asymmetric Hydroamination/Cyclization Catalyzed by Group IV Metal Complexes with Chiral Biaryl-Based Ligands. J. Organomet. Chem. 2011, 696, 68–75. 10.1016/j.jorganchem.2010.07.034. [DOI] [Google Scholar]; k Patil N. T.; Singh V. Alkyne Hydroamination Triggered Cyclizations: A Powerful Tool for the Construction of Biologically Important Structural Motifs. J. Organomet. Chem. 2011, 696, 419–432. 10.1016/j.jorganchem.2010.10.027. [DOI] [Google Scholar]; l Reznichenko A. L.; Hultzsch K. C. Early Transition Metal (Group 3–5, Lanthanides and Actinides) and Main Group Metal (Group 1, 2, and 13) Catalyzed Hydroamination. Top. Organomet. Chem. 2011, 43, 51–114. 10.1007/3418_2011_22. [DOI] [Google Scholar]; m Coman S. M.; Parvulescu V. I. Nonprecious Metals Catalyzing Hydroamination and C-N Coupling Reactions. Org. Process Res. Dev. 2015, 19, 1327–1355. 10.1021/acs.oprd.5b00010. [DOI] [Google Scholar]; n Ryken S. A.; Schafer L. L. N,O-Chelating Four-Membered Metallacyclic Titanium(IV) Complexes for Atom-Economic Catalytic Reactions. Acc. Chem. Res. 2015, 48, 2576–2586. 10.1021/acs.accounts.5b00224. [DOI] [PubMed] [Google Scholar]; o Hannedouche J.; Schulz E. Hydroamination and Hydroaminoalkylation of Alkenes by Group 3 – 5 Elements: Recent Developments and Comparison with Late Transition Metals. Organometallics 2018, 37, 4313–4326. 10.1021/acs.organomet.8b00431. [DOI] [Google Scholar]; p Manßen M.; Schafer L. L. Titanium Catalysis for the Synthesis of Fine Chemicals – Development and Trends. Chem. Soc. Rev. 2020, 49, 6947–6994. 10.1039/D0CS00229A. [DOI] [PubMed] [Google Scholar]
  3. a Holleman A. F.; Wiberg E.; Wiberg N. In Inorganic Chemistry; W. de Gruyter: Berlin, 2001; pp 1756–1759. [Google Scholar]; b Holleman A. F.; Wiberg E.; Wiberg N. In Inorganic Chemistry; W. de Gruyter: Berlin, 2001; p XXXVIII. [Google Scholar]
  4. Smolensky E.; Eisen M. S. Design of Organometallic Group IV Heteroallylic Complexes and Their Catalytic Properties for Polymerizations and Olefin Centered Transformations. Dalton Trans. 2007, 5623–5650. 10.1039/b707983b. [DOI] [PubMed] [Google Scholar]
  5. Rezaei Kheirkhah B.; Al-Shboul T. M. A.; Pröhl F. E.; Krieck S.; Görls H.; Westerhausen M. Isomerism in Hexacoordinate Ti(IV) and Zr(IV) Complexes with a Tetradentate ONNO-Schiff Base Ligand. Eur. J. Inorg. Chem. 2022, 2022, e202200528. 10.1002/ejic.202200528. [DOI] [Google Scholar]
  6. a Lee A. V.; Schafer L. L. Modular N,O-Chelating Ligands: Group-4 Amidate Complexes for Catalytic Hydroamination. Eur. J. Inorg. Chem. 2007, 2245–2255. 10.1002/ejic.200700036. [DOI] [Google Scholar]; b Yim J. C.-H.; Schafer L. L. Efficient Anti-Markovnikov-Selective Catalysts for Intermolecular Alkyne Hydroamination: Recent Advances and Synthetic Applications. Eur. J. Org. Chem. 2014, 2014, 6825–6840. 10.1002/ejoc.201402300. [DOI] [Google Scholar]
  7. a Zhang Z.; Schafer L. L. Anti-Markovnikov Intermolecular Hydroamination: A Bis(amidate) Titanium Precatalyst for the preparation of Reactive Aldimines. Org. Lett. 2003, 5, 4733–4736. 10.1021/ol0359214. [DOI] [PubMed] [Google Scholar]; b Thomson R. K.; Zahariev F. E.; Zhang Z.; Patrick B. O.; Wang Y. A.; Schafer L. L. Structure, Bonding, and Reactivity of Ti and Zr Amidate Complexes: DFT and X-Ray Crystallographic Studies. Inorg. Chem. 2005, 44, 8680–8689. 10.1021/ic0502980. [DOI] [PubMed] [Google Scholar]; c Payne P. R.; Thomson R. K.; Medeiros D. M.; Wan G.; Schafer L. L. Synthesis, Structure, and Reactivity of Tris(amidate) Mono(amido) and Tetrakis(amidate) Complexes of Group 4 Transition Metals. Dalton Trans. 2013, 42, 15670–15677. 10.1039/c3dt51868j. [DOI] [PubMed] [Google Scholar]; d Lui E. K. J.; Hergesell D.; Schafer L. L. N-Silylenamines as Reactive Intermediates: Hydroamination for the Modular Synthesis of Selectively Substituted Pyridines. Org. Lett. 2018, 20, 6663–6667. 10.1021/acs.orglett.8b02703. [DOI] [PubMed] [Google Scholar]; e Lui E. K. J.; Brandt J. W.; Schafer L. L. Regio- and Stereoselective Hydroamination of Alkynes Using an Ammonia Surrogate: Synthesis of N-Silylenamines as Reactive Synthons. J. Am. Chem. Soc. 2018, 140, 4973–4976. 10.1021/jacs.7b13783. [DOI] [PubMed] [Google Scholar]; f Hao H.; Schafer L. L. Metal-Ligand Cooperativity in Titanium-Catalyzed Anti-Markovnikov Hydroamination. ACS Catal. 2020, 10, 7100–7111. 10.1021/acscatal.0c00491. [DOI] [Google Scholar]; g Hao H.; Schafer L. L. Titanium-Catalzed Hydroamination of an Organometallic Acetylide to Access Copper Enamides. Organometallics 2021, 40, 3235–3239. 10.1021/acs.organomet.1c00416. [DOI] [Google Scholar]; h Hao H.; Bagnol T.; Pucheault M.; Schafer L. L. Using Catalysts to Make Catalysts: Titanium-Catalyzed Hydroamination to Access P,N-Ligands for Assembling Catalysts in One Pot. Org. Lett. 2021, 23, 1974–1979. 10.1021/acs.orglett.0c04212. [DOI] [PubMed] [Google Scholar]
  8. Li C.; Thomson R. K.; Gillon B.; Patrick B. O.; Schafer L. L. Amidate Complexes of Titanium and Zirconium: A New Class of tunable Precatalysts for the Hydroamination of Alkynes. Chem. Commun. 2003, 2462–2463. 10.1039/b304176j. [DOI] [PubMed] [Google Scholar]
  9. a Zi G.; Liu X.; Xiang L.; Song H. Synthesis of Group 4 Metal Amides with New Chiral Biaryldiimine-Based Ligands and Their Use as Catalysts for Asymmetric Hydroamination/Cyclization. Organometallics 2009, 28, 1127–1137. 10.1021/om801061v. [DOI] [Google Scholar]; b Wang Q.; Song H.; Zi G. Synthesis, Structure, and Catalytic Activity of Group 4 Complexes with New Chiral Biaryl-Based NO2 Ligands. J. Organomet. Chem. 2010, 695, 1583–1591. 10.1016/j.jorganchem.2010.03.014. [DOI] [Google Scholar]
  10. Horrillo-Martinez P.; Leitch D. C.; Ryken S. A.; Thomson R. K.; Beard J. D.; Patrick B. O.; Schafer L. L.; Giesbrecht G. R. Titanium Amidate Complexes as Active Catalysts for the Synthesis of High Molecular Weight Polyethylene. Can. J. Chem. 2015, 93, 775–783. 10.1139/cjc-2015-0081. [DOI] [Google Scholar]
  11. Coles N. T.; Gasperini D.; Provis-Evans C. B.; Mahon M. F.; Webster R. L. Heterobimetallic Complexes of 1,1-Diphosphineamide Ligands. Organometallics 2021, 40, 148–155. 10.1021/acs.organomet.0c00662. [DOI] [Google Scholar]
  12. a Bexrud J. A.; Eisenberger P.; Leitch D. C.; Payne P. R.; Schafer L. L. Selective C-H Activation α to Primary Amines. Bridging Metallaaziridines for Catalytic, Intramolecular α-Alkylation. J. Am. Chem. Soc. 2009, 131, 2116–2118. 10.1021/ja808862w. [DOI] [PubMed] [Google Scholar]; b Beweries T.; Hansen S.; Kessler M.; Klahn M.; Rosenthal U. Catalytic Dehydrogenation of Dimethylamine Borane by Group 4 Metallocene Alkyne Complexes and Homoleptic Amido Compounds. Dalton Trans. 2011, 40, 7689–7692. 10.1039/c1dt10366k. [DOI] [PubMed] [Google Scholar]; c Bielefeld J.; Doye S. Dimethylamine as a Substrate in Hydroaminoalkylation Reactions. Angew. Chem., Int. Ed. 2017, 56, 15155–15158. 10.1002/anie.201708959. [DOI] [PubMed] [Google Scholar]; d See also the comparable aziridine formation from a Ta(V)-bound NMe2 group:Eisenberger P.; Ayinla R. O.; Lauzon J. M. P.; Schafer L. L. Tantalum-Amidate Complexes for the Hydroaminoalkylation of Secondary Amines: Enhanced Substrate Scope and Enantioselective Chiral Amine Synthesis. Angew. Chem., Int. Ed. 2009, 48, 8361–8365. 10.1002/anie.200903656. [DOI] [PubMed] [Google Scholar]
  13. Yonson N.; Yim J. C.-H.; Schafer L. L. Alkene Hydroamination with a Chiral Zirconium Catalyst. Connecting Ligand Design, Precatalyst Structure and Reactivity Trends. Inorg. Chim. Acta 2014, 422, 14–20. 10.1016/j.ica.2014.07.073. [DOI] [Google Scholar]
  14. Catherall A. L.; Hill M. S.; Johnson A. L.; Kociok-Köhn G.; Mahon M. F. Homoleptic Zirconium Amidates: Single Source Precursors for the Aerosol-Assisted Chemical Vapour Deposition of ZrO2. J. Mater. Chem. C 2016, 4, 10731–10739. 10.1039/C6TC03631G. [DOI] [Google Scholar]
  15. Giesbrecht G. R.; Shafir A.; Arnold J. Synthesis and Structure of a Linked-Bis(amidate) Ligand and Some Complexes with Titanium. Inorg. Chem. 2001, 40, 6069–6072. 10.1021/ic010533o. [DOI] [PubMed] [Google Scholar]
  16. a Gott A. L.; Clarke A. J.; Clarkson G. J.; Scott P. Structure-Activity Relationship for Group 4 Biaryl Amidate Complexes in Catalytic Hydroamination/Cyclization of Aminoalkenes. Organometallics 2007, 26, 1729–1737. 10.1021/om061087l. [DOI] [Google Scholar]; b Wood M. C.; Leitch D. C.; Yeung C. S.; Kozak J. A.; Schafer L. L. Chiral Neutral Zirconium Amidate Complexes for the Asymmetric Hydroamination of Alkenes. Angew. Chem., Int. Ed. 2007, 46, 354–358. 10.1002/anie.200603017. [DOI] [PubMed] [Google Scholar]; Correction:2007, 48, 6937. 10.1002/anie.200990199; c Zi G.; Zhang F.; Xiang L.; Chen Y.; Fang W.; Song H. Synthesis and Characterization of Group 4 Metal Amides with new C2-Symmetric Binaphthyldiamine-Based Ligands and Their Use as Catalysts for Asymmetric Hydroamination/Cyclization. Dalton Trans. 2010, 39, 4048–4061. 10.1039/b923457h. [DOI] [PubMed] [Google Scholar]; d Reznichenko A. L.; Hultzsch K. C. C2-Symmetric Zirconium Bis(Amidate) Complexes with Enhanced Reactivity in Aminoalkene Hydroamination. Organometallics 2010, 29, 24–27. 10.1021/om9008907. [DOI] [Google Scholar]; e Ayinla R. O.; Gibson T.; Schafer L. L. Amidate Ligand Design Effects in Zirconium-Catalyzed Enantioselective Hydroamination of aminoalkenes. J. Organomet. Chem. 2011, 696, 50–60. 10.1016/j.jorganchem.2010.07.023. [DOI] [Google Scholar]
  17. Esarte Palomero O.; Jones R. A. Accessing Pentagonal Bipyramidal Geometry with Pentadentate Pincer Amido-bis(amidate) Ligands in Group IV and V Early Transition Metal Complexes. Organometallics 2020, 39, 3689–3694. 10.1021/acs.organomet.0c00501. [DOI] [Google Scholar]
  18. Bexrud J. A.; Li C.; Schafer L. L. Enhanced Reactivity Results in Reduced Catalytic Performance: Unexpected Ligand Reactivity of a Bis(N-2,6-diisopropylphenylperfluorophenyl-amidate)titanium-bis(diethylamido) Hydroamination Precatalyst. Organometallics 2007, 26, 6366–6372. 10.1021/om700653t. [DOI] [Google Scholar]
  19. Heutling A.; Pohlki F.; Doye S. [Ind2TiMe2]: A General Catalyst for the Intermolecular Hydroamination of Alkynes.. Chem. - Eur. J. 2004, 10, 3059–3071. 10.1002/chem.200305771. [DOI] [PubMed] [Google Scholar]
  20. Bresien J.; Goicoechea J. M.; Hinz A.; Scharnholz M. T.; Schulz A.; Suhrbier T.; Villinger A. Increasing Steric Demand Through Flexible Bulk – Primary Phosphanes with 2,6-Bis(benzhydryl)phenyl Backbones. Dalton Trans. 2019, 48, 3786–3794. 10.1039/C9DT00399A. [DOI] [PubMed] [Google Scholar]
  21. Sheldrick G. M. SHELXT – Integrated Space-Group and Crystal-Structure Determination. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3–8. 10.1107/S2053273314026370. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Sheldrick G. M. Crystal Structure Refinement with SHELXL. Acta Crystallogr. 2015, C71, 3–8. 10.1107/S2053229614024218. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. 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, 339–341. 10.1107/S0021889808042726. [DOI] [Google Scholar]
  24. Apex4 and SADABS; Bruker AXS Inc.: Madison, WI, 2001.

Associated Data

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

Supplementary Materials

om3c00291_si_005.pdf (1.1MB, pdf)

Articles from Organometallics are provided here courtesy of American Chemical Society

RESOURCES