Benzoimidazole‐Pyridylamido Zirconium and Hafnium Alkyl Complexes as Homogeneous Catalysts for Tandem Carbon Dioxide Hydrosilylation to Methane

Abstract

Neutral ZrIV and HfIV alkyl/amido complexes stabilized by a tridentate N ligand that contains a “rolling” heterodentate benzoimidazole fragment have been prepared and characterized. The ultimate nature of the ligand denticity, the electronic properties of the ligand binding pocket and the metal coordination environment are controlled by the protection/deprotection of the benzoimidazole NH group. The metal precursor used [MIV(Bn)4 or MIV(NMe2)4] also has an influence on the final coordination sphere of the complex; indeed, a permanent central pyridine dearomatization occurs in the presence of dimethylamido ancillary groups. DFT calculations on the real system have been used to elucidate the mechanism. Selected alkyl species from this series have been scrutinized for the tandem hydrosilylation of CO2 to CH4 in combination with the strong Lewis acid B(C6F5)3 using a variety of hydrosilanes. A positive effect of the hardness modification of the ligand donor atom set is observed in the catalytic outcomes. Indeed, κ3{N−,N,N−}ZrIV(Bn)2 catalyzes the process to methane selectively with a turnover frequency as high as 272 h−1 (at 96 % substrate conversion) almost twice as much as that claimed for the benchmark κ3{O−,O,O−}ZrIV(Bn)2 complex under similar experimental conditions.

Diverse Catalytic Systems and Mechanistic Pathways for Hydrosilylative Reduction of CO2

“…Based on a similar approach, Giambastiani et al. recently reported that benzoimidazole–pyridylamidozirconium and ‐hafnium complexes ( 47 ) were active for CO 2 hydrosilylation . They proposed a mechanism similar to that of the Matsuo and Kawaguchi system, and concluded that the reaction rate was largely governed by the electrophilic nature of the metal ion in the first step of CO 2 activation.…”

Partnering a Three‐Coordinate Gallium Cation with a Hydroborate Counter‐Ion for the Catalytic Hydrosilylation of CO2

“…Thus, a variety of homogenous catalytic systems based on metals (Pd/Pt, [14–17] Rh, [18] Re, [19, 20] Ru, [21–26] Ir, [8, 27–30] Co, [13, 31] Mn, [12] Zr, [32, 33] Cu, [34–38] Ni, [39–42] Sc, [43–46] Zn, [47–57] Mg [57, 58] and Sr [59] ), Lewis acids, [60–66] frustrated Lewis pairs (FLPs), [67, 68] organo‐catalysts, [69–75] alkali metal carbonates, [76, 77] and metal borohydrides [78] have been investigated for this process. Many of these catalytic systems feature reactive metal hydride or alkyl groups, which effect the initial activation of CO 2 via insertion.…”

Imidazole‐Bridged Tetrameric Group(IV) Heteroleptic Complexes from the Spontaneous Metal‐Ligand Assembly of a Potentially N4‐Tetradentate Ligand

“…In recent years, our group has been extensively working on the preparation of multidentate heteroleptic N‐ligands and their related κ 3 {N,N,N}M 3+/4+ coordination compounds (or κ 3 {N,C,N}M 3+/4+ /κ 3 {N,N,C}M 3+/4+ organometallics) based on highly electrophilic metal ions (from group IV elements of the periodic table or from lanthanides, ) for applications in homogeneous catalysis. In a recent report, we have described the synthesis, characterization and catalytic application of a series of Zr IV /Hf IV alkyl/amido complexes stabilized by a tridentate N‐ligand containing a benzoimidazole fragment . We have shown the ability of this ligand system to vary its coordination mode around the metal ion and thus the ultimate complex coordination number by means of a protection/deprotection switch of the pyrrolic N‐site at the “rolling” imidazole pendant arm (Scheme ).…”

“…Tunable κ 3 {N,N,N} L1 ligand pocket by NH protection/deprotection of a rolling benzoimidazole pendant arm and its coordination to Zr IV /Hf IV …”

“…Due to the ability of its deprotonated form (imidazolate) to act as a bridging ligand with a wide variety of metal ions, it has already provided a number of polymetallic materials and original complex architectures . Starting from our interest in the synthesis and characterization of group IV pyridylamido complexes containing pyrazole, and imidazolate units, we report herein on the synthesis and coordination chemistry of a new imidazolate‐based polydentate N‐ligand. Our aim was to redistribute the spatial assembly of the donor atom set in L1 to create a new molecular architecture L2 to be employed as tridentate mono‐ or di‐anionic κ 3 {N,N,N} system for group IV metal ions coordination (Scheme ).…”