Direct Transformation of SiH₄ to a Molecular L(H)₂Co═Si═Co(H)₂L Silicide Complex

The synthesis of bimetallic molecular silicide complexes is reported, based on the use of multiple Si-H bond activations in SiH₄ at the metal centers of 14-electron LCo^I fragments (L = Tp″, HB(3,5-diisopropylpyrazolyl)₃^-; [BP₂Pz], PhB(CH₂PBu₂)₂(pyrazolyl)). Upon exposure of (Tp″Co)₂(μ-N₂) (1) to SiH₄, a mixture of (Tp″Co)₂(μ-H) (2) and (Tp″Co)₂(μ-H)₂ (3) was formed and no evidence for Si-H oxidative addition products was observed. In contrast, [BP₂Pz]-supported Co complexes led to Si-H oxidative additions with the generation of silylene and silicide complexes as products. Notably, the reaction of ([BP₂Pz]Co)₂(μ-N₂) (5) with SiH₄ gave the dicobalt silicide complex [BP₂Pz](H)₂Co═Si═Co(H)₂[BP₂Pz] (8) in high yield, representing the first direct route to a symmetrical bimetallic silicide. The effect of the [BP₂Pz] ligand on Co-Si bonding in 7 and 8 was explored by analysis of solid-state molecular structures and density functional theory (DFT) investigations. Upon exposure to CO or DMAP (DMAP = 4-dimethylaminopyridine), 8 converted to the corresponding [BP₂Pz]Co(L)_x adducts (L = CO, x = 2; L = DMAP, x = 1) with concomitant loss of SiH₄, despite the lack of significant Si-H interactions in the starting complex. On heating to 60 °C, 8 underwent reaction with MeCl to produce small quantities of MeSiH_4- (x = 1-3), demonstrating functionalization of the μ-silicon atom in a molecular silicide to form organosilanes.