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^-; [BP₂^<i>t</i>BuPz], PhB(CH₂P^<i>t</i>Bu₂)₂(pyrazolyl)). Upon exposure of (Tp″Co)₂(μ-N₂) (<b>1</b>) to SiH₄, a mixture of (Tp″Co)₂(μ-H) (<b>2</b>) and (Tp″Co)₂(μ-H)₂ (<b>3</b>) was formed and no evidence for Si-H oxidative addition products was observed. In contrast, [BP₂^<i>t</i>BuPz]-supported Co complexes led to Si-H oxidative additions with the generation of silylene and silicide complexes as products. Notably, the reaction of ([BP₂^<i>t</i>BuPz]Co)₂(μ-N₂) (<b>5</b>) with SiH₄ gave the dicobalt silicide complex [BP₂^<i>t</i>BuPz](H)₂Co═Si═Co(H)₂[BP₂^<i>t</i>BuPz] (<b>8</b>) in high yield, representing the first direct route to a symmetrical bimetallic silicide. The effect of the [BP₂^<i>t</i>BuPz] ligand on Co-Si bonding in <b>7</b> and <b>8</b> was explored by analysis of solid-state molecular structures and density functional theory (DFT) investigations. Upon exposure to CO or DMAP (DMAP = 4-dimethylaminopyridine), <b>8</b> converted to the corresponding [BP₂^<i>t</i>BuPz]Co(L)_x adducts (L = CO, <i>x</i> = 2; L = DMAP, <i>x</i> = 1) with concomitant loss of SiH₄, despite the lack of significant Si-H interactions in the starting complex. On heating to 60 °C, <b>8</b> underwent reaction with MeCl to produce small quantities of Me_<i>x</i>SiH_4-<i>x</i> (<i>x</i> = 1-3), demonstrating functionalization of the μ-silicon atom in a molecular silicide to form organosilanes.