A [CoSiH₂] Silylene Synthon Provides Modular Access to Homo- and Heterobimetallic [Co═Si═M] (M = Co, Fe) Silicide Complexes

Base-stabilized [BP₃^<i>i</i>Pr](H)₂CoSiH₂(DMAP) (<b>1</b>, [BP₃^<i>i</i>Pr] = PhB(CH₂P^<i>i</i>Pr₂)₃^-; DMAP = 4-dimethylaminopyridine) is a rare instance of a synthon for the simplest "parent" silylene complex (LM═SiH₂). Complex <b>1</b> was accessed in high yields via double Si-H bond activation in SiH₄ by [BP₃^<i>i</i>Pr]Co(DMAP), and in solution, it undergoes rapid exchange between bound and free DMAP by an associative mechanism (as determined by variable-temperature ¹H NMR dynamic studies). The DMAP ligand of <b>1</b> is readily displaced by metal-based fragments that bind silicon and cleave the Si-H bonds of the SiH₂ moiety to produce bimetallic [Co═Si═M] (M = Co, Fe) molecular silicides. Thus, treatment of <b>1</b> with 0.5 equiv of (LCo^I)₂(μ-N₂) (L = a tripodal ligand) resulted in the spontaneous formation of [BP₃^<i>i</i>Pr](H)₂Co═Si═Co(H)₂L (L = [BP₂^<i>t</i>BuPz], PhB(CH₂P^<i>t</i>Bu₂)₂(pyrazolyl)^- (<b>3</b>); Tp″, HB(3,5-diisopropylpyrazolyl)₃^- (<b>4</b>)) with the concomitant release of DMAP. The symmetrical silicide [BP₃^<i>i</i>Pr](H)₂Co═Si═Co(H)₂[BP₃^<i>i</i>Pr] (<b>5</b>) was prepared by treatment of a mixture of <b>1</b> and [BP₃^<i>i</i>Pr]Co(DMAP) with 2 equiv of Ph₃B, which in this case is required to sequester DMAP as the elimination product Ph₃B-DMAP. A heterobimetallic silicide, [BP₃^<i>i</i>Pr](H)₂Co═Si═Fe(H)₂[SiP₃^<i>i</i>Pr] (<b>7</b>; [SiP₃^<i>i</i>Pr] = PhSi(CH₂P^<i>i</i>Pr₂)₃), was obtained via <i>in situ</i> KC₈ reduction of [SiP₃^<i>i</i>Pr]FeCl and subsequent addition of <b>1</b> and Ph₃B. These transformations involving a metal-SiH₂ derivative demonstrate a fundamentally new type of reactivity for silylene complexes and provide a unique synthetic method for construction of molecular silicide complexes.