A [CoSiH(2)] Silylene Synthon Provides Modular Access to Homo- and Heterobimetallic [Co=Si=M] (M = Co, Fe) Silicide Complexes

[Image: see text] Base-stabilized [BP(3)(iPr)](H)(2)CoSiH(2)(DMAP) (1, [BP(3)(iPr)] = PhB(CH(2)P(i)Pr(2))(3)(–); DMAP = 4-dimethylaminopyridine) is a rare instance of a synthon for the simplest “parent” silylene complex (LM=SiH(2)). Complex 1 was accessed in high yields via double Si–H bond activation in SiH(4) by [BP(3)(iPr)]Co(DMAP), and in solution, it undergoes rapid exchange between bound and free DMAP by an associative mechanism (as determined by variable-temperature (1)H NMR dynamic studies). The DMAP ligand of 1 is readily displaced by metal-based fragments that bind silicon and cleave the Si–H bonds of the SiH(2) moiety to produce bimetallic [Co=Si=M] (M = Co, Fe) molecular silicides. Thus, treatment of 1 with 0.5 equiv of (LCo(I))(2)(μ-N(2)) (L = a tripodal ligand) resulted in the spontaneous formation of [BP(3)(iPr)](H)(2)Co=Si=Co(H)(2)L (L = [BP(2)(tBu)Pz], PhB(CH(2)P(t)Bu(2))(2)(pyrazolyl)(−) (3); Tp″, HB(3,5-diisopropylpyrazolyl)(3)(–) (4)) with the concomitant release of DMAP. The symmetrical silicide [BP(3)(iPr)](H)(2)Co=Si=Co(H)(2)[BP(3)(iPr)] (5) was prepared by treatment of a mixture of 1 and [BP(3)(iPr)]Co(DMAP) with 2 equiv of Ph(3)B, which in this case is required to sequester DMAP as the elimination product Ph(3)B-DMAP. A heterobimetallic silicide, [BP(3)(iPr)](H)(2)Co=Si=Fe(H)(2)[SiP(3)(iPr)] (7; [SiP(3)(iPr)] = PhSi(CH(2)P(i)Pr(2))(3)), was obtained via in situ KC(8) reduction of [SiP(3)(iPr)]FeCl and subsequent addition of 1 and Ph(3)B. These transformations involving a metal–SiH(2) derivative demonstrate a fundamentally new type of reactivity for silylene complexes and provide a unique synthetic method for construction of molecular silicide complexes.