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

Base-stabilized [BP 3 i Pr ](H) 2 CoSiH 2 (DMAP) ( 1 , [BP 3 i Pr ] = 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 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 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 i Pr ](H) 2 Co═Si═Co(H) 2 L (L = [BP 2 t Bu 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 i Pr ](H) 2 Co═Si═Co(H) 2 [BP 3 i Pr ] ( 5 ) was prepared by treatment of a mixture of 1 and [BP 3 i Pr ]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 i Pr ](H) 2 Co═Si═Fe(H) 2 [SiP 3 i Pr ] ( 7 ; [SiP 3 i Pr ] = PhSi(CH 2 P i Pr 2 ) 3 ), was obtained via in situ KC 8 reduction of [SiP 3 i Pr ]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.