Silylene Complexes of Late 3<i>d</i> Transition Metals Supported by <i>tris</i>-Phosphinoborate Ligands

The complexes [BP3R]MX ([BP3R] = PhB(CH2PR2)3–, R = Ph, iPr; M = Ni, Co, Fe; X = halide) were explored as platforms for generation of first-row metal silylene complexes. Direct silylation of [BP3Ph]NiCl or [BP3iPr]CoCl with (THF)2LiSiHMes2 resulted in formation of the silylene complexes [BP3Ph]Ni(μ-H)(SiMes2) and [BP3iPr]Co(μ-H)(SiMes2), respectively. In contrast, [BP3iPr]FeBr reacted with (THF)2LiSiHMes2 to produce the iron-alkyl [BP3iPr]Fe(CH2-2-(SiH2Mes)-3,5-Me2C6H2), a constitutional isomer of the expected silyl or silylene complex. Preparation of the nickel benzyl complex [BP3Ph]Ni(η2-Bn) allowed for exploration of addition–elimination chemistry for access to silylene complexes from simple primary and secondary silanes. Heating toluene solutions of [BP3Ph]Ni(η2-Bn) in the presence of CySiH3 resulted in the formation of a dimeric μ-silylene complex [Ni(μ-BP2Ph)(μ-SiHCy)]2. In the presence of 4-dimethylaminopyridine (DMAP), these conditions led to exclusive formation of the base-stabilized silylene complex [BP3Ph]Ni(μ-H)[SiHCy(DMAP)].