Synthesis and reactivity of η5-silolyl, η5-germolyl, and η5-germole dianion complexes of zirconium and hafnium

Reaction of 2 equiv of Li[C4Me4GeSiMe3] with Cp*HfMe2Cl produced the first transition metal complex of a germole dianion, [Cp*(eta(5)-C4Me4Ge)HfMe2Li(THF)](2) (1), via the apparent elimination of Me3SiCl, along with C4Me4Ge(SiMe3)(2) as the final Me3Si-containing product. Compound 1 adopts a dimeric structure in which one Li atom is sandwiched in an eta(5)-fashion between two germole rings, while the other Li atom is coordinated by both germanium atoms. Reaction of 1 with an excess of Me3SiCl resulted in loss of the germole ligand as C4Me4Ge(SiMe3)(2), while 2 equiv of Me3SiOSO2CF3 reacted with 1 to give the new germolyl complex Cp*[eta(5)-C4Me4GeSiMe3]HfMe2 (2). Yet a different process results from treatment of 1 with CH3CH2OSO2CF3, involving migration of a methyl group from hafnium to germanium to produce Cp*(eta(4)-C4Me4GeMeEt)HfMe (3). Reaction of 2 with H-2 gave CH4 and Me3SiH as the result of sigma-bond metathesis involving the germole-bound trimethylsilyl group and (presumably) an intermediate hafnium hydride species. Similarly, the reaction of 2 with PhSiH3 gave PhMeSiH2 and Me3SiH. Compound 2 also reacted with Mel to produce C-4-Me4Ge(Me)SiMe3, while the reaction with (Et2O)LiCH2Ph gave 1 and Me3SiCH2Ph. Compound 2 did not react cleanly with various small molecules (CO, CN(2,6-Me2C6H3), trimethylsilylacetylene,and benzophenone), nor with the methide abstraction reagents B(C6F5)(3) and [Ph3C][B(C6F5)(4)]. In addition, reaction of 2 with these abstraction reagents in the presence of 1-hexene or cyclohexene did not result in the formation of a polymer. The germole C4Me4Ge(H)CMe3 was prepared via reaction of C4Me4GeCl2 with 1.5 equiv of Me3CLi, followed by treatment with LiAlH4. This germole was cleanly deprotonated by (BuLi)-Bu-n in THF to give the new germole anion Li[C4Me4GeCMe3] as a THF solvate. This anion reacted with Cp*HfMe2Cl to give the product of methyl migration from hafnium to germanium, Cp*[eta(4)-C4Me4Ge(Me)CMe3]HfMe (4). Analogously, Li[C4Me4GePh] reacted with Cp*HfMe2Cl to give Cp*[eta(4)-C4Me4Ge(Me)Ph]HfMe (5). Treatment of MgBr2(Et2O) with 2 equiv of K[C4Me4SiSiMe3] in THF resulted in formation of Mg[eta(1)-C4Me4SiSiMe3](2)(THF) (6). Reaction of 6 with Cp*ZrCl3 gave quantitative formation of Cp*[eta(5)-C4Me4SiSiMe3]ZrCl2 (7), while the reaction of 6 with Cp*HfCl3 provided the previously reported complex Cp*[eta(5)-C4Me4SiSiMe3]HfCl2 (8) in quantitative yield.