Synthesis and Reactivity of η⁵-Silolyl, η⁵-Germolyl, and η⁵-Germole\nDianion Complexes of Zirconium and Hafnium

Abstract

Reaction of 2 equiv of Li[C₄Me₄GeSiMe₃] with Cp*HfMe₂Cl produced the first transition metal\ncomplex of a germole dianion, [Cp*(η⁵-C₄Me₄Ge)HfMe₂Li(THF)]₂ (<b>1</b>), via the apparent elimination of Me₃SiCl, along with C₄Me₄Ge(SiMe₃)₂ as the final Me₃Si-containing product. Compound <b>1</b> adopts a dimeric structure\nin which one Li atom is sandwiched in an η⁵-fashion between two germole rings, while the other Li atom is\ncoordinated by both germanium atoms. Reaction of <b>1</b> with an excess of Me₃SiCl resulted in loss of the germole\nligand as C₄Me₄Ge(SiMe₃)₂, while 2 equiv of Me₃SiOSO₂CF₃ reacted with <b>1</b> to give the new germolyl complex\nCp*[η⁵-C₄Me₄GeSiMe₃]HfMe₂ (<b>2</b>). Yet a different process results from treatment of <b>1</b> with CH₃CH₂OSO₂CF₃, involving migration of a methyl group from hafnium to germanium to produce Cp*(η⁴-C₄Me₄GeMeEt)HfMe (<b>3</b>). Reaction of <b>2</b> with H₂ gave CH₄ and Me₃SiH as the result of σ-bond metathesis involving the\ngermole-bound trimethylsilyl group and (presumably) an intermediate hafnium hydride species. Similarly, the\nreaction of <b>2</b> with PhSiH₃ gave PhMeSiH₂ and Me₃SiH. Compound <b>2</b> also reacted with MeI to produce C₄Me₄Ge(Me)SiMe₃, while the reaction with (Et₂O)LiCH₂Ph gave <b>1</b> and Me₃SiCH₂Ph. Compound <b>2</b> did not\nreact cleanly with various small molecules (CO, CN(2,6-Me₂C₆H₃), trimethylsilylacetylene, and benzophenone),\nnor with the methide abstraction reagents B(C₆F₅)₃ and [Ph₃C][B(C₆F₅)₄]. In addition, reaction of <b>2</b> with these\nabstraction reagents in the presence of 1-hexene or cyclohexene did not result in the formation of a polymer.\nThe germole C₄Me₄Ge(H)CMe₃ was prepared via reaction of C₄Me₄GeCl₂ with 1.5 equiv of Me₃CLi, followed\nby treatment with LiAlH₄. This germole was cleanly deprotonated by ⁿBuLi in THF to give the new germole\nanion Li[C₄Me₄GeCMe₃] as a THF solvate. This anion reacted with Cp*HfMe₂Cl to give the product of methyl\nmigration from hafnium to germanium, Cp*[η⁴-C₄Me₄Ge(Me)CMe₃]HfMe (<b>4</b>). Analogously, Li[C₄Me₄GePh]\nreacted with Cp*HfMe₂Cl to give Cp^*[η⁴-C₄Me₄Ge(Me)Ph]HfMe (<b>5</b>). Treatment of MgBr₂(Et₂O) with 2 equiv\nof K[C₄Me₄SiSiMe₃] in THF resulted in formation of Mg[η¹-C₄Me₄SiSiMe₃]₂(THF) (<b>6</b>). Reaction of <b>6</b> with\nCp*ZrCl₃ gave quantitative formation of Cp*[η⁵-C₄Me₄SiSiMe₃]ZrCl₂ (<b>7</b>), while the reaction of <b>6</b> with Cp*HfCl₃\nprovided the previously reported complex Cp*[η⁵-C₄Me₄SiSiMe₃]HfCl₂ (<b>8</b>) in quantitative yield.