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

Reaction of 2 equiv of Li[C 4 Me 4 GeSiMe 3 ] with Cp*HfMe 2 Cl produced the first transition metal complex of a germole dianion, [Cp*(η 5 -C 4 Me 4 Ge)HfMe 2 Li(THF)] 2 ( 1 ), via the apparent elimination of Me 3 SiCl, along with C 4 Me 4 Ge(SiMe 3 ) 2 as the final Me 3 Si-containing product. Compound 1 adopts a dimeric structure in which one Li atom is sandwiched in an η 5 -fashion between two germole rings, while the other Li atom is coordinated by both germanium atoms. Reaction of 1 with an excess of Me 3 SiCl resulted in loss of the germole ligand as C 4 Me 4 Ge(SiMe 3 ) 2, while 2 equiv of Me 3 SiOSO 2 CF 3 reacted with 1 to give the new germolyl complex Cp*[η 5 -C 4 Me 4 GeSiMe 3 ]HfMe 2 ( 2 ). Yet a different process results from treatment of 1 with CH 3 CH 2 OSO 2 CF 3, involving migration of a methyl group from hafnium to germanium to produce Cp*(η 4 -C 4 Me 4 GeMeEt)HfMe ( 3 ). Reaction of 2 with H 2 gave CH 4 and Me 3 SiH as the result of σ-bond metathesis involving the germole-bound trimethylsilyl group and (presumably) an intermediate hafnium hydride species. Similarly, the reaction of 2 with PhSiH 3 gave PhMeSiH 2 and Me 3 SiH. Compound 2 also reacted with MeI to produce C 4 Me 4 Ge(Me)SiMe 3, while the reaction with (Et 2 O)LiCH 2 Ph gave 1 and Me 3 SiCH 2 Ph. Compound 2 did not react cleanly with various small molecules (CO, CN(2,6-Me 2 C 6 H 3 ), trimethylsilylacetylene, and benzophenone), nor with the methide abstraction reagents B(C 6 F 5 ) 3 and [Ph 3 C][B(C 6 F 5 ) 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 C 4 Me 4 Ge(H)CMe 3 was prepared via reaction of C 4 Me 4 GeCl 2 with 1.5 equiv of Me 3 CLi, followed by treatment with LiAlH 4 . This germole was cleanly deprotonated by n BuLi in THF to give the new germole anion Li[C 4 Me 4 GeCMe 3 ] as a THF solvate. This anion reacted with Cp*HfMe 2 Cl to give the product of methyl migration from hafnium to germanium, Cp*[η 4 -C 4 Me 4 Ge(Me)CMe 3 ]HfMe ( 4 ). Analogously, Li[C 4 Me 4 GePh] reacted with Cp*HfMe 2 Cl to give Cp * [η 4 -C 4 Me 4 Ge(Me)Ph]HfMe ( 5 ). Treatment of MgBr 2 (Et 2 O) with 2 equiv of K[C 4 Me 4 SiSiMe 3 ] in THF resulted in formation of Mg[η 1 -C 4 Me 4 SiSiMe 3 ] 2 (THF) ( 6 ). Reaction of 6 with Cp*ZrCl 3 gave quantitative formation of Cp*[η 5 -C 4 Me 4 SiSiMe 3 ]ZrCl 2 ( 7 ), while the reaction of 6 with Cp*HfCl 3 provided the previously reported complex Cp*[η 5 -C 4 Me 4 SiSiMe 3 ]HfCl 2 ( 8 ) in quantitative yield.