SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF TRIPHENYLSILYL, TRIPHENYLGERMYL, AND TRIPHENYLSTANNYL DERIVATIVES OF ZIRCONIUM AND HAFNIUM

The crystalline lithium silyl compound (THF)3LiSiPh3 (1) was isolated from the reaction of Ph3SiSiPh3 with lithium in tetrahydrofuran. This compound and tetrahydrofuran solutions of LiEPh3 (E = Ge, Sn) were used to prepare the complexes CpCp*Zr(EPh3)Cl (2, E = Si; 3, E = Ge), CpCp*Hf(EPh3)Cl (5, E = Si; 6, E = Ge; 7, E = Sn), Cp*2Zr(EPh3)Cl (8, E = Si; 9, E = Ge; 10, E = Sn), and Cp*2Hf(SiPh3)Cl (11). This method did not provide the zirconium stannyl complex CpCp*Zr(SnPh3)Cl (4) but instead gave the phenyl derivative CpCp*Zr(Ph)Cl via phenyl transfer. Compound 4 may be obtained via reactions of HSnPh3 with 2,3, or CpCp*Zr[Si(SiMe3)3]Cl. Reactions of 8 and 11 with MeMgBr gave Cp*2M(SiPh3)Me (12, M = Zr; 13, M = Hf). Hydrogenolysis of 2, 5, 8, and 11 provides routes to the corresponding hydrides CpCp*MHCl or Cp*2MHCl. Likewise, the reactions of 12 and 13 with hydrogen give Cp*2ZrH2 and Cp*2Hf(H)Me, respectively. The germyl and stannyl complexes were found to be significantly less reactive toward hydrogen. Reactions of 2-11 with PhSiH3 gave sigma-bond metathesis products in some cases and no reaction in other cases, such that the observed reactivity trends are CpCp*M > Cp*2M; Zr > Hf, M-Si > M-Ge > M-Sn. Carbonylation of 8 resulted in formation of Cp*2Zr(eta-2-COSiPh3)Cl (14), which reacts with HCl to give the thermally stable formylsilane Ph3SiCHO (15) and with 2,6-Me2C6H3NC to afford the ketenimine Cp*2Zr[OC(SiPh3)(CN-2,6-Me2C6H3)]Cl (16). The silyl complexes 5, 8, and 11 react with 2,6-Me2C6H3NC to give eta-2-iminosilaacyl insertion products, as does the germyl 3. However, no reaction is observed between 2,6-Me2C6H3NC and stannyl complexes 7 or 10. These investigations establish the reactivity trends M-SiPh3 > M-GePh3 > M-SnPh3 for sigma-bond metathesis processes with hydrogen and phenylsilane and for insertion reactions with carbon monoxide and 2,6-Me2C6H3NC. It is suggested that, for these analogues d0 metal silyl, germyl, and stannyl complexes, the energetics of the reactions are influenced primarily by the new E-element bond strengths of the products rather than by the d0 M-E bond strengths of the starting materials.