M.C. White, Chem 153 Hydrozirconation -292 Week of november 18. 2002 Alkene/ Alkyne hydrozirconation orbital on zr via g-donation (T-backbonding is not possible ause the complex has no d electrons) Schwartzs reagent, 16e-(d0 Internally metalated omplexes rapidly isomerize at rt via 18e 6e-(d) B-hydride elimination, reinsertion sequences to the least sterically Moisture and O sensitive alkylzirconium SchwartzJACS 1974(96)8115 hindered 1 alkylzirconium produc product Olefin insertion into the Zr-C bond has never been observed Morokuma OM 1993(12)2777 nCI H Zr(CI)Cp2 Zr( ciCp nzene,rt, N2 84:16 Stereospecific cis hydrometallation occurs wit H regioselectivity in formation of the least sterically Zr(cl)cp2 vinylzirconium species. The use of excess Schwartz's reagent results in higher regioselectivities via formation of a dimetalated alkyl intermediate that preferentially p-hydride eliminates at the more sterically hindered Zr center Schwartz JACS 1975(97)679M.C. White, Chem 153 Hydrozirconation -292- Week of November 18, 2002 Alkene/Alkyne Hydrozirconation ZrI V H Cl C6H13 (stoichiometric) benzene, rt, N2 ZrI V H Cl R 18e - (d0) Schwartz's reagent, 16e - (d0) ZrI V Cl 16e - (d0) R Moisture and O2 sensitive alkylzirconium product. Olefin insertion into the Zr-C bond has never been observed. Internally metalated alkylzirconium complexes rapidly isomerize at rt via β-hydride elimination, reinsertion sequences to the least sterically hindered 1o alkylzirconium product. Schwartz JACS 1974 (96) 8115. Morokuma OM 1993 (12) 2777. Olefin binds weakly to vacant d orbital on Zr via σ-donation (π-backbonding is not possible because the complex has no d electrons). ZrIV H Cl benzene, rt, N2 H Zr(Cl)Cp2 + Zr(Cl)Cp2 H 84:16 1 eq ZrI V H Cl benzene, rt, N2 catalytic Cp2(Cl)Zr H H Zr(Cl)Cp2 H Zr(Cl)Cp2 + Zr(Cl)Cp2 H 98:2 Stereospecific cis hydrometalation occurs with high regioselectivity in formation of the least sterically hindered vinylzirconium species. The use of excess Schwartz's reagent results in higher regioselectivities via formation of a dimetalated alkyl intermediate that preferentially β-hydride eliminates at the more sterically hindered Zr center. Schwartz JACS 1975 (97) 679