title: Zincocene and dizincocene N-heterocyclic carbene complexes and catalytic hydrogenation of imines and ketones.
abstract: The N-heterocyclic carbene (NHC) adducts Zn(Cp(R))(2) (NHC)] (Cp(R) =C(5)HMe(4), C(5)H(4) SiMe(3); NHC=ItBu, IDipp (Dipp=2,6-diisopropylphenyl), IMes (Mes=mesityl), SIMes) were prepared and shown to be active catalysts for the hydrogenation of imines, whereas decamethylzincocene [ZnCp*(2)] is highly active for the hydrogenation of ketones in the presence of noncoordinating NHCs. The abnormal carbene complex [Zn(OCHPh(2))(2) (aItBu)](2) was formed from spontaneous rearrangement of the ItBu ligand during incomplete hydrogenation of benzophenone. Two isolated Zn(I) adducts [Zn(2)Cp*(2) (NHC)] (NHC=ItBu, SIMes) are presented and characterized as weak adducts on the basis of (13)C NMR spectroscopic and X-ray diffraction experiments. A mechanistic proposal for the reduction of [ZnCp*(2)] with H(2) to give [Zn(2)Cp*(2)] is discussed.
authors.affiliation: Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6 (Canada).
authors.forename: Phillip
authors.initials: P
authors.lastname: Jochmann
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Stephan
keywords: carbene ligands; homogeneous catalysis; hydrogenation; reaction mechanisms; zinc