Normal and Inverse Primary Kinetic Deuterium Isotope Effects for C−H Bond Reductive Elimination and Oxidative Addition Reactions of Molybdenocene and Tungstenocene Complexes: Evidence for Benzene σ-Complex Intermediates

摘要: The overall reductive elimination of RH from the ansa-molybdenocene and -tungstenocene complexes [Me(2)Si(C(5)Me(4))(2)]Mo(Ph)H [Me(2)Si(C(5)Me(4))(2)]W(R)H (R = Me, Ph) is characterized by an inverse primary kinetic isotope effect (KIE) for tungsten system but a normal KIE molybdenum system. Oxidative addition PhH to [[Me(2)Si(C(5)Me(4))(2)]M] also differs two systems, with exhibiting substantial intermolecular KIE, while no observed These differences in KIEs indicate significant difference reactivity hydrocarbon adducts [Me(2)Si(C(5)Me(4))(2)]M(RH) systems. Specifically, oxidative cleavage favored over dissociation system, whereas A kinetics analysis interconversion [Me(2)Si(C(5)Me(4))(2)]W(CH(3))D [Me(2)Si(C(5)Me(4))(2)]W(CH(2)D)H, accompanied methane, provides evidence that coupling step this KIE. This observation demonstrates result equilibrium (EIE) not single step. previous report 0.76 C-H [Tp]Pt(CH(3))H(2) shown be erroneous. Finally, computational study [Me(2)Si(C(5)Me(4))(2)]W(Ph)H proceeds via initial formation benzene sigma-complex, rather than eta(2)-pi-benzene complex.