Transition-Metal Mediated Formation and Cleavage of Carbon-Hydrogen Bonds: Hydrogenolysis of Trinuclear Alkylidyne Clusters and Oxidative Addition of Carbon-Hydrogen Bonds to Rhenium

摘要

Treatment of dicobalt alkyne complexes Co sub 2 (CO) sub 6 (HCCR) (R = alkyl, aryl) with H sub 2 and Co sub 2 (CO) sub 8 or CpMo(CO) sub 3 H leads to mu sub 3 -alkylidyne complexes with molecular formula Co sub 3 (CO) sub 9 CCH sub 2 R and CpMo(CO) sub 2 Co sub 2 (CO) sub 6 CCH sub 2 R, respectively, in high yield and purity. Hydrogenation of these clusters occurs under mild conditions (60 to 90 exp 0 C, benzene solution, 3 to 4 atm of H sub 2 ) and gives olefins, paraffins, and carbonyl compounds. A radical pathway for the hydrogenolyses is suggested. ESR experiments involving the reaction of Co sub 3 (CO) sub 9 CCH sub 2 (CH sub 3 ) sub 3 (2) with H sub 2 in the presence of the spin-trap t-BuNO confirm the intervention of vinyl radical intermediates and reveal that a hydrogen atom donor is generated. Evidence consistent with vinyl radical intermediates is also provided by isotope labelling. Inter- and intramolecular C-H oxidative addition reactions have been observed from two related organorhenium intermediates: Cp*Re(CO)(PMe sub 3 ) (11) and Cp*Re(PMe sub 3 ) sub 2 c (12) (Cp* = eta exp 5 -C sub 5 (CH sub 3 ) sub 5 ). The cyclometallated compounds undergo reductive elimination; the coordinatively unsaturated species thus formed can be trapped to give intermolecular C-H activation products under mild thermal conditions. In contrast to its (carbonyl)phosphine analog 11, 12 is capable of insertion into the C-H bonds of methane as well as cyclopropane and benzene. 100 refs., 20 figs., 1 tab. (ERA citation 10:031675)