ABSTRACT
Catalyzed hydrogen transfer to a range of organics is achieved using NiBr2 in alkaline, aqueous NaOH/'PrOH solutions under reflux, and the system seems of practical application for ketones and a,p-unsaturated ketones. The systems are homogeneous, and detailed kinetic studies on the catalyzed hydrogenation of cyclohexanone to cyclohexanol, particularly a 1st-to close to zero-order dependence on [NiBr2] with increasing nickel concentration and a 2nd-order dependence on [NaOH], are interpreted in terms of an active monomeric Niisopropoxide species present in equilibrium with a high nuclearity Ni cluster. The catalytic cycle likely involves hydride transfer from coordinated isopropoxide to coordinated substrate, a conventional step in such catalyzed hydrogen transfer hydrogenations. At the optimum [NaOH] of ~ 0.5 M, there is sufficient trace Ni salt impurity in the base to effect some catalytic transfer hydrogenation in the "base-only" blank systems.
