OSHCL(CO)(O-2) (PCY3)(2)-CATALYZED HYDROGENATION OF ACRYLONITRILE-BUTADIENE COPOLYMERS

A new homogeneous catalyst precursor, OsHCl(CO)(L)(PCy3)(2) (1, L vaca nt; 2, L = O-2). has been identified for the selective hydrogenation o f olefin within acrylonitrile-butadiene copolymers. This report detail s a study of its catalytic behavior at hydrogenation conditions approa ching those used industrially. Carefully acquired kinetic data, collec ted within a statistical design framework, define the influence of [Os ], [RCN], [H-2], [PCy3], and temperature on the catalytic activity. Re versible coordination of nitrile to complex 1 not only reduces the hyd rogenation rate but creates an unprecedented sensitivity of the proces s to pressure. Unique to this system is an apparent second-order depen dence of the hydrogenation rate on [H-2], which diminishes toward zero order as pressures exceed 60 bar. In contrast, hydrogenation of subst rates that lack nitrile is virtually indifferent to [H-2] at all press ures. These kinetic measurements, coupled with recently acquired knowl edge of the structures and reactivities of complexes 1 and 2, provide the basis of a plausible reaction mechanism.