Orthometallated palladium(II) complexes as versatile catalysts for homogeneous catalytic hydrogenation

Abstract

Catalytic dihydrogenation of some alkenes, alkynes, organic nitro compounds and compounds containing the functional groups > C = O, > C = N -, - N = N - and - C = N has been carried out using orthopalladated complexes of the types <em>trans-</em>Pd₂L₂X₂ and PdLL’Cl (LH= 2-benzoylpyridine, 2-benzylpyridine, N,N-dimethylbenzylamine; L'=pyridine, triphenylphosphine; X=OAc, Cl) in DMF medium. Nitroalkanes, benzonitrile and benzophenone have been reduced under superatmospheric pressure while others require normal pressure for hydrogenation. The isolated intermediates, characterized as Pd(LXH)DMF(LH =2-benzoylpyridine and 2-benzylpyridine), are the actual catalytic species. A tentative mechanism for the reduction processes has been suggested on the basis of the isolated intermediates and the kinetic data.