Is it homogeneous Pt(II) or heterogeneous Pt(0)n catalysis? Evidence that Pt(1,5-COD)Cl2 and Pt(1,5-COD)(CH3)2 plus H2 form heterogeneous, nanocluster plus bulk-metal Pt(0) hydrogenation catalysts

An investigation of the question of “Is it homogeneous or heterogeneous catalysis?” is reported when using PtII(1,5-COD)X2 (X = halogen, alkyl) precatalysts for the hydrogenation of olefins. Using product studies, kinetic evidence, and Hg0 poisoning experiments, it is shown that PtII(1,5-COD)Cl2 is a precatalyst and must be reduced to Pt0 nanoclusters and bulk metal as the true hydrogenation catalyst. An investigation of the related complex PtII(1,5-COD)(CH3)2 reveals that this complex does not form a hydrogenation catalyst by itself under H2, in agreement with the literature. Kinetic and Hg0 poisoning evidence confirms that PtII(1,5-COD)(CH3)2, too, forms a Pt0 heterogeneous catalyst if other metals (Ir0, Pt0) are used as seeds to initiate the reduction of PtII. A short review of the use of PtII(1,5-COD)Cl2 in hydrosilylation reactions is given, illustrating the continued controversy surrounding the nature of the true catalyst in that literature system.