Catalysis with platinum carbonyl clusters

In order to explain our interest in the selective reduction by proton and e lectron addition, and asymmetric hydrogenation, the historical background a nd the current status of carbonyl clusters as catalysts are briefly describ ed, The unique redox chemistry of the anionic platinum carbonyl clusters (C hini clusters) has been utilized to design a model for the DH-driven transp ort of electrons through biological membranes. The platinum clusters have a lso been used as catalysts for the reduction of biological co-factors and p roteins by dihydrogen. To overcome the water insolubility problem of the pl atinum clusters, tao approaches have been adopted, In the first, a biphasic system consisting of water and a solution of the platinum cluster in a wat er immiscible organic solvent is used, In such a reaction system, by using a redox active dye such as Safranine O as the shuttle carrier for two elect rons and one proton, the reduction of flavin and nicotinamide cofactors by dihydrogen could be effected, The regeneration of NADH from NAD(+) by dihyd rogen can be further coupled with lactate dehydrogenase catalysed reduction of pyruvate to lactate. In the second approach, the platinum clusters are anchored onto a biocompatible anion exchange resin such as QAE-SEPHADEX. Th e sephadex-supported material catalyses the reduction of flavin cofactors a nd CytC(ox) by dihydrogen in Mister. The platinum clusters could also be an chored onto cross-linked polystyrene, functionalized with chiral quaternary ammonium groups, This material becomes an active heterogeneous hydrogenati on catalyst after thermal decarbonylation, and reduces methyl pyruvate to m ethyl lactate with high enantioselectivity.