Kinetic investigations on the redox reactions of platinum carbonyl clusters with dihydrogen and acid

Redox reactions of the Chini clusters, [Pt-3(CO)(6)](n)(2-) (n = 3, 4, 5), with dihydrogen and acid have been kinetically studied. The reduction of th e tetramer to the trimer by dihydrogen is found to be second order with res pect to the cluster concentration. Within the pressure range of 1-7 bar, th e rate is independent of hydrogen pressure. The acid-induced oxidations of the trimer to the tetramer in DMF and the tetramer to the pentamer in both DMF and acetonitrile proceed through fast protonation equilibria followed b y rate-determining steps; The consecutive oxidation of the trimer --> tetra mer --> pentamer can be accurately simulated by assuming a three rate const ant kinetic model. While the oxidation of the trimer involves more than one protonation equilibria between the free cluster and the protonated species , for the tetramer there is one equilibrium with a 1:1 cluster to proton mo lar ratio. Cyclic voltammetric studies on the trimer in DMF and the tetrame r in acetonitrile show three and two anodic responses in the potential rang es -0.42 to -0.08 and 0.4 to 0.75 V, respectively. The kinetic findings and literature-reported spectroscopic and other observations are consistent wi th a mechanism that involves the formation of weak aggregates of the cluste rs and disproportionation of the aggregates.