(ETA-5-CYCLOPENTADIENYL)TRIALKYLPLATINUM PHOTOHYDROSILYLATION CATALYSTS - MECHANISM OF ACTIVE CATALYST FORMATION AND PREPARATION OF A NOVEL BIS(SILYL)PLATINUM HYDRIDE

The use of (eta5-cyclopentadienyl)trialkylplatinum complexes as photohydrosilylation catalysts is described. Photolysis of CpPtMe3 in the presence of a silane leads to the formation of an active hydrosilylation catalyst that evidence suggests is a heterogeneous platinum colloid. The catalyst is poisoned by elemental mercury but is not inhibited by dibenzo[a,e]cyclooctatetraene. In the presence of certain reactive silanes such as HMe2SiOSiMe3 the novel bis(silyl)platinum hydrides CpPt(SiR3)2H are formed as isolable species, which are not, however, intermediates on the primary pathway to the active hydrosilylation catalyst. The evidence suggests that the silyl methyl hydride complex CpPtMe(SiR3)H is the critical intermediate which is partitioned under the reaction conditions between colloidal platinum and CpPt(SiR3)2H. When they are treated with a second reactive silane, bis(silyl)platinum hydride complexes may undergo facile silane exchange via sequential reductive-elimination/oxidative-addition reactions at platinum to give other bis(silyl)platinum hydrides CpPt(SiR3')2H. A mechanism connecting CpPtMe3, CpPt(SiR3)2H, and colloidal platinum is proposed and discussed.