SOLVENT-INDUCED REDUCTIVE ELIMINATION OF PENTAMETHYLCYCLOPENTADIENE FROM A (PENTAMETHYLCYCLOPENTADIENYL)METAL HYDRIDE

In acetonitrile solution, CpIr(PPh3)(H)3+BF4- smoothly undergoes elim ination of pentamethylcyclopentadiene (CpH) to yield Ir(H)2(PPh3)(NCM e)3+BF4- as the only Ir-containing product (DELTAH(double dagger) = 69 .0 +/- 2.1 kJ/mol, DELTAS(double dagger) = -82.0 +/- 7.6 J/(K.mol), k( 20-degrees-C) = 1.6 x 10(-4) s-1). The elimination of CpH did not tak e place in neat dichloromethane. The rate law exhibited a mixed first- and second-order dependence on the acetonitrile concentration, in acc ord with a mechanism involving successive acetonitrile-mediated eta5 t o eta3 to eta1 ring slippage reactions, the first of which is reversib le.