Single-step hydride transfer from CpMo(CO)(2)(PPh(3))H to protonated ketones

The only alcohol complex formed during the ionic hydrogenation of acetone by CpMo(CO)(2)(PPh(3))H (2b) and CF3SO3H in acetonitrile is trans-CpMo(CO)(2)(PPh(3))(i-PrOH)(+) (4); on standing the coordinated isopropyl alcohol of 4 is replaced by solvent, forming trans-CpMo(CO)(2)(PPh(3))(CH3CN)(+) (2b). Treatment of 1b in the same solvent with CF3SO3H alone yields the more stable cis acetonitrile complex 3b. The final products from treating an acetonitrile solution of acetone and 1b with CF3SO3H thus include both 2b and 3b. The trans stereochemistry of 4 implies that the ionic hydrogenation of acetone by 1b involves a single-step hydride transfer rather than separate e(-) and H-. transfers. The equilibrium constant for the protonation of acetone by CF3SO3H in CH3CN at 25 degrees C is 2.4 x 10(-2), and the rate constant for hydride transfer from 1b to Me(2)COH(+) is 12 300 M(-1) s(-1) under the same conditions. Other ketones undergo ionic hydrogenation more slowly.