SINGLE-STEP HYDRIDE TRANSFER FROM CPMO(CO)(2)(PPH(3))H TO PROTONATED KETONES

The only alcohol complex formed during the ionic hydrogenation of acet one 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 isopro pyl 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 pr oducts from treating an acetonitrile solution of acetone and 1b with C F3SO3H thus include both 2b and 3b. The trans stereochemistry of 4 imp lies that the ionic hydrogenation of acetone by 1b involves a single-s tep hydride transfer rather than separate e(-) and H-. transfers. The equilibrium constant for the protonation of acetone by CF3SO3H in CH3C N at 25 degrees C is 2.4 x 10(-2), and the rate constant for hydride t ransfer from 1b to Me(2)COH(+) is 12 300 M(-1) s(-1) under the same co nditions. Other ketones undergo ionic hydrogenation more slowly.