The heterobimetallic complexes [Y] [M(N)R-2(mu-O)(2)CrO2] (where Y is eithe
r N(n-Bu)(4)(+) or PPh4+; M is either Ru or Os; and R is an alkyl or aryl l
igand) catalyze the selective oxidation of alcohols with molecular oxygen.
The rate of the reaction is higher with a ruthenium-containing complex than
with an analogous osmium-containing catalyst. The rate decreases with ster
ic bulk in either the catalyst or substrate. Single-crystal X-ray diffracti
on studies of [N(n-Bu)4][Ru(N)(CH2SiMe3)(2)(mu-O)(2)CrO2] and [PPh4] [Os(N)
Me(CH2SiMe3)(mu-O)(2)CrO2] show the chromate group coordinated to each nitr
ido(dialkyl)metal center through two oxo ligands. The oxidation of benzyl a
lcohol by [N(n-Bu)(4)][Os(N)(CH2SiMe3)(2)(mu-O)(2)CrO2] was examinined in d
etail. It is first order in alcohol and substrate, and, when oxygen partial
pressure is low, the rate depends directly on the O-2 partial pressure. A
mechanism in which alcohol coordinates to the osmium center and is oxidized
by P-hydrogen elimination is consistent with the data. [N(n-Bu)(4)][Os(N)(
CH2SiMe3)(2)(mu-O)(2)CrO2] catalyzes the oxidation of dppe with Oz through
a different pathway.