Coordinatively unsaturated pentameehylcyclopentadienyl pinacolate complexes
of the group 9 transition metals (4-6) have been prepared and characterize
d. Photolysis of either the cobalt complex 4 or the rhodium complex 5 resul
ts in cleavage of the central carbon-carbon bond in the diolate, generating
acetone. Various trapping studies demonstrate that an intact [Cp*M] fragme
nt is produced in these reactions, and in the absence of added traps this f
ragment reacts either with aromatic solvents or with an intact molecule of
the starting pinacolate complex. The oxidation of the resulting rhodium(II)
product II by air (or Oz) in the presence of pinacol regenerates the rhodi
um(III) pinacolate complex 5. Photolysis of rhodium complex 5 in the presen
ce of pinacol and oxidant (either O-2 or N2O) results in the catalytic conv
ersion of pinacol to acetone.