Abstract
[cis-(CO)4W(PR3)]n(py') (n = 1, 2) were prepd. by electron transfer-catalyzed CO substitution of (CO)5W(py') (py' = R-substituted-pyridine, R = COMe, COPh, COOMe, CN). The synthesis involves the generation of substitutionally labile, ESR-detectable anion radical complexes by the addn. of a substoichiometric (10-20\%) quantity of K metal; hyperconjugation between the primarily reduced pyridine p-system and the W(CO)5 fragment is responsible for substitution of 1 (and only 1) CO group at each metal fragment in cis position. Electrochem. data illustrate the differences in redn. potentials which are crucial for electron transfer catalysis; the substituted anion radical complexes must be able to reduce the starting materials. Carbonyl substitution via this ligand-based electron transfer catalysis is rather slow, but the complexes cannot be obtained in comparable yields by the usual thermal or photochem. routes. The intermediate redox pole reversal during this kind of electron transfer catalysis produced interesting compds. because donor/acceptor substitution at the W carbonyl fragment causes small frontier orbital differences and, as a result, long-wavelength metal-to-ligand charge transfer transitions. [on SciFinder(R)]
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