Elektrontransfer-katalysierte Carbonyl-Substitution III. Synthese und Spektroskopie von ein- und zweikernigen cis-Phosphantetracarbonylwolfram(0)-Komplexen elektronenarmer Pyridine

Article abstract of DOI:10.1016/0022-328X(89)87006-8

New mixed donor/acceptor-substituted tetracarbonyltungsten(0) complexes 1.2(py') have been prepared by electron transfer catalyzed carbonyl substitution of the precursor complexes (CO)5W(py') containing the 4-acceptor (COMe, COPh, COOMe, CN) substituted pyridines py'.The synthesis involves the generation of substitutionally labile, ESR-detectable anion radical complexes by the addition of a sub-stoichiometric (10-20percent) quantity of potassium metal; hyperconjugation between the primarily reduced pyridine ?-system and the W(CO)5 fragment is responsible for substitution of one (and only one) CO group at each metal fragment in cis position.Electrochemical data illustrate the differences in reduction 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 photochemical routes.The intermediate redox umpolung during this kind of electron transfer catalysis produces interesting compounds because donor/acceptor substitution at the tungsten carbonyl fragment causes small frontier orbital differences and, as a result, long-wavelength metal-to-ligand charge transfer transitions.