SPECTROSCOPY AND PHOTOCHEMISTRY OF NICKEL(II), PALLADIUM(II), AND PLATINUM(II) BETA-DIKETONATES

The spectroscopy and photochemistry of several group 10(II) beta-diketonates have been investigated. The spectral shifts observed upon replacing the methyl groups of the acetylacetonate ligand with phenyl groups have been correlated with the changes in frontier orbital energies and the allowed electronic transitions calculated using the semiempirical INDO/S-SCF-CI (ZINDO) algorithm. All of the group 10(II) beta-diketonates undergo inefficient decomposition upon 254 nm irradiation in ethanol or dichloromethane solution to produce free metal and beta-diketone. Photoisomerization of cis- and trans-platinum(II) benzoylacetonate is more efficient than photodecomposition. Irradiation of the platinum beta-diketonates in the presence of hydrosilanes or olefins results in the formation of primary products which revert to starting material in the dark and can be converted to free metal and beta-diketone by continued irradiation or heating. Reaction with added hydrosilane effectively inhibits photoisomerization. Both the efficiency of intermediate formation and its dark stability are dependent upon the structure of the hydrosilane or olefin and the beta-diketonate ligand. A mechanism is proposed in which one-bond cleavage results in the formation of a short-lived three-coordinate intermediate which can recombine with retention or inversion of configuration, react with solvent to form unstable intermediates, or react with added hydrosilanes or olefins to form primary photoproducts of variable stability. Possible structures for the primary photoproducts are discussed.