Irradiation of platinum(II) bis(/3-diketonates) in the presence of hydrosilanes and olefins results in olefin hydrosilation. The initial rate of hydrosilation is dependent upon the choice of /3-diketonate ligand, hydrosilane, and olefin. Formation of an active catalyst requires the presence of either triethylsilane or triethylvinylsilane during a brief period of irradiation. Addition of the second reactant results in hydrosilation without further irradiation. Substantial inhibition of hydrosilation is observed when dibenzo[a,e]cyclooctatetraene is added following irradiation and prior to addition of the second reactant, but not when mercury is added following irradiation. These results indicate that the active form of the photogenerated catalyst is homogeneous rather than heterogeneous. Correlation of hydrosilation reactivity with the spectroscopic changes which occur during irradiation suggests that the primary photoproduct is not catalytically active and that a secondary photochemical reaction results in the loss of one of the two /3-diketonate ligands and the formation of the active catalyst.

The spectroscopy and photochemistry of several group 10(11) /3-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-Cl (ZINDO) algorithm. All of the group 10(11) /3-diketonates undergo inefficient decomposition upon 254 nm irradiation in ethanol or dichloromethane solution to produce free metal and /3-diketone.Photoisomerization of cisand frans-platinum(II) benzoylacetonate is more efficient than photodecomposition. Irradiation of the platinum /3-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 /3-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 /3-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.

The electronic structure and optical spectra of Ni(acac)2 and Pd(acac)2 have been investigated using the semiemperical INDO/S-SCF-CI (ZINDO) algorithm. The results of the electronic structure calculations are in good agreement with those of previous ab initio calculations for these complexes. Increasing the atomic number of the metal is found to increase the metal-ligand covalency, to increase the separation of the two highest occupied and two lowest unoccupied, ligand-localized ( and t*) molecular orbitals, and to decrease the separation between the highest occupied and lowest unoccupied molecular orbitals. The effects of electronic relaxation (due to Coulomb and exchange integrals) and configuration interaction on the calculated energies of singlet-singlet transitions are analyzed using Platt diagrams to illustrate the origin of the d-*d transitions, observed for Ni(acac)2 but not for Pd(acac)2 or Pt(acac)2, and the increasing complexity of the ultraviolet portion of the spectrum with increasing atomic number. Thus the ZINDO calculations provide the basis for the first detailed rationalization of the complex optical spectra of the group 10(11) 3-diketonates.

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