Theoretical Studies on Ethene Formation from Ethyl-Palladium(II) Complexes by Using DFT Method Including Solvent Effects

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Density functional theory calculations are applied to investigate roles of cationic and neutral intermediate species in palladium catalyzed reactions of interest, including solvent effects. We have developed a catalyst model to investigate both cationic and neutral intermediate species in the same model system, which made it possible to evaluate the energy difference between cationic and neutral intermediate systems. Solvent effects on homogeneous catalytic reactions are very important. To model such systems, discrete solvent molecules are introduced to accommodate coordination of a solvent molecule to central palladium atom and further COSMO method is applied to whole molecular system to include solvent screening effect. Using this methodology, decomposition of mono-ethyl-palladium(II) complex, bis-trimethylphosphine-ethyl-Pd(II) Br·(Solv.)2, Solv. = acetonitrile, to produce ethene and hydrido-Pd(II) complex was examined. In this process, β-hydrogen elimination of ethyl group plays an important role. The cationic agostic Pd(II) complex is well stabilized and is obtained at an equilibrium state. Substitution of Br− ligand of the bis-trimethylphosphine-ethyl-Pd(II) Br complex by AgBF4 forms the cationic Pd(II) species, and ethene formation from the cationic bis-trimethlphosphine-ethyl-PdII complex having BF4− anion was also examined.