Kinetics and Mechanism of the Decarbonylation of Benzoylformyl Palladium(II) Complex

The benzoylformyl Pd(II) complex, Pd(PPh 3 ) 2 (Cl)(COCOPh), thermally decomposes to the corresponding benzoyl complex by the loss of CO. The predominant route of decarbonylation is led by a reversible dissociation of a phosphine ligand. The disappearance of the benzoylformyl complex in solutions follows first order kinetics not only in the existence of excess PPh 3 but also in the absence of added PPh 3 . Through the treatments of both preequilibrium and the steady state approximations to the kinetic data, the rate constants of the intramolecular acyl migration, k 1 and k 2 ; as well as the equilibrium constant and the individual rate constants of the reversible phosphine dissociation step, K, k d and k d , were determined in CHCl 3 . The activation parameters for k d , being Δ H ‡ = 25.4 Kcal Mol −1 , Δ S ‡ = 15.9 eu, Δ G ‡ = 20.7 Kcal Mol −1 ;and for k −d , being Δ H ‡ = 13.0 Kcal Mol −1 , Δ S ‡ = −7.9 eu, Δ G ‡ = 15.4 Kcal Mol −1 , were evaluated.