Kinetics and Equilibrium of the Reaction between Bis(trifluoroacetylacetonato)palladium(II) and Tri-o-tolylphosphine

Article abstract of DOI:10.1246/bcsj.54.1704

Tri-o-tolylphosphine reacts with bis(trifluoroacetylacetonato)palladium(II), Pd(tfac)2, to convert one of the chelating ligands into the unidentate state, resulting in Pd(tfac)(tfac-O)P(o-tolyl)3.The reaction was studied by a spectrophotometric method.The equilibrium constant was determined at several temperatures, K being 1.38*10³, 4.35*10³ dm³ mol^-1 and more than 10⁹ dm³ mol^-1 in benzene, dichloromethane, and methanol, respectively, at 25 deg C.In the presence of excess phosphine, the reaction proceeds as a pseudo first order reaction to attain equilibrium.The forward and reverse rate constants, k₁ and k_-1, were obtained as 0.172 dm³ mol^-1 s^-1 and 1.22*10^-4 s^-1 in benzene and 2.28 dm³ mol^-1 s^-1 and 4.9*10^-4 s^-1 in dichloromethane at 25 deg C, respectively.In methanol the forward rate was measured under irreversible pseudo first order conditions and conforms with the usual two term rate law, k_obsd/s^-1=2*10^-3 + 56.6.The remarkable dependence of K and k₁ on the nature of solvent is related to the hydrogen bonding interaction between the carbonyl group of the coordinated tfac anion and a solvent molecule.