The existence and stability of mononuclear and binuclear organopalladium hydroxo complexes, [(R(3)P)(2)Pd(R')(OH)] and [(R(3)P)(2)Pd-2(R')(2)(mu-OH)(2)]

Adding excess phosphines (Cy(3)P, i-Pr3P) to binuclear hydroxo complexes of palladium, [(Cy(3)P)(2)- Pd-2(Ph)(2)(mu-OH)(2)] and [(i-Pr3P)(2)Pd-2(Ph)(2)(mu-OH)(2)], in hexane resulted in precipitation of the first mononuclear sigma-phenylpalladium hydroxides, [(Cy(3)P)(2)Pd(Ph)(OH)] (1) and [(i-Pr3P)(2)Pd(Ph)(OH)] (2), respectively. Both 1 and 2 were isolated, characterized, and found to be stable in the solid state. In solution, ho,ever, they reversibly lost one of the two phosphine ligands, converting back to the binuclear hydroxides. Equilibrium between [L(2)Pd(2)(R)(2)(mu-OH)(2)] and [L(2)Pd(R)(OH)] (L = Ph(3)P, Cy(3)P, i-Pr3P, and R = Ph, Me) was studied by variable-temperature P-31 NMR spectroscopy, and the corresponding K-eq and Delta G were calculated. The free energy values obtained at 333-235 K were in the range of +19 to -16 kJ/mol.