Ligand Effects in Bimetallic High Oxidation State Palladium Systems

Abstract

Ligand effects in bimetallic high oxidation state systems containing a X−Pd−Pd−Y framework have been explored with density functional theory (DFT). The ligand X has a strong effect on the dissociation reaction of Y to form [X−Pd−Pd]⁺ + Y⁻. In the model system examined where Y is a weak σ-donor ligand and a good leaving group, we find that dissociation of Y is facilitated by greater σ-donor character of X relative to Y. We find that there is a linear correlation of the Pd−Y and Pd−Pd bond lengths with Pd−Y bond dissociation energy, and with the σ-donating ability of X. These results can be explained by the observation that the Pd d_z² population in the PdY fragment increases as the donor ability of X increases. In these systems, the Pd^III−Pd^III arrangement is favored when X is a weak σ-donor ligand, while the Pd^IV−Pd^II arrangement is favored when X is a strong σ-donor ligand. Finally, we demonstrate that ligand exchange to form a bimetallic cationic species in which each Pd is six-coordinate should be feasible in a high polarity solvent.