The origin of the unequal catalytic acceleration of ligand exchange at Pd(II) center by ReO4–

An in-depth understanding of the kinetic aspects of ligand exchange is valuable for designing and controlling metal-catalyzed reactions and coordination self-assembly under kinetic control. Based on our recent finding that the self-assembly of cis-protected mononuclear Pd(II) complex (M) and tritopic ligand (L) was largely improved by ReO4–, affording an M6L4 square-based pyramid almost quantitatively, which is much higher than under thermodynamic control, we investigated the origin of the unusual catalytic effect of ReO4– by quantitative analysis of a mononuclear model system. The acceleration of ligand exchange by ReO4– was largely affected by the coordination ability of the leaving ligand, whereas NO3– similarly accelerated ligand exchange regardless of the coordination ability of the leaving ligands. DFT calculations of the transition state (TS) of ligand exchanges indicate that unequal acceleration by ReO4– is due to its late TS, in which the stability of TS is affected by the nature of the leaving ligand, whereas the ligand exchange with NO3– proceeds via an early TS.