Ligand-Modulated Metallophilicity: Influence of π-Acceptor and σ-Donor Strength

Abstract

Metal–metal (M–M) closed-shell interaction, also known as metallophilicity, is frequently observed in d10 and d8 metal complexes featuring a close M–M distance. It has shown significant impact in diverse chemical systems, influencing structural, catalytic, and photophysical properties. Both the strength of M–M interactions and the resulting M–M distances are highly dependent on various types of coordinating ligands. Recent studies have revealed that metallophilicity is repulsive in nature due to strong M–M Pauli repulsion (PNAS. 2021, 118, e2019265118). However, little is known about the role of ligands in M–M repulsions. Here, we elucidate how metal–ligand (M–L) coordination modulates M–M repulsion through two key mechanisms: π-backbonding and σ-donor interactions. By systematically evaluating ligands spanning a spectrum of π-accepting and σ-donating strengths, we uncover opposing ligand effects. Strong π-backbonding weakens M–M Pauli repulsion, enabling shorter intermetallic distances, whereas σ-donating interaction increases the repulsion, lengthening M–M contacts. These computational insights establish a ligand-design framework for tuning metallophilicity in closed-shell metal complexes and advance the fundamental understanding of M–M interactions from the perspective of M–L coordination.