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 a significant impact on diverse chemical systems, influencing structural, catalytic, and photophysical properties. The strength of both M–M interactions and the resulting M–M distances is 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 (Q. Wan, J. Yang, W.-P. To and C.-M. Che, Strong metal–metal Pauli repulsion leads to repulsive metallophilicity in closed-shell d8 and d10 organometallic complexes, Proc. Natl. Acad. Sci. U. S. A., 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 the 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.