From covalent to noncovalent: The role of metals in activating ligand sites toward noncovalent interactions (NCIs)

This review highlights an emerging area in chemistry at the intersection of coordination and supramolecular chemistry: the metal-induced enhancement of ligand sites for noncovalent interactions (NCIs). This novel field explores how metal coordination amplifies ligands' capacity to engage in various NCIs, including halogen, chalcogen, pnictogen, and tetrel bonding, as well as π-hole interactions. Recent studies reveal two distinct types of activation: electrophilic enhancement by high-oxidation state metals, and the rarer nucleophilic activation by low-oxidation state metals. Both mechanisms often increase NCI binding energies significantly and can even generate new noncovalent binding sites on ligands. A notable discovery is the copper(I)-induced nucleophilic activation of isocyanide carbons for halogen bonding, contrasting with the more common electrophilic activation. The metal-induced enhancement and creation of ligand sites for noncovalent binding offers innovative strategies for designing solid metal-containing systems, potentially impacting diverse areas such as crystal engineering and materials science.