Protonation-Induced Electron Density Redistribution Facilitates Aggregation in PNNP Dicopper Hydride Complexes

Copper(I) hydride complexes often exhibit diverse aggregation behavior that can profoundly influence their structure and reactivity. In this study, we investigate a series of dicopper hydride complexes supported by PNNP expanded pincer ligands that vary in both aggregation and ligand protonation state. Using a combined experimental and computational approach, we examine how these properties correlate and identify key structural and electronic factors that govern aggregation. Our analysis shows that electrostatic stabilization is reduced in charged monomers relative to the neutral system, making dimerization less favorable. At the same time, protonation of the ligands redistributes electron density at the hydride-bridged dicopper core, lowering interfragment overlap of occupied orbitals, which facilitates dimer formation in more protonated species. These results highlight the importance of ligand-controlled electronic structure in dictating the aggregation behavior of copper hydride complexes.