Hemilabile Ligand Architectures in Platinum Group Metal Catalysis: Structure–Activity Relationships and Process Engineering Perspectives

Abstract

The rational design of hemilabile ligand frameworks has emerged as a pivotal strategy for modulating the catalytic performance of platinum group metal (PGM) complexes in homogeneous catalysis. This review examines the coordination chemistry and catalytic applications of rhodium, palladium, and iridium complexes bearing chalcogen-functionalized phosphine (P–O, P–S, P–Se) and nitrogen-donor ligands, with particular emphasis on structure–activity relationships that govern industrial processes. We analyze how the differential donor strengths of "hard" oxygen versus "soft" sulfur/selenium atoms within heterobidentate frameworks enable dynamic site generation through reversible M–X bond dissociation, and how this hemilability translates into enhanced turnover frequencies in carbonylation, hydroformylation, and cross-coupling reactions. Critical evaluation of landmark systems—including the Monsanto and Cativa acetic acid processes, rhodium-catalyzed hydroformylation generations, and palladium-mediated Suzuki–Sonogashira couplings—reveals the interplay between ligand bite angle, electronic tuning, and steric congestion in optimizing catalytic cycles. The review further addresses current challenges in scaling laboratory catalysts to continuous-flow industrial operations, with perspectives on ligand degradation pathways and catalyst recovery strategies. By bridging molecular-level coordination chemistry with reactor engineering principles, this work provides a mechanistic foundation for the next generation of PGM catalysts in sustainable chemical manufacturing.