Pincer and Macrocyclic Pyridylidene Amide (PYA) AuIII Complexes

Gold-based homogeneous catalysis is dominated by redox neutral AuI systems. Redox-active gold-based catalysts are less common, principally because of redox cycles between AuI and AuIII being hampered by unfavorable potentials. We report gold(III) complexes containing pincer-based, donor-flexible pyr-idylidene amide (PYA) ligands to address these issues. These complexes act as electron reservoirs through two limiting resonance structures consisting of either soft, imine coordination sites or harder, zwitterionic amide donors. We further alter the donor properties by using the ortho-, meta-, and para-pyridylidene amide variants of the PYA pincer arms. These bis-PYA pincer ligands exhibited a high contribution of amide coordination in the solid-state of the gold(III) complexes; however, the solution data suggests a high contribution from the neutral L-type resonance forms. This L -type contribution, primarily shown through cyclic voltammetry studies, prevents reversible gold(III) reduction and also disfavors abstraction of the ancillary chloride ligand. Furthermore, a novel macrocyclic-PYA ligand is introduced, which shows secondary metal-ligand interactions.

Automated summary

Gold-based homogeneous catalysis is mainly achieved through AuI systems. The limited availability of AuIII catalysts for redox reactions is due to the unfavorable potentials for redox cycles between AuI and AuIII. This study presents gold(III) complexes with pincer-based PYA ligands to address these issues. The complexes act as electron reservoirs through two resonance structures, allowed by the flexible coordination sites of the ligands. The presence of a neutral L-type resonance form, as observed in solution data, prevents reversible AuIII reduction and impedes the removal of a chloride ligand. Additionally, a novel macrocyclic-PYA ligand with secondary metal-ligand interactions is introduced.