Consolidation of the Oxidant-Free Au(I)/Au(III) Catalysis Enabled by the Hemilabile Ligand Strategy

In this minireview we survey the challenges and strategies in gold redox catalysis. Gold's reluctance to oxidative addition reactions due to its high redox potential limits its applicability. Initial attempts to overcome this problem focused on the use of sacrificial external oxidants in stoichiometric amounts to bring Au(I) compounds to Au(III) reactive species. Recently, innovative approaches focused on employing hemilabile ligands, which are capable of coordinating to Au(I) and stabilizing square-planar Au(III) intermediates, thus facilitating oxidative addition steps and enabling oxidant-free catalysis. Notable examples include the use of the (P<^>N) bidendate MeDalphos ligand to achieve various cross-coupling reactions via oxidative addition Au(I)/Au(III). Importantly, hemilabile ligand-enabled catalysis allows merging oxidative addition with pi-activation, such as oxy- and aminoarylation of alkenols and alkenamines using organohalides, expanding gold's versatility in C-C and C-heteroatom bond formations and unprecedented cyclizations. Moreover, recent advancements in enantioselective catalysis using chiral hemilabile (P<^>N) ligands are also surveyed. Strikingly, versatile bidentate (C<^>N) hemilabile ligands as competitors of MeDalphos have appeared recently, by designing scaffolds where phosphine groups are substituted by N-heterocyclic or mesoionic carbenes. Overall, these approaches highlight the evolving landscape of gold redox catalysis and its tremendous potential in a broad scope of transformations. In this minireview we survey the novel approaches for oxidant-free Au(I)/Au(III) catalysis focusing on the hemilabile ligand strategy, where (P<^>N) MeDalphos hemilabile ligand stands as the most successful example. Moreover, hemilabile ligand-enabled catalysis allows merging oxidative addition with pi-activation, expanding gold's versatility in C-C and C-heteroatom couplings and unprecedented cyclizations. Moreover, recent enantioselective catalysis using chiral hemilabile (P<^>N) ligands and novel (C<^>N) hemilabile ligands are also reviewed. image