Synthesis of Carbene‐Metal‐Amido (CMA) Complexes and Their Use as Precatalysts for the Activator‐Free, Gold‐Catalyzed Addition of Carboxylic Acids to Alkynes
Ishfaq Ibni Hashim, Nikolaos V. Tzouras, Wim Janssens, Thomas Scattolin, Laurens Bourda, Subhrajyoti Bhandary, Kristof Van Hecke, Steven P. Nolan, Catherine S. J. Cazin
Abstract
A straightforward synthetic protocol leading to carbene-metal-amido (CMA) complexes (metal=Au, Cu) using a mild base and an environmentally desirable solvent (EtOH) has been explored, with a focus on complexes bearing backbone-substituted N-heterocyclic carbene (NHC) ligands, including BIAN-NHCs (BIAN=bis(imino)acenaphthene). The novel CMAs were structurally characterized, and gold-based CMAs bearing diverse NHCs were screened as simple, Brønsted-basic precatalysts. The readily accessible complexes display high catalytic activity in the intermolecular and intramolecular hydrocarboxylation of internal alkynes and alkynoic acids respectively, while the screening reveals the ancillary ligand effect of NHCs in these catalytic systems.