Synthesis of Carbene‐Metal‐Amido (CMA) Complexes and Their Use as Precatalysts for the Activator‐Free, Gold‐Catalyzed Addition of Carboxylic Acids to Alkynes

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.[a] I.

Improved synthetic routes toN-heterocyclic carbene-metal-diketonato complexes of gold and copper

“…The data match the literature reported values. 16 Synthesis of 6-methylenetetrahydro-2H-pyran-2-one (4). 4 was synthesized by charging a 4 mL vial with 5-hexynoic acid (110 μL, 1 mmol) and [Au(acac)(IPr)] (1) (1.0 mol%, 0.01 mmol, 6.8 mg).…”

“…Various routes have been devised to access such complexes that span the traditional freecarbene or transmetallation route 8 to the more recently developed, sustainable "weak-base-route". 9,10 The complexes bearing halides as the counterions are noteworthy as they are easily accessed and can be utilized to yield powerful synthons such as [M(X)(NHC)] (M = Au, Cu; X = hydroxide), 5,11 [Au(NHC) (acetonyl)], 12 [Au(NHC)(aryl)], 13 [M(NHC)(amido)] 1, [14][15][16] and can be further transformed into various NHC-Coinage metal derivatives and catalysts via transmetallation and deprotonation reactions. 11,17 The evolution of NHC stabilized Coinage metal complexes has given great impetus to the development of coinage metal-catalyzed transformations, paving the way for additional advances.…”

Access to Azetidines via Gold Mediated Energy Transfer Photocatalysis

“…Alternatives are needed to address the sustainability aspects of photocatalysis. We have recently reported a very promising family of NHC-gold-amido complexes (NHC = N-heterocyclic carbene), with high E T values (∼66 kcal/mol), lifetimes in the range of several hundred microseconds enabling photocatalyzed cycloadditions …”

“…We selected conditions closely mimicking the ones employed by Schindler in this transformation using an Ir-based photosensitizer . We also selected a green solvent, ethyl acetate, as the operating solvent, as it had already proven successful in photocatalysis with our gold complexes . Under these initial conditions, some conversion was achieved and the different product isomers (diastereomers and regioisomers of 1 ) were observed by 1 H NMR spectroscopy (Table , entry 1).…”

“…We initially selected 365 nm as the operating wavelength that proved the most effective in our previous work with [Au­(cbz)­(NHC)] complexes . To show that this wavelength remains optimal for oximes sensitization, we tested reactions with other LED lamps.…”