Palladium complexes of amido-functionalized N-heterocyclic carbenes as effective precatalysts for the Suzuki–Miyaura C–C cross-coupling reactions of aryl bromides and iodides

Abstract

A series of air-stable, robust and highly active palladium based precatalysts of amido-functionalized N-heterocyclic carbenes for the Suzuki–Miyaura C–C cross-coupling reaction has been designed. In particular, the [1-R-3-{ N-(benzylacetamido)imidazol-2-ylidene] 2PdCl 2 [R = i-Pr ( 1c) and CH 2Ph ( 2c)] complexes efficiently carried out the Suzuki–Miyaura coupling of the aryl bromide and iodide substrates with phenyl boronic acid in good to excellent yields in air at 90 °C in 12 h. Quite interestingly, of these palladium precatalysts, the i-propyl derivative ( 1c) exhibited superior activity as compared to the benzyl derivative ( 2c). The density functional theory (DFT) studies carried out on the 1c and 2c complexes revealed the strong σ-donating nature of the NHC ligand as reflected in their high d/ b ratio [ i.e. forward σ-donation ( d) to backward π-donation ( b)] of these complexes and, thus, point towards greater stability of the Pd–NHC interaction in these complexes.