Synthesis and characterization of gold(I) N-heterocyclic carbenes complexes bearing methacrylate moiety

The study focuses on gold(I) N-heterocyclic carbene (NHC) complexes. The research aims to synthesize a family of four mono- and four bis-gold(I) N-heterocyclic carbene complexes, each bearing a methacrylate motif, with yields ranging from 63% to 98%. Two model complexes from this series were tested toward sulfur-based nucleophilic attack to assess the possibility of a Michael addition to the acrylate motif, with a view to future bioconjugation. Experimental results reveal that thiolate addition occurs exclusively at the gold(I) center, regardless of whether the N-heterocyclic carbene is a mono- or a bis-carbene, leaving the acrylate motif untouched. This outcome is supported by theoretical calculations, which predict an activation energy of at least 4 kcal/mol favoring nucleophilic attack at the gold(I) center. These findings suggest that gold(I) NHC complexes could serve as effective "clickable" motifs in themselves, challenging the necessity of further functionalizing them with additional clickable groups for bioconjugation applications.