Nucleophilic Substitution at Difluoro-Carbene Complexes of the Coinage Metals

Abstract

Carbene functionalization through direct substitution at the carbene center is well established for Fischer-type carbene complexes of early transition metals but remains exceedingly rare for carbene complexes of late transition metals. Here, we report a general strategy for carbene functionalization at coinage metals based on nucleophilic substitution of difluorocarbene complexes. Persistent LnAu(I)=CF2+ complexes undergo efficient fluorine-to-nitrogen and fluorine-to-oxygen substitution with nucleophiles, providing direct access to fluoro-amino- and fluoro-oxy-carbene complexes. The methodology is also applicable to transient Au(I) difluorocarbenes and extends to Cu(I) and Ag(I) systems, enabling carbene functionalization across the coinage metal series. Access to a family of closely related group 11 carbenes (10 examples) enables direct comparison of their structure and bonding. Spectroscopic and computational studies reveal that fluorine-to-nitrogen substitution profoundly impacts the electronic structure of the carbene complex, affording species best described as metalated fluoro-iminium ions. Density functional theory supports a highly exergonic addition−elimination mechanism driven by Si−F bond formation and identifies metal-to-carbene π-backdonation as the key factor governing the stability of difluorocarbene intermediates, following the trend Au > Cu > Ag. These findings establish nucleophilic substitution as a general strategy for the functionalization of coinage-metal carbene complexes and demonstrate that heteroatom substitution provides direct access to electronically distinct metalated iminium and oxonium species.