Nucleophilic Substitution at Difluoro-Carbene Complexes of the Coinage Metals

Le résumé fourni par la source

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 metallated fluoro-iminium ions. Density functional theory supports a highly exergonic additionelimination 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 versatile platform for carbene functionalization and carbene-to-carbene interconversion at coinage metals.

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