Synthesis and Reactivity of Re(III) and Re(V) Fischer Carbenes

Direct insertion of CO and isocyanides, RNC, into Re–R bonds results in high-oxidation-state acyl and iminoacyl complexes that can be treated with an electrophile to generate rare examples of rhenium­(III) and oxorhenium­(V) Fischer carbenes. Experimental and computational studies suggest that, as expected, the carbene ligands are electrophilic at carbon. Further, an interesting correlation was observed between the 13C NMR chemical shift and the natural charge at the carbene carbon, which suggests that the electrophilicity of the ligand can be tuned, with the substituent attached to the carbene carbon having the most influence.