Terminal Iron Carbyne Complexes Derived from Arrested CO2 Reductive Disproportionation.

The encumbered tetraisocyanide dianion Na2 [Fe(CNArMes2 )4 ] reacts with two molecules of CO2 to effect reductive disproportionation to CO and carbonate ([CO3 ]2- ). When the reaction is performed in the presence of silyl triflates, reductive disproportionation is arrested by silylative esterification of a mono-CO2 adduct. This results in the formation of four-coordinate terminal iron carbynes possessing an aryl carbamate substituent owing to the direct attachment of an C(O)OSiR3 group to an isocyanide nitrogen atom. Crystallographic, spectroscopic, and computational analyses of these iron-carbon multiply bonded species reveal electronic structure properties indicative of a conformationally locked iron carbyne unit.