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Dinitrosyl Iron Complex [K-18-crown-6-ether][(NO)2Fe(MePyrCO2)]: Intermediate for Capture and Reduction of Carbon Dioxide
Y.-T. Tseng, W.-M. Ching, W.-F. Liaw*, and T.-T. Lu* 
Continued efforts are made for the utilization of CO2 as a C1 feedstock for regeneration of valuable chemicals and fuels. Mechanistic study of molecular (electro‐/photo‐)catalysts disclosed that initial step for CO2 activation involves either nucleophilic insertion or direct reduction of CO2. In this study, nucleophilic activation of CO2 by complex [(NO)2Fe(μ‐MePyr)2Fe(NO)2]2− (2, MePyr=3‐methylpyrazolate) results in the formation of CO2‐captured complex [(NO)2Fe(MePyrCO2)]− (2‐CO2, MePyrCO2=3‐methyl‐pyrazole‐1‐carboxylate). Single‐crystal structure, spectroscopic, reactivity, and computational study unravels 2‐CO2 as a unique intermediate for reductive transformation of CO2 promoted by Ca2+. Moreover, sequential reaction of 2 with CO2, Ca(OTf)2, and KC8 established a synthetic cycle, 2 → 2‐CO2 → [(NO)2Fe(μ‐MePyr)2Fe(NO)2] (1) → 2, for selective conversion of CO2 into oxalate. Presumably, characterization of the unprecedented intermediate 2‐CO2 may open an avenue for systematic evaluation of the effects of alternative Lewis acids on reduction of CO2.