Partial Deoxygenative CO Homocoupling by a Diiron Complex

One route to address climate change is converting carbon dioxide to synthetic carbon-neutral fuels. Whereas carbon dioxide to CO conversion has precedent in homo- and heterogeneous catalysis, deoxygenative coupling of CO to products with C-C bonds-as in liquid fuels-remains challenging. Here, we report coupling of two CO molecules by a diiron complex. Reduction of Fe₂ (CO)₂ L (2), where L^2- is a bis(β-diketiminate) cyclophane, gives [K(THF)₅ ][Fe₂ (CO)₂ L] (3), which undergoes silylation to Fe₂ (CO)(COSiMe₃ )L (4). Subsequent C-OSiMe₃ bond cleavage and C=C bond formation occurs upon reduction of 4, yielding Fe₂ (μ-CCO)L. CO derived ligands in this series mediate weak exchange interactions with the ketenylidene affording the smallest J value, with changes to local metal ion spin states and coupling schemes (ferro- vs. antiferromagnetism) based on DFT calculations, Mössbauer and EPR spectroscopy. Finally, reaction of 5 with KEt₃ BH or methanol releases the C₂ O^2- ligand with retention of the diiron core.