The generation of fuels and commodity chemicals by electrochemical reduction of the greenhouse gas CO₂ can be considered as a promising approach towards a more sustainable economy.[1] In this context, the quest for selective and efficient noble metal-free catalysts poses one of the key challenges. Among the typical products of CO₂ reduction, carbon monoxide is particularly attractive due to numerous possibilities for further processing as C₁-building block. Due to the high overpotential and a variety of possible reaction pathways, a selective electroreduction of CO₂ to CO is not trivial.[2] In this regard, considerable progress has been recently made with homogeneous electrocatalysts.[3-5] However, most of the methods reported so far require either precious metal centers such as Ru or Re, ligand-systems with limited availability such as porphyrine analogues and/or excess amounts of a proton donor such as trifluoroethanol or phenol.

Herein we report a highly active (cyclopentadienone)iron-tricarbonyl complex (see figure below) for the selective electroreduction of CO₂ to CO in aprotic electrolytes. Using this robust and easy-to-synthesize system, the electrochemical generation of CO becomes feasible without addition of proton donor. Electroanalytical experiments were carried out in order to characterize the complexes and to evaluate their catalytic behavior. These experiments show high turnover frequencies and a remarkable influence of the ligand substitution and the solvent on the catalytic performance. The application in bulk electrolysis under optimized conditions rendered excellent Faradaic yields and turnover numbers. Along with the catalytic performance, possible mechanisms are discussed based on voltammetric data and spectroelectrochemical results.

References:

[1] J. Qiao, Y. Liu, F. Hong, J. Zhang, Chem. Soc. Rev. 2014, 43, 631.

[2] C. Costentin, M. Robert, J.-M. Savéant, Chem. Soc. Rev. 2013, 42, 2423.

[3] J. Agarwal, T. W. Shaw, C. J. Stanton III, G. F. Majetich, A. B. Bocarsly, H. F. Schaefer III, Angew. Chem. Int. Ed. 2015, 53, 5152.

[4] M.D. Sampson, A. D. Nguyen, K. A. Grice, C. E. Moore, A. L. Rheingold, C. P. Kubiak, J. Am. Chem. Soc. 2014, 136, 5460.

[5] E. A. Mohamed, Z. N. Zahran, Y. Naruta, Chem. Comm. 2015, 51, 16900.