trans-(Cl)-[Ru(5,5′-diamide-2,2′-bipyridine)(CO)2Cl2]: Synthesis, Structure, and Photocatalytic CO2 Reduction Activity

• Published in: Chemistry : a European journal Vol. 21; no. 28; pp. 10049 - 10060
• Main Authors: Kuramochi, Yusuke, Fukaya, Kyohei, Yoshida, Makoto, Ishida, Hitoshi
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 06.07.2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Chemistry; homogeneous catalysis; ligand effects; photochemistry; reduction; ruthenium; ruthenium; homogeneous catalysis; reduction; photochemistry; ligand effects
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201500782

A series of trans‐(Cl)‐[Ru(L)(CO)2Cl2]‐type complexes, in which the ligands L are 2,2′‐bipyridyl derivatives with amide groups at the 5,5′‐positions, are synthesized. The C‐connected amide group bound to the bipyridyl ligand through the carbonyl carbon atom is twisted with respect to the bipyridyl plane, whereas the N‐connected amide group is in the plane. DFT calculations reveal that the twisted structure of the C‐connected amide group raises the level of the LUMO, which results in a negative shift of the first reduction potential (Ep) of the ruthenium complex. The catalytic abilities for CO2 reduction are evaluated in photoreactions (λ>400 nm) with the ruthenium complexes (the catalyst), [Ru(bpy)3]2+ (bpy=2,2′‐bipyridine; the photosensitizer), and 1‐benzyl‐1,4‐dihydronicotinamide (the electron donor) in CO2‐saturated N,N‐dimethylacetamide/water. The logarithm of the turnover frequency increases by shifting Ep a negative value until it reaches the reduction potential of the photosensitizer. Minor adjustments for maximum results: A series of trans‐(Cl)‐[Ru(5,5′‐ diamide‐2,2′‐bipyridine)(CO)2Cl2]‐type complexes have been synthesized, and their catalytic abilities for CO2 reduction evaluated in photoreactions (see figure). The catalytic activities are dramatically affected by the amide substituents, and are discussed with respect to the first reduction potentials of the catalysts.