Alcohol oxidation reactions catalyzed by ruthenium–carbonyl complexes of thioarylazoimidazoles

Alcohols are oxidized by N ‐methylmorpholine‐ N ‐oxide (NMO), Bu t OOH and H 2 O 2 to the corresponding aldehydes or ketones in the presence of catalyst, [RuH(CO)(PPh 3 ) 2 (SRaaiNR′)]PF 6 ( 2 ) and [RuCl(CO)(PPh 3 )(S κ RaaiNR′)]PF 6 ( 3 ) (SRaaiNR′ ( 1 ) = 1‐alkyl‐2‐{( o ‐thioalkyl)phenylazo}imidazole, a bidentate N(imidazolyl) (N), N(azo) (N′) chelator and S κ RaaiNR′ is a tridentate N(imidazolyl) (N), N(azo) (N′), S κ ‐R is tridentate chelator; R and R′ are Me and Et). The single‐crystal X‐ray structures of [RuH(CO)(PPh 3 ) 2 (SMeaaiNMe)]PF 6 ( 2a ) (SMeaaiNMe = 1‐methyl‐2‐{( o ‐thioethyl)phenylazo}imidazole) and [RuH(CO)(PPh 3 ) 2 (SEtaaiNEt)]PF 6 ( 2b ) (SEtaaiNEt = 1‐ethyl‐2‐{( o ‐thioethyl)phenylazo}imidazole) show bidentate N,N′ chelation, while in [RuCl(CO)(PPh 3 )(S κ EtaaiNEt)]PF 6 ( 3b ) the ligand S κ EtaaiNEt serves as tridentate N,N′,S chelator. The cyclic voltammogram shows Ru III /Ru II (~1.1 V) and Ru IV /Ru III (~1.7 V) couples of the complexes 2 while Ru III /Ru II (1.26 V) couple is observed only in 3 along with azo reductions in the potential window +2.0 to −2.0 V. DFT computation has been used to explain the spectra and redox properties of the complexes. In the oxidation reaction NMO acts as best oxidant and [RuCl(CO)(PPh 3 )(S κ RaaiNR′)](PF 6 ) ( 3 ) is the best catalyst. The formation of high‐valent Ru IV =O species as a catalytic intermediate is proposed for the oxidation process. Copyright © 2014 John Wiley & Sons, Ltd.