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Alcohol oxidation reactions catalyzed by ruthenium–carbonyl complexes of thioarylazoimidazoles
Author(s) -
Sarkar Shyamal Kumar,
Jana Mahendra Sekhar,
Mondal Tapan Kumar,
Sinha Chittaranjan
Publication year - 2014
Publication title -
applied organometallic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 71
eISSN - 1099-0739
pISSN - 0268-2605
DOI - 10.1002/aoc.3174
Subject(s) - chemistry , denticity , imidazole , catalysis , ruthenium , chelation , medicinal chemistry , ligand (biochemistry) , alcohol , redox , stereochemistry , alcohol oxidation , crystal structure , inorganic chemistry , organic chemistry , biochemistry , receptor
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.