Alcohol oxidation reactions catalyzed by ruthenium–carbonyl complexes of thioarylazoimidazoles

Abstract

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-{(othioethyl)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 À2.0 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.

Chemical fixation of CO2into cyclic carbonates by azo-containing Schiff base metal complexes

“…CO 2 is a renewable source of carbon and 25 identified to be a naturally abundant, economic, recyclable and non-toxic C 1 building block in organic synthesis that can occasionally replace toxic chemicals 2,3 . Due to the great properties, chemical fixation of CO 2 becomes more and more important for decrease of carbon emission day by day 4 .…”

Coumarinyl azoimidazolyl complexes of osmium(II) hydridocarbonyls: spectroscopic and structural characterization, oxidation catalysis, photovoltaic effect and density functional theory computation

“…Data reduction was carried out using the Bruker SAINT programme. The structure was solved by direct method using SHELXS‐97 and successive difference Fourier syntheses. All non‐hydrogen atoms were refined anisotropically.…”

“…The vibrational frequency calculation was also performed for both complexes to ensure that the optimized geometries represent the local minima and there are only positive eigenvalues. To assign the low‐lying electronic transitions in the experimental spectra, time‐dependent (TD)‐DFT calculations of the complexes were done. We computed the lowest 25 singlet–singlet transitions and results of the TD calculations were qualitatively very similar.…”

Peroxidative catalytic oxidation of alcohols catalyzed by heterobinuclear vanadium(V) complexes using H2O2 as terminal oxidizing agents

“…In many cases, the use of noble metal catalysts such as ruthenium, gold, palladium and platinum, shows excellent activities and selectivity's for this chemical process. However, the use of these novel metals find many drawbacks and limited services because of their expensive nature, hence, in order to reduce their usage, some non‐noble transitional metals are required.…”