Alcohol oxidation reactions catalyzed by ruthenium-carbonyl complexes of thioarylazoimidazoles

作者：Sarkar Shyamal Kumar; Jana Mahendra Sekhar; KumarMondal Tapan; Sinha Chittaranjan^*

来源：Applied Organometallic Chemistry, 2014, 28(8): 641-651.

DOI：10.1002/aoc.3174

• Ru-CO-thioarylazoimidazole
• flexidenticity
• X-ray structure
• redox
• DFT
• catalytic oxidation

Alcohols are oxidized by N-methylmorpholine-N-oxide (NMO), (BuOOH)-O-t and H2O2 to the corresponding aldehydes or ketones in the presence of catalyst, [RuH(CO)(PPh3)(2)(SRaaiNR%26apos;)]PF6 (2) and [RuCl(CO)(PPh3)(S(kappa)RaaiNR%26apos;)]PF6 (3) (SRaaiNR%26apos; (1) = 1-alkyl-2-{(o-thioalkyl) phenylazo} imidazole, a bidentate N(imidazolyl) (N), N(azo) (N%26apos;) chelator and S(kappa)RaaiNR%26apos; is a tridentate N(imidazolyl) (N), N(azo) (N%26apos;), S-kappa-R is tridentate chelator; R and R%26apos; are Me and Et). The single-crystal X-ray structures of [RuH(CO)(PPh3)(2)(SMeaaiNMe)]PF6 (2a) (SMeaaiNMe = 1-methyl-2-{(o-thioethyl)phenylazo}imidazole) and [RuH(CO)(PPh3)(2)(SEtaaiNEt)]PF6 (2b) (SEtaaiNEt = 1-ethyl-2-{(o-thioethyl)phenylazo} imidazole) show bidentate N,N%26apos; chelation, while in [RuCl(CO)(PPh3)(S(kappa)EtaaiNEt)]PF6 (3b) the ligand S(kappa)EtaaiNEt serves as tridentate N, N%26apos;, S chelator. The cyclic voltammogram shows Ru-III/Ru-II (similar to 1.1 V) and Ru-IV/Ru-III (similar to 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)(PPh3)(S(kappa)RaaiNR%26apos;)](PF6) (3) is the best catalyst. The formation of high-valent Ru-IV=O species as a catalytic intermediate is proposed for the oxidation process.

• 出版日期2014-8