Alcohol oxidation reactions catalyzed by ruthenium–carbonyl complexes of thioarylazoimidazoles. (2nd July 2014)

• Record Type: Journal Article
• Authors: Sarkar, Shyamal Kumar; Jana, Mahendra Sekhar; Mondal, Tapan Kumar; Sinha, Chittaranjan
• Is Part Of: Applied organometallic chemistry. Volume 28:Number 8(2014:Aug.)
• Page Start: 641
• Page End: 651
• Publication Date: 2014-07-02
• Subjects: Organometallic chemistry -- Periodicals; Organometallic compounds -- Periodicals; 547.05
• DOI: 10.1002/aoc.3174
• Languages: English
• ISSNs: 0268-2605

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Alcohols are oxidized by <italic>N</italic>‐methylmorpholine‐<italic>N</italic>‐oxide (NMO), Bu<sup>t</sup>OOH and H<sub>2</sub>O<sub>2</sub> to the corresponding aldehydes or ketones in the presence of catalyst, [RuH(CO)(PPh<sub>3</sub>)<sub>2</sub>(SRaaiNR′)]PF<sub>6</sub> (<bold>2</bold>) and [RuCl(CO)(PPh<sub>3</sub>)(S<sub>κ</sub>RaaiNR′)]PF<sub>6</sub> (<bold>3</bold>) (SRaaiNR′ (<bold>1</bold>) = 1‐alkyl‐2‐{(<italic>o</italic>‐thioalkyl)phenylazo}imidazole, a bidentate N(imidazolyl) (N), N(azo) (N′) chelator and S<sub>κ</sub>RaaiNR′ is a tridentate N(imidazolyl) (N), N(azo) (N′), S<sub>κ</sub>‐R is tridentate chelator; R and R′ are Me and Et). The single‐crystal X‐ray structures of [RuH(CO)(PPh<sub>3</sub>)<sub>2</sub>(SMeaaiNMe)]PF<sub>6</sub> (<bold>2a</bold>) (SMeaaiNMe = 1‐methyl‐2‐{(<italic>o</italic>‐thioethyl)phenylazo}imidazole) and [RuH(CO)(PPh<sub>3</sub>)<sub>2</sub>(SEtaaiNEt)]PF<sub>6</sub> (<bold>2b</bold>) (SEtaaiNEt = 1‐ethyl‐2‐{(<italic>o</italic>‐thioethyl)phenylazo}imidazole) show bidentate N, N′ chelation, while in [RuCl(CO)(PPh<sub>3</sub>)(S<sub>κ</sub>EtaaiNEt)]PF<sub>6</sub> (<bold>3b</bold>) the ligand S<sub>κ</sub>EtaaiNEt serves as tridentate N, N′, S chelator. The cyclic voltammogram shows Ru<sup>III</sup>/Ru<sup>II</sup> (~1.1 V) and Ru<sup>IV</sup>/Ru<sup>III</sup> (~1.7 V) couples of the complexes 2 while Ru<sup>III</sup>/Ru<sup>II</sup> (1.26 V) couple is observed only in <bold>3</bold> 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 <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">oxidation reaction</named-content> NMO acts as best oxidant and [RuCl(CO)(PPh<sub>3</sub>)(S<sub>κ</sub>RaaiNR′)](PF<sub>6</sub>) (<bold>3</bold>) is the best catalyst. The formation of high‐valent Ru<sup>IV</sup>=O species as a catalytic <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">intermediate</named-content> is proposed for the oxidation process. Copyright © 2014 John Wiley & Sons, Ltd.</p> </abstract>