Low-Energy Pyrocatechol to Cobalt(III) Electron Transfer in the Cobaloxime-Catalyzed Oxidation of 3,5-Di-tert-butylpyrocatechol

Activation of Dioxygen by Cobaloxime and Nitric Oxide for Efficient TEMPO‐Catalyzed Oxidation of Alcohols

“…Indeed, the complex bisdimethylglyoximatocobalt(II) (cobaloxime) could be generated easily by the reaction of cobalt salts and DH 2 , [7] and often serves as oxygen carrier analogue via absorbing dioxygen. [6] After the oxidation with CoA C H T U N G T R E N N U N G (NO 3 ) 2 had ended, a dark red suspension was found in the reaction mixture, and this was in agreement with the phenomenon of cobaloxime preparation observed previously, [7] which showed that a similar suspension was generated when cobalt salts and DH 2 reacted in methanol. Therefore, it is believed that cobaloxime was in situ formed during the oxidation when CoA C H T U N G T R E N N U N G (NO 3 ) 2 and DH 2 were used, and provided some more active catalytic species through activating dioxygen for the aerobic oxidation of alcohol.…”

“…[6] Upon recognizing the successful performance of CoA C H T U N G T R E N N U N G (NO 3 ) 2 /DH 2 / TEMPO, we could suggest that during the oxidation the activation of dioxygen proceeded via the formation of the superoxo complex [(TEMPO)-Co(DH) 2 (O 2 )] (Scheme 1). Due to the trans effect of TEMPO, the superoxo complex was quite active, and became the crucial catalytic species.…”

“…Dimethylglyoxime (DH 2 ), as a simple ligand, readily coordinates to various metal centers to form complexes with a square planar structure, and some of them, especially Co(II) complexes, could activate dioxygen efficiently. [6] However, the catalytic properties of transition metal complexes of DH 2 for aerobic oxidation of alcohols have not been studied. Moreover, it was notable that DH 2 was simple and inexpensive.…”

Solvent effect in the kinetics of cobaloxime(II)-catalyzed oxidative dehydrogenation of 3,5-di-tert-butylcatechol by O2

“…We have previously reported that in MeOH the cobaloxime(lI) derivative [Co(Hdmg)2(Ph3P~h] is active in the selective catalytic conversion of 3,5-~-tertbutylcatechol (3,5-DBCatH2)to 3,5-~fi-tert-butyl-l,2-benzoqtfinone (DTBQ) with dioxygen at room temperature [7,8]. The blue complex [Co(Hdmgh(Ph3P)(3,5-DBCatH)], containing a unidentate catecholato ligand in axial position, has been isolated from the reaction mixture and characterized by X-ray diffraction.…”

“…The blue complex [Co(Hdmgh(Ph3P)(3,5-DBCatH)], containing a unidentate catecholato ligand in axial position, has been isolated from the reaction mixture and characterized by X-ray diffraction. ESR studies have revealed the involvement of the free 3,5-DBSQ'-anion radical and the complex [Co(Hdmg)2(Ph3P)(DBSQ'-)] as intermediates [7,8]. We were interested in looking at the effect of solvent on the kinetic behavior, with the objective of obtaining further information on the reaction mechanism and the nature of intermediates.…”