Alkane oxidation by the system 'tert-butyl hydroperoxide-[Mn2L2O3][PF6](2) (L=1,4,7-trimethyl-1,4,7-triazacyclononane)-carboxylic acid'

摘要

The kinetics of cyclohexane (CyH) oxygenation with tert-butyl hydroperoxide (TBHP) in acetonitrile at 50 degrees C catalysed by a dinuclear manganese(IV) complex 1 containing 1,4,7-trimethyl-1,4,7-triazacyclononane and co-catalysed by oxalic acid have been studied. It has been shown that an active form of the catalyst (mixed-valent dimeric species '(MnMnIV)-Mn-III') is generated only in the interaction between complex 1 and TBHP and oxalic acid in the presence of water. The formation of this active form is assumed to be due to the hydrolysis of the Mn-O-Mn bonds in starting compound 1 and reduction of one Mn-IV to Mn-III. A species which induces the CyH oxidation is radical tert-BuO. generated by the decomposition of a monoperoxo derivative of the active form. The constants of the equilibrium formation and the decomposition of the intermediate adduct between TBHP and 1 have been measured: K = 7.4 mol(-1) dm(3) and k = 8.4 x 10(-2) s(-1), respectively, at [H2O] = 1.5 mol dm(-3) and [oxalic acid] = 10(-2) mol dm(-3). the constant ratio for reactions of the monomolecular decomposition of tert-butoxy radical (tert-BuO center dot -> CH3COCH3 + CH3) and its interaction with the CyH (tert-BuO center dot + CyH -> tert-BuOH + Cy-center dot) was calculated: 0.26 mol dm(-3). One of the reasons why oxalic acid accelerates the oxidation is due to the formation of an adduct between oxalic acid and 1 (K approximate to 10(3) mol(-1) dm(3)). Copyright (c) 2007 John Wiley & Sons, Ltd.