Alkane oxidation by the system 'tert-butyl hydroperoxide-[Mn 2L2O3][PF6]2 (L = 1,4,7trimethyl-1,4,7-triazacyclononane)-carboxylic acid'

Article abstract of DOI:10.1002/poc.1295

The kinetics of cyclohexane (CyH) oxygenation with terf-butyl hydroperoxide (TBHP) in acetonitrile at 50°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 'Mn^IIIMn^IV,) 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 = 7.4mol^-1dm³ and k = 8.4 × 10 ^-2s^-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 → CH₃COCH₃+ CH₃) and its interaction with the CyH (terf-BuO + CyH → fert-BuOH + Cy) 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 ≈ 10³ mol^-1 dm³). Copyright