| Sumario: | The oxidation of various alkanes catalyzed by [Mn(N)(CN)] using various terminal oxidants at room temperature has been investigated. Excellent yields of alcohols and ketones (>95%) are obtained using HO as oxidant and CFCHOH as solvent. Good yields (>80%) are also obtained using (NH)2[Ce(NO)] in CFCHOH/HO. Kinetic isotope effects (KIEs) are determined by using an equimolar mixture of cyclohexane (c-CH) and cyclohexane-d (c-CD) as substrate. The KIEs are 3.1 ± 0.3 and 3.6 ±0.2 for oxidation by HO and Ce(IV), respectively. On the other hand, the rate constants for the formation of products using c-CH or c-CD as single substrate are the same. These results are consistent with initial rate-limiting formation of an active intermediate between [Mn(N)(CN)] and HO or Ce, followed by H-atom abstraction from cyclohexane by the active intermediate. When PhCHC(CH)OOH (MPPH) is used as oxidant for the oxidation of c-CH, the major products are c-CHOH, c-CHO, and PhCHC(CH)OH (MPPOH), suggesting heterolytic cleavage of MPPH to generate a Mn-O intermediate. In the reaction of HO with [Mn(N)(CN)] in CFCHOH, a peak at m/z 628.1 was observed in the electrospray ionization mass spectrometry, which is assigned to the solvated manganese nitrido oxo species, (PPh)[Mn(N)(O)(CN)]∙CFCHOH. On the basis of the experimental results the proposed mechanism for catalytic alkane oxidation by [Mn(N)(CN)]/ROOH involves initial rate-limiting O-atom transfer from ROOH to [Mn(N)(CN)] to generate a manganese(VII) nitrido oxo active species, [Mn(N)(O)(CN)], which then oxidizes alkanes (R'H) via a H-atom abstraction/O-rebound mechanism. The proposed mechanism is also supported by density functional theory calculations.
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