Catalytic oxidation of organic substrates and water by manganese(V) nitrido and ruthenium(II) polypyridyl complexes


Student thesis: Doctoral Thesis

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  • Li MA


Awarding Institution
Award dateJan 2015


The thesis is divided into five parts. Part I reports the catalytic oxidation of alkanesby a manganese nitrido complex (PPh4)2[Mn v(N)(CN)4] using H2O2 and (NH4)2[Ce(NO3)6] as oxidants. Part II describes the catalytic oxidation of alkanes and alcohols by (PPh4)2[Mn V (N)(CN)4] using nBu4N[IO4] as oxidant. Part III presents alkanes and alcohols oxidation by various manganese(V) nitrido complexes. Part IV discloses Ce IV-driven water oxidation using [N(CH3)4]2Na[Mn(N)(CN)5] and (PPh4)2[Mn V(N)(CN)4] as catalysts. Part V is about alkane oxidation catalyzed by Ru II diaqua complexes and using CIO4-, NO3- or NO2- as oxidant.

In part one, the oxidation of various alkanes catalyzed by [Mn V(N)(CN)4]2- using various terminal oxidants at room temperature has been investigated. Excellent yields of alcohols and ketones (>95%) are obtained using H2O2 as oxidant and CF3CH2OH as solvent. Good yields (>80%) are also obtained using (NH4)2[Ce(NO3)6] in CF3CH2OH/H2O. Based on the experimental results, the proposed mechanism for catalytic alkane oxidation by [Mn V(N)(CN)4]2-/ROOH involves initial rate-limiting O-atom transfer from ROOH to [Mn(N)(CN)4]2- to generate a manganese(VII) nitrido oxo active species, [Mn VII(N)(O)(CN)4]2-, which then oxidizes alkanes (R'H) via a H-atom abstraction/O-rebound mechanism. The proposed mechanism is alsosupported by DFT calculations.

In part two, the oxidation of various alkanes and alcohols catalyzed by [Mn V(N)(CN)4]2- using nBu4N[IO4] as terminal oxidant at room temperature has been investigated in CF3CH2OH. Excellent yields of the corresponding alcohols and ketones from oxidation of alkanes, and ketones from oxidation of various alcohols were obtained.

In part three, the oxidation of cyclohexane and cyclohexanol catalyzed by (PPh4)2[Mn(N)(CN)4(py)].(py) (py = pyridine), (PPh4)2[Mn(N)(CN)3(pic)] (pic = picolinate) and PPh4[Mn(N)(CN)3(bpy)](bpy = 2,2'-bipyridine) were studied by using peroxide as terminal oxidants at room temperature. The effects of solvents and acetic acid in cyclohexane and cyclohexanol oxidation have been investigated.

In part four, the manganese(V) nitrido complex [Mn(N)(CN)4]2- catalyzed water oxidation by (NH4)2[Ce(NO3)6] was investigated at room temperature, with TON > 180. The initial rate of O2 evolution depends linear on the catalyst concentration, which suggests a 'water nucleophilic attack' mechanism for this catalytic water oxidation system. [Mn VII(N)(O)(CN)4]2- is proposed to be the active intermediate. The catalyst eventually loses its water oxidation activity due mainly to competing N...N coupling reaction of the proposed [Mn VII(N)(O)(CN)4]2- active intermediate, the N2 produced from this N...N coupling reaction was detected by GC-TCD.

In part five, the oxidation of various alkanes catalyzed by the Ru II diaqua complexes, [Ru(dmp)2(H2O)2](PF6)2 and [Ru(6,6'-Cl2bipy)2(H2O)2](OTf)2(dmp = 2,9-dimethyl-1,10-phenanthroline; 6,6'-Cl2-bpy = 6,6'-dichloro-2,2'-bipyridine; OTf = CF3SO3-), using ClO4-, NO3- and NO2- as oxidants were studied. When ClO4- was used as oxidant, around 20% of the oxidized products can be obtained. On the other hand, when NO3- and NO2- were used as oxidants, they were completely inefficient, and no oxidized product could be detected.