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Catalytic oxidation of alcohols with novel non-heme N4-tetradentate manganese(II) complexes

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Abstract

We report the preparation and characterisation of a series of novel non-heme N4-tetradentate Mn(OTf)2 complexes of the type, [(L)MnOTf2], where L = R,R and S,S enantiomers of BPMCN, its 6-methyl and 6-bromo derivatives as well as the novel ligand BMIMCN (BPMCN = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)-(R,R/S,S)-1,2-diaminocyclohexane, BMIMCN = N,N′-dimethyl-N,N′-bis(1-methyl-2-imidazolemethyl)-(R,R/S,S)-1,2-diaminocyclohexane). Solid state structural analysis of the BMIMCN-ligated Mn-triflate complexes (R,R-C4 and S,S-C4) revealed opposite helicity but identical metal site accessibility. This feature was exploited in the catalytic oxidation of primary and secondary alcohols, with hydrogen peroxide as oxidant and acetic acid as co-catalyst. Complexes R,R-C4 and S,S-C4 displayed the highest activity in benzyl alcohol oxidation, attributed to the electron-donating property of the BMIMCN ligand. Complex S,S-C4, displayed high activity for a variety of primary alcohol substrates, but the reaction suffered from reduced selectivity and side-reactions due to the presence of acetic acid. In contrast, secondary alcohol substrates could be oxidised to the corresponding ketone products in excellent isolated yields under mild reaction conditions and short reaction times.

Graphical abstract: Catalytic oxidation of alcohols with novel non-heme N4-tetradentate manganese(ii) complexes

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Publication details

The article was received on 20 Sep 2018, accepted on 31 Oct 2018 and first published on 05 Nov 2018


Article type: Paper
DOI: 10.1039/C8DT03808B
Citation: Dalton Trans., 2018, Advance Article
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    Catalytic oxidation of alcohols with novel non-heme N4-tetradentate manganese(II) complexes

    V. Vermaak, D. A. Young and A. J. Swarts, Dalton Trans., 2018, Advance Article , DOI: 10.1039/C8DT03808B

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