Issue 46, 2018

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

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

Supplementary files

Article information

Article type
Paper
Submitted
20 Sep 2018
Accepted
31 Oct 2018
First published
05 Nov 2018

Dalton Trans., 2018,47, 16534-16542

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, 47, 16534 DOI: 10.1039/C8DT03808B

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