Paper
Tuning the olefin epoxidation by manganese(III) complexes of bisphenolate ligands: Role of Lewis basicity of ligands on reactivity
Dalton Trans., 2013, Accepted Manuscript
DOI: 10.1039/C3DT51766G
Received 01 Jul 2013, Accepted 23 Sep 2013
First published online 23 Sep 2013
A new family of manganese(III) complexes of the type [Mn(L)Cl], where H2L is 1,4-bis(2-hydroxy-benzyl)-1,4-diazepane (H2(L1)), 1,4-bis(2-hydroxy-4-methylbenzyl)-1,4-diazepane (H2(L2)), 1,4-bis(2-hydroxy-3,5-dimethylbenzyl)-1,4-diazepane (H2(L3)) and 1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-1,4-diazepane (H2(L4)), has been isolated and studied as functional models for cyt P450 enzymes. The complexes 1 - 4 have been characterized using elemental analysis, electronic spectral and electrochemical methods and ESI-MS. The single crystal X-ray structures of 1 and 3 contain MnN2O2Cl chromophore with novel square pyramidal coordination geometry (: 1, 0.11; 3, 0.00). All the complexes possess a distorted square pyramidal coordination geometry in solution, as revealed by the characteristic bands observed in the electronic spectra. The Mn(III)/Mn(II) redox potentials (E1/2) of 1 - 4 fall within the narrow range of 0.279 - 0.320 V. The catalytic ability of the complexes towards olefin epoxidation has been investigated using PhIO at room temperature under N2 atmosphere. Addition of N-methylimidazole to the complexes leads to an increase in the epoxide yield. A correlation between the redox potential of Mn(III)/Mn(II) couple and reactivity of the complexes towards olefin epoxidation has been observed.
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