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Issue 38, 2009
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Mn(II) complexes containing the polypyridylic chiral ligand (−)-pinene[5,6]bipyridine. Catalysts for oxidation reactions

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Abstract

A series of mononuclear and dinuclear chiral manganese(II) complexes containing the neutral bidentate chiral nitrogen ligand (−)-pinene[5,6]bipyridine, (−)-L, were prepared from different manganese salts. The chirality in these complexes arises from the pinene ring that has been fused to the 5,6 positions of one pyridine group of the bipyridine ligand. These complexes have been characterized through analytical, spectroscopic (IR, UV/Vis, ESI-MS) and electrochemical techniques (cyclic voltammetry). Single X-ray structure analysis revealed a five-coordinated Mn(II) ion in [{MnCl((−)-L)}2(μ-Cl)2] (2), [{Mn((−)-L)}2(μ-OAc)3](PF6) (3) and [MnCl2(H2O)((−)-L)] (4) and a six-coordinated one in [MnCl2((−)-L)2] (5), [Mn(CF3SO3)2((−)-L)2] (6) and [Mn(NO3)(H2O)((−)-L)2)](NO3) (7). The magnetic properties of the binuclear compounds 2 and 3 have been studied. Both compounds show a weak antiferromagnetic coupling (2, J = −0.22 cm−1; 3, J = −0.85 cm−1). The catalytic activity of the whole set of complexes has been tested with regard to the epoxidation of aromatic alkenes with peracetic acid. In the particular case of styrene, good selectivities and moderate enantioselectivities were obtained. Furthermore, total retention of the initial cis configuration was achieved when epoxidizing cis-β-methylstyrene with the chloride complexes. In general, the epoxidation activity of these manganese complexes is strongly dependent on the steric encumbrance of the substrates employed.

Graphical abstract: Mn(ii) complexes containing the polypyridylic chiral ligand (−)-pinene[5,6]bipyridine. Catalysts for oxidation reactions

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Publication details

The article was received on 07 Apr 2009, accepted on 15 Jul 2009 and first published on 19 Aug 2009


Article type: Paper
DOI: 10.1039/B906435D
Dalton Trans., 2009, 8117-8126

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    Mn(II) complexes containing the polypyridylic chiral ligand (−)-pinene[5,6]bipyridine. Catalysts for oxidation reactions

    J. Rich, M. Rodríguez, I. Romero, L. Vaquer, X. Sala, A. Llobet, M. Corbella, M. Collomb and X. Fontrodona, Dalton Trans., 2009, 8117
    DOI: 10.1039/B906435D

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