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Issue 40, 2011
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Origins of stereoselectivity in optically pure phenylethaniminopyridinetris-chelates M(NN′)3n+ (M = Mn, Fe, Co, Ni and Zn)

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Abstract

One-pot reactions of 2-pyridinecarboxaldehyde, chiral phenylethanamines and Fe(II) give single diastereomer facdiimine complexes at thermodynamic equilibrium so that no chiral separations are required (d.r. > 200 : 1). The origins of this stereoselectivity are partly steric and partly a result of the presence of three sets of inter-ligand parallel-offset π-stacking interactions. Mn(II), Co(II), Co(III), Ni(II) and Zn(II) give similar fac structures, alongside the imidazole analogues for Fe(II). While most of the complexes are paramagnetic, the series of molecular structures allows us to assess the influence of the π-stacking present, and there is a strong correlation between this and the M–N bond length. Fe(II) is close to optimal. For the larger Zn(II) ion, very weak π-stacking leads to poorer measured stereoselectivity (NMR) but this is improved with increased solvent polarity. The mechanism of stereoselection is further investigated via DFT calculations, chiroptical spectroscopy and the use of synthetic probes.

Graphical abstract: Origins of stereoselectivity in optically pure phenylethaniminopyridinetris-chelates M(NN′)3n+ (M = Mn, Fe, Co, Ni and Zn)

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Article information


Submitted
06 Apr 2011
Accepted
24 May 2011
First published
11 Jul 2011

Dalton Trans., 2011,40, 10416-10433
Article type
Paper

Origins of stereoselectivity in optically pure phenylethaniminopyridinetris-chelates M(NN′)3n+ (M = Mn, Fe, Co, Ni and Zn)

S. E. Howson, L. E. N. Allan, N. P. Chmel, G. J. Clarkson, R. J. Deeth, A. D. Faulkner, D. H. Simpson and P. Scott, Dalton Trans., 2011, 40, 10416
DOI: 10.1039/C1DT10588D

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