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Issue 15, 2012
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Jahn–Teller effects on π-stacking and stereoselectivity in the phenylethaniminopyridine tris-chelates Cu(NN′)32+

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Abstract

Optically pure phenylethaniminopyridine (SC-L) tris-chelates of Fe(II) and other first row transition metal systems have previously been shown to give exclusively the fac structures in the solid state. Here it is shown by powder X-ray diffraction that the complex [CuL3][ClO4]2 crystallises exclusively as the mer isomer, although – for a given absolute configuration of the ligand – of the same helicity (Δ/Λ) as that displayed by the other metal complexes. The similar ligand RC-LFF, which contains a peripheral 19F spin label, gave [CuLFF3][ClO4]2 which also adopts exclusively the mer structure in the crystal, but is shown by NMR spectroscopy to have a fac : mer ratio of 1 : 6 in solution at low temperature. Molecular mechanics calculations for a number of isomers and conformers are consistent with the presence of such a mixture of isomers in solution for both complexes. The origin of the difference in behaviour between Fe(II) and Cu(II) is the presence of a Jahn–Teller distortion (and the generally longer M–N bonds) in the Cu(II) complexes. This disturbs intra-ligand π-stacking, leading to the poor fac/mer stereoselectivity while leaving enantioselectivity Δ/Λ apparently unaffected.

Graphical abstract: Jahn–Teller effects on π-stacking and stereoselectivity in the phenylethaniminopyridine tris-chelates Cu(NN′)32+

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Supplementary files

Article information


Submitted
08 Dec 2011
Accepted
07 Jan 2012
First published
13 Jan 2012

Dalton Trans., 2012,41, 4477-4483
Article type
Paper

Jahn–Teller effects on π-stacking and stereoselectivity in the phenylethaniminopyridine tris-chelates Cu(NN′)32+

S. E. Howson, N. P. Chmel, G. J. Clarkson, R. J. Deeth, D. H. Simpson and P. Scott, Dalton Trans., 2012, 41, 4477
DOI: 10.1039/C2DT12378A

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