Issue 9, 2010

Chirality and diastereoselection in the μ-oxo diiron complexes L2Fe–O–FeL2 (L = bidentate salicylaldiminato)

Abstract

A number of bis(salicylaldiminato) (Schiff base) complexes of Fe(II) i.e. L2Fe with a variety of ligand substituents and functionality are synthesised, usually by salt metathesis but on one occasion via the (sal)2Fe complex, and characterised by standard methods. Two molecular structure determinations indicate the expected tetrahedral geometry. Treatment with dry oxygen yielded the Fe(III) complexes [(FeL2)2-μ-O], generally in high yield and in the absence of hydroxylated impurities; one bulky complex L2Fe gave no oxidation product for steric reasons, and one hydroxyl-substituted compound gave an insoluble product. Five molecular structures of these [(FeL2)2-μ-O] compounds were determined. All were homochiral in the sense that the absolute configuration at Fe was the same for both atoms. Three of the structures – those based on optically pure salicylaldimine ligands – were diastereomeric. For two, the diastereomers observed are those predicted on the basis of steric considerations, while a third highly distorted and congested structure represents the unexpected diastereomer. Powder X-ray diffraction confirms high phase purity of the bulk samples (i.e. they are diastereomerically pure to the level detectable). These investigations, coupled with molecular structure and NMR studies on model gallium complexes, indicate that the diastereoselection arises from cooperative interactions across the oxo bridge.

Graphical abstract: Chirality and diastereoselection in the μ-oxo diiron complexes L2Fe–O–FeL2 (L = bidentate salicylaldiminato)

Supplementary files

Article information

Article type
Paper
Submitted
23 Mar 2009
Accepted
05 Dec 2009
First published
14 Jan 2010

Dalton Trans., 2010,39, 2309-2326

Chirality and diastereoselection in the μ-oxo diiron complexes L2Fe–O–FeL2 (L = bidentate salicylaldiminato)

J. M. Becker, J. Barker, G. J. Clarkson, R. van Gorkum, G. K. Johal, R. I. Walton and P. Scott, Dalton Trans., 2010, 39, 2309 DOI: 10.1039/B905706D

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