Non-planar manganese Schiff-base complexes; synthesis and molecular structures

The reactions of anhydrous sodium salts of three chiral biaryl-bridged salicylaldimine tetradentate proligands H2L with manganese(II) chloride give the corresponding solvated complexes [(MnL)-L-II]. The molecular structure of one chiral nonracemic example with a relatively low steric demand ligand set is shown to be composed of a homochiral dimer with bridging phenoxy groups. Both LMn units adopt the cis-beta structure with Delta helicity as predetermined by the (R)-configuration of the biaryls. Oxidation of these compounds with halogens gives manganese(III) complexes. A complex [(MnLI)-L-III] has a trigonal bipyramidal structure with similar cis-beta structure to that above. In contrast, the complex [MnL(OH2)(2)]Cl has the rather rare C-2-symmetric cis-alpha structure. It is thus apparent then that while the biaryl unit in these and similar compounds is able to predetermine the chirality-at-metal very efficiently, it is quite possible for conversions between diastereomeric forms cis-beta and cis-alpha, albeit with the same helicity, to occur in response to the nature of the co-ligands. (C) 2003 Elsevier Science Ltd. All rights reserved.