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

Abstract

The reactions of anhydrous sodium salts of three chiral biaryl-bridged salicylaldimine tetradentate proligands H 2L with manganese(II) chloride give the corresponding solvated complexes [Mn IIL]. 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-β structure with Δ helicity as predetermined by the ( R)-configuration of the biaryls. Oxidation of these compounds with halogens gives manganese(III) complexes. A complex [Mn IIILI] has a trigonal bipyramidal structure with similar cis-β structure to that above. In contrast, the complex [MnL(OH 2) 2]Cl has the rather rare C 2-symmetric cis-α 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-β and cis-α, albeit with the same helicity, to occur in response to the nature of the co-ligands.