SYNTHESIS AND PHOTOPHYSICAL PROPERTIES OF CHIRAL, BINUCLEAR METAL-COMPLEXES

The synthesis of isomerically pure multicentred species is an importan t task for preparative chemists. Only stereochemically well-defined st ructures of polynuclear metal complexes lead to photophysical results that are clearly interpretable. We have developed several strategies t o synthesise such compounds that have a predetermined chirality (Delta - or Lambda-helix) at each metal center. The approximate local symmetr y of the described metal complexes is D-3 (octahedral, tris-bidentate) . The methods are the following: (a) resolving a racemic building bloc k followed by substitution of the two labile monodentate Ligands by a bidentate diimine ligand under total retention of configuration. (b) S ynthesis of an optically pure precursor complex in which two chelating bipyridine ligands are bridged and each contain an optically active p inene unit. The remaining coordination sites are then replaced by a bi dentate diimine ligand. (c) Use of ligands that have sterically demand ing substituents perpendicular to the molecular plane. The use of such ligands leads direct to optically active compounds. Examples of these methods will be given, while considering their photophysical applicat ion. (C) 1997 Elsevier Science S.A.