SYNTHESES OF SEGMENTAL HETEROLEPTIC LIGANDS FOR THE SELF-ASSEMBLY OF HETERONUCLEAR HELICAL SUPRAMOLECULAR COMPLEXES

The development of a modified Phillips reaction allows the synthesis o f complicated heteroleptic ligands based on pyridine and 1H-benzimidaz ole moieties. The key-step formation of aromatic IH-benzimidazole ring s from N-(2-nitroaryl)arenecarboxamides significantly improves the pos sibilities of the classical intermolecular Phillips reactions and can be applied to the synthesis of large oligo-muitidentate units. Segment al heteroleptic ligands containing two different bidentate coordinatin g units (see 14) or bidentate and terdentate sites connected by 'diphe nylmethane' (= methylenebis(phenylene)) spacers (see 15 and 16) were o btained in fair to good yield by using multistep syntheses following t his strategy. Heterotrileptic ligands (bidentate-terdentate-bidentate, see 19 and 20; terdentate-terdentate-terdentate, see 23) requiring th e simultaneous formation of four 1H-benzimidazole rings in one step we re prepared and demonstrate the extended possibilities of this methodo logy. Data are presented to show that the milder conditions used for t his modified Phillips reaction together with its flexibility are essen tial for the development of ligands adapted for the self-assembly of h eteronuclear helical complexes.