CHELATION-CONTROLLED REGIOSELECTIVITY IN THE SYNTHESIS OF SUBSTITUTEDPYRAZOLYLPYRIDINE LIGANDS - 3 - UNSYMMETRICALLY SUBSTITUTED TRIDENTATES AND DITOPIC BIS(TRIDENTATES) EN-ROUTE TO SINGLY STRANDED

A strategy for the synthesis of helical multinuclear complexes (helica tes) of any length is outlined, making use of ditopic ligands to bridg e between metals and monotopic ligands to cap the chain's termini. We present the syntheses of both ditopic and monotopic ligands with tride ntate binding units for octahedral metals, in liposoluble and function alized varieties. Of special interest are ligands bearing benzoic acid or toluic acid side-chains which can ionize and serve as counteranion s. Several singly N(1)-substituted 2,6-bis(4,5,6,7-tetrahydroindazol-3 -yl)pyridines were prepared by regioselective, chelation-controlled mo no;ni-alkylation or -arylation of the tautomeric N,N'-H-2 parent compo und. These were then either coupled with CH2 linkages to provide the d itopic ligands or were further N-functionalized to give unsymmetricall y substituted capping ligands. The regiochemistry of the N-substitutio ns and the ring-to-ring conformations were ascertained by H-1 NMR spec tra with and without added complexands (H+, D+, Zn2+, and Na+). The fo rmation of a bis(ZnBr2) adduct confirmed the independence of the metal binding sites while Na+ formed the 2:2 helicate.