DICOMPARTMENTAL LIGANDS WITH HEXADENTATE AND TETRADENTATE COORDINATION SITES - ONE-STEP SYNTHESIS OF LIGANDS AND METAL-COMPLEXES AND THEIR X-RAY STRUCTURE-ANALYSIS

Examples of interesting ligands previously requiring lengthy synthetic procedures have been prepared by onestep routes, opening the way to m ore extensive studies of their complexes and to possible applications. New dicompartmental ligands bearing picolyl pendant arms on the amine nitrogen donors have been synthesized, via the Mannich condensation, from 5-substituted salicylaldehydes, formaldehyde, and N,N'-bis(2-pyri dylmethyl)-1,2-diaminoethane. The protonated acyclic ligand salt, two mononuclear complexes of a macrocyclic ligand with a second compartmen t featuring a Schiff base, and one of the decomposition products resul ting from a retro-Mannich reaction have been structurally characterize d. The ligand salt (L1b) has an extended conformation with the ethylen ediamine fragment displaying the trans configuration, very different f rom that of the corresponding closed-site macrocyclic complexes NiH2(L 2b)(2+) and ZnH2(L2b)(2+). The mononuclear macrocyclic complex NiH2(L2 b)(2+) has a much smaller ligand twist than the corresponcing Zn(II) c omplex. The degree of ligand distortion is correlated with the M-N bon d length between the metal ions and the pyridine nitrogens; longer M-N bonds cause the pyridine rings to tilt and twist the phenolic rings o ut of the main ligand plane. The ability of the macrocyclic ligand L2b to accommodate a second metal ion has been demonstrated by successful synthesis of dinuclear complexes. The free carbonyl groups of the ope n-site ligand were transformed into oxime groups, and the correspondin g dinuclear bis(nickel) complex has been prepared. Acetal formation by the free carbonyl groups of ligand and retro-Mannich rearrangements a re found to be possible pathways for the decomposition of this family of dicompartmental ligands.