Dicompartmental Ligands with Hexa- and Tetradentate Coordination Sites:  One-Step Synthesis of Ligands and Metal Complexes and Their X-ray Structure Analysis

Abstract

Examples of interesting ligands previously requiring lengthy synthetic procedures have been prepared by onestep routes, opening the way to more 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-pyridylmethyl)-1,2-diaminoethane. The protonated acyclic ligand salt, two mononuclear complexes of a macrocyclic ligand with a second compartment featuring a Schiff base, and one of the decomposition products resulting from a retro-Mannich reaction have been structurally characterized. The ligand salt (L1b) has an extended conformation with the ethylenediamine fragment displaying the trans configuration, very different from that of the corresponding closed-site macrocyclic complexes NiH 2 (L2b) 2+ and ZnH 2 (L2b) 2+ . The mononuclear macrocyclic complex NiH 2 -(L2b) 2+ has a much smaller ligand twist than the corresponcing Zn(II) complex. The degree of ligand distortion is correlated with the M-N bond length between the metal ions and the pyridine nitrogens; longer M-N bonds cause the pyridine rings to tilt and twist the phenolic rings out 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 open-site ligand were transformed into oxime groups, and the corresponding dinuclear bis(nickel) complex has been prepared. Acetal formation by the free carbonyl groups of ligand and retro-Mannich rearrangements are found to be possible pathways for the decomposition of this family of dicompartmental ligands.

Structural, magnetic, electrochemical, catalytic, DNA binding and cleavage studies of new macrocyclic binuclear copper(II) complexes

“…The larger electronegative oxygen present in alkyl oxime moiety makes the copper(II) ion to reduce at more positive potentials than the copper(II) ion, which is located in azomethine moiety [16a]. As the chain length of the alkylimine compartment increases, the entire macrocyclic becomes more flexible, which enables the easier reduction [33][34][35]. As the size of macrocycle is increased, shifting of both first and second reduction potentials towards anodic is observed for the binuclear copper(II) complexes.…”

Bis{2-[3-(cyclohexylaminio)propyliminomethyl]-4-nitrophenolato}dimethanolnickel(II) dinitrate dihydrate

“…Transition metal complexes containing Schiff base ligands have been of great interest for many years (Yamada, 1999). These complexes play an important role in the coordination chemistry related to catalysis and enzymatic reactions, magnetism and molecular architectures (Lacroix, 1996;Goswami & Eichhorn, 1999;Rybak-Akimova et al, 1998). Studying the variety of products in the self-assembly processes between labile metal ions and flexible multidentate ligands is an interesting topic in supramolecular chemistry (You, 2005a,b,c,d,e,f;You & Zhu, 2005).…”

Synthesis of a New Dicompartment Multifunctional Groups Ligand

“…Binucleating ligands containing two different compartments have received great attention because they may be capable of binding two different metal centers in close proximity with different coordination environments. [1][2][3][4][5][6][7][8] Aside from the synthetic challenge which may target such systems, four principal goals have guided many of the investigations of heterobimetallic compounds. Some systems were synthesized in order to better understand the behaviour of the biological systems.…”