Synthesis, complexation and cyclisation reactions of a new acyclic diamide: observation of intramolecular ligand exchange in a structurally characterised nickel(II) complex

• Published in: Polyhedron Vol. 18; no. 5; pp. 679 - 688
• Main Authors: Brooker, Sally, Dunbar, Geoffrey S, Jameson, Geoffrey B
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-01-1999
• Subjects: Amide; Barium; Exchange; Nickel; Structure; Exchange; Amide; Barium; Nickel; Structure
• ISSN: 0277-5387
• DOI: 10.1016/S0277-5387(98)00338-6

A new acyclic diamide ligand H
2L1 has been prepared and characterised H
2L12 6-bis(1-propanecarboxamido-3-amino)pyridine is prepared from 26-dimethylpyridinedicarboxylate and excess 13-diaminopropane Nickel(II) complexes derived from H
2L1 [Ni(L1+H)]X are orange square planar and diamagnetic (X=ClO
4
− CF
3SO
3
− or NO
3
−) A single-crystal X-ray analysis of [Ni(L1+H)]ClO
4 confirmed that both of the amide groups are deprotonated and are bound to the nickel ion with a
trans-amide configuration and that the remaining coordination sites are occupied by the pyridine nitrogen atom and one of the amine arms The second amine arm is protonated and participates in an array of hydrogen bonds in the solid state In solution intramolecular exchange of the arms is observed on the NMR timescale Three macrocycles have been prepared from this acyclic ligand Reaction of H
2L1 with 26-diacetylpyridine or 2 6-diformylpyridine in the presence of a barium(II) template ionresults in two new unsymmetrical amide-containing and potentially dinucleating macrocycles as the complexes [Ba(H
2L2)](ClO
4)
2 and [Ba (H
2L3)] (ClO
4)
2 respectively In contrast to the template cyclisations a symmetrical metal-free tetraamide macrocycle H
4L4 is produced from the direct cyclisation of H
2L1 with 2 6-dimethylpyridinedicarboxylate.