Studies on the metalamide bond. IX. Metal complexes of some sterically hindered bis-picolinamide tetradentate ligands

The synthesis is described of some bis-picollinamide ligands in which N₄ tetradentate function on coordination would enfore severe intramolecular steric interactions. These ligands are N,N′-bis(6′-methylpyridine-2′-carboxamide)-1-ethane (6-mebpenH₂), N,N′-bis(6′-mehtylpyridine-2′-carboxamide)-1,2-benzene (6-mebpbH₂) and N,N′N-bis(2′-quinolylcarboxamine)-1,2-ethane (bqenH₂). Their complexing abilities with bivalent Cu, Ni and Pd have been studies, and comparison are made with analogous unhindered ligands reported previously. The complexes isolated each have characterized by microanalysis, magnetic susceptibility, thermogravimetrinc analysis, and by visible, i.r. and n.m.r. spectral data. In the compound Pd(6-mebpenH₂)Cl₂ the ligand displays an apparent unique trans-bidentate function. The deprotonated complexes isolated with the three ligands have N₄ tetradentate coordination, with resultant steric strain. Deuterium isotopic substitution has been used to assist with i.r. assignments.