Syntheses, structures, and properties of Co(III) complexes derived from polypyridine ligands containing one carboxamido nitrogen donor

Four cobalt(III) complexes containing the polypyridine pentadentate ligands N,N-bis(2-pyridylmethyl)amine-N'-ethyl-2-pyridine-2-carboxamide (PaPY3H), N,N-bis(2-pyridylmethyl)amine-N'-[1-(2-pyridylethyl)acetamide (MePcPy3H), and N,N-bis(2-pyridylmethyl)amine-N'-(2-pyridylmethyl)acetamide (PCPy3H), have been synthesized. All three ligands bind the Co(111) center in the same fashion with the exception of loss of conjugation between the carboxamide moiety and the pyridine ring in the latter two. The structures of [(PaPy3)Co(OH)][(PaPy3)Co(H2O)](ClO4)(3) (.) 3H(2)O (1), [(PaPy3)Co(NO2VClO4) (.) 2MeCN (2), [(MePcPy3)Co(MeCN)](ClO4)(2) (.) 0.5-MeCN (3), and [(PCPy3)Co(Cl)](ClO4) (.) 2MeCN (4) have been determined. These ligands with strong-field carboxamido N donor stabilize the +3 oxidation state of the Co center as demonstrated by the facile oxidation of the corresponding Co(H) complexes (prepared in situ) by H2O2, [Fe(Cp)(2)](BF4), or nitric oxide (NO). The Co-N-amido bond distances of 1-4 lie in the narrow range of 1.853-1.898 angstrom. H-1 NMR spectra of these complexes confirm the low-spin d(6) ground states of the metal centers. (c) 2006 Elsevier B.V. All rights reserved.