First Row Divalent Transition Metal Complexes of Aryl-Appended Tris((pyridyl)methyl)amine Ligands: Syntheses, Structures, Electrochemistry, and Hydroxamate Binding Properties

Divalent manganese, cobalt, nickel, and zinc complexes of 6-Ph2TPA (N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; [(6-Ph2TPA)Mn(CH3OH)3](ClO4)2 (1), [(6-Ph2TPA)Co(CH3CN)](ClO4)2 (2), [(6-Ph2TPA)Ni(CH3CN)(CH3OH)](ClO4)2 (3), [(6-Ph2TPA)Zn(CH3CN)](ClO4)2 (4)) and 6-(Me2Ph)2TPA (N,N-bis((6-(3,5-dimethyl)phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; [(6-(Me2Ph)2TPA)Ni(CH3CN)2](ClO4)2 (5) and [(6-(Me2Ph)2TPA)Zn(CH3CN)](ClO4)2 (6)) have been prepared and characterized. X-ray crystallographic characterization of 1A·CH3OH
and 1B·2CH3OH (differing solvates of 1), 2·2CH3CN, 3·CH3OH, 4·2CH3CN, and 6·2.5CH3CN revealed mononuclear
cations with one to three coordinated solvent molecules. In 1A·CH3OH and 1B·2CH3OH, one phenyl-substituted
pyridyl arm is not coordinated and forms a secondary hydrogen-bonding interaction with a manganese bound
methanol molecule. In 2·2CH3CN, 3·CH3OH, 4·2CH3CN, and 6·2.5CH3CN, all pyridyl donors of the 6-Ph2TPA and
6-(Me2Ph)2TPA ligands are coordinated to the divalent metal center. In the cobalt, nickel, and zinc derivatives,
CH/π interactions are found between a bound acetonitrile molecule and the aryl appendages of the 6-Ph2TPA and
6-(Me2Ph)2TPA ligands. 1H NMR spectra of 4 and 6 in CD3NO2 solution indicate the presence of CH/π interactions,
as an upfield-shifted methyl resonance for a bound acetonitrile molecule is present. Examination of the cyclic
voltammetry of 1−3 and 5 revealed no oxidative (M(II)/M(III)) couples. Admixture of equimolar amounts of 6-Ph2TPA, M(ClO4)2·6H2O, and Me4NOH·5H2O, followed by the addition of an equimolar amount of acetohydroxamic
acid, yielded the acetohydroxamate complexes [((6-Ph2TPA)Mn)2(μ-ONHC(O)CH3)2](ClO4)2 (8), [(6-Ph2TPA)Co(ONHC(O)CH3)](ClO4)2 (9), [(6-Ph2TPA)Ni(ONHC(O)CH3)](ClO4)2 (10), and [(6-Ph2TPA)Zn(ONHC(O)CH3)](ClO4)2
(11), all of which were characterized by X-ray crystallography. The Mn(II) complex 8·0.75CH3CN·0.75Et2O exhibits
a dinuclear structure with bridging hydroxamate ligands, whereas the Co(II), Ni(II), and Zn(II) derivatives all exhibit
mononuclear six-coordinate structures with a chelating hydroxamate ligand.