NMR Studies of Mononuclear Octahedral Ni(II) Complexes Supported by Tris((2-pyridyl)methyl)amine-Type Ligands

The recent discovery of acireductone dioxygenase (ARD), a metalloenzyme containing a mononuclear octahedral
Ni(II) center, necessitates the development of model systems for evaluating the role of the metal center in substrate
oxidation chemistry. In this work, three Ni(II) complexes of an aryl-appended tris((2-pyridyl)methyl)amine ligand
(6-Ph2TPA, N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine), [(6-Ph2TPA)Ni(CH3CN)(CH3OH)](ClO4)2
(1), [(6-Ph2TPA)Ni(ONHC(O)CH3)]ClO4 (3), and [(6-Ph2TPA)Ni−Cl(CH3CN)]ClO4 (4), and one Ni(II) complex of tris((2-pyridyl)methyl)amine, [(TPA)Ni(CH3CN)(H2O)](ClO4)2 (2), have been characterized in acetonitrile solution using
conductance methods and NMR spectroscopy. In acetonitrile solution, 1−4 have monomeric cations that exhibit
isotropically shifted 1H NMR resonances. Full assignment of these resonances was achieved using one- and two-dimensional 1H NMR techniques and 2H NMR of analogues having deuteration of the supporting chelate ligand.
COSY cross peaks were observed for pyridyl protons of the 6-Ph2TPA ligand in 1 and 3. This study lays the
groundwork for using NMR methods to examine chemical reactions of 1 and 2 with model substrates of relevance
to ARD.