Monomeric metal complexes of first-row transition metal ions with terminal hydroxido ligands are often difficult to prepare because hydroxido ligands have a strong tendency to bridge between metal centers. This talk describes methods to prepare a monomeric Ni(II)–OH complex supported by a tripodal, tris-ureayl ligand in which the hydroxido ligand is derived from water. The solid state structure of this complex reveals a distorted trigonal bipyramidal Ni(II) complex, with hydrogen bonding observed from the ureayl ligand N-H groups to the hydroxido ligand oxygen atom. The reactivity of this species has been explored, including its ability to be oxidized. The one-electron oxidized species, Ni(III)–OH, is another rare Ni complex that is believed to be a key intermediate in Ni based oxidations. Treatment of the high spin S = 1 Ni(II) complex with mild one-electron oxidants produced a low-spin S = 1/2 Ni(III) species that has been characterized by perpendicular-mode X-band EPR, UV-visible, and FTIR spectroscopies. The oxidized complex displays a lack of reactivity towards external substrates. Additionally, the Ni(III) species is not stable at room temperature, converting to an EPR silent species that is different from the original Ni(II)–OH species by UV-visible spectroscopy. FTIR and NMR studies on this new species suggest the possibility of ligand modification as a source of the instability of the Ni(III) species.

Chemical and spectroscopic characterization of a monomeric Ni(II)–OH complex derived from water

251st National Meeting (2016)

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