title: A trinuclear nickel(II) enediolate complex: synthesis, characterization, and O2 reactivity.
abstract: Using a new N(4)-donor chelate ligand having a mixture of hydrophobic phenyl and hydrogen-bond-donor appendages, a trinuclear nickel(II) complex of the doubly deprotonated form of 2-hydroxy-1,3-diphenylpropane-1,3-dione was isolated, characterized (X-ray crystallography, elemental analysis, UV-vis, (1)H NMR, FTIR, and magnetic moment measurement), and evaluated for O(2) reactivity. This complex, [(6-NA-6-Ph(2)TPANi)(2)(mu-PhC(O)C(O)C(O)Ph)(2)Ni](ClO(4))(2) (4), has two terminal pseudooctahedral Ni(II) centers supported by the tetradentate chelate ligand and a central square-planar Ni(II) ion ligated by oxygen atoms of two bridging enediolate ligands. In CH(3)CN, 4 exhibits a deep orange/brown color and lambda(max) = 463 nm (epsilon = 16 000 M(-1)cm(-1)). The room temperature magnetic moment of 4, determined by Evans method, is mu(eff) = 5.3(2) mu(B). This is consistent with the presence of two noninteracting high-spin Ni(II) centers, a diamagnetic central Ni(II) ion, and an overall quintet ground state. Exposure of a CH(3)CN solution of 4 to O(2) results in the rapid loss of the orange/brown color to give a green solution. The products identified from this reaction are [(kappa(3)-6-NA-6-Ph(2)TPA)Ni(O(2)Ph)(H(2)O)]ClO(4) (5), benzil [PhC(O)C(O)Ph], and CO. Identification of 5 was achieved via its independent synthesis and a comparison of its (1)H NMR and mass spectral features with those of the 6-NA-6-Ph(2)TPA-containing product generated upon reaction of 4 with O(2). The independently prepared sample of 5 was characterized by X-ray crystallography, elemental analysis, UV-vis, mass spectrometry, and FTIR. The O(2) reactivity of 4 has relevance to the active-site chemistry of Ni(II)-containing acireductone dioxygenase (Ni(II)ARD).
authors.affiliation: Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300, USA.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Rudzka
authors.forename: Atta M
authors.initials: AM
authors.lastname: Arif
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Berreau
mesh_terms: D001565:Benzoates / Q000737:chemistry; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D001565:Benzoates; D008024:Ligands; D009942:Organometallic Compounds; D010100:Oxygen