A Trinuclear Nickel(II) Enediolate Complex: Synthesis, Characterization, and O2 Reactivity

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• 作者：Katarzyna Rudzka ; Atta M. Arif ; Lisa M. Berreau
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：December 1, 2008
• 年：2008
• 卷：47
• 期：23
• 页码：10832-10840
• 全文大小：283K
• 年卷期：v.47,no.23(December 1, 2008)
• ISSN：1520-510X

文摘

Using a new N₄-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, ¹H NMR, FTIR, and magnetic moment measurement), and evaluated for O₂ reactivity. This complex, [(6-NA-6-Ph₂TPANi)₂(μ-PhC(O)C(O)C(O)Ph)₂Ni](ClO₄)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 CH₃CN, 4 exhibits a deep orange/brown color and λ_max = 463 nm (ε = 16000 M⁻¹cm⁻¹). The room temperature magnetic moment of 4, determined by Evans method, is μ_eff = 5.3(2) μ_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 CH₃CN solution of 4 to O₂ results in the rapid loss of the orange/brown color to give a green solution. The products identified from this reaction are [(κ³-6-NA-6-Ph₂TPA)Ni(O₂Ph)(H₂O)]ClO₄ (5), benzil [PhC(O)C(O)Ph], and CO. Identification of 5 was achieved via its independent synthesis and a comparison of its ¹H NMR and mass spectral features with those of the 6-NA-6-Ph₂TPA-containing product generated upon reaction of 4 with O₂. The independently prepared sample of 5 was characterized by X-ray crystallography, elemental analysis, UV−vis, mass spectrometry, and FTIR. The O₂ reactivity of 4 has relevance to the active-site chemistry of Ni^II-containing acireductone dioxygenase (Ni^IIARD).