A disubstituted benzoate polydentate ligand, 2,6-bis[bis(pyridinyl-2- methyl)aminoethoxyl]benzoate (HL), was prepared to synthesize nickel mimics for the active site of urease. Reaction of the deprotonated L- with Ni(ClO4)2 · 6H2O afforded a dinickel complex, [LNi2(CH3CN)(THF)](ClO4)3 (1), characterized by UV/vis spectroscopy and X-ray crystallography. Addition of urea to an acetonitrile solution of 1 afforded a dinickel urea adduct, [LNi2(urea)2](ClO4)3 · 2CH3CN (2), which was structurally and spectroscopically characterized. 1H NMR and ESI-MS spectra of 2 both evidenced that urea molecules remained coordinated to the nickel centers of 2 in solution. With the inspiration of urea coordination to the nickel centers of 1, the conjugate additions of thiophenols to α,β-enones catalyzed by complex 1 were examined and found to proceed in good yields. In contrast, the same catalytic reaction by Ni(ClO4)2 · 6H2O and HL was far less effective. Also, addition of NaOAc or NaOAcPh2 to an acetonitrile solution of 1 gave tetranuclear nickel complexes, [LNi 2-(μ-OAc)]2(ClO4)4 · 3H2O (3) and [LNi2(μ-OAcPh2)] 2(ClO4)4 · 5CH3CN · 2THF (4), and their molecular structures determined by X-ray diffraction can be described as dimers of dimers. Each dinickel core of 3 and 4 closely mimics the active site of urease. The magnetic data of 1, 3, and 4 exhibited a very weak antiferromagnetic coupling (J =-0.72 cm-1 for 1,-0.65 cm-1 for 3 and 4) between two metal centers in the dinickel core.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry