Hydroxamate-bridged dinuclear nickel complexes as models for urease inhibition

Facile reaction of the model urease complex [Ni-2(OAc)(3)(urea)(tmen)(2)] [OTf] (A) with acetohydroxamic acid (AHA) gives the monobridged hydroxamate complex (I) [Ni-2(OAc)(2)(AA)(urea)(tmen)(2)] [OTf] with a Ni-Ni distance of 3.434(1) Angstrom compared to that of 3.5 Angstrom in urease (OAc, CH3COO-; tmen, N,N,N',N'-tetramethylethylenediamine; OTf, CF3SO3; AHA, acetohydroxamic acid; AA, acetohydroxamate anion). I is a close model of one proposed mode of urease inhibition by hydroxamic acids, recently observed in the acetohydroxamate-inhibited C319A variant of Klebsiella aerogenes urease. Reaction of [Ni-2(OH2) (OAc)(4)(tmen)(2)] (B) with AHA gives the dibridged hydroxamate complex (II) [Ni-2(OAc)(AA)(2)(tmen)(2)] [OAc] with a Ni-Ni distance of 3.005(1) Angstrom. Infrared spectroscopic studies provide evidence for the bridging acetate groups undergoing carboxylate shifts thereby assisting replacement of acetate by hydroxamate. Both I and II show ferromagnetic exchange coupling.