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) Å compared to that of 3.5 Å in urease (OAc, CH 3 COO -; tmen, N, N, N ‘, N ‘-tetramethylethylenediamine; OTf, CF 3 SO 3; 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 (OH 2 )(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) Å. 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.