Mononuclear and dinuclear model hydrolases of nickel and cobalt

Reaction between the dinuclear model hydrolases [M2(μ-OAc)2(OAc)2(μ-H2O)(tmen)2]; M = Ni (1); M = Co (2) and trimethylsilyltrifluoromethanesulphonate (TMS-OTf) under identical reaction conditions gives the mononuclear complex [Ni(OAc)(H2O)2(tmen)][OTf] · H2O (3) in the case of nickel and the dinuclear complex [Co2(μ-OAc)2(μ-H2O)2(tmen)2][OTf]2 (4) in the case of cobalt. Reaction of (3) with urea gives the previously reported [Ni(OAc)(urea)2(tmen)][OTf] (5), whereas (4) gives [Co2(OAc)3(urea)(tmen)2][OTf] (6) previously obtained by direct reaction of (2) with urea. Both (3) and (4) react with monohydroxamic acids (RHA) to give the dihydroxamate bridged dinuclear complexes [M2(μ-OAc)(μ-RA)2(tmen)2][OTf]; M = Ni (7); M = Co (8) previously obtained by the reaction of (1) and (2) with RHA, illustrating the greater ability of hydroxamic acids to stabilize dinuclear complexes over that of urea by means of their bridging mode, and offering a possible explanation for the inhibiting effect of hydroxamic acids by means of their displacing bridging urea in a possible intermediate invoked in the action of urease.