Magnetic, Spectroscopic, and Structural Studies of Dicobalt Hydroxamates and Model Hydrolases^‖

The cobalt(II) urease model complex [Co2(μ-OAc)3(urea)(tmen)2][OTf] (2) prepared from the cobalt model hydrolase [Co2(μ-H2O)(μ-OAc)2(OAc)2(tmen)2] (1) undergoes facile reaction with acetohydroxamic acid (AHA) to give the monobridged hydroxamate complex [Co2(μ-OAc)2(μ-AA)(urea)(tmen)2][OTf] (3) while 1 gives the dibridged hydroxamate complex [Co2(μ-OAc)(μ-AA)2(tmen)2][OTf] (4). The structures and Co−Co distances of the hydroxamate derivatives of 1 and 2 are very close to those of their nickel analogues and suggest that hydroxamic acids can also inhibit cobalt-based hydrolases as well as inhibiting urease. 1 also reacts with glutarodihydroxamic acid (gluH2A2) to eliminate hydroxylamine with formation of [Co2(μ-OAc)2{μ-O(N) (OC)2(CH2)3}(tmen)2][OTf] (5), the structure of which is very close to that of its nickel analogue. Both 1 and 3 show weak antiferromagnetic coupling. Oxidation of 1 with H2O2 gives three dicobalt(III) hydroxy complexes (7−9), the first of which [Co2(μ-OAc)2(OAc)2(μ-OH)(tmen)2][OTf] (7) contains a bridging hydroxyl and the second [Co2(μ-OAc)2(OAc)(μ-OH)(OH)(tmen)2][OTf] (8) containing both a bridging and terminal hydroxyl, while the third [Co2(μ-OAc) (OAc)2(μ-OH)2(tmen)2][OTf] (9) contains two bridging OH groups with mixed-valence Co(II)/(Co(III) intermediates.