Magnetic, spectroscopic, and structural studies of dicobalt hydroxamates and model hydrolases

The cobalt(II) urease model complex [Co-2(mu -OAc)(3)(urea)(tmen)(2)][OTf] (2) prepared from the cobalt model hydrolase [Co-2(mu -H2O)(mu -OAc)(2)(OAc )(2)(tmen)(2)] (1) undergoes facile reaction with acetohydroxamic acid (ARA ) to give the monobridged hydroxamate, complex [Co-2(mu -OAc)(2)(mu -AA)(ur ea)(tmen)(2)][OTf] (3) while 1 gives the dibridged hydroxamate complex [Co- 2(mu -OAc)(mu -AA)(2)(tmen)(2)][OTf] (4). The structures and Co-Co distance s of the hydroxamate derivatives of 1 and 2 are very close to those of thei r nickel analogues and suggest that hydroxamic acids can also inhibit cobal t-based hydrolases as well as inhibiting urease 1 also reacts, with glutaro dihydroxamic acid (gluH(2)A(2)) to eliminate hydroxylamine with formation o f [CO2(mu -OAC)(2){mu -O(N) (OC)2(CH2)(3)}(tmen)(2)][OTf] (5), the structur e 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 dico balt(M) hydroxy complexes (7-9), the first of which [Co-2(mu -OAc)(2)(OAc)( 2) mu -OH)(tmen)(2)][OTf] (7) contains a bridging hydroxyl and the second [ CO2(mu -OAc)(2)(OAc)(mu -OH)(OH)(tmen)(2)][OTf] (8) containing both a bridg ing and terminal hydroxyl, while the third [Co-2(mu -OAc): (OAC)(2)(mu -OM) (2)(tmen)(2)][OTf] (9) contains, two bridging OH groups with mixed-valence Co(II)/(Co(III) intermediates.