REACTIONS OF COORDINATED IMIDAZOLE - OXIDATION-PRODUCTS AND RING CLEAVAGE IN THE REACTIONS OF (NH3)5COIMH3+ WITH CH3COOBR AND HOBR

Treatment of RImH3+ (R = (NH3)5Co, ImH = imidazole) with aqueous Br2 in acetate (or phosphate) buffer at pH 4-6 results in R(parabanate)2+ (2) as the only product (parabanic acid = imidazolidine-2,4,5-trione). A crystal structure of [R(parabanate)]Cl2.3H2O (orthohombic, P2(1)2(1)2(1); a = 6.936 (1), b = 11.032 (3), c = 19.652 (3) angstrom; Z = 4; R = 0.0491, 1301 reflections) is reported. Formation of 2 appears to occur via initial reaction with Br2(aq) to give R4,5-Br2ImH3+ and R2,4,5-Br3Im2+ (1), followed by further bromination at C-2 by AcOBr to give a tetrabromo species (4), which rapidly hydrolyses. The same product results from oxidation by Cl2(aq) in the absence of acetate buffer. Treatment of RImH3+ with HOBr in aqueous solution results in three main products. These were identified as R(C2N2H3O2)2+ (7) containing (probably) the N-coordinated conjugate base of dioxamide, RN(CHO)2(2+) (11) containing the N-coordinated conjugate base of diformamide, and R(C3N2O3H3)2+ (12) containing N-coordinated 2-hydroxyimidazolidine-4,5-dione. A crystal structure of [R(2-hydroxyimidazolidine-4,5-dione)](CF3SO3)2 (monoclinic, C2/m; a = 32.325 (20), b = 8.037 (4), c = 7.195 (5) angstrom; beta = 91.92 (5)-degrees; Z = 4; R = 0.0951, 1348 reflections) is reported.