PREPARATION OF A SERIES OF (IMIDAZOLE)PENTAAQUACHROMIUM(III) COMPLEXES AND KINETICS OF THEIR REDUCTION BY 1-HYDROXY-1-METHYLETHYL RADICALS

A series of (imidazole) pentaaquachromium(III) complexes, (H2O)5Cr(Im-X,Y)3+ were prepared and characterized in acidic aqueous solution. These complexes are reduced by .C(CH3)2OH radicals with rate constants that vary with substituents on the imidazole ring. At 25-degrees-C the values of the rate constants, k/10(5) L mol-1 s-1 (X, Y), are 1.1 (1-CH3, H), 2.1 (2-CH3, H), 3.8 (4-CH3, H), 6.6 (H, H), 7.2 (4-CH3, 5-CONH2), and 16 (4-Cl, 5-Cl). A mechanism is proposed whereby the initial electron transfer takes place at coordinated imidazole, followed by a rapid intramolecular electron transfer to yield Cr(H2O)6(2+) and X,Y-ImH+.