Kinetics and mechanisms of the reduction of µ-amido-µ-superoxo- and µ-amido-µ-peroxo-bis[bis(ethylenediamine)cobalt(III)] complexes by sulphite, nitrite, and arsenite in aqueous solutions: evidence for bonded and non-bonded activated complexes in the reduction of dioxygen-bridged complexes

Abstract

The p-amido-y-superoxo-complex (en),Co.p( NH,,O,) ~Co(en),~+ and the p-amido-p-peroxo-complex (en),Co.p( NH,.O,) .C~(en),~+ both react with sulphite ions to give the p-amido-p-sulphato-complex (en),Co*p(NH,,SO,)*-C ~( e n ) , ~+ . The p-amido-p-superoxo-reaction proceeds with the intermediate formation of the p-amido-p-peroxocomplex and the sulphite radical. Stoicheiometries a t pH 1-3 are (complex :sulphite) 2 : 3 for the superoxo-and 1 : 1 for the peroxo-complex, and rate laws are of the form k,[superoxo] [SO3,-] and k,[peroxo] [H,S03] respectively, where k, = 3.80(&0.07) x l o 4 I mol-l s-1 and kD = 55.4(*6.1) I mol-l s-l, both at 1 -4 "C and / = 1 .OM ( LiC104). The protonated p-peroxo-complex may be the reactive species in the latter, in which case the rate law can be expressed in an alternative form. The complexes also react with nitrite ions to give the p-amido-p-nitritocomplex (en),C0~p(NH,,N0,)*Co(en),~~. With arsenite ions a different reaction path is operative, and the product is the p-amido-p-hydroxo-complex, (en),Co.( NH,,OH) ~Co(en),~+.. Chemistry, The University, Leeds LS2 9JT REACTIONS of molecular oxygen bonded to metals are of the p-amido-p-peroxo-and p-amido-p-superoxoimportant processes in the chemistry of living organisms dicobalt (1x1) complexes with sulphite, nitrite, and and any insight into the mechanism of the stepwise arsenite ions respectively, and consider different mechanreduction of oxygen (02+ O,-+ OZ2-, etc.) is isms which are apparent. One unprotonated and highly relevant. We report in this study the reactions two singly protonated forms of the p-peroxo-complex [4/009 Received, 3vd Januavy, 19741 l9 A. I. Vogel, ' Quantitative Inorganic Analysis,' Longmans, London. 1960.

Kinetics and Mechanism of Oxidation of S2O32− by a Co‐Bound μ‐Amido‐μ‐Superoxo Complex

“…The assumption behind the formation of complex 3 is supported by the fact that when S 2 O 3 2− reacts with the similar Co‐bound peroxo complex or SO 3 2− reacts with Co‐bound superoxo complex , corresponding μ‐thiosulfato and μ‐sulfato complexes are produced. Crystal structures of μ‐thiosulfato complex also reveals that two of the cobalt ions are bridged by the sulfur atom of the thiosulfato group.…”

“…The results of the kinetic analyses suggest that though the title reaction involves only the oxidant, the μ‐superoxo complex, [(NH 3 ) 4 Co III (μ‐NH 2 ,μ‐O 2 )Co III (NH 3 ) 4 ] 4+ ( 1 ), and the reductant, S 2 O 3 2− , the reaction proceeds through a biphasic consecutive reaction path. The reductant, S 2 O 3 2− is an one‐electron donor and thus it reduces complex 1 to its corresponding peroxo complex, [(NH 3 ) 4 Co III (μ‐NH 2 ,μ‐O 2 )Co III (NH 3 ) 4 ] 3+ ( 2 ) , which in acid media fast isomerizes to the corresponding hydroperoxo complex [(NH 3 ) 4 Co III (μ‐NH 2 ,μ‐HO 2 )Co III (NH 3 ) 4 ] 4+ ( 5 ). Now the formation of the precipitate indicates that along with reduction, S 2 O 3 2− simultaneously substitutes the bridging NH 2 group to produce the intermediate complex, [(NH 3 ) 4 Co III (μ‐S 2 O 3 ,μ‐O 2 )Co III (NH 3 ) 4 ] 3+ ( 3 ).…”