Department of Chemistry, Jadavpur University, Kolkata, India.
Dalton Trans. 2012 Mar 7;41(9):2714-9. doi: 10.1039/c2dt12019d. Epub 2012 Jan 13.
The metal bound superoxide in μ-superoxo-bispentaamminecobalt(III) (1) oxidizes the nitrosodisulfonate anion radical (NDS(2-)) by two electrons. Oxidized NDS(2-) quickly decomposes to SO(4)(2-) and NO. 1 is itself reduced to the corresponding hydroperoxo complex which also decomposes fast to Co(ii), NH(4)(+) ions and oxygen. 1.5 moles of volatile products formed per mole of 1 mixed with excess NDS(2-). In the absence of superoxide in a bridged complex, e.g. the μ-amido-bispentaamminecobalt(III) complex fails to oxidize the nitroxyl radicals, NDS(2-), TEMPO and 4-oxo TEMPO. With excess NDS(2-) over 1, the reaction is first-order with respect to [1], [NDS(2-)] and inverse first order in [H(+)]. The activation entropy, ΔS(≠), is largely negative, increased ionic strength decreased the rate and a Brønsted plot is fairly linear with a negative slope. Oxidant μ-superoxo-bis(ethylenediamine)(diethylenetriamine)cobalt(III) has ligands sterically more crowded though more basic than ammonia in 1. It oxidizes NDS(2-) much more slowly. No solvent kinetic isotope effect (k(H(2)O/D(2)O)≈ 1) could be seen; a spin-adduct formation by the conjugate base of 1 followed by electron transfer is postulated.
μ-超氧双[五氨合钴(III)]（1）中的金属结合的超氧离子将硝酰二磺酸盐阴离子自由基（NDS（2-））氧化两个电子。氧化后的 NDS（2-）迅速分解为 SO4（2-）和 NO。1 本身被还原为相应的过氧配合物，该配合物也迅速分解为 Co（ii）、NH4（+）离子和氧气。1 与过量的 NDS（2-）混合时，每摩尔 1 形成 1.5 摩尔的挥发性产物。在桥联配合物中没有超氧离子的情况下，例如 μ-酰胺双[五氨合钴(III)]（5+）配合物无法氧化氮氧自由基、NDS（2-）、TEMPO 和 4-氧 TEMPO。当 1 过量时，反应对[1]、[NDS（2-）]和[H+]呈一级反应，对[H+]呈负一级反应。活化熵，ΔS（≠），主要为负，离子强度增加会降低反应速率，而 Brønsted 图则相当线性，斜率为负。尽管在 1 中，氧化剂μ-超氧双[（乙二胺）（二乙三胺）钴(III)]（5+）的配体空间位阻更大，但碱性比氨更强。它氧化 NDS（2-）的速度要慢得多。没有观察到溶剂动力学同位素效应（k（H2O/D2O）≈1）；推测 1 的共轭碱通过自旋加合物形成，然后进行电子转移。
