Yang Zhiyong, Gould Edwin S
Department of Chemistry, Kent State University, Kent, OH 44242, USA.
Dalton Trans. 2005 May 21(10):1781-4. doi: 10.1039/b416975c. Epub 2005 Apr 18.
Solutions of titanium(II), prepared by dissolving titanium wire in mixtures of hydrofluoric and triflic acids, reduce quinones, nitrosodisulfonate anion, and complexes of cobalt(III). When the oxidant is taken in excess, these reactions yield Ti(IV), whereas with excess reductant, the principal product is Ti(III). These reactions are compared with those by Ti(III). Despite differences in rate laws, it is clear that rate ratios for the two reductants (kTiII/kTiIII) fall well below 10(4), the minimum selectivity corresponding to estimated differences in formal potentials, and in some instances, Ti(II), the stronger reductant, reacts more slowly. For both Ti(III) and Ti(II), reductions within the series [Co(NH3)5X]2+(where X=F, Cl, Br, and I), the fluoro complex reacts much more rapidly than its congeners, and the bromo and iodo complexes are slowest, an order similar to that for Eu2+ reductions, but opposite to that for Cr(II) and Cu(I). The [Co(NH3)5Br]2+ reaction with excess Ti(II) proceeds at rates very nearly independent of [oxidant] during the first 80-90% reaction, implying that initiation occurs via unimolecular conversion of Ti(II) to an activated cationic reducing species, in the same manner as the earlier described reduction of I3- by Ge(II) in aqueous HCl.
通过将钛丝溶解在氢氟酸和三氟甲磺酸的混合物中制备的钛（II）溶液，能还原醌、亚硝基二磺酸盐阴离子和钴（III）配合物。当氧化剂过量时，这些反应生成Ti（IV），而当还原剂过量时，主要产物是Ti（III）。将这些反应与Ti（III）的反应进行了比较。尽管速率定律存在差异，但很明显，两种还原剂的速率比（kTiII/kTiIII）远低于10^4，这是与形式电位估计差异相对应的最小选择性，而且在某些情况下，较强的还原剂Ti（II）反应更慢。对于Ti（III）和Ti（II），在[Co(NH3)5X]2+系列（其中X = F、Cl、Br和I）内的还原反应中，氟配合物的反应速度比其同系物快得多，溴和碘配合物最慢，这一顺序与Eu2+还原反应的顺序相似，但与Cr（II）和Cu（I）的顺序相反。在最初80 - 90%的反应过程中，[Co(NH3)5Br]2+与过量Ti（II）的反应速率几乎与[氧化剂]无关，这意味着引发是通过Ti（II）单分子转化为活化的阳离子还原物种发生的，与之前描述的Ge（II）在盐酸水溶液中还原I3-的方式相同。
