Department of Chemistry and Center for Metals in Biocatalysis, 207 Pleasant Street SE, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Am Chem Soc. 2010 Dec 8;132(48):17118-29. doi: 10.1021/ja1045428. Epub 2010 Nov 11.
In the absence of base, the reaction of [Fe(II)(TMCS)]PF6 (1, TMCS = 1-(2-mercaptoethyl)-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) with peracid in methanol at -20 °C did not yield the oxoiron(IV) complex (2, [Fe(IV)(O)(TMCS)]PF6), as previously observed in the presence of strong base (KO(t)Bu). Instead, the addition of 1 equiv of peracid resulted in 50% consumption of 1. The addition of a second equivalent of peracid resulted in the complete consumption of 1 and the formation of a new species 3, as monitored by UV-vis, ESI-MS, and Mössbauer spectroscopies. ESI-MS showed 3 to be formulated as Fe(II)(TMCS) + 2O, while EXAFS analysis suggested that 3 was an O-bound iron(II)-sulfinate complex (Fe-O = 1.95 Å, Fe-S = 3.26 Å). The addition of a third equivalent of peracid resulted in the formation of yet another compound, 4, which showed electronic absorption properties typical of an oxoiron(IV) species. Mössbauer spectroscopy confirmed 4 to be a novel iron(IV) compound, different from 2, and EXAFS (Fe═O = 1.64 Å) and resonance Raman (ν(Fe═O) = 831 cm(-1)) showed that indeed an oxoiron(IV) unit had been generated in 4. Furthermore, both infrared and Raman spectroscopy gave indications that 4 contains a metal-bound sulfinate moiety (ν(s)(SO2) ≈ 1000 cm (-1), ν(as)(SO2) ≈ 1150 cm (-1)). Investigations into the reactivity of 1 and 2 toward H(+) and oxygen atom transfer reagents have led to a mechanism for sulfur oxidation in which 2 could form even in the absence of base but is rapidly protonated to yield an oxoiron(IV) species with an uncoordinated thiol moiety that acts as both oxidant and substrate in the conversion of 2 to 3.
在缺乏碱的情况下，[Fe(II)(TMCS)]PF6（1，TMCS = 1-(2-巯基乙基)-4,8,11-三甲基-1,4,8,11-四氮杂环十四烷）与过酸在甲醇中的反应在-20°C 下并未生成先前在强碱（KO(t)Bu）存在下观察到的氧代铁(IV)配合物（2，[Fe(IV)(O)(TMCS)]PF6）。相反，加入 1 当量的过酸会导致 1 的 50%消耗。加入第二当量的过酸会导致 1 的完全消耗，并通过紫外-可见、ESI-MS 和穆斯堡尔光谱监测到形成新物种 3。ESI-MS 表明 3 的化学式为Fe(II)(TMCS) + 2O，而 EXAFS 分析表明 3 是一个氧结合的铁(II)-亚磺酸盐配合物（Fe-O = 1.95 Å，Fe-S = 3.26 Å）。加入第三当量的过酸会导致另一种化合物 4 的形成，4 显示出典型的氧代铁(IV)物种的电子吸收性质。穆斯堡尔光谱证实 4 是一种新型的铁(IV)化合物，与 2 不同，EXAFS（Fe═O = 1.64 Å）和共振拉曼（ν(Fe═O) = 831 cm(-1))表明 4 中确实生成了一个氧代铁(IV)单元。此外，红外和拉曼光谱都表明 4 含有一个金属结合的亚磺酸盐部分（ν(s)(SO2) ≈ 1000 cm(-1)，ν(as)(SO2) ≈ 1150 cm(-1)）。对 1 和 2 对 H(+)和氧原子转移试剂的反应性的研究导致了一种硫氧化机制，其中 2 甚至在缺乏碱的情况下也可以形成，但会迅速质子化生成一个具有未配位巯基部分的氧代铁(IV)物种，该巯基部分既是氧化剂又是底物，将 2 转化为 3。
