Sulfur versus Iron Oxidation in an Iron−Thiolate Model Complex

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• 作者：Aidan R. McDonald ; Michael R. Bukowski ; Erik R. Farquhar ; Timothy A. Jackson ; Kevin D. Koehntop ; Mi Sook Seo ; Raymond F. De Hont ; Audria Stubna ; Jason A. Halfen ; Eckard Mnck ; Wonwoo Nam ; Lawrence Que
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：December 8, 2010
• 年：2010
• 卷：132
• 期：48
• 页码：17118-17129
• 全文大小：369K
• 年卷期：v.132,no.48(December 8, 2010)
• ISSN：1520-5126

文摘

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^tBu). 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 Mssbauer 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. Mssbauer 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.