Department of Chemistry, Tufts University, Medford, MA, USA.
Dalton Trans. 2013 Apr 7;42(13):4427-35. doi: 10.1039/c2dt32599c.
Two intermediates (2 and 3) are formed consecutively in the reaction of a diiron(III) complex Fe(III)(2)(μ-O)(OH)(H(2)O)(TPA)(2)(3) (TPA = tris(2-pyridylmethyl)amine, tris(picolyl)amine) with H(2)O(2) in CH(3)CN at -40 °C. Low-temperature stopped-flow studies showed that both species are kinetically competent in oxidation of phosphines and phenols. The first intermediate (2) reacts with substrates very rapidly (second-order rate constants reach 10(5)-10(6) M(-1) s(-1) for substituted triarylphosphines and 10(3)-10(5) M(-1) s(-1) for substituted phenols), in keeping with a diiron(IV)-oxo formulation. The second intermediate (3), a mixed-valent Fe(III)Fe(IV) species, is more stable than 2, and reacts with substrates more slowly (second-order rate constants range from 150 to 550 M(-1) s(-1) for triaryl phosphine oxidation, and from 18 to 790 M(-1) s(-1) for phenol oxidation). Reaction rates increase with increasing electron donating abilities of substituents, indicating that both 2 and 3 act as electrophilic oxidants.
在 -40°C 的 CH₃CN 中，二价铁(III)配合物Fe(III)(2)(μ-O)(OH)(H₂O)(TPA)(2)(3) (TPA = 三(2-吡啶基甲基)胺，三(吡啶基甲基)胺)与 H₂O₂反应时，连续形成两种中间体(2 和 3)。低温停流研究表明，这两种物质在氧化膦和酚类物质方面都具有动力学活性。第一个中间体(2)与底物反应非常迅速(取代三芳基膦的二级速率常数达到 10(5)-10(6) M(-1) s(-1)，取代酚的二级速率常数达到 10(3)-10(5) M(-1) s(-1) )，符合二价铁(IV)-氧的结构。第二个中间体(3)，一种混合价态的 Fe(III)Fe(IV)物种，比 2 更稳定，与底物反应更慢(取代三芳基膦氧化的二级速率常数范围为 150-550 M(-1) s(-1)，取代酚氧化的二级速率常数范围为 18-790 M(-1) s(-1))。反应速率随取代基供电子能力的增加而增加，表明 2 和 3 都作为亲电氧化剂起作用。
