A tale of two topological isomers: Uptuning [FeIV(O)(Me4cyclam)]2+for olefin epoxidation

• 成果类型: Article
• 署名作者: Chandra, Bittu; Ahsan, Faiza; Sheng, Yuan; Swart, Marcel; Que Jr, Lawrence
• 署名单位: University of Minnesota System; University of Minnesota Twin Cities; Universitat de Girona; Universitat de Girona; ICREA
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-14695
• DOI: 10.1073/pnas.2319799121
• 发表日期: 2024-03-19
• 关键词: spectroscopic characterization; iron(iv)-oxo complex; oxoiron(iv) complex; 2-state reactivity; nonheme; ligand; hydroxylation; oxidation; energy; abstraction

摘要

TMC-anti and TMC-syn, the two topological isomers of [FeIV(O)(TMC)(CH3CN)]2+ (TMC = 1,4,8,11- tetramethyl- 1,4,8,11- tetraazacyclotetradecane, or Me4cyclam), differ in the orientations of their FeIV=O units relative to the four methyl groups of the TMC ligand framework. The FeIV=O unit of TMC-anti points away from the four methyl groups, while that of TMC-syn is surrounded by the methyl groups, resulting in differences in their oxidative reactivities. TMC-syn reacts with HAT (hydrogen atom transfer) substrates at 1.3- to 3-fold faster rates than TMC-anti, but the reactivity difference increases dramatically in oxygen-atom transfer reactions. R2S substrates are oxidized into R2S=O products at rates 2-to-3 orders of magnitude faster by TMC-syn than TMC-anti. Even more remarkably, TMC-syn epoxidizes all the olefin substrates in this study, while TMC-anti reacts only with cis- cyclooctene but at a 100-fold slower rate. Comprehensive quantum chemical calculations have uncovered the key factors governing such reactivity differences found between these two topological isomers.