Spectroscopic Characterization and Reactivity Studies of a Mononuclear Non-Heme Fe(III)−Hydroperoxo Complex

Abstract

Mononuclear iron(III)-peroxo and -hydroperoxo complexes bearing a 13-TMC ligand (13-TMC = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclotridecane), [(13-TMC)FeIII(O2)]+ and [(13-TMC)FeIII(O2H)]2+, were generated and characterized by various spectroscopic techniques. The reactivity of [(13-TMC)FeIII(O2H)]2+ complex was investigated in the oxidation of naphthalene derivatives as well as hydrogen atom transfer(HAT) and oxygen atom transfer (OAT) reactions. We found that iron(III)-hydroperoxo intermediate is highly reactive oxidant capable of oxidizing naphthalene derivatives and activating strong C-H bonds of alkanes such as cyclohexane and cyclooctane. Then, the ring size effect of macrocyclic TMC ligands in nonheme iron(III)-hydroperoxo complexes has been examined in naphthalene oxidation and HAT and OAT reactions : [(13-TMC)FeIII(O2H)]2+ is strong oxidant capable of hydroxylating naphthalene to afford 1,4-naphthoquinone, whereas no reaction between [(14-TMC)FeIII(O2H)]2+ (14-TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and naphthalene occurred. The reactivity of [(13-TMC)FeIII(O2H)]2+ is also much greater than that of [(14-TMC)FeIII(O2H)]2+ in HAT and OAT reactions, indicating that an iron(III)-hydroperoxo complex bearing a smaller TMC ligand is more reactive species. To the best of our knowledge, the present study reports the first example of the ring size effect of macrocyclic ligands in nonheme iron(III)-hydroperoxo complexes.;본 연구에서는 13-TMC 리간드를 가진 단핵 철-퍼옥소, 하이드로퍼옥소 종들을 합성하고 분광학적 방법으로 특성화하였다. 철-하이드로퍼옥소 종의 나프탈렌 산화 반응, 수소 원자 전달, 산소 원자 전달 등 다양한 반응성을 보았을 때, 높은 산화 퍼텐셜을 가진 나프탈렌을 산화시키고 알케인의 강한 탄소-수소 결합을 활성화 시킬 수 있는 강한 산화제임을 알 수 있었다. [(13-TMC)FeIII(O2H)]2+가 나프탈렌 산화 반응, 수소 원자 전달, 산소 원자 전달 반응에서 [(14-TMC)FeIII(O2H)]2+ 보다 훨씬 큰 반응성을 보였고, 따라서 더 작은 크기의 TMC 리간드를 가진 철-하이드로퍼옥소 종이 더 반응성이 좋다는 것을 알 수 있었다.