Reactivities of Metal-oxygen Species Bearing N-methylated Macrocyclic Ligands

Abstract

We have studied comparison of reactivity for metal-oxygen species bearing a common N-methylated macrocyclic ligand. Metal-active oxygen adducts are key intermediates detected in the catalytic cycles of dioxygen activation by metalloenzymes and biomimetic compounds. In the first part, we have reported the structural and spectroscopic characterization and reactivity of mononuclear Mn(III)-peroxo complexes as biomimetic complexes. A number of bis(μ-oxo)Mn(III)_(2) species have also been prepared and investigated as model complexes of photosystem II. However, there have been no studies on direct comparison between the mononuclear Mn(III)-peroxo species and the bis(μ-oxo)Mn(III)_(2) species. We report the differences in the structure and reactivity of the active oxygen complexes (i.e., [Mn^(III)(12-TMC)(O_(2))]^(+) vs [Mn^(III)(12-TMC)(O)]_(2)^(2+); 12-TMC = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) on the basis of the detailed comparison of these systems with the same ligand. In the second part, we compared that an end-on Cr(III)-superoxo species with Cr(IV)-oxo species (i.e., [Cr^(III)(14-TMC)(O_(2))(Cl)]^(+) vs [Cr^(IV)(14-TMC)(O)(Cl)]^(+);14-TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), is capable of activation weak C-H bonds of alkylaromatic hydrocarbons via an H-atom abstraction mechanism. By comparing the second-order rate constants of Cr(III)-superoxo and Cr(IV)-oxo species in the CHD oxidation reaction, the reactivity of the Cr(IV)-oxo species is about 3 times greater than that of the Cr(III)-superoxo species in C-H bond activation reactions.;본 연구에서는 일반적인 거대고리 리간드(macrocyclic ligand)를 가진 철-산소 화합물을 합성하고, 반응성을 비교하였다. 철-활성산소 화합물은 금속효소(metalloenzyme)와 생체모방화합물의 이산화 활성화(dioxygen activation) catalytic cycle에서 중요한 중간체로 알려져 있다. 1장에서는, 생체모방화합물인 단핵(mononuclear) Mn(III)-peroxo 화합물을 구조적, 분광학적 방법을 통해 성질을 규명하고, 반응성에 대해 연구하였다. 또한, bis(μ-oxo)Mn(III)_(2) 화합물은 광화학계(photosystem) II의 모델화합물로 잘 알려져 있다. 그러나, 단핵 Mn(III)-peroxo 화합물과 bis(μ-oxo)Mn(III)_(2) 화합물을 직접적으로 비교한 연구는 없었다. 본 연구에서는 같은 리간드를 가진 활성산소 화합물 (i. e., [Mn^(III)(12-TMC)(O_(2))]^(+) vs [Mn^(III)(12-TMC)(O)]_(2)^(2+))의 구조와 반응성의 차이를 상세하게 비교하였다. 2장에서는, end-on Cr(III)-superoxo 화합물과 Cr(IV)-oxo 화합물이 수소추출 메커니즘(H atom abstraction mechanism)에서 alkylaromatic hydrocarbon의 약한 C-H 결합이 활성화 될 수 있음을 연구하고 비교하였다. CHD 산화반응(oxidation reaction)에서 Cr(III)-superoxo와 Cr(IV)-oxo 화합물의 2차 반응속도 상수(second-order rate constant)를 비교함에 따라, 탄소-수소 활성화 반응(C-H bond activation reaction)에서 Cr(IV)-oxo 화합물의 반응성이 Cr(III)-superoxo 화합물보다 3배 더 큼을 알 수 있다.