| Autor: |
Zhu W; Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea., Wu P; State Key Laboratory of High-Efficiency Utilization of Coal and Green Chemical Engineering, School of Chemistry and Chemical Engineering, Ningxia University, Yinchuan 750021, P. R. China., Larson VA; Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States., Kumar A; Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea., Li XX; Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea.; Institute of Molecular Sciences and Engineering, Institute of Frontier and Interdisciplinary Science, Shandong University, Qingdao 266237, P. R. China., Seo MS; Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea., Lee YM; Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea., Wang B; Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P. R. China., Lehnert N; Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States., Nam W; Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea.; College of Chemistry and Chemical Engineering, Yan'an University, Yan'an, Shaanxi Province 716000, P. R. China. |
| Abstrakt: |
We report the macrocyclic ring size-electronic structure-electrophilic reactivity correlation of mononuclear nonheme iron(III)-peroxo complexes bearing N -tetramethylated cyclam analogues ( n -TMC), [Fe III (O 2 )(12-TMC)] + ( 1 ), [Fe III (O 2 )(13-TMC)] + ( 2 ), and [Fe III (O 2 )(14-TMC)] + ( 3 ), as a model study of Rieske oxygenases. The Fe(III)-peroxo complexes show the same δ and pseudo-σ bonds between iron and the peroxo ligand. However, the strength of these interactions varies depending on the ring size of the n -TMC ligands; the overall Fe-O bond strength and the strength of the Fe-O 2 δ bond increase gradually as the ring size of the n -TMC ligands becomes smaller, such as from 14-TMC to 13-TMC to 12-TMC. MCD spectroscopy plays a key role in assigning the characteristic low-energy δ → δ* LMCT band, which provides direct insight into the strength of the Fe-O 2 δ bond and which, in turn, is correlated with the superoxo character of the iron-peroxo group. In oxidation reactions, reactivities of 1 - 3 toward hydrocarbon C-H bond activation are compared, revealing the reactivity order of 1 > 2 > 3 ; the [Fe III (O 2 )( n -TMC)] + complex with a smaller n -TMC ring size, 12-TMC, is much more reactive than that with a larger n -TMC ring size, 14-TMC. DFT analysis shows that the Fe(III)-peroxo complex is not reactive toward C-H bonds, but it is the end-on Fe(II)-superoxo valence tautomer that is responsible for the observed reactivity. The hydrogen atom abstraction (HAA) reactivity of these intermediates is correlated with the overall donicity of the n -TMC ligand, which modulates the energy of the singly occupied π* superoxo frontier orbital that serves as the electron acceptor in the HAA reaction. The implications of these results for the mechanism of Rieske oxygenases are further discussed. |
