화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.141, No.5, 1867-1870, 2019
Formation of a Reactive, Alkyl Thiolate-Ligated Fe-III-Superoxo Intermediate Derived from Dioxygen
Herein, we describe an alkyl thiolate-ligated iron complex that reacts with dioxygen to form an unprecedented example of an iron superoxo (O-2 center dot(-)) intermediate, [Fe-III((S2N3)-N-Me2(Pr,Pr))(O-2)] (4), which is capable of cleaving strong C-H bonds. A cysteinate-ligated iron superoxo intermediate is proposed to play a key role in the biosynthesis of beta-lactam antibiotics by isopenicillin N-synthase (IPNS). Superoxo 4 converts to a metastable putative Fe(III)-OOH intermediate, at rates that are dependent on the C-H bond strength of the H atom donor, with a kinetic isotope effect (k(H)/k(D) = 4.8) comparable to that of IPNS (k(H)/k(D) = 5.6). The bond dissociation energy of the C-H bonds cleaved by 4 (92 kcal/mol) is comparable to C-H bonds cleaved by IPNS (93 kcal/mol). Both the calculated and experimental electronic absorption spectra of 4 are comparable to those of the putative IPNS superoxo intermediate, and are shown to involve RS- -> Fe-O-2 center dot(-) and O-2 center dot- -> Fe charge transfer transitions. The pi-back-donation by the electron-rich alkyl thiolate presumably facilitates this reactivity by increasing the basicity of the distal oxygen. The frontier orbitals of 4 are shown to consist of two strongly coupled unpaired electrons of opposite spin, one in a superoxo pi*(O-O) orbital, and the other in an Fe(d(xy)) orbital.