Seeing the cis-Dihydroxylating Intermediate: A Mononuclear Nonheme Iron-Peroxo Complex in cis-Dihydroxylation Reactions Modeling Rieske Dioxygenases

Abstract

The nature of reactive intermediates and the mechanism of the cis-dihydroxylation of arenes and olefins by Rieske dioxygenases and synthetic nonheme iron catalysts have been the topic of intense research over the past several decades. In this study, we report that a spectroscopically well characterized mononuclear nonheme iron(III)-peroxo complex reacts with olefins and naphthalene derivatives, yielding iron(III) cycloadducts that are isolated and characterized structurally and spectroscopically. Kinetics and product analysis reveal that the nonheme iron(III)-peroxo complex is a nucleophile that reacts with olefins and naphthalenes to yield cis-diol products. The present study reports the first example of the cis-dihydroxylation of substrates by a nonheme iron(III)-peroxo complex that yields cis-diol products.

Finding a mononuclear cobalt(iii)-peroxo complex with 1,4,7,10-tetraazacyclododecane, an intermediate for dioxygen reduction

“…This loss of reversibility and increase in current suggests that O 2 binds to the cobalt complex. 11,12…”

“…The values of 16 Δ– 18 Δ of 44.3546 cm −1 are like those predicted by Hooke's law calculations for the O–O vibrations ( 16 Δ– 18 Δ O–O (calcd) = 48.6552 cm −1 ). 12…”

“…These spur efforts to develop catalysts based on earth abundant transition metals such as cobalt and iron. [7][8][9][10][11][12] In Nature, cytochrome c oxidase (CcO) can efficiently catalyze the reduction of O 2 to H 2 O under mild conditions; 13 however, the stability is often limited outside of their native environment, because this reduction reaction takes place without releasing toxic partially reduced oxygen species. 14,15 To obtain a clear approach for the design of catalysts for O 2 reduction, many works were focused on the research of the catalytic oxygen reduction mechanism.…”

Dearomative syn-Dihydroxylation of Naphthalenes with a Biomimetic Iron Catalyst

“…It is known that iron catalysts can syn-dihydroxylate olefins through two different mechanisms (Figure 5a). 31,32,61,62 Class A catalysts contain strong field N-rich tetradentate ligands (L N4 ) and form [L N4 Fe V (O)(OH)] 2+ species III a oxo (where subindex a refers to class A catalyst) that syn-dihydroxylate olefins via a 3 + 2 mechanism (formal cycloaddition between the Fe V (O)(OH) and the olefin).…”

Mononuclear Non-Heme Manganese-Catalyzed Enantioselective cis-Dihydroxylation of Alkenes Modeling Rieske Dioxygenases

“…Excellent examples are naturally occurring Rieske dioxygenases that can perform the enantioselective cis -dihydroxylation of arenes with molecular oxygen (O 2 ) activation, in which both O-atoms of O 2 are incorporated into arenes (or olefins) to produce cis -diol products (Figure A). − Moreover, iron–oxygen species, such as iron­(V)-oxo-hydroxo (HO–Fe V O), iron­(IV)-dihydroxo, iron­(III)-superoxo, and iron­(III)-hydroperoxo, have been invoked as the active oxidant(s) in cis -dihydroxylation of olefinic double bonds by Rieske dioxygenases and non-heme iron model catalysts (Figure A). − Inspired by the structural mononuclear non-heme ferrous center and the mechanistic principles that underlie their function as catalysts for aerobic cis -dihydroxylation of aromatic and olefinic CC double bonds with exquisite stereo- and enantioselectivities, much effort has been devoted to the development of non-heme iron and manganese catalysts that mimic the reactivity of Rieske dioxygenases. − In this regard, Que and co-workers reported the first example of asymmetric cis -dihydroxylation by non-heme iron complexes in the presence of large excess of olefins (e.g., cat/H 2 O 2 /substrate = 1:20:1000), and the enantiomeric excess (ee) of cis -diols was improved from 82 to 97% upon replacement of the trans -1,2-diaminocyclohexane backbone with a more rigid bipyrrolidine; this pioneering work provides a starting point for the development of synthetic cis -dihydroxylation catalysts as functional mimics of Rieske dioxygenases, although the use of large excess of olefins relative to the oxidant is required to obtain satisfied turnover numbers and high product ratios of cis -dihydroxylation to epoxidation . Only recently have non-heme iron complexes supported by tetradentate aminoquinoline ligands been demonstrated to engender highly enantioselective cis -dihydroxylation under substrate-limiting conditions by Che, Wang, and their co-workers (Figure B) …”