Direct
CAr–F arylation is effective and sustainable
for synthesis of polyfluorobiaryls with different degrees of fluorination,
which are important motifs in medical and material chemistry. However,
with no aid of transition metals, the engagement of CAr–F bond activation has proved difficult. Herein, an unprecedented
transition-metal-free strategy is reported for site-selective CAr–F arylation of polyfluoroarenes with simple (het)arenes.
By merging N,N-bis(2,6-diisopropylphenyl)perylene-3,4,9,10-bis(dicarboximide)-catalyzed
electrophotocatalytic reduction and anodic nitroxyl radical oxidation
in an electrophotocatalytic cell, various polyfluoroaromatics (2F–6F
and 8F), especially inactive partially fluorinated aromatics, undergo
sacrificial-reagents-free C–F bond arylation with high regioselectivity,
and the yields are comparable to those for reported transition-metal
catalysis. This atom- and step-economic protocol features a paired
electrocatalysis with organic mediators in both cathodic and anodic
processes. The broad substrate scope and good functional-group compatibility
highlight the merits of this operationally simple strategy. Moreover,
the easy gram-scale synthesis and late-stage functionalization collectively
advocate for the practical value, which would promote the vigorous
development of fluorine chemistry.
This manuscript describes a general method for the intramolecular dehydrative Friedel-Crafts reactions of alcohols catalyzed by Re2O7 in hexafluoroisopropanol (HFIP). Under the optimized condition, -aryl alcohols react in high efficiency...
The nonheme diiron toluene/o-xylene monooxygenase (ToMO) is the most studied toluene monooxygenase that mediates an aromatic hydroxylation reaction. In this work, QM/MM calculations were performed to understand the reaction mechanism. It is revealed that the μ-η 2 :η 2 peroxodiferric species is the reactive intermediate after the binding of the O 2 molecule to the reduced diferrous center. Subsequently, both a stepwise and a concerted mechanism involving the critical OÀ O bond cleavage and CÀ O bond formation were considered. The latter was calculated to be more favorable, suggesting that the formation of a highvalent diferryl Q intermediate is not needed. The isomeric formation of the phenol product was found very facile. The first step was calculated to be rate-limiting, with a barrier of 17.6 kcal/mol for the ortho-hydroxylation.
Isethionate sulfite-lyase (IseG)
is a recently characterized glycyl
radical enzyme (GRE) that catalyzes radical-mediated C–S bond
cleavage of isethionate to produce acetaldehyde and sulfite. Herein,
we use quantum mechanical/molecular mechanical (QM/MM) calculations
to investigate the detailed catalytic reaction mechanism of IseG.
Our calculations indicate that a previously proposed direct 1,2-elimination
mechanism is disfavored. Instead, we suggest a new 1,2-migration mechanism
for this enzymatic reaction: a key stepwise 1,2-SO3
– radical migration occurs after the catalytically active
cysteinyl radical grabs a hydrogen atom from isethionate, followed
by hydrogen atom transfer from cysteine to a 1-hydroxylethane-1-sulfonate
radical intermediate. Finally, the elimination of sulfite from 1-hydroxylethane-1-sulfonate
to result in the final product is likely to occur outside the enzyme.
Glu468 in the active site is found to help orient the substrate rather
than grabbing a proton from the hydroxyl group of the substrate. Our
findings help reveal the mechanisms of radical-mediated C–S
bond cleavage of organosulfonates catalyzed by GREs and expand the
understanding of radical-based enzymatic catalysis.
A diamido-bridged dicobalt complex supported by a diamidonaphthalene ligand, Cp* 2 Co 2 (μ-1,8-C 10 H 8 (NH) 2 ) (1), was synthesized, and the reactivity relevant to redox transformations of the Co 2 N 2 core was investigated. It was found that the Co(II)− Co(II) bond allows for protonation by [HPPh 3 ][BF 4 ] resulting in a bridging hydride, [1H] + , with pK a ∼ 7.6 in CH 2 Cl 2 . The diamidonaphthalene ligand can stabilize the binuclear system in the Co(II)Co(III) mixed-valent state (1 + ), which is capable of binding CO to afford [1-CO] + . Surprisingly, the mixed-valent complex also activates H 2 O to furnish a Co(III)Co(III) hydroxy complex [1-OH] + accompanied by release of H 2 . The hydroxy ligand in [1-OH] + is exchangeable, as demonstrated by 18 O-labeling experiments on [1-OH] + with H 2 18O that led to the heavier isotopolog [1-18 OH] + .
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