scholarly journals Concerted proton-electron transfer oxidation of phenols and hydrocarbons by a high-valent nickel complex

2020 ◽  
Vol 11 (6) ◽  
pp. 1683-1690 ◽  
Author(s):  
Katherine J. Fisher ◽  
Margalit L. Feuer ◽  
Hannah M. C. Lant ◽  
Brandon Q. Mercado ◽  
Robert H. Crabtree ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Thermodynamic Analysis ◽  
Nickel Complex ◽  
High Reactivity ◽  
Oxidizing Power ◽  
Oxidation Of Phenols ◽  
High Valent

A high-valent nickel(III) compound performs fast concerted proton–electron transfer on O–H and C–H bonds. Thermodynamic analysis suggests that the oxidizing power of the compound and the formation of a strong ligand O–H bond lead to high reactivity.

scholarly journals Mechanism and Chemoselectivity of Mn-Catalyzed Intramolecular Nitrene Transfer Reaction: C–H Amination vs. C=C Aziridination

Catalysts ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 292
Author(s):  
Juping Wang ◽  
Kangcheng Zheng ◽  
Ting Li ◽  
Xiaojing Zhan
Keyword(s):  
Density Functional ◽  
Structural Features ◽  
High Reactivity ◽  
Strong Electron ◽  
Functional Theory ◽  
Design Elements ◽  
Nitrene Transfer ◽  
Electrophilic Reactivity ◽  
High Valent ◽  
Orbital Character

The reactivity, mechanism and chemoselectivity of the Mn-catalyzed intramolecular C–H amination versus C=C aziridination of allylic substrate cis-4-hexenylsulfamate are investigated by BP86 density functional theory computations. Emphasis is placed on the origins of high reactivity and high chemoselectivity of Mn catalysis. The N p orbital character of frontier orbitals, a strong electron-withdrawing porphyrazine ligand and a poor π backbonding of high-valent MnIII metal to N atom lead to high electrophilic reactivity of Mn-nitrene. The calculated energy barrier of C–H amination is 9.9 kcal/mol lower than that of C=C aziridination, which indicates that Mn-based catalysis has an excellent level of chemoselectivity towards C–H amination, well consistent with the experimental the product ratio of amintion-to-aziridination I:A (i.e., (Insertion):(Aziridination)) >20:1. This extraordinary chemoselectivity towards C–H amination originates from the structural features of porphyrazine: a rigid ligand with the big π-conjugated bond. Electron-donating substituents can further increase Mn-catalyzed C–H amination reactivity. The controlling factors found in this work may be considered as design elements for an economical and environmentally friendly C–H amination system with high reactivity and high chemoselectivity.

scholarly journals Mechanism of protein oxidative damage that is coupled to long-range electron transfer to high-valent haems

2016 ◽  
Vol 473 (12) ◽  
pp. 1769-1775 ◽  
Author(s):  
Zhongxin Ma ◽  
Heather R. Williamson ◽  
Victor L. Davidson
Keyword(s):  
Reactive Oxygen Species ◽  
Electron Transfer ◽  
Oxidative Damage ◽  
Long Range ◽  
Direct Contact ◽  
Reactive Oxygen ◽  
Oxygen Species ◽  
High Valent

The present study describes how oxidative damage to a protein may occur without direct contact with a reactive oxygen species, and how that radical-mediated damage can be propagated through the protein. This process is coupled to the reactivity of high-valent haems within the same protein.

Electron transfer and catalysis with high-valent metal-oxo complexes

2015 ◽  
Vol 44 (15) ◽  
pp. 6696-6705 ◽  
Author(s):  
Shunichi Fukuzumi
Keyword(s):  
Electron Transfer ◽  
Photoinduced Electron Transfer ◽  
Transfer Reactions ◽  
Electron Transfer Reactions ◽  
Oxo Complexes ◽  
High Valent

High-valent metal-oxo complexes are produced by thermal and photoinduced electron-transfer reactions, acting as catalysts for oxygenation of substrates using water or dioxygen as an oxygen source.

Electron-Transfer and Redox Reactivity of High-Valent Iron Imido and Oxo Complexes with the Formal Oxidation States of Five and Six

2020 ◽  
Vol 142 (8) ◽  
pp. 3891-3904 ◽  
Author(s):  
Xiaoyan Lu ◽  
Xiao-Xi Li ◽  
Yong-Min Lee ◽  
Yuri Jang ◽  
Mi Sook Seo ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Oxidation States ◽  
Oxo Complexes ◽  
Redox Reactivity ◽  
High Valent

Gas-phase heteroaromatic substitution. 10. Reaction of free phenylium ion with simple five-membered heteroarenes in the gaseous and liquid phase

1991 ◽  
Vol 69 (4) ◽  
pp. 732-739 ◽  
Author(s):  
Antonello Filippi ◽  
Giorgio Occhiucci ◽  
Maurizio Speranza
Keyword(s):  
Electron Transfer ◽  
Gas Phase ◽  
High Reactivity ◽  
Ion Chemistry ◽  
Β Decay ◽  
Reactivity Pattern ◽  
Gas Phase Ion Chemistry ◽  
Liquid Phases ◽  
Ionic Intermediates ◽  
Gas Phase Ion

Phenylium ion, obtained from the spontaneous β decay of 1,4-ditritiobenzene, has been allowed to react with pyrrole, N-methylpyrrole, furan, and thiophene, in both the gaseous and liquid phases. The differences between the reactivity pattern of phenylium ion in the two environments can be essentially reduced to significant ion-neutral electrostatic interaction in the gas phase and to the much greater efficiency of collisional stabilization in the condensed phase, allowing a larger fraction of the excited ionic intermediates, from the highly exothermic attack of phenylium ion on the aromatic substrate, to survive dissociation and isomerization. The mechanism of the phenylation process and of the subsequent isomerization of the relevant ionic intermediates is discussed and the intrinsic substrate and positional selectivity of the phenylium ion evaluated. While the limited substrate discrimination of phenylium ion fully agrees with its well-known exceedingly high reactivity, its pronounced affinity toward the α carbons of the selected heteroarenes does not conform with the relatively "hard" character of the reactant, expected on the grounds of its STO-3G calculated LUMO energy. The conceivable occurrence of an intimate entropy-favored two-step addition mechanism, involving a preliminary single-electron transfer (SET) from the heteroaromatic substrate to the ionic electrophile, which is thermochemically allowed only for phenylium and methyl cations and prevented for other alkylating electrophiles, is discussed. Key words: gas-phase ion chemistry, electrophilic heteroaromatic substitution, nuclear decay chemistry, phenylium ion, electron transfer.

scholarly journals Semiempirical method for examining asynchronicity in metal–oxido-mediated C–H bond activation

2021 ◽  
Vol 118 (36) ◽  
pp. e2108648118
Author(s):  
Suman K. Barman ◽  
Meng-Yin Yang ◽  
Trenton H. Parsell ◽  
Michael T. Green ◽  
A. S. Borovik
Keyword(s):  
Electron Transfer ◽  
Bond Activation ◽  
Dominant Role ◽  
Bond Cleavage ◽  
Semiempirical Method ◽  
Proton Coupled Electron Transfer ◽  
Enzymatic Function ◽  
Synthetic Metal ◽  
High Valent ◽  
Free Energy Analysis

The oxidation of substrates via the cleavage of thermodynamically strong C–H bonds is an essential part of mammalian metabolism. These reactions are predominantly carried out by enzymes that produce high-valent metal–oxido species, which are directly responsible for cleaving the C–H bonds. While much is known about the identity of these transient intermediates, the mechanistic factors that enable metal–oxido species to accomplish such difficult reactions are still incomplete. For synthetic metal–oxido species, C–H bond cleavage is often mechanistically described as synchronous, proton-coupled electron transfer (PCET). However, data have emerged that suggest that the basicity of the M–oxido unit is the key determinant in achieving enzymatic function, thus requiring alternative mechanisms whereby proton transfer (PT) has a more dominant role than electron transfer (ET). To bridge this knowledge gap, the reactivity of a monomeric MnIV–oxido complex with a series of external substrates was studied, resulting in a spread of over 104 in their second-order rate constants that tracked with the acidity of the C–H bonds. Mechanisms that included either synchronous PCET or rate-limiting PT, followed by ET, did not explain our results, which led to a proposed PCET mechanism with asynchronous transition states that are dominated by PT. To support this premise, we report a semiempirical free energy analysis that can predict the relative contributions of PT and ET for a given set of substrates. These findings underscore why the basicity of M–oxido units needs to be considered in C–H functionalization.

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