Advances in electrochemical transformation of N_(2)using molecular catalysts

The conversion of N_(2)to NH_(3)holds great importance due to the essential role of NH_(3)in fertilizer production,energy storage and the synthesis of key industrial chemicals.Development of novel methods for N_(2)transformation is a worthwhile goal and researchers have turned their attention to electrochemical N_(2)reduction as a potentially sustainable solution.The development of molecular electrocatalysts has gained considerable momentum over the last decades,and this review focuses on the advances and challenges in the field of molecular electrochemical nitrogen fixation and aims to inspire further research into the realm of nitrogen fixation chemistry from an electrochemical perspective.

Mechanistic Studies on Programmed C—O/C—H Activation with Valence-Adjusted Ti-Complexes

Two-electron reduction of[N_(2)NBn]Ti^(Ⅳ)Cl2(3)gave a highly reactive[N_(2)N]Ti^(Ⅱ)species,which underwent C—O bond activation of THF(tetrahydrofuran)to generate[N2NBn]Ti^(Ⅳ)[O(CH2)4](4)through oxidative addition.The resulted Ti^(Ⅳ)-Csp^(3)bond in oxametallacyclo-hexane was tantamount to the elaborately-designed Ti-alkyl complexes,competent to activate intramolecular Csp^(2)-H bond,forming ortho-cyclometalated complex[N_(2)NCH_(2)C_(6)H_(4)]Ti^(Ⅳ)(O^(n)Bu)(5).Key intermediates were isolated and fully characterized by X-ray crystal-lography.Mechanistic studies revealed that the oxidative addition of C-O bond took place at Ti^(Ⅱ)-center via a radical intermediate,while a Csp^(2)-H bond activation proceeded byσ-bond metathesis with a kitelike four-centered Ti^(Ⅳ)-transition state.

Transition Metal Catalyzed Direct Oxidative Borylation of C--H Bonds

Organoboron is well-developed and broadly utilized organometallic reagents in organic synthesis due to its extraordinary performances in transition-metal catalyzed C-C and C-X bonds construction. Catalytic C--H borylation and further transformations catalyzed by transition metal catalysts in the absence of oxidants were well studied in decades. However, as known, transition metal catalyzed oxidative C-H borylations were not reviewed up to date. In this article the oxidative borylation of C（sp2）-H and C（sp3）-H bonds were summarized and their mechanisms were also accounted.

Methylation of Arenols through Ni-catalyzed C--O Activation with Methyl Magnesium Bromide

Direct alkylation of arenols with alky] organometallic reagents has never been approached, Herein we reported the first successful example of nickel-catalyzed methylation of arenols with methyl Grignard reagents to construct C（sp2）-C（sp3） bond under mild conditions. The transformation was compatible with broad substrate scope of 2-naphthol derivatives. Benzyl alcohol and biphenols were also suitable substrates for this methylation.

Conversion of Carbonyl Compounds to Olefins via Enolate Intermediate

Summary of main observation and conclusion A general and efficient protocol to synthesize substituted olefins from carbonyl compounds via nickel catalyzed C-O activation of enolates was developed.Besides ketones,aldehydes were also suitable substrates for the presented catalytic system to produce di-or tri-substituted olefins.It is worth noting that this approach exhibited good tolerance to highly reactive tertiary alcohols,which could not survive in other reported routes for converting carbonyl compounds to olefins.This method also showed good regio-and stereo-selectivity for olefin products.Preliminary mechanistic studies indicated that the reaction was accomplished through nickel catalyzed C-O activation of enolates,thus offering helpful contribution to current enol chemistry.

Photo-induced deep aerobic oxidation of alkyl aromatics

Oxidation is a major chemical process to produce oxygenated chemicals in both nature and the chemical industry.Presently,the industrial manufacture of benzoic acids and benzene polycarboxylic acids(BPCAs)is mainly based on the deep oxidation of polyalkyl benzene,which is somewhat suffering from environmental and economical disadvantage due to the formation of ozone-depleting Me Br and corrosion hazards of production equipment.In this report,photo-induced deep aerobic oxidation of(poly)alkyl benzene to benzene(poly)carboxylic acids was developed.CeCl_(3) was proved to be an efficient HAT(hydrogen atom transfer)catalyst in the presence of alcohol as both hydrogen and electron shuttle.Dioxygen(O_(2))was found as a sole terminal oxidant.In most cases,pure products were easily isolated by simple filtration,implying large-scale implementation advantages.The reaction provides an ideal protocol to produce valuable fine chemicals from naturally abundant petroleum feedstocks.

Carbon-hydrogen activation in China

Transition metal catalyzed C-H Functionalization is one of the most important and challenging research fields in organic chemistry and has rapidly evolved in recent decades.Some recent achievements in the field include i)minimizing the pre-activation procedures of substrates,ii)reducing waste production,and iii)shortening synthetic steps by developing direct activations and straightforward transfor-

Preface

Direct C–H functionalization has become one of the most important and emerging topics in organic synthesis.In this regard,Chinese chemists have made significant contributions for promoting the study of such chemistry from different aspects.Encouraged by the considerable progress made in this field by Chinese organic chemists。

A mixed-valent high spin(μ-hydroxo)dicobalt(Ⅱ/Ⅲ) complex and its end-on type dioxygen adduct: synthesis, geometric and electronic structure studies

A mixed-valent high spin (μ-hydroxo)dicobalt(Ⅱ/Ⅲ) complex bearing N,N′-bis(5-tertbutylsalicylidene)-1,2-diaminobenzene(Salophen^(tBu)) ligand was synthesized by reacting (Salophen^(tBu))Co(Ⅱ)(Py) with O_(2) at low temperature.This complex was isolated and structurally characterized by single crystal X-ray diffraction and infrared spectrum.Magnetic measurement showed a quartet ground state for this complex at room temperature,which was also supported by electron paramagnetic resonance (EPR)characterization.Computational investigations indicated the deviation of the equatorial N_(2)O_(2) coordination geometry around the Co(Ⅱ) center from plane stabilized the quartet state.The end-on type O_(2) adduct of this (μ-hydroxo)dicobalt(Ⅱ/Ⅲ) complex was isolated as dark-brown crystals and structurally and spectroscopically characterized.EPR measurement of this compound in solid state at room temperature presented an isotropic singlet at g~2,revealing the superoxide-like electronic feature of the coordinated O_(2) and was in line with the calculation results.The reactivity of the Co(Ⅲ)-O_(2) complex with N-hydroxyphthalimide,which can act as hydrogen atom donor,was also examined.

Direct Transformation of Arenols Based on C—O Activation

Contents 1.Introduction 8562.C—O Activation via the in-situ Formed Intermediate 8562.1.C—C bond formation 8562.2.C—X bond formation 8573.C—O Activation via Dearomatization-Condensation-Rearomatization Process 8573.1.Heterogeneous catalyzed C—O cleavage of phenols,dearomatization-condensation-rearomatization process in a gas phase 8573.2.Dearomatization-condensation-rearomatization process in a liquid phase 8574.Deoxygenation 8585.Direct C—O Activation of Phenol Salts 8596.Direct C—O Activation of Phenol 8607.Conclusions and Perspective 8601.Introduction Transition-metal-catalyzed cross-coupling reactions of aryl electrophiles with organic or organometallic reagents emerged as one of the most powerful tools for constructing aromatic compounds.[1]In the early days,the most popular electrophiles werearyl halides because of their high reactivity and availability.

Regio-Divergent C—H Alkynylation with Janus Directing Strategy via Ir(Ⅲ)Catalysis

Summary of main observation and conclusion Directing strategy has been extensively exploited to maintain activity and selectivity for the rapid access to functionalized molecules and pharmaceutical targets.However,‘one-to-one’activation model was usually achieved through traditional directing strategy.Herein,we achieved‘one-to-two'activation model by slight modification of simple and practical ketoxime and amide functionality.With judicious choice of directing groups,Csp3—H and Csp2—H bond alkynylation reaction,and more significantly,dehydrogenative Csp3—H alkynylation,were realized,enabling the regio-divergent late-stage modifications of pharmaceuticals.