Nitrene-Mediated P-N Coupling Under Iron Catalysis

P-N and P=N bonds play important roles in the design and synthesis of functional molecules such as bioactive compounds and organic ligands for catalysis.Existing methods for P-N coupling mostly rely on Staudinger condensation or nucleophilic substitution between phosphorus electrophiles and amine nucleo philes.Herein,we report a nitrene-mediated intermolecular P-N coupling reaction between various phos phorus nucleophiles and dioxazolones under simp le iron-catalyzed conditions.These reactions offer an efficient,versatile,and broadly applicable method for synthesis of a range of N-P compounds,including amidophosphines,iminophosphonamides,phosphinamides,aminophosphines,and iminophospho ranes,from readily available precursors under mild conditions.

Removal of SO_2 from flue gas using Bayer red mud:Influence factors and mechanism

The absorbent composing of Bayer red mud and water was prepared and applied to removing SO2 from flue gas.Effects of the ratio of liquid to solid(L/S),the absorption temperature,the inlet SO2 concentration,the O2 concentration,SO4^2-and other different components of Bayer red mud on desulfurization were conducted.The mechanism of flue gas desulfurization was also established.The results indicated that L/S was the prominent factor,followed by the inlet SO2 concentration and the temperature was the least among them.The optimum condition was as follows:L/S,the temperature and the SO2 concentration were 20:1,25℃and 1000 mg/m^3,respectively,under the gas flow of 1.5 L/min.The desulfurization efficiency was not significantly influenced when O2 concentration was above 7%.The accumulation of SO4^2-inhibited the desulfurization efficiency.The alkali absorption and metal ions liquid catalytic oxidation were involved in the process,which accounted for 98.61%.

Carbon film encapsulated Fe_2O_3: An efficient catalyst for hydrogenation of nitroarenes

Iron catalysis has attracted a wealth of interdependent research for its abundance,low price,and nontoxicity.Herein,a convenient and stable iron oxide(Fe2O3)‐based catalyst,in which active Fe2O3nanoparticles(NPs)were embedded into carbon films,was prepared via the pyrolysis of iron‐polyaniline complexes on carbon particles.The obtained catalyst shows a large surface area,uniform pore channel distribution,with the Fe2O3NPs homogeneously dispersed across the hybrid material.Scanning electron microscopy,Raman spectroscopy and X‐ray diffraction analyses of the catalyst prepared at900°C(Fe2O3@G‐C‐900)and an acid‐pretreated commercial activated carbon confirmed that additional carbon materials formed on the pristine carbon particles.Observation of high‐resolution transmission electron microscopy images also revealed that the Fe2O3NPs in the hybrid were encapsulated by a thin carbon film.The Fe2O3@G‐C‐900composite was highly active and stable for the direct selective hydrogenation of nitroarenes to anilines under mild conditions,where previously noble metals were required.The synthetic strategy and the structure of the iron oxide‐based composite may lead to the advancement of cost‐effective and sustainable industrial processes.

Iron-Catalyzed Oxidative Deconstruction of Polyethylene Terephthalate to Terephthalic Acid under O2

It is urgent to recycle polyethylene terephthalate(PET)effectively,since it is the most consumed synthetic polyester and its improper disposal has caused significant environmental pollution.The existing chemical recycling methods highly rely on the nucleophilic substitutions and hydrogenative depolymerizations,which typically require the use of excess of nucleophiles,excess strong acids or bases,expensive metal catalysts,and explosive gas atmosphere.Here,we demonstrate a mild and efficient protocol for oxidative depolymerization of PET to terephthalic acid using only an O2 balloon.Terephthalic acid can be recycled from PET-containing materials including a series of plastic products in daily life.The employing of relatively low loading of iron complex,the most earth-abundant transition metal,as the catalyst and the preliminary results on the large-scale reaction using 38 g of PET waste demonstrate the practical feasibility of this degradation method.This method can be also applicable for selective degradation of PET from mixed plastics.This work represents a rare example of a selective oxidative depolymerization and demonstrates the great potentials of such a concept in polyester recycling.

Iron/B_(2)pin_(2)catalytic system enables the generation of alkyl radicals from inert alkyl C-O bonds for amine synthesis

A method for the generation of alkyl radicals from inert alkyl C-o bonds has been developed via an iron/borane reagent/alkoxide catalytic system,which can be employed for the synthesis of amines from nitroarenes with excellent efficiency.This reductive amination features good functional group compatibility and enables the late-stage amination of bio-relevant compounds,thus providing good opportunities for applications in medicinal chemistry.Preliminary mechanistic studies reveal that the amine synthesis may be involving a Fe/Li cation-assisted single electron transfer pathway to form alkyl radicals,and the low-valent iron speciesmaybetheactive intermediates.

Eco-friendly iron-catalyzed oxidation of unstrained tertiary aromatic alcohols to ketones

A general,facile and eco-friendly iron catalysis enables oxidation of unstrained tertiary aromatic alcohols to ketones through C-C bond cleavage even with H_(2)O_(2) as the oxidant.Notably,this transformation can tolerate oxidation-labile functional groups.The robustness of this method is further demonstrated on the late-stage oxidation of complex bioactive molecules.

Photoelectrochemical Iron-Catalyzed C(sp^(3))-H Borylation of Alkanes in a Position-Selective Manner

Catalytic C-H borylation is of prime topical importance,since easily available feedstock chemicals can thereby be transformed into valuable transient functional groups in the absence of directing groups.Herein,we disclose an iron-catalyzed C(sp^(3))-H borylation of simple,non-prefunctionalized alkanes,providing access to value-added products in a single step by means of photoelectrochemistry.The power of merging photo-and electrochemistry was mirrored by ample scope and exceedingly mild reaction conditions.Moreover,an outstanding position-selectivity in favor of primary C(sp^(3))-H proved viable within the photoelectrochemical borylation through a chemo-selective anodic overoxidation manifold.The ferro-photoelectrochemistry strategy avoids toxic precious transition metals,enabling C(sp^(3))-H borylations in a site-selective fashion.

Iron-Catalyzed Alkenylzincation of Internal Alkynes

The alkenylzincation of internal alkynes is an effective method for the synthesis of multi-substituted conjugated dienes;however,the current catalytic systems for this reaction are limited in terms of substrate scope and selectivity control,which restricts its practical applications.Herein,we report the first iron-catalyzed alkenylzincation of internal alkynes,which features mild conditions,simple operation,broad substrate scope (including aryl/alkyl,diaryl,and dialkyl acetylenes),excellent functional group tolerance (tolerating highly active functional groups such as ester,methylthio,amide,sulfonyl,cyano,etc.),and high activity (with a turnover number of up to 11500,the highest record for carbometallation reactions).Notably,the catalytic system described in this article also realized the highly selective vinylzincation of unfunctionalized internal alkynes as well as the alkenylzincation of unsymmetrical diarylacetylenes and dialkyl acetylenes,which have not been achieved with other catalytic systems reported in the literatures.The current study provides a highly selective access to synthetically important multi-substituted conjugated dienes.

Iron-Catalyzed Aerobic Oxidation of Aldehydes： Single Component Catalyst and Mechanistic Studies

An aerobic oxidation of aldehydes towards carboxylic acids in MeCN using 1 atm of pure oxygen or oxygen in air as the oxidant and a catalytic amount of single component catalyst, Fe（NO3）3.9H20, has been developed. Carboxylic acids with different synthetically useful functional groups were obtained at room temperature. Two mechanistic pathways have been proposed based on isotopic labeling, NMR monitoring, and control experiments. The practicality of this reaction has been demonstrated by conducting several 50 mmol-scale reactions using pure oxygen or an air-flow of -30 mL/min.

Iron-Catalyzed Intramolecular C-H Amidation of N-Benzoyloxyureas

Main observation and conclusion A redox-neutral Fe-catalyzed intramolecular C-H amidation of N-benzoyloxyureas is described.This methodology employs a simple iron complex in situ generated from Fe(OTf)2 and bipyridine as the catalyst and N-benzoyloxyureas as the nitrene precursors without using exogenous oxidants.An array of cyclic ureas were synthesized via aliphatic C(sp^(3))-H amidation in excellent yields.In addition,this catalytic system is also amenable to aryl C(sp^(2))-H nitrene insertion to provide benzimidazolones in moderate yields.

Iron-catalyzed aerobic oxidative amidation of tertiary amines with carboxylic acids

An oxidative amidation of tertiary amines with carboxylic acids has been developed in the presence of FeC13- 6H20 as catalyst and oxygen as oxidant. A variety of tertiary amides were obtained in good to excellent yields from inexpensive and readily available reagents. The possible reaction pathways were investigated.

Iron-catalyzed cyanoalkylation of difluoroenol silyl ethers with cyclobutanone oxime esters

An iron-catalyzed coupling reaction of difluoroenol silyl ethers and cyclobutanone oxime esters is described. This protocol provides a convenient access to various previously unknown and potentially useful gem-difluoromethylenated ketonitriles inmoderate to good yields. The transformations of resulting products to other fluorinecontaining products is also documented.

Iron(Ⅱ) hydrides bearing a tetradentate PSNP ligand

A new class of iron（II） hydrides based on a tetradentate PSNP ligand were synthesized and fully characterized. All the iron（II） complexes feature a folded PSNP ligand with cis reactive sites. The hydrido iron complex [2 H（NCMe[2_TD$IF]1）]（BF4） is capable of catalyzing aldehyde hydroboration by pinacolborane（HBpin） and with extremely high efficiency at room temperature. Aldehydes with various functional groups are compatible.

Iron-Catalyzed Cross-Electrophile Coupling of Inert C-O Bonds with Alkyl Bromides

An example of iron-catalyzed cross-electrophile couplingof inert C-O bonds with alkyl bromides via aniron/B_(2)pin_(2) catalytic system has been developed.Aryl and heteroaryl carbamates can smoothly undergothis transformation under mild conditions, deliveringthe alkylated products with good efficiency.This protocol exhibits good functional group compatibilityand enables the late-stage functionalizationof biorelevant compounds, thus providingexcellent opportunities for applications in medicinalchemistry. Control experiments and computationalstudies reveal that a high spin Fe(I/II/III) catalyticmechanism might be involved in this reactionthrough single electron transfer to activate alkylbromides, oxidative addition of aryl carbamates, andreductive elimination to form Csp^(2)-Csp^(3) bonds.

Iron-Catalyzed Borylation and Silylation of Unactivated Tertiary,Secondary,and Primary Alkyl Chlorides

Herein,we describe an iron-catalyzed borylation and silylation of unactivated alkyl chlorides,delivering the tertiary,secondary,and primary alkylboronic esters,and secondary,primary alkylsilanes with high efficiency.This protocol exhibits broad substrate scope and good functional group compatibility,allowing the efficient late-stage borylation of biorelevant compounds,thus offering an excellent platform in drug discovery and development.Preliminary mechanistic studies suggest that an alkyl radical was involved in this catalytic system.

Photoinduced FeCl_(3)-Catalyzed Alkyl Aromatics Oxidation toward Degradation of Polystyrene at Room Temperature

While polystyrene is widely used in daily life as a synthetic plastic,the subsequently selective degradation is still very challenging and highly required.Herein,we disclose a highly practical and selective reaction for the catalytically efficient oxidation of alkyl aromatics(including 1°,2°,and 3°alkyl aromatics)to carboxylic acids.While dioxygen was used as the sole terminal oxidant,this protocol was catalyzed by the inexpensive and readily available ferric compound(FeCl_(3))with irradiation of visible light(blue LEDs)under only 1 atmosphere of O_(2) at room temperature.This system could further facilitate the selective degradation of polystyrene to benzoic acid,providing an important and practical tool to generate high-value chemical from abundant polystyrene wastes.

Catalytic Hydrogen Transfer Reactions

Our recently studies on three types of reactions with hydrogen transfer as a key step,including catalytic asymmetric proton transfer reactions using"chiral proton transfer shuttle",catalytic B—H bond insertion containing a hydrogen atom transfer,and iron-catalyzed hydrosilylation reactions containing hydride transfer were briefly introduced.

Fe-Catalyzed Pictet-Spengler-Type Cyclization via Selective Four-Electron Reductive Functionalization of CO_(2)

Main observation and conclusion Herein,we describe a novel catalytic Pictet-Spengler-type cyclization using CO_(2) as a nontoxic and sustainable C1 feedstock with envi-ronmentally benign and non-precious-metal iron as catalyst.The reaction is achieved by selective four-electron reduction of CO_(2) into methylene level intermediate through carefully tuning the reaction parameters.A variety of tetrahydro-B-carbolines and other nitro-gen-containing heterocycles can be easily obtained under mild conditions.Mechanistic studies have shown that tetrahy-dro-B-carbolines are probably obtained via spiroindolenine intermediates.