Particle-Scale Understanding of Arsenic Interactions with Sulfidized Nanoscale Zerovalent Iron and Their Impacts on Dehalogenation Reactivity.

Co-occurrence of organic contaminants and arsenic oxoanions occurs often at polluted groundwater sites, but the effect of arsenite on the reactivity of sulfidized nanoscale zerovalent iron (SNZVI) used to remediate groundwater has not been evaluated. Here, we study the interaction of arsenite [As(III)] with SNZVI at the individual-particle scale to better understand the impacts on the SNZVI properties and reactivity. Surface and intraparticle accumulation of As was observed on hydrophilic FeS-Fe0 and hydrophobic FeS2-Fe0 particles, respectively. X-ray absorption spectroscopy indicated the presence of realgar-like As-S and elemental As0 species at low and high As/Fe concentration ratios, respectively. Single-particle inductively coupled plasma time-of-flight mass spectrometry analysis identified As-containing particles both with and without Fe. The probability of finding As-containing particles without Fe increased with the S-induced hydrophobicity of SNZVI. The interactions of SNZVI materials with coexisting arsenite inhibited their reactivity with water (∼5.8-230.7-fold), trichloroethylene (∼3.6-67.5-fold), and florfenicol (∼1.1-5.9-fold). However, the overall selectivity toward trichloroethylene and florfenicol relative to water was improved (up to 9.0-fold) because the surface-associated As increased the SNZVI hydrophobicity. These results indicate that reactions of SNZVI with arsenite can remove As from groundwater and improve the properties of SNZVI for dehalogenation selectivity.

Tailoring Fe0 Nanoparticles via Lattice Engineering for Environmental Remediation.

Lattice engineering of nanomaterials holds promise in simultaneously regulating their geometric and electronic effects to promote their performance. However, local microenvironment engineering of Fe0 nanoparticles (nFe0) for efficient and selective environmental remediation is still in its infancy and lacks deep understanding. Here, we present the design principles and characterization techniques of lattice-doped nFe0 from the point of view of microenvironment chemistry at both atomic and elemental levels, revealing their crystalline structure, electronic effects, and physicochemical properties. We summarize the current knowledge about the impacts of doping nonmetal p-block elements, transition-metal d-block elements, and hybrid elements into nFe0 crystals on their local coordination environment, which largely determines their structure-property-activity relationships. The materials' reactivity-selectivity trade-off can be altered via facile and feasible approaches, e.g., controlling doping elements' amounts, types, and speciation. We also discuss the remaining challenges and future outlooks of using lattice-doped nFe0 materials in real applications. This perspective provides an intuitive interpretation for the rational design of lattice-doped nFe0, which is conducive to real practice for efficient and selective environmental remediation.

Bora-alkenes: Metal Coordination and Reactions with BH-boranes.

The neutral N-heterocyclic carbene stabilized bora-alkene 1, conveniently prepared by a BH borenium/hydroboration route, forms stable copper, gold or palladium π-complexes. The polar bora-alkene B=C system undergoes regioselective hydroboration reactions with the (C6 F5 )2 BH or C6 F5 BH2 ⋅ SMe2 boranes. The latter reaction involves a subsequent rearrangement that leads to internal hydride vs. isothiocyanate substituent exchange at the borane pair.

Boraalkenes Made by a Hydroboration Route: Cycloaddition and B=C Bond Cleavage Reactions.

Hydroboration of styrene or vinylcyclohexane with the IMes(C6 F5 )BH+ cation followed by deprotonation provided a convenient synthetic entry to the [B]=CHCH2 R boraalkenes 9 a and 9 b. The in situ generated IMes(SCN)BH+ system reacted similarly with 1,1-diphenylethene followed by deprotonation to give the isothiocyanato substituted boraalkene 9 c. The boraalkenes underwent [2+2] cycloaddition reactions with a small series of heterocumulenes to give the respective four-membered heterocycles. The [B]=CHCH2 R+CO2 cycloadducts 13 a and 13 b added the borane HB(C6 F5 )2 with cleavage of the central B-C σ-bond. CS2 underwent an unusual reaction with the boraalkenes, namely insertion into the B=C bond with formation of the borylated dithioketene acetal under complete rupture of the strong B=C double bond. The intermediate dithiobora-ß-lactone type intermediate was isolated in the case of the isothiocyanato-boraalkene reaction and characterized by X-ray diffraction.

Generation of boryl-nitroxide radicals from a boraalkene via the nitroso ene reaction.

Examples of isolated boron substituted nitroxide radicals are rare. The reaction of the reactive cyclic boraalkene 3 with nitrosobenzene yields a mixture of the [2 + 2] cycloaddition product 4a, the B-nitroxide radicals 5a and 6a and the azoxybenzene co-product 7avia a bora nitroso ene reaction pathway, the boron analogue of the nitroso ene reaction. The products were separated by flash chromatography, and the B-nitroxide radicals were characterized by X-ray diffraction and EPR spectroscopy. Radical 5a was shown to be a hydrogen atom abstractor. Both the B-nitroxide radicals are more easily oxidized compared to e.g. TEMPO, as shown by cyclic voltammetry.

A deprotonation pathway to reactive [B]CH2 boraalkenes.

The BH compounds IMes(ArF)BH(NTf2) (ArF: C6F5 or FpXyl) were converted to the IMes(ArF)BCH2 boraalkenes in a three step reaction sequence of B-methylation with methyllithium, hydride abstraction and deprotonation. The BCH2 boraalkenes reacted with elemental sulfur to give a thiaborirane product. They underwent [2+2] cycloaddition reactions with carbon dioxide or sulfur dioxide to give four-membered boron containing heterocycles. The boraalkenes added strongly Lewis acidic boranes at their CH2 carbon atoms. The corresponding HB(C6F5)2/boraalkene adduct reduced carbon monoxide to a -OCH(C6F5)- moiety inside a five-membered heterocycle at the B-CH2-B template. The boraalkenes reacted with the [(Me2S)AuCl] reagent to form the corresponding (boraalkene)AuCl complexes.

N-Heterocyclic Carbene Stabilized 1-Bora-1,3-butadienes.

Deprotonation of [(NHC)(Fmes)B-allyl]+ borenium cations (NHC, IMes (a) or IMe2 (b); Fmes, 2,4,6-(CF3)3C6H2) provides an easy entry to the NHC-stabilized 1-bora-1,3-butadienes. They feature a planar s-trans-conformation just like 1,3-butadiene. The 1-borabutadiene 7a undergoes hydroboration reactions; the HB(C6F5)2 hydroboration product is trapped with CO or an isonitrile to give the respective cyclic zwitterionic borenium-borate enolate or enamide products. 1-Borabutadiene 7b undergoes 1,4-chalcogenation with elemental sulfur or selenium, and it gives the six-membered heterocyclic 1,4-addition product with the S═O bond of sulfur dioxide. Compound 7b served as a precursor for the formation of a borylated η3-allyl ligand at Ru. 7b formed a Rh complex by reaction with [Rh(ethylene)2Cl]2. It subsequently underwent an intramolecular C-H activation reaction to a mixture of η3-methyl-boraallyl Rh complex isomers.

Formation and Cycloaddition Reactions of a Reactive Boraalkene Stabilized Internally by N-Heterocyclic Carbene.

The synthesis of element-carbon double bonds is of great importance for the development and understanding of reactive π-bonded systems in chemistry. The seven-membered heterocyclic system 4 b is readily made by internal C-H activation at a pendent isopropyl methyl group of the respective [(IPr)C6 F5 BH]+ borenium ion. Subsequent deprotonation with the IMes carbene gives the neutral cyclic boraalkene system 5 b. The B=C double bond in compound 5 b adds carbon dioxide, CS2 , sulfur dioxide, phenyl isocyanate, an acetylenic ester or two NO molecules to give the corresponding four-membered ring annulated heterocycles. With sulfur or selenium 5 b gives the respective three-membered ring systems. N2 O reacts with 5 b to give a mixture of the related oxaborirane 18 and a unique [B]OH containing diazoalkane product 19.

A BH Borenium-Derived Thioxoborane, Its Persulfide, and Their Li+-Induced Reactions with Alkynes and with Carbon Dioxide.

Insertion of sulfur into the B-H bond of the BH borenium salt [IMes(C6F5)BH]+ followed by deprotonation gave the thioxoborane IMes(C6F5)B═S. Subsequent treatment with additional sulfur gave the corresponding boron persulfide, a NHC-stabilized boradithiirane. The B═S compound reacted with carbon dioxide in the presence of the lithium salt Li[B(C6F5)4] by formal [2+2] cycloaddition to give a boron thiocarbonate-type product. The boron persulfide formally inserted phenyl acetylene into the B-S bond in the presence of Li[B(C6F5)4] to give the respective five-membered heterocycle.

A rare olefin 1,1-carboboration reaction opens a synthetic pathway to an unusually structured frustrated Lewis pair.

(2,6-Dimesitylphenyl)P(vinyl)25d reacts with HB(C6F5)2 in a sequence involving a rare example of a 1,1-carboboration of an olefin to give the borylated tetrahydrophosphole derivative 6d. Compound 6d is an active frustrated Lewis pair that splits dihydrogen under mild conditions and serves as a metal-free hydrogenation catalyst. It also adds to carbon dioxide. Compound 6d serves as an intermediate in the HB(C6F5)2 catalyzed aryl(divinyl)phosphane (5d) to dihydrophosphole conversion.

The [(NHC)B(H)C6 F5 ]+ Cations and Their [B](H)-CO Borane Carbonyls.

Hydride abstraction from the heterocyclic carbene borane adducts (NHC)BH2 C6 F5 (NHC: IMes or IMe4 ) gave the B-H containing [(NHC)B(H)C6 F5 ]+ borenium cations. They added carbon monoxide to give the respective [(NHC)B(H)(C6 F5 )CO]+ boron carbonyl cations. Carbon nucleophiles add to the boron carbonyl to give [B](H) acyls. Hydride reduced the [B]CO cation to hydroxymethylborane derivatives.

Palladium(II)-Catalyzed Enantioselective Aminotrifluoromethoxylation of Unactivated Alkenes using CsOCF3 as a Trifluoromethoxide Source.

Asymmetric PdII -catalyzed intramolecular aminotrifluoromethoxylation of unactivated alkenes using readily accessible and stable CsOCF3 as a trifluoromethoxide source has been developed, which affords a wide variety of enantiomerically enriched ß-substituted OCF3 -containing piperidines in good yields. Introducing a sterically bulky group into pyridine-oxazoline (Pyox) ligands is crucial to increasing both reactivity and enantioselectivity for the reaction. Additionally, the reaction features good functional group compatibility and mild reaction conditions.

Enantioselective Pd(II)-Catalyzed Intramolecular Oxidative 6- endo Aminoacetoxylation of Unactivated Alkenes.

A novel asymmetric 6-endo aminoacetoxylation of unactivated alkenes by palladium catalysis, which yields chiral ß-acetoxylated piperidines with excellent chemo-, regio- and enantioselectivities under very mild reaction conditions, has been established herein by employing a new designed pyridine-oxazoline (Pyox) ligand. Importantly, introducing a sterically bulky group into the C-6 position of Pyox is crucial to enhance the reactivity of the aminoacetoxylation of alkenes.

Palladium-Catalyzed Intermolecular Ditrifluoromethoxylation of Unactivated Alkenes: CF3O-Palladation Initiated by Pd(IV).

A novel palladium-catalyzed intermolecular ditrifluoromethoxylation of unactivated alkenes has been developed, using a new electrophilic reagent, SelectfluorCN, as a strong oxidant, and AgOCF3 as a trifluoromethoxide source. Preliminary mechanistic studies revealed that the reaction was possibly initiated by Pd(IV) species, and an unusual cis-addition of CF3O-Pd(IV) into the double bond leads to the formation of the first C-OCF3 bond; in addition, the second C-OCF3 bond was produced through reductive elimination at high-valent palladium center.

Palladium-Catalyzed Intramolecular Aminotrifluoromethoxylation of Alkenes.

The first catalytic trifluoromethoxylation of unactivated alkenes has been developed, in which Pd(CH3CN)2Cl2 was used as catalyst, AgOCF3 as trifluoromethoxide source, and Selectfluor-BF4 as oxidant. A variety of 3-OCF3 substituted piperidines were selectively obtained in good yields. Direct evidence was provided to address the facile reductive elimination of Pd(IV)-OCF3 complex to form sp(3) C-OCF3 bond.

Copper-catalyzed trifluoromethylselenolation of aryl and alkyl halides: the silver effect in transmetalation.

A catalytic trifluoromethylselenolation of aryl and alkyl halides by a Cu(I) catalyst has been developed. A key intermediate, [(phen)Cu(SeCF3)]2 (5) was successfully isolated and characterized by X-ray diffraction. The important role of silver in the transmetalation process during the catalytic cycle was elucidated. A wide range of trifluoromethylselanes have been prepared from readily available starting materials from a method that tolerates various important functional groups.

Synthesis of Cu(I) trifluoromethylselenates for trifluoromethylselenolation of aryl and alkyl halides.

The development of new strategies for synthesis of trifluoromethylthiolate compounds is of considerable importance in pharmaceuticals, agrochemicals, and advanced materials. Accordingly, currently much attention is being devoted to the development of effective methods and reagents for their synthesis. In contrast, considerably less effort has been afforded to the development of preparing CSeCF3 bonds. Herein we report a concise route to synthesize a family of copper(I) trifluoromethylselenolate reagents by the reaction of CuI with the Ruppert's reagent (Me3 SiCF3 ), KF, and elemental selenium in the presence of dinitrogen ligands in CH3 CN at room temperature. The reagent [Cu(bpy)(SeCF3 )]2 was proven to be air-stable and highly efficient for nucleophilic trifluoromethylthselenolation of a broad range of (hetero)aryl halides and alkyl halides. This method represents a powerful protocol for the construction trifluoromethylselenolate compounds.

Synthesis of Copper(I) Thiolate Complexes in the Thioetherification of Aryl Halides.

The copper(I) thiophenolato complexes 1-3 containing 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (Me(2)phen) were isolated in excellent yields from reactions of [CuOtBu](4) with the dative ligands and subsequent addition of 1 equiv of arylthiol and characterized spectroscopically. X-ray structural analysis of a single crystal of [(phen)Cu(µ-SC(6)H(5))](2) (1) revealed that this complex adopts a neutral dimeric form with a weak Cu-Cu bonding interaction. These complexes were found to react with iodoarenes to form aryl sulfide products. The intermediacy of such complexes in copper-catalyzed thioetherification of aryl halides was demonstrated by the reactivity with p-tolyl iodide and o-tolyl iodide to form two aryl thioethers with selectivities similar to those of catalytic reactions conducted with the same two iodoarenes.

Thermosensitive hydrogels composed of hyaluronic acid and gelatin as carriers for the intravesical administration of cisplatin.

The aim of this work was to evaluate the use of thermosensitive hydrogels for intravesical cisplatin delivery into the bladder. Poly(N-isopropylacrylamide) (PNIPAM) was grafted onto hyaluronic acid (HA) to synthesize an HPN copolymer, which was further grafted with gelatin to form an HPNG copolymer. A 3% concentration of HPN and HPNG was sufficient to exert a thermosensitive response, whereas a concentration of 8% was needed for PNIPAM to form the hydrogel. The physicochemical and drug delivery properties were examined by scanning electron microscopy (SEM), the lower critical solution temperature (LCST), hydration ratio, and in vitro cisplatin release. The incorporation of HA and gelatin produced a different microstructure compared to the parent PNIPAM hydrogel. Gelatin conjugation increased the fibrous structure in the matrix. The LCSTs of PNIPAM, HPN, and HPNG were 32.3, 32.0, and 30.7°C, respectively. The copolymers showed an eightfold increase in the hydration capacity compared to PNIPAM, with no significant difference in values between HPN and HPNG. The release of cisplatin from an aqueous solution (control) was nearly complete after 8 h, compared to 85, 80, and 52% release from PNIPAM, HPN, and HPNG, respectively. In vivo evaluation of cisplatin levels in bladder tissues was performed following intravesical instillation in rats. When the dwell time was extended to 6 h, PNIPAM showed a sevenfold enhancement in the drug concentration in the bladder wall. HPNG also showed a twofold increase in the drug concentration. The administration of cisplatin by the HPN carrier did not change the drug accumulation compared to the control. Confocal laser scanning microscopic results confirmed the trend of drug absorption from various systems. A histological examination showed no adverse change in the urothelium with HPN or HPNG application. PNIPAM caused partial desquamation of umbrella cells. The thermosensitive hydrogels prepared in this study may be promising carriers for targeted drug delivery to the bladder.