Addition Of Halides Research Articles

Fate of typical organic halogen compounds in the coexistence of endogenic chlorine atoms and exogenic X-

The transformation of halogenated organics in advanced oxidation processes (AOPs) has been extensively investigated. However, we currently know little about the fate of halogenated pollutants in the presence of exogenic halides (Cl− or Br−). Herein, the degradability, mineralization rate, and accumulation capacity of adsorbable organic halogen (AOX) for chlorophenols (2-chlorophenol (2-CP), 3-chlorophenol (3-CP), 4-chlorophenol (4-CP), and 2,4,6-trichlorophenol (TCP)) were compared in the Fe2+/persulfate (PS) process with the addition of exogenic halides. Results indicate that exogenic X− can lead to a decrease in chlorophenols degradation and mineralization rate, undesirable accumulation of AOX, and generation of halogenated by-products which are more toxic than precursor chlorophenols. Results of kinetics modeling show that Cl2•- plays more important role than SO4•- with an addition of Cl−, while SO4•-, Br2•-, and Br2 are responsible for the effect of Br−. As well, the effect of endogenic chlorine atoms on chlorophenols reveals that the degradability and AOX formation potential of 3-CP are highest while that of TCP are the lowest. This study demonstrates the significant influence of endogenic chlorine atoms and exogenic X− on the fate of typical organic halogen compounds. Consequently, the X− level and position/number of halogen atoms should be considered simultaneously when treating organohalogen compounds.

Microscopic Reactivity of Phenylferrate Ions toward Organyl Halides.

Despite its practical importance, organoiron chemistry remains poorly understood due to its mechanistic complexity. Here, we focus on the oxidative addition of organyl halides to phenylferrate anions in the gas phase. By mass-selecting individual phenylferrate anions, we can determine the effect of the oxidation state, the ligation, and the nuclearity of the iron complex on its reactions with a series of organyl halides RX. We find that Ph2 Fe(I)- and other low-valent ferrates are more reactive than Ph3 Fe(II)- ; Ph4 Fe(III)- is inert. The coordination of a PPh3 ligand or the presence of a second iron center lower the reactivity. Besides direct cross-coupling reactions resulting in the formation of RPh, we also observe the abstraction of halogen atoms. This reaction channel shows the readiness of organoiron species to undergo radical-type processes. Complementary DFT calculations afford further insight and rationalize the high reactivity of the Ph2 Fe(I)- complex by the exothermicity of the oxidative addition and the low barriers associated with this reaction step. At the same time, they point to the importance of changes of the spin state in the reactions of Ph3 Fe(II)- .

High Pressure Sulfur Microwave Lamps with Metal Halides Additives

Effects of metal halides additives on radiation characteristics of microwave-driven high pressure sulphur lamp were experimentally studied. Electrodeless discharge was excited and maintained in the mixture of sulphur vapour (5–6) atmospheres and vapour of NaI (~ 0.07 Torr) and LiI (~ 0.12 Torr) at microwave frequency of 2.45 GHz and power of (280–560) W in the quartz spherical bulb of 35 mm in diameter inserted in the cylindrical resonator of 73 mm in diameter and 125 mm in height. To maintain bulb walls at homogeneous temperature, the bulb was rotated with the speed of the 12 r/c. It was found that the addition of low pressure sodium and lithium halides caused the increase of lamp efficacy by (11–13) %, colour temperature by 16 %, and colour rendering index by 4 %. To further improve lamp characteristics, the increase of additives partial pressures was recommended.

Metal-free oxidative activation of enaminone C[dbnd]C bond by ammonium halide and DMSO: An access to synthetic pyridines

Herein, we reported a metal-free oxidative activation of enaminone CC double bond by ammonium halide and DMSO to synthetic pyridines. This reaction proceeded smoothly without metal catalysts, strong oxidants, or free radical initiators. In addition, no direct addition of halogen or hydrogen halide is required, providing rapid access to a variety of 3,5-disubstituted-pyridines in moderate to excellent yields.

Nickel Bromide Catalyzed Ligand‐Free and Activator‐less Suzuki Coupling Reactions

AbstractReadily available and inexpensive bromide salt based on earth‐abundant nickel has been used to catalyze the Suzuki coupling of a variety of aryl halides (ca. 37 examples) in high yields under ambient conditions with good functional group tolerance. The reactivity of various aryl halides follows the corresponding C−X (X=I, Br and Cl) bond strength in the order Ar−I>Ar−Br>Ar−Cl. EPR analysis, mercury‐drop experiments and reactions with radical scavenger such as TEMPO point to the involvement of well‐defined molecular species that operate via a Ni(0)/Ni(II) catalytic cycle where oxidative addition of the aryl halide to Ni(0) is likely to be the rate‐determining‐step (RDS). For the first time, valuable new polycyclic aromatic hydrocarbons (PAHs) with exciting photophysical properties have been synthesized (ca. 23 examples) via a Ni(II) catalyzed multi‐fold Suzuki coupling.

Critical Role of Perovskite Film Stoichiometry in Determining Solar Cell Operational Stability: a Study on the Effects of Volatile A-Cation Additives.

Volatile A-cation halide (AX) additives such as formamidinium chloride and methylammonium chloride have been widely employed for high-efficiency perovskite solar cells (PSCs). However, it remains unstudied how they influence the perovskite film stoichiometry and the solar cell performance and operational stability. Hereby, our work shows that over annealing of formamidinium chloride-containing perovskite films leads to a Pb-rich surface, resulting in a high initial efficiency, which however decays during maximum power point tracking (MPPT). On the contrary, perovskite films obtained by a shorter annealing time at the same temperature provide good stability during MPPT but a lower initial efficiency. Thus, we deduce that an optimal annealing is vital for both high efficiency and operational stability, which is then confirmed in the case where methylammonium chloride additive is used. With optimized perovskite annealing conditions, we demonstrate efficient and stable p-i-n PSCs that show a best power conversion efficiency of 20.7% and remain 90% of the initial performance after a 200 h MPPT at 60 °C under simulated 1 sun illumination with high UV content. Our work presents a comprehensive understanding on how volatile AX impacts perovskite film stoichiometry and its correlation to the device performance and operational stability, providing a new guideline for fabricating high-efficiency and operationally stable PSCs.

Elucidating the effect of barium halide promoters on La2O3/CaO catalyst for oxidative coupling of methane

The industrialization of oxidative coupling of methane (OCM) is restricted by the low once through yield of C2 hydrocarbons. Recently, the halogen-assisted OCM process has been attempted to overcome this issue, but the reaction stability was poor due to the rapid loss of gas-phase halides or molten alkali halides. In this work, the barium salts, particularly barium halides (BaCl2 and BaF2), were demonstrated to be efficient promoters to improve the OCM reactivity of La2O3/CaO catalyst by increasing both C2 selectivity and C2H4/C2H6 ratio, and simultaneously achieving outstanding reaction stability. The promoting mechanism can be understood in two aspects. On the one hand, the introduction of barium salts increased the amount of surface electrophilic oxygen species, serving as the alkaline active sites for selective methane activation. On the other hand, the barium halide additives induced the in-situ formation of methyl halide intermediates facilitating C2H6 dehydrogenation, and their intimate contact with catalyst substrate restricted the rapid halogen loss and thereby improved the catalytic stability. This work not only provides a class of efficient OCM catalyst, but also offers a highly stable halogen-assisted reaction strategy.

Salt-Enhanced Oxidative Addition of Iodobenzene to Pd: An Interplay Between Cation, Anion, and Pd–Pd Cooperative Effects

Halide salts facilitate the oxidative addition of organic halides to Pd(0). This phenomenon originates from a combination of anionic, cationic, and Pd-Pd cooperative effects. Exhaustive computational exploration at the density functional theory level of the complexes obtained from [Pd0(PPh3)2] and a salt (NMe4Cl or LiCl) showed that chlorides promote phosphine release, leading to a mixture of mononuclear and dinuclear Pd(0) complexes. Anionic Pd(0) dinuclear complexes exhibit a cooperativity between Pd(0) centers, which favors the oxidative addition of iodobenzene. The higher activity of Pd(0) dimers toward oxidative addition rationalizes the previously reported kinetic laws. In the presence of Li+, the oxidative addition to mononuclear [Pd0L(Li2Cl2)] is estimated barrierless. LiCl coordination polarizes Pd(0), enlarging both the electrophilicity and the nucleophilicity of the complex, which promotes both coordination of the substrate and the subsequent insertion into the C-I bond. These conclusions are paving the way to the rational use of the salt effects in catalysis for the activation of more challenging bonds.

Ni-Catalyzed Divergent Synthesis of 2-Benzazepine Derivatives via Tunable Cyclization and 1,4-Acyl Transfer Triggered by Amide N-C Bond Cleavage.

Ligand-directed divergent synthesis can transform common starting materials into distinct molecular scaffolds by simple tuning different ligands. This strategy enables the rapid construction of structurally rich collection of small molecules for biological evaluation and reveals novel modes of catalytic transformation, representing one of the most sought-after challenges in synthetic chemistry. We herein report a Ni-catalyzed ligand-controlled tunable cyclization/cross-couplings for the divergent synthesis of pharmacologically important 2-benzazepine frameworks. The bidentate ligand facilitates the nucleophilic addition of the aryl halides to the amide carbonyl, followed by 1,4-acyl transfer and cross-coupling to obtain 2-benzazepin-5-ones and benzo[c]pyrano[2,3-e]azepines. The tridentate ligand promotes the selective 7-endo cyclization/cross-coupling to access to 2-benzazepin-3-ones. The protocol operates under mild reaction conditions with divergent cyclization patterns that can be easily modulated through the ligand backbone.

Ni‐Catalyzed Divergent Synthesis of 2‐Benzazepine Derivatives via Tunable Cyclization and 1,4‐Acyl Transfer Triggered by Amide N‐C Bond Cleavage

AbstractLigand‐directed divergent synthesis can transform common starting materials into distinct molecular scaffolds by simple tuning different ligands. This strategy enables the rapid construction of structurally rich collection of small molecules for biological evaluation and reveals novel modes of catalytic transformation, representing one of the most sought‐after challenges in synthetic chemistry. We herein report a Ni‐catalyzed ligand‐controlled tunable cyclization/cross‐couplings for the divergent synthesis of pharmacologically important 2‐benzazepine frameworks. The bidentate ligand facilitates the nucleophilic addition of the aryl halides to the amide carbonyl, followed by 1,4‐acyl transfer and cross‐coupling to obtain 2‐benzazepin‐5‐ones and benzo[c]pyrano[2,3‐e]azepines. The tridentate ligand promotes the selective 7‐endo cyclization/cross‐coupling to access to 2‐benzazepin‐3‐ones. The protocol operates under mild reaction conditions with divergent cyclization patterns that can be easily modulated through the ligand backbone.

1,10‐Phenanthroline Copper(I) Complexes with A3 Coupling to Access Allenes for Cycloaddition Reactions

AbstractPropargylamines are significant building blocks for the generation of polyfunctional amino analogues, natural products, and pharmacologically active drugs. Herein we report the most straightforward approach is to use 1,10‐phenanthroline copper(I) complexes as a catalyst to promote the (Alkyne‐Alkyne‐Amine) A3 coupling reaction between cyclic secondary amines and two terminal alkynes that generates a ketimine intermediate in situ through hydroamination, which subsequently interacts with the alkenyl copper complex to produce tetrasubstituted propargylamine. In the addition of zinc halide, the propargylamines converted into trisubstituted allenes with up to 90% yield. When Sc(OTf)3 is used to perform the [4+2] cycloaddition reaction with enophile (alkene), the cyclized product obtained in up to 72% yield. On the other hand, the allene was subjected to a metal‐free intermolecular cyclization reaction to produce the highly substituted pyridine derivative, although this provides only up to 30% yield.

Oxidative Addition of Aryl Halides to a Ni(I)-Bipyridine Complex.

The oxidative addition of aryl halides to bipyridine- or phenanthroline-ligated nickel(I) is a commonly proposed step in nickel catalysis. However, there is a scarcity of complexes of this type that both are well-defined and undergo oxidative addition with aryl halides, hampering organometallic studies of this process. We report the synthesis of a well-defined Ni(I) complex, [(CO2Etbpy)NiICl]4 (1). Its solution-phase speciation is characterized by a significant population of monomer and a redox equilibrium that can be perturbed by π-acceptors and σ-donors. 1 reacts readily with aryl bromides, and mechanistic studies are consistent with a pathway proceeding through an initial Ni(I) → Ni(III) oxidative addition to form a Ni(III) aryl species. Such a process was demonstrated stoichiometrically for the first time, affording a structurally characterized Ni(III) aryl complex.

Deciphering the mechanism of the Ni-photocatalyzed C\u2012O cross-coupling reaction using a tridentate pyridinophane ligand

Photoredox nickel catalysis has emerged as a powerful strategy for cross-coupling reactions. Although the involvement of paramagnetic Ni(I)/Ni(III) species as active intermediates in the catalytic cycle has been proposed, a thorough spectroscopic investigation of these species is lacking. Herein, we report the tridentate pyridinophane ligands RN3 that allow for detailed mechanistic studies of the photocatalytic C–O coupling reaction. The derived (RN3)Ni complexes are active catalysts under mild conditions and without an additional photocatalyst. We also provide direct evidence for the key steps involving paramagnetic Ni species in the proposed catalytic cycle: the oxidative addition of an aryl halide to a Ni(I) species, the ligand exchange/transmetalation at a Ni(III) center, and the C–O reductive elimination from a Ni(III) species. Overall, the present work suggests the RN3 ligands are a practical platform for mechanistic studies of Ni-catalyzed reactions and for the development of new catalytic applications.

Addition of Benzyl Halides to Aldehydes and Imines Using Photoactivated TDAE: Access to 3,4-Dihydroisocoumarins, 1,2-Diarylethanols, and 1,2-Diarylcarbamates under Metal-Free Conditions.

We describe herein the intermolecular addition reaction of benzyl halides to aldehydes and imines using photoactivated tetrakis(dimethylamino)ethylene (TDAE) as superphotoreductant. 3,4-Dihydroisocoumarins, 1,2-diarylethanols, and 1,2-diarylcarbamates were obtained with good functional group tolerance using simple, mild, and metal-free conditions.

DFT reveals the support effects in Pd nanoclusters over defect-ridden graphene for the oxidative addition of bromobenzene

Oxidative addition of aryl halides is an elementary and the rate limiting step common to several cross-coupling reactions. Metal complex-based homogeneous catalysts are conventionally used for catalysing such reactions. In search for heterogeneous catalysts, graphene has been widely used as a support for immobilising catalytically active Pd nanoparticles or clusters. In this study, we investigated the activities of small Pdn (n = 3, 4) clusters immobilised over pristine and defected graphenes for the oxidative addition of bromobenzene in the presence of water solvation. We compared the adsorption energetics and activation barriers of oxidative addition for a series of graphene supports and contrasted them with homogeneous free Pdn catalysts. Our theoretical investigations reveal the defected graphene supports to act as charge donors thereby drastically reducing the activation barriers of oxidative addition of bromobenzene when compared to free Pdn clusters. Double vacancy defected graphene and B-doped graphene were concluded as the best support materials providing stronger traps for small Pdn (n = 3, 4) clusters and reducing the oxidative addition barriers, making them potential heterogeneous catalysts for cross-coupling reactions.

Design and Synthesis of Tunable Chiral 2,2′‐Bipyridine Ligands: Application to the Enantioselective Nickel‐Catalyzed Reductive Arylation of Aldehydes

AbstractA new class of chiral 2,2′‐bipyridine ligands, SBpy, featuring minimized short‐range steric hindrance and structural tunability was rationally designed and developed, and the effectiveness was demonstrated in the first highly enantioselective Ni‐catalyzed addition of aryl halides to aldehydes. In comparison with known approaches using preformed aryl metallic reagents, this reaction is more step‐economical and functional group tolerant. The reaction mechanism and a model of stereocontrol were proposed based on experimental and computational results.

Design and Synthesis of Tunable Chiral 2,2'-Bipyridine Ligands: Application to the Enantioselective Nickel-Catalyzed Reductive Arylation of Aldehydes.

A new class of chiral 2,2'-bipyridine ligands, SBpy, featuring minimized short-range steric hindrance and structural tunability was rationally designed and developed, and the effectiveness was demonstrated in the first highly enantioselective Ni-catalyzed addition of aryl halides to aldehydes. In comparison with known approaches using preformed aryl metallic reagents, this reaction is more step-economical and functional group tolerant. The reaction mechanism and a model of stereocontrol were proposed based on experimental and computational results.

Revealing the Solution Structure of Pd(OAc)2 with Halide Additives

Comprehensive SummaryMechanistic studies of the palladium catalyst activation with halide additives are of great importance to palladium catalysis. In this work, XAFS spectroscopy and cyclic voltammetry were utilized to study real structures of Pd(OAc)2 in solution with different inorganic halogen additives. XAFS results demonstrate that Pd maintained +2 in the presence of excessive LiCl, LiBr, ZnCl2, ZnBr2, and NaI. Fitting results of EXAFS spectra revealed that the Pd's first shell is replaced by halogen partially or completely depending on the halogen species. DFT calculations were conducted to identify the most reliable solvated structures. The combined experimental and computational studies elucidate the critical role of inorganic halide additives in Pd chemistry.

Mechanistic insight into deep holes from interband transitions in Palladium nanoparticle photocatalysts

SummaryUtilizing hot electrons generated from localized surface plasmon resonance is of widespread interest in the photocatalysis of metallic nanoparticles. However, hot holes, especially generated from interband transitions, have not been fully explored for photocatalysis yet. In this study, a photocatalyzed Suzuki-Miyaura reaction using mesoporous Pd nanoparticle photocatalyst served as a model to study the role of hot holes. Quantum yields of the photocatalysts increase under shorter wavelength excitations and correlate to “deeper” energy of the holes from the Fermi level. This work suggests that deeper holes in the d-band catalyze the oxidative addition of aryl halide R-X onto Pd0 at the nanoparticles' surface to form R-PdII-X complex, thus accelerating the rate-determining step of the catalytic cycle. The hot electrons do not play a decisive role. In the future, catalytic mechanisms induced by deep holes should deserve as much attention as the well-known hot electron transfer mechanism.

Acceleration effect of sodium halide on zeolite crystallization: ZSM-12 as a case study

In this work, the sodium halide, e.g., NaBr, NaCl, or NaF, was added into the synthesis system of ZSM-12 zeolite. The addition of sodium halide accelerated the crystallization of ZSM-12 zeolite, and the acceleration effect of different sodium halide increased in the order of NaBr < NaCl < NaF. To understand the acceleration mechanism of sodium halide, the crystallization process of ZSM-12 zeolite synthesized with and without sodium halide was studied comparatively by using XRD, SEM, TEM, TG and FTIR characterizations. Experimental results revealed that the accelerated crystallization of ZSM-12 zeolite arose from the combined effects of sodium cation and halide anion. The sodium cation induced the coagulation of colloidal particles of initial sol and avoided the formation of gel, resulting in the improved mass transfer. The halide anion promoted the combination of tetraethylammonium cation (as structure-directing agent) with the solid phase. A ZSM-12 zeolite with abundant mesopores was finally obtained from the synthesis system containing sodium halide. The Pt/ZSM-12 catalyst using the mesoporous zeolite as the support exhibited excellent activity and isomerization selectivity in the hydroisomerization of n -dodecane. • The addition of sodium halide significantly accelerated the crystallization of ZSM-12 zeolite. • Both sodium cations and halide anions contributed to the accelerated crystallization. • The mesoporous ZSM-12 zeolites were obtained from the synthesis system containing sodium halide. • The Pt/mesoporous ZSM-12 catalyst exhibits excellent hydroisomerization performance.