Nucleophilic Halide Research Articles

Bypassing halide immobilization with cooperative polymers for the cycloaddition of atmospheric CO2 to epoxides

Atom-economic syntheses of cyclic organic carbonates by cycloaddition of CO2 to epoxides have risen to prominence among various approaches for CO2 fixation. In current literature, there is a general lack of recyclable fully heterogeneous organocatalytic systems which are active under mild conditions (T≤60 °C, atmospheric pressure), and that do not involve elaborated synthetic steps for the synthesis of monomers or the coimmobilization of active sites such as hydrogen bond donors (HBDs) and halide nucleophiles. From the standpoint of cost reduction and sustainability, it is also highly desirable to obtain the catalytic materials from biobased sources, especially waste materials. To address such gaps in the literature, we disclose in this work that a lignin derivative (phenolated lignin, PL) can be used as HBD in cooperation with readily available ionic polymers to form recyclable heterogeneous catalytic systems able to carry out the target cycloaddition reaction under atmospheric pressure at 60 °C. This unprecedented approach allows the upcycling of readily available biobased materials for the mild synthesis of cyclic carbonates from CO2 and bypasses the need for elaborated synthetic procedures for the synthesis of coimmobilized HBD-halide systems. PL/QPBAE (quaternized polyaminoester) emerged among various PL/ionic polymer pairs as the most active and efficient catalyst. Such a result is justified through a spectroscopic and analytical investigation as an effect of the ability of PL and QPBAE to closely interact and disperse in the reaction medium, and of the higher flexibility of QPBAE compared to other ionic polymers such as quaternized polyvinylpyridine. The resulting catalytic pair can be used as an efficient recyclable system for the cycloaddition of CO2 to several epoxides under atmospheric conditions with a catalytic performance that compared very well to that of more complex oil-based state-of-the-art polymeric organocatalysts for the same reaction.

Stereospecific syn-dihalogenations and regiodivergent syn-interhalogenation of alkenes via vicinal double electrophilic activation strategy

Whereas the conventional anti-dihalogenation of alkenes is a valuable synthetic tool with highly predictable stereospecificity, the restricted reaction mechanism makes it challenging to alter the diastereochemical course into the complementary syn-dihalogenation process. Only a few notable achievements were made recently by inverting one of the stereocenters after anti-addition using a carefully designed reagent system. Here, we report a conceptually distinctive strategy for the simultaneous double electrophilic activation of the two alkene carbons from the same side. Then, the resulting vicinal leaving groups can be displaced iteratively by nucleophilic halides to complete the syn-dihalogenation. For this purpose, thianthrenium dication is employed, and all possible combinations of chlorine and bromine are added onto internal alkenes successfully, particularly resulting in the syn-dibromination and the regiodivergent syn-bromochlorination.

Monodentate H-bond donor bifunctional catalyst in fixation of atmospheric pressure carbon dioxide into cyclic carbonates

The efficient conversion of epoxides and CO2 into cyclic carbonates by employing H-bond donor (HBD) and nucleophilic halide cooperating catalysis under mild conditions is an attractive research topic. Herein, we report a new onium halide bearing a CON(H) moiety as a weak HBD catalyst to facilitate the cycloaddition reaction of epoxides and CO2 under mild conditions. The structural influences on the catalytic activity were scrutinized, which included tunable substituents, the distance between functional groups, and counter anions. The result indicated that the catalyst of the bis-meta-substitutions on an aromatic ring exhibited excellent activity for converting epichlorohydrin into cyclic carbonate under atmospheric pressure at 25–70 °C. Twelve terminal epoxides were converted into corresponding cyclic carbonates in 72–99 % isolated yield. A reasonable activation mechanism was proposed and validated by using control experiments and NMR titrations. In addition, the good recyclability proves that the onium halide is a sustainable green organocatalyst.

Microwave-assisted halogen-bond catalyzed CO2 conversion to cyclic carbonates

The drive to efficiently convert carbon dioxide to added-value products is a major topic in modern science with one of the utmost relevance, whether in the context of reducing the net amount of CO2 in the atmosphere with it being a greenhouse gas or to make use of it as the world’s largest C1 carbon stock. Recently, first examples have been published using halogen-bond donors as co-catalysts in the conversion of epoxides to cyclic carbonates. However, due to the use high pressure conditions and bifunctional catalysts containing both, nucleophilic halides and halogen bond (XB) donor, it is difficult to estimate the sole contribution of the latter. Herein, we have applied various XB donors as co-catalyst under initial atmospheric CO2 pressure to more accurately determine the impact of non-covalent halogen bonding on the catalytic activity. Furthermore, the reproducibility of the reaction was significantly improved by implementing microwave-assisted heating.

Exploring the Nature of Anion-π Interactions: Complexes of π-Acceptors with Fluoro- or Oxoanions Compared to the Associations with Halides.

The variations in the nature and properties of the anion-π complexes with different types of anions are identified via experimental (UV-vis and X-ray crystallographic) measurements and computational analysis of the associations of tetracyanopyrazine, tetrafluoro-, or dichlorodicyano-p-benzoquinone. Co-crystals of these π-acceptors with the salts of fluoro- and oxoanions (PF6-, BF4-, CF3SO3-, or ClO4-) comprised anion-π bonded alternating chains or 1:2 complexes showing interatomic contacts of up to 15% shorter than the van der Waals separations. DFT computations confirmed that binding energies between the neutral π-acceptors and polyatomic noncoordinating oxo- and fluoroanions are comparable to those in the previously reported anion-π complexes with more nucleophilic halides. Yet, while the latter show distinct charge-transfer bands in the UV-vis range, the absorption spectra of the solutions containing oxo- and fluoroanions and the π-acceptors were close to those of the individual reactants. The natural bond orbital (NBO) analysis revealed a very small charge transfer of Δq = 0.01-0.02 e in the complexes with oxo- or fluoroanions as compared to the Δq = 0.05-0.22 e found for analogous complexes with halides. These distinctions were related to the smaller frontier orbital energy gap and better overlap in the complexes with halides (since the highest occupied orbitals of these monoatomic anions are closer in energy to the lowest unoccupied orbitals of the π-acceptors) as compared to that in the multicenter-bonded associations with polyatomic oxo- and fluoroanions. In accordance with these data, the energy decomposition analysis showed that while the complexes of neutral π-acceptors with the fluoro- and oxoanions are formed predominantly via electrostatic interaction, the associations with halides comprised significant orbital (charge-transfer) interactions and they explain their spectral and structural features.

Nickel-Catalyzed Enantioselective Electrochemical Reductive Cross-Coupling of Aryl Aziridines with Alkenyl Bromides.

An electrochemically driven nickel-catalyzed enantioselective reductive cross-coupling of aryl aziridines with alkenyl bromides has been developed, affording enantioenriched β-aryl homoallylic amines with excellent E-selectivity. This electroreductive strategy proceeds in the absence of heterogeneous metal reductants and sacrificial anodes by employing constant current electrolysis in an undivided cell with triethylamine as a terminal reductant. The reaction features mild conditions, remarkable stereocontrol, broad substrate scope, and excellent functional group compatibility, which was illustrated by the late-stage functionalization of bioactive molecules. Mechanistic studies indicate that this transformation conforms with a stereoconvergent mechanism in which the aziridine is activated through a nucleophilic halide ring-opening process.

Halogenation Reactions of Alkyl Alcohols Employing Methyl Grignard Reagents.

Grignard reagents are commonly used as carbanion equivalents. Herein, we report an example of Grignard reagents acting as halide nucleophiles to form alkyl iodides and bromides. We establish that Grignard reagents can convert alkyl mesylates into alkyl halides, as well as be employed in a one-pot halogenation reaction starting from alcohols, which proceed through mesylate intermediates. The halogenation reaction is confirmed to occur by an SN2 pathway with inversion of configuration and is demonstrated to be efficient on multi-gram scale.

Nicotinamide onium halide bidentate hybrid H–bond donor organocatalyst for CO2 fixation

H-bond donor (HBD) and nucleophilic halide cooperating catalysis was well developed in cycloaddition of CO2 with epoxide (CCE) reactions where common strong HBD was prevalent. Here a type of onium halide organocatalyst featured weak C–H and N–H HBD was proposed, designed and evaluated in CCE reactions. Based on biobased nicotinamide, nicotinamidium halide catalyst was prepared by simple alkylation on pyridyl N and/or on amide NH. A mono-alkylated on pyridyl N, 1-octyl nicotinamidium iodide, was screened an optimal catalyst that achieved 96 % yield of carbonate under 1 mol% catalyst loading, 1 atm pressure of CO2, 80 °C, by 24 h. Terminal epoxides were converted successfully into their corresponding cyclic carbonates by 84–99 % yields with 99 % selectivity. Scale-up preparation of styrene carbonate with 100 g of styrene epoxide (by 88 % yield and 98 % selectivity), and preparation of bis(cyclic carbonate) of a commercial diglycidyl ether of bisphenol A (by 79 % yield and 98 % selectivity) showed practical utility. The H-bonding activation between C–H and N–H HBDs with epoxide was validated by 1H NMR titrations. Designed analog catalysts to 1-octyl nicotinamidium iodide with blocked C–H or blocked N–H revealed the bidentate HBDs worked synergistically. The observations of the beneficial outcome of weak pyridium α-C–H and amide N–H H-bond donors proposed a protocol for simple yet efficient biobased H-bond donor organocatalyst development for CCE reactions.

Efficient ionic functionalization of metal-organic frameworks for efficient addition of carbon dioxide to epoxides

The use of homogeneous and polluting halides as nucleophilic cocatalysts lowers the economy and benignity of the CO 2 -epoxide cycloaddition over heterogeneous Lewis-acid catalysts like metal-organic frameworks (MOFs). Creating net positive charge at frameworks is a reasonable strategy to heterogenize halide anions within MOFs, but it is still challenging to achieve high halide loading while keeping adequate porosity. In this article, we report a facile approach to ionic MOFs with high halide content and improved catalytic activity. The catalysts were prepared by reacting azide-tagged MIL-101 with alkyne-tagged organic bromide salts. The efficient azide–alkyne click reaction within the mesoporous MOF allows quantitative cationization of the linkers, and the resultant bifunctional ionic MOFs contain one halide ion per metal center to the benefit of the cooperative catalysis. Catalytic studies suggest that the effects of varying the cationic groups and halide anions in the confined ionic space are different from those observed for homogeneous organic halides. The highest catalytic activity was demonstrated for the MOF having the smallest cationic group (quaternized trimethyl ammonium) and the intermediately nucleophilic halide (Br − ). The catalyst also outperforms the ionic MOF catalysts reported prior to this work. • A series of ionic MOFs were prepared by facile alkyne-azide click reactions. • The MOFs contain one halide per metal to the benefit of cooperative catalysis. • The confined ionic space changes the effects of cationic groups and halide anions. • The optimal catalyst, MIL-101-tz-TMA-Br, outperforms previous ionic MOF catalysts.

Tolerant Bimetallic Macrocyclic [OSSO]-Type Zinc Complexes for Efficient CO2 Fixation into Cyclic Carbonates

A new type of sustainable bimetallic zinc complexes bearing macrocyclic thioetherphenolate [OSSO]-type ligands has been developed and employed toward the chemical fixation of carbon dioxide into cyclic carbonates. The effects of reaction variables such as temperature, time, pressure, and molar ratio of epoxide to catalyst on the catalytic performance were systematically investigated. Based on the observations from structural and spectroscopic analyses, a plausible catalytic mechanism for the present reaction system was proposed, in which a Lewis acidic zinc center activates the epoxide and a nucleophilic halide counterion from the cocatalyst to ring open the activated epoxide. The two zinc centers are situated sufficiently close to each other to rationally allow a synergistic effect in the cycloaddition. The macrocyclic thioetherphenolate [OSSO]-type catalyst showed excellent conversions and selectivity for CO2 fixation into cyclic carbonates from a broad range of terminal epoxides, including bis-epoxides and biomass-derived epoxides substrates. Additionally, these catalysts demonstrate high stability to moisture and oxygen, resistance to many kinds of impurity, and good recyclability with negligible losses in catalytic activity.

Synergistically Converting Carbon Dioxide into Cyclic Carbonates by Metalloporphyrin‐Based Cationic Polymers with Imidazolium Functionality

AbstractConsidering to the synergistic activation behavior in the cycloaddition reaction of CO2 to epoxides, the integration of metalloporphyrins and nucleophilic halide anions to afford functional organic polymers is one of the most important approaches and still remains challenging. Herein, a class of novel porphyrin‐based cationic polymer (Por‐CP) has been successfully prepared through a one‐pot and atom‐efficient polycondensation of pyrrole and tailorable imidazolium‐based ionic liquid bearing trialdehyde groups in refluxed propanoic acid. Subsequently, a direct metalation of Por‐CP with zinc acetate resulted in the formation of a zinc porphyrin‐based cationic polymer (ZnPor‐CP). The rigid and charged ZnPor‐CP having spatially‐separated active Zn‐porphyrin sites and abundant imidazolium functionalities in the covalently‐linked skeletons can cooperatively promote the reaction under mild conditions, thereby achieving an efficient unification of high activity and good recyclability.

Chlorotrifluoromethylthiolation of Sulfur Ylides for the Formation of Tetrasubstituted Trifluoromethylthiolated Alkenes.

Tetrasubstituted trifluoromethylthiolated alkenes can be accomplished directly through the chlorotrifluoromethylthiolation of sulfur ylides utilizing nucleophilic halide reagent and electrophilic SCF3 reagent. This cascade reaction is mild, highly practical, easy to manipulate, uses catalyst-free conditions, and demonstrates a wide substrate range with excellent functional group tolerance, furnishing E-selective products in good to high yields. The synthetic utility of this approach is documented through gram-scale preparation and late-stage modification of pharmaceutically relevant compounds, making it suitable for drug discovery.

C3-symmetric zinc complexes as sustainable catalysts for transforming carbon dioxide into mono- and multi-cyclic carbonates

In this study, we report a single-step preparation method for the synthesis of a series of C3-symmetric zinc complexes containing both a Lewis acidic zinc center and a nucleophilic halide counter ion for coupling CO2 with epoxides. The Zn-complexes were shown to be effective one-component bifunctional catalysts and displayed high catalytic activity and selectivity for the transformation of CO2 into cyclic carbonates under mild conditions. This strategy is simple, efficient, environmentally benign, and does not require an additional cocatalyst or solvent, and the catalyst can be easily recovered and reused several times without significant loss in catalytic activity. The CO2 coupling reaction proceeded on broad range of substrates and exhibited good tolerance to functional groups, and the cyclic carbonate products were isolated in high yields. On the basis of the experimental results, a plausible reaction mechanism was proposed, and the high catalytic activity was explained.

Tungstate-Catalyzed Biomimetic Oxidative Halogenation of (Hetero)Arene under Mild Condition.

SummaryAryl halide (Br, Cl, I) is among the most important compounds in pharmaceutical industry, material science, and agrochemistry, broadly utilized in diverse transformations. Tremendous approaches have been established to prepare this scaffold; however, many of them suffer from atom economy, harsh condition, inability to be scaled up, or cost-unfriendly reagents and catalysts. Inspired by vanadium haloperoxidases herein we presented a biomimetic approach for halogenation (Br, Cl, I) of (hetero)arene catalyzed by tungstate under mild pH in a cost-efficient and environment- and operation-friendly manner. Broad substrates, diverse functional group tolerance, and good chemo- and regioselectivities were observed, even in late-stage halogenation of complex molecules. Moreover, this approach can be scaled up to over 100 g without time-consuming and costly column purification. Several drugs and key precursors for drugs bearing aryl halides (Br, Cl, I) have been conveniently prepared based on our approach.

Fluorohalogenation of gem-Difluoroalkenes: Synthesis and Applications of α-Trifluoromethyl Halides.

A novel strategy for 1,2-dihalogenation of alkenes is reported that occurs through a sequential nucleophilic halide addition and electrophilic halogenation. By trapping the in situ generated unstable α-trifluoromethyl carbanion intermediates derived from the nucleophilic fluoride addition to electron-poor gem-difluoroalkenes, this fluorohalogenation of gem-difluoroalkenes with electrophilic haloalkynes affords various useful α-trifluoromethyl halides in high yields. A pesticidal active compound and various attractive trifluromethylated molecules could be smoothly synthesized from these obtained α-trifluoromethyl halides.

Borinic Acid‐Catalyzed Regioselective Ring‐Opening of 3,4‐ and 2,3‐Epoxy Alcohols with Halides

AbstractMethods for the regioselective ring‐opening of 3,4‐epoxy alcohols and 2,3‐epoxy alcohols with halide nucleophiles, using a diarylborinic acid catalyst, are disclosed. Ring‐opening occurs at the position proximal to the OH group, an effect ascribed to a catalytic tethering mechanism whereby coordination to the substrate OH group positions the diarylborinic acid to deliver a coordinated halide nucleophile. These methods provide access to halohydrin substitution patterns that were not previously accessible through catalytic epoxide ring‐opening reactions.magnified image

Redox chemistry of \u03c0-extended tellurophenes

In the past decade, the incorporation of tellurophene motifs into organic devices has been a promising strategy for the design of advanced materials. However, fundamental redox behavior of tellurophene-containing materials have never been comprehensively explored. Here, we report unique redox behavior of π-extended tellurophenes. The facile coordination of solvent molecules and/or anions becomes evident, in addition to the attachment of nucleophilic halides. This indicates that the tellurium center in oxidized 2,5-diphenyltellurophene is highly electron-deficient and easily yields coordinated structures. This coordination appears to trap the positive charge on the tellurium center rather than delocalizing it over the π-system. When no coordinating counter ion is present, however, oxidation appears to be delocalized over the entire π-system. Additionally, by using more delocalized structures, we show that coordination and charge-delocalization can co-exist. These results provide important insights to understand the properties of tellurophene-containing molecules and materials with extended π-systems.

Highly Stereo-Controlled Synthesis of Fatty Acid-Derived Cyclic Carbonates by Using Iron(II) Complex and Nucleophilic Halide

A catalytic system comprising an iron(II) complex and a nucleophilic halide for the preparation of a series of stereo-bio-derived cyclic carbonates was developed. The protocol allows for the coupling of various cis-fatty acid-derived epoxides. For example, cis-epoxy substrates can be reacted with CO2 to selectively yield either the cis- or trans-cyclic carbonates by adjusting the nucleophilic halide. These reactions are highly stereoselective and have excellent yields even under mild reaction conditions. The stereochemical divergence in the fatty acid-derived products strongly depends on the leaving ability of the halide anion in the cocatalyst.

Pyridine-bridged bifunctional organocatalysts for the synthesis of cyclic carbonates from carbon dioxide

Hydroxyl- and carboxyl-functionalized imidazolium halides are used as efficient bifunctional organocatalysts for the synthesis of cyclic carbonates from CO2 and epoxides under mild reaction conditions. Control experiments suggest that the cycloaddition reaction is realized by the combination of the nucleophilic halide anions with hydroxyl and carboxyl groups as hydrogen bond donors. Moreover, the bifunctional organocatalysts can be easily recycled five times by simple filtration; however, a loss of activity was observed.

Nucleophilic halo-Michael addition under Lewis-base activation.

A simple and general conjugate nucleophilic halogenation is presented. The THTO/halosilane combination has shown the ability to act as a nucleophilic halide source in the conjugate addition to a variety of Michael acceptors. In addition, a straightforward diastereoselective halogen installation using α,β-unsaturated acyloxazolidinones as platforms has been developed.