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Halogenated arenes and alkenes are of prime importance in many areas of science, especially in the pharmaceutical, agrochemical, and chemical industries. While the simplest ones are commercially available, some of them are still hardly accessible depending on their substitution patterns and the nature of the halogen atom. Reactions enabling the sel...
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Following our quest for stable group 14 divalents, novel N-heterocyclic plumbylenes (NHPbs), composed of 2,4,6-cycloheptatriene-2,7-diazaplumbylene (1), benzannulated with one (2), two (3, 4), and three benzene rings (5), are compared and contrasted at the density functional theory level. Results indicate that in going from 1 to 5, the absolute val...
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... [21] Aryl halides may also be susceptible to Finkelstein-type reactivity in the presence of nickel or copper catalysts. [36] However, we observed a slightly higher 7.1% yield of 3 aa and a cleaner reaction profile when conducting the reaction without this additive (entry 4). Noteworthy, control experiments in the absence of nickel or copper did not yield the desired product (see ESI). ...
The alkyne motif is present in several naturally occurring molecules and specialty chemicals. The Sonogashira reaction is recognized as one of the most exploited methods for the synthesis of substituted alkynes. While palladium catalysts have been traditionally employed, recent efforts have been directed towards developing alternatives based on Earth‐abundant metals such as nickel. However, nickel‐catalyzed Sonogashira couplings still present important substrate limitations. While more reactive aryl iodides have been well documented, the coupling of more challenging yet cost‐effective aryl bromides and chlorides lags significantly behind. Herein, we present a method for the nickel‐catalyzed Sonogashira coupling of aryl bromides and chlorides, whose discovery was accelerated thanks to high‐throughput experimentation. Fine‐tuning of the bipyridine ligand was essential to activate chemoselectively C(sp²)−Br or C(sp²)−Cl bonds. A wide range of functionally diverse alkynes, including examples of active ingredients and their intermediates, were accessed in a single step and with yields up to 98%. The developed methodology is expected to be widely adopted by academia and industry, marking a step forward in the field of base metal catalysis.
... This indicated that the advantage afforded by wider approach angles could not compensate for the relatively poor chloride leaving group and the inferior nucleophilicity of 1-methylimidazole relative to sodium azide. To improve reaction conversion, sodium iodide (NaI) was added to generate HEC-I in situ, since iodide is a better leaving group than chloride (Evano et al. 2018), following the Curtin-Hammett principle (Pollak and Curtin 1950;Winstein and Holness 1955). After addition of 3 equivalents of NaI per Cl, we were encouraged to obtain a water-soluble polymer. ...
Chemical modification of cellulose is challenging due to its low reactivity and poor solubility. Halogenation followed by displacement reactions has been demonstrated to be a valuable strategy for appending new functionalities to the anhydroglucose rings of cellulose and cellulose derivatives. In this paper, we report a simple and efficient pathway to modify the inexpensive, commercial cellulose ether, hydroxyethyl cellulose (HEC). First, methanesulfonyl chloride (MsCl) in N, N-dimethyl formamide (DMF) can selectively chlorinate the terminal primary hydroxyl groups from hydroxyethyl cellulose (HEC), thereby affording high terminal chloride content. Then, the resulting chlorinated HEC undergoes displacement reactions with various nucleophiles including azide (NaN3), amine (1-methylimidazole), and thiols (3-mercaptopropionic acid and 2-mercaptoethanol). All products were characterized by NMR and FT-IR spectroscopic methods. Exploiting this strategy, we prepared a library of HEC derivatives, including cationic and anionic derivatives, which are of great interest in various applications including as surfactants, in gas separation membranes, and as crystallization inhibitors in amorphous solid dispersions for oral drug bioavailability enhancement.
... Just the conversion of halide precursors to the corresponding iodides as coupling partners is far from a new, although strategies along these lines are typically viewed as unattractive; indeed, since the original disclosure over two decades ago, 3 only two reports using this approach have appeared. [4][5][6] This is, perhaps, not surprising, as the conditions required (vide infra) are especially harsh and far from environmentally attractive as in all known cases waste-generating organic solvents are used as reaction media. Moreover, isolation of product iodides presents additional practical issues, such as light sensitivity and hence, limited shelf stability. ...
... In terms of commercial availability, iodides tend to be more expensive, should they even be items of commerce. 6 One solution stems from the opportunity to capitalize on the high local concentrations associated with the inner cores of nanomicelles characteristic of aqueous micellar media, 7 formed by designer surfactants such as TPGS-750-M 8 and Savie (Fig. 2). 9 These concentrations are known to be roughly ten times those traditionally utilized in organic solvents, 7 thereby potentially enabling in situ halide interconversion under milder reaction conditions, leading to greater functional group tolerance, in contrast to those that require elevated temperatures. ...
Palladium-catalyzed reactions that involve functionalized substrates are oftentimes problematic. Those involving aryl or heteroaryl bromides that are either resistant to, or inefficient in such couplings present challenges that are difficult to overcome and may require development of an entirely new route, or worse, no opportunity to install the desired group using a standard coupling strategy. In this report, we describe a solution that allows for the in situ conversion of such bromo educts to transient iodide derivatives that can be made and used under environmentally responsible conditions, for subsequent reactions to highly functionalized, complex targets.
... [6][7][8] While halide exchange in aryl halides is also precedented, [9][10] it took nearly a century following Finkelstein's discovery, until Buchwald's report on the copper-catalyzed aromatic Finkelstein reaction appeared, realizing a synthetically useful protocol for C-Br to C-I exchange at Csp2 centers with a broad substrate scope (Figure 1B). 11 Despite a renewed interest in the development of milder methods to achieve aromatic Finkelstein chemistry due to the synthetic importance of aryl iodides in cross-coupling chemistry, [12][13][14][15][16] Buchwald's method remains state-of-the-art. Indeed, the traditional copper mediated approach that operates via an efficient oxidative addition / halide exchange / reductive elimination sequence has shown utility in various synthetic campaigns. ...
A first-of-its-kind enantioselective aromatic Finkelstein reaction is disclosed for the remote desymmetrization of diarylmethanes. The reaction operates through a copper-catalyzed C‒I bond forming event and high levels of enantioselectivity are achieved through the deployment of a tailored guanidinylated peptide ligand. Strategic use of transition-metal mediated reactions enabled the chemoselective modification of the aryl iodide, thus, the synthesis of a diverse set of otherwise difficult-to-access diarylmethanes in excellent levels of selectivity is realized from a common intermediate. A mixed experimental/computational analysis of steric parameters and substrate conformations identifies the importance of remote conformational effects as a key to achieving high enantioselectivity in this desymmetrization reaction.
... To our surprise, even in the absence of any further reagent (except KOH, which would serve as a base for other reactions) we found conversion of [B 12 H 11 I] 2− to the corresponding [B 12 H 11 Br] 2− . Halogen exchange is known to occur in aryl halides [22], but we had not observed this reaction when further, probably better, groups with good ability to interact with the Pd cation were present. We therefore checked further salts, first with the tetrabutylammonium cation, and then with Na + as the counterion. ...
... To our surprise, even in the absence of any further reagent (except KOH, which would serve as a base for other reactions) we found conversion of [B12H11I] 2− to the corresponding [B12H11Br] 2− . Halogen exchange is known to occur in aryl halides [22], but we had not observed this reaction when further, probably better, groups with good ability to interact with the Pd cation were present. We therefore checked further salts, first with the tetrabutylammonium cation, and then with Na + as the counterion. ...
... We speculate that the exchange with the halides and pseudohalides happens after the oxidative insertion of the Pd into the B-I bond, similar to the mechanisms proposed for the aryl halide exchange [22]. The iodide that had been bound originally to the cluster can exchange with the incoming halide or pseudohalide, and the resulting complex undergoes reductive elimination to the final product. ...
Cross-coupling reactions with [B12H11I]2− as one partner have been used successfully for Kumada and Buchwald Hartwig couplings with Pd catalysis. Here, we found that the iodide could be substituted easily, and unexpectedly, with other halides such as Br and Cl, and with pseudohalides such as cyanide, azide, and isocyanate. We found that for Cl, Br, N3, and NCO, tetrabutylammonium salts—or sodium salts—were successful halide sources, whereas for cyanide, CuCN was the only halide source that allowed a successful exchange. The azide could be reacted further in a click reaction with triazoles. While no substitution with fluoride occurred, tetrabutylammonium fluoride in the presence of water led to [B12H11OH]2−. Yields were high to very high, and reaction times were short when using a microwave oven as a heating source.
... Recently, a study was conducted using fluoride ions as an initiator in polymerizing N-PMI. As a catalyst, the fluoride anion can speed up a variety of reactions, including the alkylation and arylation of phenols, catechols, alcohols (Gangaram, 2013), and other compounds, the Michael addition reaction, esterification reactions (Ooi, 2011), Knoevenagel reactions (Yu, 2013), aldol condensations, intramolecular cyclization reactions (Bhalla, 2010), oxidations, nucleophilic fluorination reactions (Evano, 2018), multicomponent reactions (Gao, 2008), and some specific polymerizations (Zheng, 2019). Fluoride ions are usually utilized in numerous chemical processes as a base, an oxidant, or a nucleophile (Bozdemir, 2010). ...
The polymerization of N-phenylmaleimide (N-PMI) employing sodium phosphate tribasic as a catalyst has been successfully investigated in this study. The effect of dimethyl sulfoxide (DMSO) solvent on the principal catalyst, sodium phosphate tribasic, was extensively studied. The effects of several catalysts, including tetrabutylammonium acetate (TBAA), 4-dimethylaminopyridine (DMAP), Benzyl triethylammonium chloride (BTEAC), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-diazabicyclo[2.2.2]octane (DABCO), 1-Methylimidazole (1MA) and potassium phthalimide salt on polymerization of N-PMI have been discussed in this study. Additionally, the kinetics of polymerization in DMSO with Na3PO4 as the initiator is investigated. By using 1H and 13C nuclear magnetic resonance (NMR) spectrum analysis, attenuated total Reflection-Fourier transform infrared (ATR-FTIR), the resultant polymers were identified. Thermogravimetric and differential scanning calorimetric analyses were used to study the thermal behaviors. Our results prove that a salt form of catalyst can initiate the polymerization of N-PMI in dimethyl sulfoxide at a suitable concentration and under favorable conditions. | KEYWORDS
... For this purpose, potassium iodide was added to the reaction mixture in order to mechanochemically exchange the bromine substituent for the more reactive iodine atom. [24] This technique enhanced the reactivity of brominated compounds, enabling us to couple bromobenzene with a good yield of 86 % after 1 h of milling. In situ XRD measurements were performed using the standard reaction (cf. Figure 1A, Entry 1 Br) with 10 mol-% potassium iodide added. ...
The molecular Suzuki cross‐coupling reaction was conducted mechanochemically, without solvents, ligands, or catalyst powders. Utilizing one catalytically active palladium milling ball, products could be formed in quantitative yield in as little as 30 min. In contrast to previous reports, the adjustment of milling parameters led to the complete elimination of abrasion from the catalyst ball, thus enabling the first reported systematic catalyst analysis. XPS, in situ XRD, and reference experiments provided evidence that the milling ball surface was the location of the catalysis, allowing a mechanism to be proposed. The versatility of the approach was demonstrated by extending the substrate scope to deactivated and even sterically hindered aryl iodides and bromides.
... [6,24,25] Importantly, the substitution of ions also induces changes in the emission and absorption spectrum of the parent composition, resulting in a tunable bandgap by tailoring of the ionic composition. [26] Substitution of halides in particular can be leveraged to tune the emission maxima of the perovskite between 400 ≤ λ ≤ 800 nm. [27][28][29] Therefore, halide substitution offers the best avenue for improving the stability of ABX 3 perovskites, while simultaneously allowing bandgap tunability. ...
Herein, diblock copolymer reverse micelle templating (RMD) is used to control the reaction kinetics of metal halide hybrid perovskites formation to fabricate systems showing dual‐phase emission. Through micelle templating, desired compositions can be engineered which show high phase stability of mixtures of perovskite nanoparticles (NPs) through micellar shielding and stabilizing of the cage structure. In addition, Stokes shift of around 150 nm, one of the largest reported for perovskite systems, can be obtained with careful control over synthesis kinetics. Using an unconventional approach, that is, mixing methylammonium iodide (MAI) and lead bromide PbBr 3 , systems consisting of both green‐ and red‐emitting NPs are fabricated by a two‐step reaction process using RMD. By obtaining two stable phases in a single solution, the NP system can absorb in the ultraviolet region and emit in the red region, making them excellent candidates for downconversion to improve solar cells efficiency, as shown for two polymer active layers in organic bulk heretojunction solar cells (OPVs). Exploiting the phase stabilizing effect of the micelles, the reaction kinetics of perovskite formation can be tuned for various halide substitutions, opening up new avenues for coexisting perovskite phases for photovoltaic and light‐emitting applications. Taking advantage of slower reaction kinetics using diblock copolymer reverse micelle templates, dual‐emission organohalide perovskite nanoparticles with large Stokes shift can be used as UV downconverters for absorbance‐matched organic photovoltaics.
... 45 One way to further enhance the gas permeability of PEEK and related materials is to introduce free volume promoting groups into the polymer backbone. 46 Herein, we present a general strategy for the design of membrane materials based on non-ladder architecture and readily available free-volume generating aryl dihalide [47][48][49] and bisphenol monomers. 41 In the present study we focus on structurally rigid aryl dibromide and bisphenol monomers to produce spirobifluorene(SBF)-based microporous PAEs, including SBF-TBTrip-I (Figure 1b). ...
Membrane-based gas separations are viewed as a critical component to accessing low-energy feedstocks and decarbonizing the chemical industry. However, it is exceedingly challenging to synthesize membrane materials that are high-performing, scalable, and processable. As a class of materials, microporous organic polymers (MOPs), which combine the gas sieving ability of microporous materials with the solution-processability of organic polymers, are highly desirable. Herein, we report the rational design and synthesis of linear microporous poly(arylene ether)s (PAEs) via Pd-catalyzed C-O polycondensation reaction. The scaffold of these microporous polymers consists of rigid three-dimensional triptycene and highly stereocontorted spirobifluorene, which endow these polymers with large internal free volume as well as high porosity with angstrom-sized pores. Unlike classic polymers of intrinsic microporosity (PIMs), this robust methodology for the synthesis of poly(arylene ether)s allows for the facile incorporation of functionalities and branched linkers for control of permeation and mechanical properties. CO2-philic groups, such as nitrile and tertiary amine groups, can be incorporated into this microporous polymeric scaffold for enhancing CO2 separation performance. In addition, a solution-processable branched polymer prepared using this synthetic strategy showed good gas separation performance and enhanced mechanical properties, which allowed for the formation of a submicron defect-free film with permeance-selectivity property sets that are comparable to high-performance ultrathin polymer membranes that have been optimized at industrial scale. In contrast with commercially available polymer membranes, the easily accessible PAE branching motif endows these materials with plasticization resistance. The structural tunability, high physical stability, and ease of processing suggest that this new platform of microporous polymers provides generalizable design strategies to address outstanding separation challenges for gas separation membranes.
... 45 One way to further enhance the gas permeability of PEEK and related materials is to introduce free volume promoting groups into the polymer backbone. 46 Herein, we present a general strategy for the design of membrane materials based on non-ladder architecture and readily available free-volume generating aryl dihalide [47][48][49] and bisphenol monomers. 41 In the present study we focus on structurally rigid aryl dibromide and bisphenol monomers to produce spirobifluorene(SBF)-based microporous PAEs, including SBF-TBTrip-I ( Figure 1b). ...
Membrane-based gas separations are viewed as a critical component to accessing low-energy feedstocks and decarbonizing the chemical industry. However, it is exceedingly challenging to synthesize membrane materials that are high-performing, scalable, and processable. As a class of materials, microporous organic polymers (MOPs), which combine the gas sieving ability of microporous materials with the solution-processability of organic polymers, are highly desirable. Herein, we report the rational design and synthesis of linear microporous poly(arylene ether)s (PAEs) via Pd-catalyzed C-O polycondensation reaction. The scaffold of these microporous polymers consists of rigid three-dimensional triptycene and highly stereocontorted spirobifluorene, which endow these polymers with large internal free volume as well as high porosity with angstrom-sized pores. Unlike classic polymers of intrinsic microporosity (PIMs), this robust methodology for the synthesis of poly(arylene ether)s allows for the facile incorporation of functionalities and branched linkers for control of permeation and mechanical properties. CO2-philic groups, such as nitrile and tertiary amine groups, can be incorporated into this microporous polymeric scaffold for enhancing CO2 separation performance. In addition, a solution-processable branched polymer prepared using this synthetic strategy showed good gas separation performance and enhanced mechanical properties, which allowed for the formation of a submicron defect-free film with permeance-selectivity property sets that are comparable to high-performance ultrathin polymer membranes that have been optimized at industrial scale. In contrast with commercially available polymer membranes, the easily accessible PAE branching motif endows these materials with plasticization resistance. The structural tunability, high physical stability, and ease of processing suggest that this new platform of microporous polymers provides generalizable design strategies to address outstanding separation challenges for gas separation membranes.
