Air-stable Catalyst Research Articles

Aminophosphonium organocatalysts for the ring-opening copolymerisation of epoxide and cyclic anhydride.

The Kirsanov reaction has been used to synthesise air stable, efficient and selective bifunctional aminophosphonium catalysts for the alternating ring-opening copolymerisation of cyclohexene oxide and phthalic anhydride without the need for a co-initiator.

Toward rapid and efficient protocols: Synthesis of benzotriazole-based π-conjugated polymers via direct arylation polycondensation under aerobic conditions

π-Conjugated polymers (CPs) are widely used in the field of high-performance plastic electronics. However, the development of sustainable and efficient methods for synthesizing donor-acceptor (D–A)-type CPs remains challenging for their industrialization. In this study, we introduce a simple and rapid direct arylation polycondensation (DArP) technique for preparing various D–A benzotriazole-based π-CPs with high molecular weights under aerobic conditions in two hours. Additionally, the method demonstrates not only excellent yields but also copolymers with nearly defect-free structures. Via a minor modification involving the use of twenty or more equivalents of the base K2CO3 and refluxing the solvent, high molecular weight copolymers can be achieved in a short reaction time under oxygen and moisture conditions. Therefore, this finding presents a direct synthetic protocol that utilizes commercially available and air-stable catalyst precursors to produce high-quality π-CPs suitable for optoelectronic applications.

Synthesis of imines from the coupling reaction of alcohols and amines catalyzed by phosphine-free cobalt(II) complexes.

Phosphine-free, air stable cobalt(II) based complexes (1a and 1b) consisting of ligands L1H2 and L2H2 (L1H2 = N,N'-((1,2-phenylenebis(azaneylylidene))bis(methaneylylidene))diphenol and L2H2 = N,N'-bis(4-diethylaminosalicylidene)-4,5-dichloro-1,2-phenylenediamine) were synthesized and utilized as catalysts in the coupling reaction of alcohols with amines into imines following an acceptorless dehydrogenative pathway. The reactions were carried out in the presence of t-BuOK base with low catalyst loading (1 mol%) in an open atmosphere. The corresponding imines were isolated in moderate to excellent yields. The methodology was screened with different substituted alcohols and amines. The proposed mechanistic pathway of this reaction was ascertained through intermediate mass and 1H NMR analyses. Most of the previously reported 3d transition metal catalysts used in imine synthesis reactions have a phosphine ligand environment, and the reactions were performed under inert conditions. Herein we have developed a sustainable route for the synthesis of imines from the coupling reaction of alcohols with amines under aerial reaction conditions using phosphine-free air stable cobalt catalysts.

Bench-stable Nickel(II)–aryl Complex-Catalyzed cyclotrimerisation of diynes and alkynes to synthesis multisubstituted benzene derivatives

Herein, we report a (PPh3)2Ni(o-tolyl)Cl complex-catalyzed cyclotrimerisation reaction of diynes and alkynes to furnish multi-substituted benzene derivatives in moderate to excellent yields. This method features an air-stable catalyst, green reaction conditions, and excellent functional group tolerance. Additionally, this approach enables gram-scale synthesis, and the target product could also be further derivatised into important isoindolinone scaffolds. These demonstrate the potential application of this methodology.

Electrochemical dinitrogen to ammonia reduction at a nickel(ii) site: an easy access to an air-stable catalyst

The electrochemical nitrogen reduction reaction (NRR) for producing NH3 (ammonia) is a suitable alternative to the Haber–Bosch process due to its eco-friendly and non-polluting nature.

High-Activity and High-Selectivity Air-Stable Nickel and Copper Complexes for Copolymerization of Epoxides with Anhydrides.

Ring-opening copolymerization (ROCOP) of epoxides with anhydrides presents a highly promising pathway for the synthesis of diverse polyester copolymers. This process involves the simultaneous opening of the epoxide ring and the anhydride ring, resulting in the formation of copolymer chains with alternating repeating units. Here, we synthesized a series of nickel and copper complexes coordinated by amine-bis(benzotriazole phenolate) ligands (C1NNBiBTP-H2). Different acid-base conditions can result in the synthesis of diverse coordination structures. The six-coordinated mononuclear Ni catalyst synthesized in this study exhibited competitive turnover frequencies (TOF = 450 h-1) compared to previous studies involving copolymerization of epoxides with anhydrides. This indicates the catalyst's high activity in facilitating the copolymerization reaction. The results indicate that the catalyst exhibited a high molecular weight control ability and high polymer selectivity for the ROCOP of epoxides and anhydrides. Thus, this air-stable catalyst has the potential for use in industries.

Borrowing hydrogen and dehydrogenative/oxidative cyclization reactions catalyzed by a CCC-NHC pincer Re complex: An air stable catalyst for the synthesis of α-alkylated ketones and quinolines

Successful catalytic activity of the CCC-NHC pincer Re(I) complex was achieved for the borrowing hydrogen coupling reaction between primary and secondary benzylic alcohols. An expansive scope of 17 aromatic and 2 aliphatic substrates were investigated and isolated yields from 40% to 91% were collected. The aliphatic substrates yielded complex aldol self-condensation by-products. The catalytic activity of the CCC-NHC pincer Re(I) complex was also evaluated for the formation of quinolines via the dehydrogenative/oxidative cyclization of 2-aminobenzyl alcohols with benzylic ketones or secondary benzylic alcohols. Isolated yields from 68% to 87% were obtained for 12 examples. All products and by-products were fully characterized by 1H &13C NMR and mass spectroscopies. Control studies such as dehydrogenative and hydrogen transfer reaction were carried out, and the results from these experiments supported a proposed mechanism of a borrowing hydrogen coupling reaction catalyzed by the CCC-NHC pincer Re(I) complex.

Straightforward synthesis of N-arylindoles via one-pot Fischer indolisation-indole N-arylation.

A microwave-promoted, one-pot, three-component synthesis of N-arylindoles has been developed, utilising sequential Fischer indolisation then copper(i)-catalysed indole N-arylation. Novel arylation conditions were identified that use a simple and cheap catalyst/base system (Cu2O/K3PO4) in an environmentally benign solvent (ethanol), with no requirement for ligands, additives or exclusion of air or water, and microwave irradiation enabled significant acceleration of this commonly sluggish process. These conditions were designed to dovetail with Fischer indolisation, and the resulting one-pot, two-step sequence is rapid (total reaction time = 40 minutes), operationally straightforward, generally high yielding and it draws upon readily available hydrazine, ketone/aldehyde and aryl iodide building blocks. This process shows broad substrate tolerance and we have demonstrated its utility in the synthesis of 18 N-arylindoles bearing varied and useful functionality.

Synthesis of a CCC‐NHC pincer Re complex: An air stable catalyst for coupling ketones with primary alcohols via borrowing hydrogen

To date, no CCC‐NHC pincer complexes of Re have been reported in the literature. The first CCC‐NHC pincer complex of Re is reported. It was fully characterized by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy, elemental analysis, and X‐ray crystallographic methods to determine the molecular structure. It was synthesized via transmetallation from an isolated Zr precursor and was found to be air stable. The catalytic activity of the CCC‐NHC Re(I) pincer complex was demonstrated for the borrowing hydrogen coupling reaction between benzylic ketones and primary alcohols to generate a new C–C bond in an environmentally friendly catalysis requiring no activating groups for the alcohol functionality. This borrowing hydrogen coupling reaction produced a stoichiometric amount of water as the only by‐product and did not require the conversion of the primary alcohol to a leaving group. A broad range of substrates was examined, and isolated yields from 53% to 92% were obtained. A catalytic cycle for the CCC‐NHC Re(I) pincer complex catalyzed borrowing hydrogen coupling reaction is proposed.

Novel magnetic lignosulfonate-supported Pd complex as an efficient nanocatalyst for N-arylation of 4-methylbenzenesulfonamide

This study presents a novel, economical, and environmentally technique for synthesizing magnetic palladium complex conjugated to activated calcium lignosulfonate with triethylenetetramine (Fe3O4@lignosulfonate@triethylenetetramine@Pd complex (FLT-Pd complex)) as a practical and air-stable catalyst. FLT-Pd complex is used as a catalyst for the fabrication of 4-methyl-N-phenyl-benzenesulfonamide derivatives via N-arylation of 4-methylbenzenesulfonamide in good yields. Furthermore, because of the complex magnetic reparability and high stability, it could be removed easily from the reaction media using a magnet and reused 5 cycles without a remarkable loss of catalytic prowess.

Reversible PCET and Ambient Catalytic Oxidative Alcohol Dehydrogenation by {V=O} Perfluoropinacolate Complexes.

A new air-stable catalyst for the oxidative dehydrogenation of benzylic alcohols under ambient conditions has been developed. The synthesis and characterization of this compound and the related monomeric and dimeric V(IV)- and V(V)-pinF (pinF = perfluoropinacolate) complexes are reported herein. Monomeric V(IV) complex (Me4N)2[V(O)(pinF)2] (1) and dimeric (μ-O)2-bridged V(V) complex (Me4N)2[V2(O)2(μ-O)2(pinF)2] (3a) are prepared in water under ambient conditions. Monomeric V(V) complex (Me4N)[V(O)(pinF)2] (2) may be generated via chemical oxidation of 1 under an inert atmosphere, but dimerizes to 3a upon exposure to air. Complexes 1 and 2 display a perfectly reversible VIV/V couple at 20 mV (vs Ag/AgNO3), whereas a quasi-reversible VIV/V couple at -865 mV is found for 3a. Stoichiometric reactions of 3a with both fluorenol and TEMPOH result in the formation of (Me4N)2[V2(O)2(μ-OH)2(pinF)2] (4a), which contains two V(IV) centers that display antiferromagnetic coupling. In order to structurally characterize the dinuclear anion of 4a, {K(18C6)}+ countercations were employed, which formed stabilizing K···O interactions between the counterion and each terminal oxo moiety and H-bonding between the oxygen atoms of the crown ether and μ-OH bridges of the dimer, resulting in {K(18C6)}2[V2(O)2(μ-OH)2(pinF)2] (4b). The formal storage of H2 in 4a is reversible and proton-coupled electron transfer (PCET) from crystals of 4a regenerates 3a upon exposure to air over the course of several days. Furthermore, the reaction of 3a (2%) under ambient conditions with excess fluorenol, cinnamyl alcohol, or benzyl alcohol resulted in the selective formation of fluorenone (82% conversion), cinnamaldehyde (40%), or benzaldehyde (7%), respectively, reproducing oxidative alcohol dehydrogenation (OAD) chemistry known for VOx surfaces and demonstrating, in air, the thermodynamically challenging selective oxidation of alcohols to aldehydes/ketones.

Tuning the Reactivity of a Heterogeneous Catalyst using N-Heterocyclic Carbene Ligands for C-H Activation Reactions.

We report the dramatic impact of the addition of N-heterocyclic carbenes (NHCs) on the reactivity and selectivity of heterogeneous Ru catalysts in the context of C-H activation reactions. Using a simple and robust method, we prepared a series of new air-stable catalysts starting from commercially available Ru on carbon (Ru/C) and differently substituted NHCs. Associated with C-H deuteration processes, depending on Ru/C-NHC ratios, the chemical outcome can be controlled to a large extent. Indeed, tuning the reactivity of the Ru catalyst with NHC enabled: 1) increased chemoselectivity and the regioselectivity for the deuteration of alcohols in organic media; 2) the synthesis of fragile pharmaceutically relevant deuterated heterocycles (azine, purine) that are otherwise completely reduced using unmodified commercial catalysts; 3) the discovery of a novel reactivity for such heterogeneous Ru catalysts, namely the selective C-1 deuteration of aldehydes.

Catalytic Synthesis of Oligosiloxanes Mediated by an Air Stable Catalyst, (C6F5)3B(OH2).

The utility of (C6F5)3B(OH2) as catalyst for the simple and environmentally benign synthesis of oligosiloxanes directly from hydrosilanes, is reported. This protocol offers several advantages compared to other methods of synthesizing siloxanes, such as mild reaction conditions, low catalyst loading, and a short reaction time with high yields and purity. The considerable H2O-tolerance of (C6F5)3B(OH2) promoted a catalytic route to disiloxanes which showed >99% conversion of three tertiary silanes, Et3SiH, PhMe2SiH, and Ph3SiH. Preliminary data on the synthesis of unsymmetrical disiloxanes (Si-O-Si') suggests that by modifying the reaction conditions and/or using a 1:1 combination of silane to silanol the cross-product can be favored. Intramolecular reactions of disilyl compounds with catalytic (C6F5)3B(OH2) led to the formation of novel bridged siloxanes, containing a Si-O-Si linkage within a cyclic structure, as the major product. Moreover, the reaction conditions enabled recovery and recycling of the catalyst. The catalyst was re-used 5 times and demonstrated excellent conversion for each substrate at 1.0 mol% catalyst loading. This seemingly simple reaction has a rather complicated mechanism. With the hydrosilane (R3SiH) as the sole starting material, the fate of the reaction largely depends on the creation of silanol (R3SiOH) from R3SiH as these two undergo dehydrocoupling to yield a disiloxane product. Generation of the silanol is based on a modified Piers-Rubinsztajn reaction. Once the silanol has been produced, the mechanism involves a series of competitive reactions with multiple catalytically relevant species involving water, silane, and silanol interacting with the Lewis acid and the favored reaction cycle depends on the concentration of various species in solution.

N-heterocyclic carbene-palladium-imine complex catalyzed α-arylation of ketones with aryl and heteroaryl chlorides under air atmosphere

A new structure of saturated ring skeleton monoligated NHC-Pd-Imine complex was easily synthesized and unambiguously confirmed by X-ray single crystal diffraction. It was found to be an efficient and air-stable catalyst for the α-arylation of ketones. The reaction could be operated in air without any negative effect. Non-activated aryl and heteroaryl chlorides have been successfully applied in the reaction with only 0.5 mol% catalyst loadings under air atmosphere. Excellent to good product yields were afforded.

First Example of Copper(I) Catalyzed Decarboalkoxymethylation of Alkyl 2‐[1‐(Pyridin‐2‐yl)‐1H‐pyrrol‐2‐yl]acetates

Herein we report an unprecedented functional group assisted decarboalkoxymethylation (–CH2CO2R) of N‐pyridinyl pyrrolo esters by using air stable and cheap copper(I) catalyst. 2‐formyl substituent of pyrrole unit is the key isolated intermediate for this novel transformation. This methodology is quick and tolerates a wide range of functional groups in open flask conditions. This protocol provides a large array of tricyclic N‐pyridinyl 2, 5 unsubstituted fused pyrrole derivatives with high yield (up to 92 %).

Cobalt-catalyzed regioselective hydrohydrazination of epoxides.

Using an air-stable cobalt catalyst [Cp*Co(1,2-Ph2PC6H4S)(NCMe)]BF4 (1, Cp* = Me5C5-), we have achieved catalytic regioselective hydrohydrazination of epoxides to 1,1-hydrazinoalcohols in an atom-economical manner. The catalysis involves a cobalt-hydrazine intermediate, in which the NH2 group of the hydrazine binds to the metal center, inhibiting its nucleophilic reactivity and allowing the NH group to participate in the regioselective hydrohydrazination.

Nitrogen Doped Carbon–Silica Based Cu(0) Nanometal Catalyst Enriched with Well-Defined N-moieties: Synthesis and Application in One-Pot Synthesis of 1,4-Disubstituted-1,2,3-triazoles

A novel, air stable, water dispersible and efficient catalyst based on copper nanoparticles immobilized on nitrogen doped carbons derived from inorganic–organic composite [Cu(0)@NDC-Sil] has been prepared. Doping of carbons i.e. inorganic–organic (silica–starch) composite using 5-phenyl-1,2,3,4-tetrazole, a nitrogen-rich precursor imparts a variety of nitrogen functionalities even at moderate temperature and enables the generation of active sites for the immobilization of Cu(0) nanoparticles. The novel catalyst system has been well characterized by various techniques like SEM, HRTEM, STEM, TGA, CHN, EDX, ICP-AES, XRD and XPS and was found to be highly efficient for the one-pot synthesis of 1,4-disubstituted-1,2,3-triazoles via click chemistry approach with a wide range of substrate scope such as benzyl/allyl halides and alkyl bromides. Moreover, it could be easily recovered by filtration and reused without significant loss in its activity.

An efficient Pd(II)-(2-aminonicotinaldehyde) complex as complementary catalyst for the Suzuki-Miyaura coupling in water

An efficient new Pd(II)-(2-aminonicotinaldehyde)-catalyzed Suzuki-Miyaura coupling of the aryl halides (Br, Cl and I) and organoboronic acids at moderate temperature in water is described. Low catalyst loading, easy accessibility, being an air-stable catalyst, functional group compatibility, and water as the reaction medium are some of the key features of this synthetic method. This protocol is also applicable for gram scale.

A Novel Route to Substituted 2‐(N‐Arylamino)benzothiazoles via Iron‐Promoted C‐S Bond Formation

AbstractThe synthesis of 2‐aminobenzothiazoles has been demonstrated in the presence of transition metal under mild reaction conditions. In this paper, disubstituted thioureas have also been reported from isothiocyanates at room temperature. Subsequently, C−S cross‐coupling reaction was described for the construction of benzothiazoles using cheap, readily available and air stable Iron catalyst. Moreover, no other byproducts could be observed except target products. Furthermore, control experiments were performed for reveal the mechanism. In addition, a broad range of substrate scope has been explored.

Cobalt-promoted regioselective preparation of aryl tetrazole amines

A highly general, efficient and simple methodology for the regioselective synthesis of aryl tetrazole amines has been explored. The present method involves consecutive desulphurization and $$C\hbox {-}N$$ cross-coupling reaction. Cheap, readily available and air stable cobalt catalyst has been used for this methodology. In addition, the substrate scope has been demonstrated. A highly general, efficient and simple methodology for the regioselective synthesis of aryl tetrazole amines has been explored. The present method involves consecutive desulphurization and $$C\hbox {-}N$$ cross-coupling reaction.