CN Bond Cleavage Research Articles

Uncommon Phosphonylation of Pyrazine‐2,3‐dicarbonitrile Derivatives via C(sp2)−CN Bond Cleavage

AbstractA direct phosphonylation of the C(sp2)−CN bond under mild catalytic and non‐catalytic reaction conditions is disclosed. Pyrazine‐2,3‐dicarbonitriles are readily coupled with HPO(OEt)2 to produce the corresponding dialkoxyphosphoryl‐substituted pyrazines. The phosphonylation reaction occurs in the presence of a base (Et3N, Cs2CO3) as nucleophilic substitution of the CN groups. The yield of target diphosphonates depends on the nature of substituents in the 5,6‐positions of the pyrazine ring: it exceeds 90 % for di‐5,6‐aryl‐substituted pyrazines and is significantly lower when electron‐donating alkyl (n‐propyl) groups are attached to the 5,6‐positions. It should be noted that for pyrazine‐2,3‐dicarbonitriles bearing vicinal 4‐bromophenyl groups, the nucleophilic phosphonylation leading to C−CN/P−H coupling in the pyrazine ring is predominant over Pd‐catalyzed Hirao's C−Br/P−H coupling reaction in phenyl rings. Detailed structural characterization, both in solution by means of 1H, 13C and 31P NMR spectroscopy and in the solid state by single crystal X‐ray diffraction, of a series of newly synthesized pyrazine phosphonates is reported.

Ferrate(Ⅵ) oxidative degradation of capecitabine in aquatic matrices: Degradation performance, mechanisms, and toxicity assessment

The growing utilization of anticancer drugs in recent years has resulted in their presence in surface water and sewage, which could have ecological consequences. In this work, ferrate (Fe(VI)) was utilized to oxidize capecitabine (CAP), a frequently used anticancer drug that has gained attention lately. The experiments have demonstrated that Fe(VI) was quite reactive with CAP at pH 7. The addition of humic acid (0.1–10 mg L−1) significantly inhibited the oxidation process. Then, four reaction pathways, mainly including hydroxyl substitution, direct oxidation and cleavage of CO and CN bond were proposed based on twelve products detected by high-resolution hybrid quadrupole time-of-flight mass spectrometer. These pathways were further validated by theoretical calculations. Experiments conducted in water matrices assessed the applicability of Fe(VI) technology. Toxicity assessments of CAP and its intermediates were performed using the TEST program, and predictions indicated that the intermediates were generally less toxic than CAP. Overall, this work revealed that Fe(VI) has great potential to solve the environmental pollution problems associated with capecitabine in water.

Efficient electrochemical degradation of ranitidine by a novel Bi-coated titanium oxide electrode: Performance and mechanism

Ranitidine (RAN) is a commonly prescribed medication that poses ecological risks due to its potential to transform into the carcinogenic byproduct N-nitrosodimethylamine (NDMA) in the environment. Herein, we synthesized a novel bismuth-coated titanium oxide (Bi-Ti4O7) electrode using a straightforward coating method and evaluated its effectiveness in the electrochemical oxidation of RAN. The Bi-Ti4O7 electrode achieved a degradation efficiency of 90.41 % for an initial RAN concentration of 10 mg/L within 120 min, greatly outperforming the pristine Ti4O7 electrode. The incorporation of Bi enhances the oxygen vacancies and charge transfer characteristics, facilitating direct electron transfer between RAN and the Bi-Ti4O7 electrode. The potential degradation pathways of RAN by the Bi-Ti4O7 electrode included C–S bond cleavage, C–N bond cleavage, and electrophilic oxidation. No NDMA was generated during the oxidation process, and the toxicity of RAN oxidation intermediates was greatly reduced. The Bi-Ti4O7 electrode demonstrated excellent stability, maintaining over 90 % degradation efficiency across 30 cycles, and showed wide applicability across different pH levels and wastewater types with negligible Bi ion release (0.148 µg/L). These results underscore the potential of Bi-Ti4O7 as an effective and sustainable solution for RAN-polluted wastewater treatment.

Effect of loading different transition metals W, Pt and Pd monolayers on quinoline hydrogenation and C–N bond cleavage over Mo2C(001)

Nitrogen-containing compounds such as quinoline in coal-based crude oils cause environmental pollution in the course of application. Consequently, dealing with the nitrogen-containing compounds from coal-based crude oil is of paramount importance. The hydrogenation and CN bond cleavage mechanisms of quinoline on the active Mo-terminated over Mo2C(001) surface, as well as on surfaces doped with W, Pt and Pd monolayers, were examined employing the density functional theory (DFT) method. The Pd and Pt-doped catalysts exhibited higher hydrogenation activity. The catalytic efficiency is enhanced by the loading of different metals, particularly with d-band center further away from the Fermi energy level. Additionally, a novel CN bond cleavage mechanism for quinoline has been proposed. The new proposed mechanism is more conducive for the CN bond cleavage. After a thorough comparison, the Pd-loaded catalyst was identified as the most effective for quinoline hydrogenation and CN bond cleavage.

[Fe(NCMe)6](BF4)2 is a bifunctional catalyst for styrene aziridination by nitrene transfer and heterocycle expansion by subsequent dipolar insertion

The solvated iron(II) salt [Fe(NCMe)6](BF4)2 (Me = methyl) is shown to be a bifunctional catalyst with respect to aziridination of styrene. The salt serves as an active catalyst for nitrene transfer from PhINTs to styrene to form 2-phenyl-N-tosylaziridine (Ph = phenyl; Ts = tosyl, –S{O}2–p-C6H4Me). The iron(II) salt also acts as a Lewis acid in non-coordinating CH2Cl2 solution, to catalyze heterolytic CN bond cleavage of the aziridine and insertion of dipolarophiles. The 1,3-zwitterionic intermediate is presumably supported by interaction of the metal dication with the anion, and by resonance stabilization of the carbocation. Nucleophilic dipolarophiles then insert to give a five-membered heterocyclic ring. The result is a two-step cycloaddition, formally [2 + 1 + 2], that is typically regiospecific, but not stereospecific. This reaction mechanism was confirmed by conducting a series of one-step, [3 + 2] additions of unsaturated molecules into pre-formed 2-phenyl-N-tosylaziridine, also catalyzed by [Fe(NCMe)6](BF4)2. Relevant substrates include styrenes, carbonyl compounds and alkynes. These yield five-membered heterocylic rings, including pyrrolidines, oxazolidines and dihydropyrroles, respectively. The reaction scope appears limited only by the barrier to formation of the dipolar intermediate, and by the nucleophilicity of the captured dipolarophile. The bifunctionality of an inexpensive, earth-abundant and non-toxic catalyst suggests a general strategy for one-pot construction of heterocyclic rings, as demonstrated specifically for pyrrolidine ring formation.

Dynamic kinetic stereodivergent transformations of propargylic ammonium salts via dual nickel and copper catalysis

The dynamic kinetic asymmetric transformation of racemic propargylic ammonium salts with prochiral aldimine esters through a stereodivergent propargylation is catalyzed by dual nickel and copper catalysis. Thus, a diverse range of optically active α-quaternary amino esters were produced via CN bond cleavage with high reaction efficiency and stereoselectivity (up to >99% ee). By selection of the appropriate pairwise combination of catalyst configurational isomers, all four possible stereoisomers of the corresponding propargylation products are obtained in high yields with excellent regio-, diastereo-, and enantioselectivities.

Synthesis of oxazolines through a Pd-catalyzed alkyne-enabled C[sbnd]N activation of oxazolidines

Strategies that enable selective CN bond activation of tertiary amines provide one of the cornerstones of modern organic synthesis. Here we describe a palladium-catalyzed selective CN bond cleavage of N-propargyl 1,3-oxazolidines, providing an efficient approach to a diverse range of oxazolines in good to excellent yields. The reaction proceeds through a domino process of the alkyne-enabled 1,5-hydrogen transfer/CN bond activation. In this way, two kinds of oxazoline skeleton that tolerates a wide variety of functional groups were formed.

Computational exploration on hydroxyl and sulfate radicals-induced aqueous degradation of imipramine

In the present work, hydroxyl (•OH) and sulfate radicals (SO4•−)-induced aqueous degradation of imipramine (IMI) was theoretically probed by carrying out density functional theory (DFT) calculation. Among the initial reactions of •OH (SO4•−) toward IMI, the hydrogen abstraction (HA) reactions occurring on saturated carbon atoms of the alkylamine side chain are the most favorable, followed by the addition (AD) reactions involving unsaturated carbon positions, and the HA reactions related to unsaturated carbon atoms are the most unfavorable. The most favorable subsequent reactions for the initial AD and HA intermediates can afford the hydroxylation, oxidation, dehydrogenation, CN or CC bond cleavage products of IMI, while the corresponding ring-opening reactions occur hard. The stronger oxidizing ability of SO4•− was predicted in comparison with •OH. The cationic form of IMI has lower reactivity than IMI.H2O and O2 molecules may exert a significant influence over aqueous degradation of IMI.

Highly efficient hydrogenation of carbamates catalyzed by pincer ruthenium complexes

The [fac-PNN]RuH(PPh3)(CO) complex (Ru1) has been identified as a highly efficient catalyst for the hydrogenation of a broad spectrum of arylcarbamates and their derivatives (49 examples). The hydrogenation reaction occurs smoothly via CN bond cleavage, affording the desired amines and alcohols or diols at a low catalyst loading of 0.25 mol% in tert-amyl alcohol. Most importantly, this catalytic system offers a promising route for the sustainable depolymerization and recycling of polyurethanes (PUs). Moreover, a detailed mechanism for the hydrogenation of carbamates has been established through combined DFT calculations and control experiments, which suggests that Ru-hydride pathways involve three cycles, with the rate-determining step most likely being the dissociation of the CN bond in the key intermediate H(CO)NHPh. These results have far-reaching implications for the development of more effective and eco-friendly catalytic systems for carbamate transformation and their potential industrial application on a large scale.

Mechanistic Investigation of the Nickel-Catalyzed Transfer Hydrocyanation of Alkynes.

The implementation of HCN-free transfer hydrocyanation reactions on laboratory scales has recently been achieved by using HCN donor reagents under nickel- and Lewis acid co-catalysis. More recently, malononitrile-based HCN donor reagents were shown to undergo the C(sp3)-CN bond activation by the nickel catalyst in the absence of Lewis acids. However, there is a lack of detailed mechanistic understanding of the challenging C(sp3)-CN bond cleavage step. In this work, in-depth kinetic and computational studies using alkynes as substrates were used to elucidate the overall reaction mechanism of this transfer hydrocyanation, with a particular focus on the activation of the C(sp3)-CN bond to generate the active H-Ni-CN transfer hydrocyanation catalyst. Comparisons of experimentally and computationally derived 13C kinetic isotope effect data support a direct oxidative addition mechanism of the nickel catalyst into the C(sp3)-CN bond facilitated by the coordination of the second nitrile group to the nickel catalyst.

Insight into pyrolysis mechanism of plastic waste with C-O/C-N bonds in the backbone

Pyrolysis is an important method for efficiently recovering plastic monomers, fuels and chemicals from plastic waste. The depolymerization of the backbone structure of plastic waste is a key step of the pyrolysis process. Currently, researches on the pyrolysis mechanism of plastics with C-O/C-N bonds in the backbone are still not sufficiently in-depth and also lack systematic and comprehensive investigation. Therefore, this study for the first time comprehensively investigated both macroscopic and microscopic pyrolysis processes of plastics with C-O/C-N bonds in the backbone, and evaluated the difficulty of breaking different backbone linkages via bond dissociation energy (BDE) obtained by density functional theory (DFT) calculations to deeply reveal the pyrolysis mechanism. The results indicated that polyethylene terephthalate (PET) had a higher initial pyrolysis temperature and its thermal stability was slightly stronger than nylon 6. The backbone of PET was mainly decomposed via the cleavage of Cα-O on the alkyl side, while the degradation of nylon 6 backbone began with NH2 groups at the end of the backbone. The pyrolysis products of PET were mainly derived from the small molecular fragments, which were generated by the degradation of the backbone through the cleavage of CO bonds or CC bonds, while the pyrolysis products of nylon 6 were always dominated by caprolactam. In addition, based on the results of DFT calculations, it could be inferred that the cleavage of CC bond in PET backbone and the cleavage of its adjacent Cα-O were most likely to occur, which followed a competitive reaction mechanism. However, in pyrolysis of nylon 6, the conversion to caprolactam was mainly via the concerted reaction of amide CN bonds. Compared with the concerted cleavage of amide CN bond, the cleavage of CC bond in the backbone of nylon 6 was not predominant.

Copper iodide mediated telescoped synthesis of 3-cyanoimidazo[1,2-a]pyridines, photophysical and DFT studies

An efficient copper iodide-mediated synthesis of 3-cyanoimidazo[1,2-a]pyridines (4a-4m) from readily available methyl ketones, amino pyridines, and ethyl(ethoxymethylene)cyanoacetate is described. Copper(I)-catalyzed annulation between different aminopyridines and various methyl ketones resulted in the formation of imidazo[1,2-a]pyridines (IPs). The resulting IPs undergo C3 cyanation by cyanide anion generated from C(sp2)-CN bond cleavage of ethyl(ethoxymethylene)cyanoacetate. Mechanistic studies indicate that the cyanation of IP derivatives proceeds through a two-step sequence: initial iodination and then cyanation. The one-pot reaction has a wide substrate scope and high functional group tolerance and can be safely conducted on a gram scale. Further, we have studied the light-emitting properties of synthesized compounds. The absorption and emission spectra of compounds 4a and 4f were experimentally and computationally analyzed. Also, HOMO/LUMO distributions of compounds 4a and 4f were elucidated theoretically.

Insight into the hydrodenitrogenation mechanism of quinoline on the MoP(010) surface with and without the effect of sulfur

The nitrogenous aromatic compounds such as quinoline in coal-based crude oil not only generate photochemical smog, but also inhibit the activity of catalyst to a certain extent. The hydrodenitrogenation (HDN) mechanism of quinoline including hydrogenation and ring opening was investigated by using the density functional theory (DFT) on the MoP(010) surface. The favorable pathway is that quinoline generates 1,2,3,4-tetrahydroquinoline (THQ1) through hydrogenation, and then undergoes CN bond cleavage through the Hoffman elimination mechanism (E2). In addition, the effect of S in coal-based crude oil on quinoline HDN was also investigated. The introduction of S leads to the transfer of more electrons from the uppermost surface of MoP(010) to the S, which improves the HDN activity for the MoP(010) surface by reducing the hydrogenation energy barrier for the quinoline to THQ1. The microkinetic analysis indicates that the actual temperature (650 K) is more favorable for the HDN of quinoline on the MoP(010) surface.

Recent Advances in the Transformation Reactions of Aromatic Nitriles via C—CN Bond Cleavage

Recent Advances in the Transformation Reactions of Aromatic Nitriles via C—CN Bond Cleavage

Hypervalent iodine mediated Pd(II)‐catalyzed ortho‐C(sp2−H) functionalization of azoles deciphering Hantzsch ester and malononitrile as the functional group surrogates

AbstractC−H bond activation has surfaced as a transformative toolbox for the efficient assembly of biologically important molecules. However, despite of major advances in palladium, rhodium and silver catalysis, yet palladium(II)‐ catalyzed, iodobenzene diacetate (PIDA) mediated C−H bond activation in azole skeleton has deluged with interesting wining outcome. Concentrating on that we herein report on the involvement of 4‐functionalized 1,4‐dihydropyridines (R‐DHPs) as the representative surrogates of benzoyl, pivalyl and ethoxycarbonyl groups and in presence of PIDA it releases appropriate functional radical (following single electron transfer oxidation of R‐DHPs under thermal condition)to become the part of ortho‐ functionalized azoles via Pd(II) catalysis. In case of cyanation reaction, malononitrile has served the key source of nitrile functionality by undergoing oxidative C−CN bond cleavage in presence of PIDA and with the help of Pd(II) catalyst it offers ortho‐cyanated azoles. Additionally, the selective formation of C‐3 benzoyl and ester functionalized indazole derivatives in absence of Pd(II)‐catalyst and the unprecedented formation of homo‐coupling products between two identical 2H‐indazoles are also notable outcome of present strategic access. Overall this protocol operates under mild condition, tolerates a wide range of structural moieties and gives versatile azole derivatives in high efficiency. The antioxidant properties of the synthesized 2‐thiophenyl benzoyl selenazole and isoselenazole are further evaluated using a chemically defined method. The Copper‐ascorbate (Cu−As) was utilized as an oxidative stress generator. Out of screened azoles, the 2‐benzoyl isoselenazole compound (3 i) displays magnificent antioxidant property as compared to the 2‐thiophenyl benzoyl selenazole (3 g).

Formation of dimethoxy bridged dinuclear iron(III) complex of pyridoxal Schiff base with iron-catalyzed oxidative C[sbnd]N bond cleavage – Structure, magnetic properties, and DFT calculations

Mononuclear Fe(III) complex [FeL(N3)]·CH3OH, where L2– is the dianion of an unsymmetrical propyl-ethyl pentadentate Schiff base ligand condensed from pyridoxal and N-(2-aminoethyl)propane-1,3-diamine, and dinuclear Fe(III) complex [{FeL’}2(μ-OCH3)2]·2.5CH3OH·H2O, where L’2– is the dianion of tetradentate Schiff base ligand based on pyridoxal and ethylenediamine, have been synthesized and characterized by elemental analysis, X-ray structural analysis, FT-IR and mass spectrometry. Tetradentate pyridoxal Schiff base ligand L’2– of the dinuclear complex was generated in situ via iron-catalyzed oxidative CN bond cleavage of the pentadentate Schiff base. The coordination geometry around the iron(III) centers of the complexes can be described as adistorted octahedron. Magnetic investigations of [FeL(N3)]·CH3OH complex revealed that the octahedral Fe(III) center retains high-spin in the entire temperature range (2–300 K) and enabled the evaluation of the axial zero-field splitting (ZFS) parameter D = –1.78 cm−1, intermolecular exchange parameter zj́ = –1.35 cm−1 and temperature-independent paramagnetism χTIM = 0.00029 cm3mol−1. Magnetic investigations of [{FeL’}2(μ-OCH3)2]·2.5CH3OH·H2O showed that Fe(III) centers are coupled by a strong antiferromagnetic interaction (J = –94.5 cm−1). The experimental magnetic properties of the complexes were compared with the data obtained from the density functional theory (DFT) calculations.

The polyoxometalates mediated preparation of phosphate-modified NiMoO4−x with abundant O-vacancies for H2 production via urea electrolysis

It is urgent to develop non-noble metal electrocatalysts with both excellent activity and durable stability for H2 production via water electrolysis. Electric energy is mainly consumed by the sluggish anodic oxygen evolution reaction (OER). The electrocatalytic urea oxidation reaction (UOR) has been regarded as a promising reaction to replace OER because of its small thermodynamic oxidation potential. However, developing a facile and large-scale preparation method for bifunctional hydrogen evolution reaction (HER) and UOR electrocatalysts is still challenging. Herein, phosphate-modified (4.46 atomic%) NiMoO4−x net-like nanostructures are formed on Ni foam (NF) via H3PMo12O40 etching strategy at room temperature (denoted as NF/P-NiMoO4−x). The etched NF can directly serve as HER electrode, and delivers overpotential of 116 mV at current density of 10 mA/cm2 with Tafel slope of 77.5 mV/dec. Furthermore, it displays excellent UOR activity with potential of 1.359 V at current density of 10 mA/cm2 and Tafel slope of 19.3 mV/dec. The apparent activation energy of NF/P-NiMoO4−x is 20.6 kJ/mol, lower than that of NF (37.7 kJ/mol), indicating smaller apparent barrier for CN bond cleavage in urea. The cell voltage of urea electrolysis is around 1.48 V for H2 production to deliver current density of 10 mA/cm2, and better long-term stability for 50 h than that of Ir/C||Pt/C. The etching solution can be recycled for five times by addition of H2O2, turning heteropoly blue into its original state. This work develops a facile and large-scale method to prepare bifunctional HER and UOR electrocatalysts for H2 production in a less-energy saving way via urea electrolysis.

Synergic degradation Chloramphenicol in photo-electrocatalytic microbial fuel cell over Ni/MXene photocathode

The abuse of Chloramphenicol (CAP) has become the increasingly serious environmental problem for its harmfulness and toxicity. A novel strategy was achieved by photocatalysis coupled with microbial fuel cell (Photo-MFC) over Ni/MXene photocathode for enhancing the degradation efficiency of (CAP). It was demonstrated that the best degradation efficiency of CAP can reach 82.62% (original concentration of 30 mg/L) after 36 h under the optimal conditions (pH = 2). Based on density functional theory (DFT) calculations and high-performance liquid chromatography-mass (HPLC-MS) spectrometry, it was speculated that the degradation mechanism of CAP in Photo-MFC over Ni/MXene photoelectrode was achieved by destroying the two asymmetric centers and nitro, including the hydrodechlorination, nitro reduction reaction, hydroxylation reaction, cleavage of CN bond and ring-opening reaction of benzene ring. Finally, the ecotoxicity evaluation of the degradation products showed that the CAP degradation in the Ni/MXene modified photo-MFC system showed a remarkable tendency to the low-toxicity level.

A Convenient Esterification of N‐Heteroarene Methanols via C–CN Bond Cleavage of Benzoyl Cyanides as Acylating Sources

AbstractAn efficient and straightforward methodology for the esterification of various N‐heteroarene methanols using benzoyl cyanides as acylating sources through a simply mixing conditions has been reported. The acyl groups were in‐situ generated via chemoselective C–CN bond cleavage to give the N‐heteroarenemethyl esters. This process features in readily accessible starting materials and offers an easy operational procedure, and broad substrate scope with excellent selectivity.

Photocatalytic redox-neutral arylation of cyclopropanols with cyanoarenes via radical-mediated C–C and C–CN bond cleavage

This work describes a photocatalytic redox-neutral arylation of cyclopropanols with cyanoarenes via radical-mediated C–C and C–CN bond cleavage to afford various β-arylated ketones.