Alkyl Species Research Articles

Synthetic Utility of Alkyl tert-Butyl Peroxides in a Copper-Catalyzed Radical Functionalization

Alkyl tert-butyl peroxides are prepared from the corresponding tert-alkyl precursors and tert-butyl hydroperoxide in the presence of a promoter. These substrates can be utilized in a mild copper-catalyzed radical functionalization that utilizes several coupling partners and has a broad substrate scope. A mechanistic study suggests that alkyl radical species participate in the coupling reactions.

Enhanced Production of Liquid Alkanes from Waste Polyethylene via the Electronic Effect‐Favored Csecondary−Csecondary Bond Cleavage

AbstractCatalytic hydrogenolysis of polyethylene to liquid alkanes has drawn particular attention. However, it remains not very clear about the factors influencing the positions (internal Csecondary−Csecondary and terminal Csecondary−Cprimary bonds) of C−C bond cleavage. Here, we clarify the influence of Ru chemical state on the positions of C−C bond cleavage by designing two Ru/CeO2 catalysts with different Ru chemical states tuned by the metal‐support interaction. It is found that the positively charged Ru species favor the hydrogenolysis of the internal Csecondary−Csecondary bond, inhibiting methane production, because these Ruδ+ species enable the selective bonding with the internal Csecondary containing higher electron density through the electron‐donating effect of adjacent alkyl species instead of the terminal Cprimary. Furthermore, a simple Ru/CeO2−I catalyst with plenty of Ruδ+ species was designed and was efficient for the hydrogenolysis of real waste polyethylene plastics. This work would guide catalyst design to enhance the selective production of liquid alkanes.

Molecular species of glycerophosphoethanolamines in obesity-associated asthma.

Bronchial asthma (BA) complicated by obesity is a progressive disease phenotype that hardly responds to standard therapy. In this regard, it is important to elucidate cellular and molecular mechanisms of development of this comorbid pathology. In recent years, lipidomics has become an active research tool, opening new opportunities not only for understanding cellular processes in health and disease, but also for providing a personalized approach to medicine. The aim of this study was to characterize the lipidome phenotype based on the study of molecular species of glycerophosphatidylethanolamines (GPEs) in blood plasma of patients with BA complicated by obesity. Molecular species of GPEs were studied in blood samples of 11 patients. Identification and quantification of GPEs was carried out using high resolution tandem mass spectrometry. For the first time in this pathology, a change in the lipidome profile of molecular species of diacyl, alkyl-acyl and alkenyl-acyl HPEs of blood plasma was shown. In BA complicated by obesity, acyl groups 18:2 and 20:4 were dominated in the sn2 position of the molecular composition of diacylphosphoethanolamines. Simultaneously with the increase in the level of GPE diacyls with the fatty acids (FA) 20:4, 22:4, and 18:2, there was a decrease in these FAs in alkyl and alkenyl molecular species of GPEs, thus indicating their redistribution between subclasses. The eicosapentaenoic acid (20:5) deficiency at the sn2 position of alkenyl GPEs in patients with BA complicated by obesity indicates a decrease in the substrate for the synthesis of anti-inflammatory mediators. The resulting imbalance in the distribution of GPE subclasses, due to a pronounced increase in the content of diacyl GPE under conditions of the deficiency of molecular species of ether forms, can probably cause chronic inflammation and the development of oxidative stress. The recognized lipidome profile characterized by the modification of the basic composition and the chemical structure of GPE molecular species in BA complicated by obesity indicates their involvement in the pathogenetic mechanisms underlying BA development. The elucidation of particular roles of individual subclasses of glycerophospholipids and their individual members may contribute to the identification of new therapeutic targets and biomarkers of bronchopulmonary pathology.

Magnetic Fe3O4@C nanoparticles separated from cold rolling mill sludge for 4-nitrophenol reduction

Magnetic iron oxides are usually employed as main components of 4-nitrophenol (4-NP) reduction catalysts. Here, magnetic Fe3O4 nanoparticles (Rec-Fe3O4) recycled from rolling oil sludge (ROS) were directly applied in 4-NP reduction reaction. The Rec-Fe3O4 nanoparticles were high purity of Fe3O4 with 0.9 % C content, which were further probed as carboxylates and hydrocarbon alkyl species. Compared with commercial nano-Fe3O4 (Com-Fe3O4), the Rec-Fe3O4 exhibited excellent 4-NP reduction performance with easy magnetic separation showing complete 4-NP conversion to 4-AP within 270 s, and its activity remained stable even after 5 consecutive cycles. Its activation energy was also estimated to be far much less than that of Com-Fe3O4. Benefiting from its special spontaneous formed Fe3O4@C structure during ROS generation, more active low valence Fe species remained and C shell accelerated electronic transfer on the Rec-Fe3O4 surface, both of which led to superior activity during 4-NP reduction reaction. This finding opens up a new insight to both of utilizing ROS waste resource and green synthesis of highly efficient 4-NP reduction catalysts.

Organophosphine as an Alkyl Transfer Shuttle for the Direct β-Alkylation of Chalcones Using Alkyl Halides.

We report an efficient alkyl transfer strategy for the direct β-alkylation of chalcones using commercially available alkyl bromides as alkyl reagents. In this transformation, the ortho-phosphanyl substituent in the chalcones is crucial for controlling their reactivity and selectivity. It also serves as a reliable alkyl transfer shuttle to transform electrophilic alkyl bromides into nucleophilic alkyl species in the form of quaternary phosphonium salts and transfer the alkyl group effectively to the β-position of the chalcones. This alkyl transfer strategy can be further extended to the alkenylation of ortho-phosphanyl benzaldehydes to assemble functionalized polyenes.

Electronic control of catalytic activity of ZnO for higher alcohols synthesis via tailoring Fermi level

Metal doping are essential for electronic modulation of semiconductors, leading to different Fermi level, which determined the surface chemisorption and catalytic properties. Here, ZnO doping with 4 mol% Cu were synthesized by four preparation routes, which tuned Cu existing states and Fermi level appearing remarkable impacts on the catalytic performance of catalysts. It shows a negative correlation between synthesis of higher alcohols and Fermi level over electronically modified ZnO catalysts, and the lower Fermi level exerted better facilitation for the carbon chain growth. Copper was incorporated into ZnO lattice and existed in the form of isolated Cu2+, which regulated the electronic structure of ZnO with lower Fermi level and boosted the process of catalysts obtaining electrons. Thus, the lower Fermi level promoted the dissociation CO bond and p-type reaction of forming surface alkyl species, and a higher proportion of straight chain higher alcohols can be achieved via CO or CHxO* inserting into alkyl species. Especially the catalyst prepared by urea hydrolysis with the lowest Fermi level significantly increased the higher alcohols fraction in total alcohol products to 69.9%. For comparison, the higher Fermi level are unfavorable for p-type reaction, leading to high methanol selectivity. This work provides a new viewpoint for promoting catalytic performance from the perspective of electronic modification of ZnO.

Structural Study of Model Rhodium(I) Carbonylation Catalysts Activated by Indole-2-/Indoline-2-Carboxylate Bidentate Ligands and Kinetics of Iodomethane Oxidative Addition

The rigid-backbone bidentate ligands Indoline-2-carboxylic acid (IndoliH) and Indole-2-carboxylic acid (IndolH) were evaluated for rhodium(I). IndoliH formed [Rh(Indoli)(CO)(PPh3)] (A2), while IndolH yielded the novel dinuclear [Rh1(Indol’)(CO)(PPh3)Rh2(CO)(PPh3)2] (B2) complex (Indol’ = Indol2−), which were characterized by SCXRD. In B2, the Rh1(I) fragment [Rh1(Indol’)(CO)(PPh3)] (bidentate N,O-Indol) exhibits a square-planar geometry, while Rh2(I) shows a ‘Vaska’-type trans-[O-Rh2(PPh3)2(CO)] configuration (bridging the carboxylate ‘oxo’ O atom of Indol2−). The oxidative addition of MeI to A2 and B2 via time-resolved FT-IR, NMR, and UV/Vis analyses indicated only Rh(III)-alkyl species (A3/B3) as products (no migratory insertion). Variable temperature kinetics confirmed an associative mechanism for A2 via an equilibrium-based pathway (ΔH≠ = (21 ± 1) kJ mol−1; ΔS≠ = (−209 ± 4) J K−1mol−1), with a smaller contribution from a reverse reductive elimination/solvent pathway. The dinuclear complex B2 showed the oxidative addition of MeI only at Rh1(I), which formed a Rh(III)-alkyl, but cleaved the bridged Rh2(I) site, yielding trans-[RhI(PPh3)2(I)(CO)] (5B) as a secondary product. A significantly smaller negative activation entropy [ΔH≠ = (73.0 ± 1.2) kJ mol−1; ΔS≠ = (−21 ± 4) J K−1mol−1] via a more complex/potential interchange mechanism (the contribution of ΔS≠ to the Gibbs free energy of activation, ΔG≠, only ±10%) was inferred, contrary to the entropy-driven oxidative addition of MeI to A2 (the contribution of ΔS≠ to ΔG≠ ± 75%).

Nonoxidative Couplings of Methane to Form Ethylene Catalyzed by Coinage Metal-Containing ZSM-5 Zeolites: A Theoretical Study

DFT-based ONIOM calculations were employed to investigate the potential energy surfaces (PESs) for the conversion of methane to ethylene by a ZSM-5 zeolite containing a single coinage metal atom whose formal charge is +1 (M-ZSM-5). According to the ONIOM calculations, two methanes are activated by M-ZSM-5 to form ethylene and H2 via ethane. The mechanisms consist of the following elementary steps: activation of a C–H bond of two methanes by M-ZSM-5 to form CH3–M–CH3, a C–C bond formation in CH3–M–CH3 to form ethane and M-ZSM-5, and sequential activation of two C–H ethane bonds by the regenerated M-ZSM-5 to form ethylene. Depending on the metal cations, various active sites appear, reflecting whether Brønsted acid sites (BASs) are formed after the alkane C–H activation. Three types of active sites are present in Cu- and Ag-ZSM-5: metal cations, methyl-metal (M–CH3) species, and BASs. In contrast, the active sites in Au-ZSM-5 consist of Au cations or H–Au–alkyl species. Looking at their PESs, we found two energy-demanding steps: the second methane activation to form CH3–M–CH3 for all M-ZSM-5 and the second C–H bond activation of ethane by BASs (M = Cu and Ag). We compared their activation energies to find that Cu- and Au-ZSM-5 are catalysts that are more suitable for forming ethylene from methane and ethane, respectively.

Hydride-Abstraction-Initiated Catalytic Stereoselective Intermolecular Bond-Forming Processes.

The stereoselective intermolecular bond-forming reactions through the direct manipulation of ubiquitous yet inert C(sp3)-H bonds represent an important and long-standing goal in chemistry. In particular, developing such a stereoselective bimolecular transformation involving carbocation intermediates generated via site-selective hydride abstraction or formal hydride abstraction by organic oxidants would avoid the preinstallation of directing groups and is therefore attractive. Hydride-abstraction-initiated bimolecular transformations have received considerable attention, but existing examples lack stereoselective studies. Prevalent stereoselective studies typically suffer from the narrow substrate scope of specific and highly reactive N-aryl amines and diarylmethanes together with limited synthetic utility. This Account describes our recent advances in the development and synthetic application of hydride-abstraction-initiated stereoselective intermolecular C-C and C-H bond-forming processes with significantly expanded scopes involving structurally diverse N-acyl amines and ethers together with nitriles, esters, and perfluoroalkyl moieties.We first explored hydride-abstraction-initiated stereoselective intermolecular C-C bond-forming processes. Utilizing triarylmethyl cations or oxoammonium ions as hydride abstractors, we accomplished the diastereoselective oxidative C-H functionalization of structurally diverse N-acyl amines and ethers with a range of organoboranes and C-H components, efficiently installing a series of alkyl, alkenyl, aryl, and alkynyl species into the α-position of heteroatoms with good levels of diastereocontrol. Subsequently, we developed an "acetal pool" strategy as the toolbox to regulate the stability of cationic intermediates and the compatibility of organic oxidants with a delicate asymmetric catalysis system. Utilizing this strategy, we achieved the catalytic enantioselective oxidative C-H alkenylation, arylation, alkynylation, and alkylation of diverse N-acyl heterocycles with a range of boronates and C-H components. Simultaneously, we extended this strategy to the asymmetric oxidative C-H alkylation of ethers. Notably, the method allows solvents that are used daily, such as tetrahydrofuran, tetrahydropyran, and diethyl ether, to be facilely transformed to high-value-added optically pure bioactive molecules. We further expanded the scope of this challenging area from the C(sp3)-H bond adjacent to electron-donating heteroatoms to valuable electron-withdrawing functional groups including nitriles, esters, and perfluoroalkyl moieties for the stereoselective construction of single and vicinal quaternary carbon stereocenters, respectively.We studied hydride-abstraction-initiated catalytic asymmetric intermolecular C-H bond-forming processes, known as redox deracemization. Utilizing the acetal pool strategy, we reported the first redox deracemization of cyclic benzylic ethers. Later, we disclosed an aerobic one-pot deracemization of diverse α-amino acid derivatives with excellent functional group compatibility. We further achieved the deracemization of the tertiary stereogenic center adjacent to electron-withdrawing groups including perfluoroalkyl, cyano, and ester moieties, which are otherwise difficult to construct.

Intercepting Elusive Intermediates in Cu-Mediated CO Electrochemical Reduction with Alkyl Species.

Understanding of the reaction network of Cu-catalyzed CO2/CO electroreduction reaction [CO(2)RR] remains incomplete despite intense research efforts. This is in part because the rate-determining step occurs early in the reaction network, leading to short lifetimes of subsequent surface-bound intermediates, the knowledge of which is key to selectivity control. In this work, we demonstrate that alkyl groups can effectively couple with surface intermediates in the Cu-catalyzed CORR and, for the first time, intercept elusive C1 and C2 intermediates. Combined reactivity data and in situ spectroscopic results demonstrated that surface-bound alkyl groups derived from the corresponding alkyl iodides are able to couple with adsorbed CO to form carboxylates and ketones via one and two successive nucleophilic attacks, respectively. Leveraging this new chemistry, CHx (x ≤ 3) and C2Hx (x ≤ 4) are intercepted and identified as precursors for methane and n-propanol in the CORR, respectively. Importantly, reaction pathways leading to methane and C2+ products are not intrinsically orthogonal, but their connection is mainly impeded by low coverages of energetic intermediates. This study shows that perturbing the reaction of interest by introducing a slightly interacting probe reaction network could be an effective and general strategy in mechanistic studies of catalytic reactions.

Regio- and Diastereoselective Formal [2+2] Cycloaddition of Allenes with Amino-Functionalized Alkenes by Rare-Earth-Catalyzed C(sp2 )-H Activation.

The [2+2] cycloaddition of allenes with alkenes is of much interest and importance as a straightforward route for the construction of four-membered carbocycles but has remained much underexplored to date. Herein we report for the first time the intermolecular regio- and diastereoselective formal [2+2] cycloaddition of a wide range of allenes with amino-functionalized alkenes by half-sandwich rare-earth catalysts. The reaction proceeded through an allene C(sp2 )-H activation mechanism initiated by the site-selective deprotonation of the allene unit by a rare-earth metal alkyl species followed by alkene insertion into the resulting metal-allenyl bond and the subsequent intramolecular cycloaddition to an allene C=C bond. This protocol offers a unique route for the synthesis of a new family of cyclobutane and cyclobutene derivatives which were difficult to access previously.

Regio‐ and Diastereoselective Formal [2+2] Cycloaddition of Allenes with Amino‐Functionalized Alkenes by Rare‐Earth‐Catalyzed C(sp2)−H Activation

AbstractThe [2+2] cycloaddition of allenes with alkenes is of much interest and importance as a straightforward route for the construction of four‐membered carbocycles but has remained much underexplored to date. Herein we report for the first time the intermolecular regio‐ and diastereoselective formal [2+2] cycloaddition of a wide range of allenes with amino‐functionalized alkenes by half‐sandwich rare‐earth catalysts. The reaction proceeded through an allene C(sp2)−H activation mechanism initiated by the site‐selective deprotonation of the allene unit by a rare‐earth metal alkyl species followed by alkene insertion into the resulting metal‐allenyl bond and the subsequent intramolecular cycloaddition to an allene C=C bond. This protocol offers a unique route for the synthesis of a new family of cyclobutane and cyclobutene derivatives which were difficult to access previously.

Nickel-Catalyzed Reductive Dicarbofunctionalization of Vinylarenes Enabled by Electrochemical Process.

An intermolecular alkene dicarbofunctionalization via electrochemical reduction that combines alkyl and aryl iodides with styrene derivatives was herein reported. The multicomponent reaction exhibited several synthetic advantages including simple operation, wide substrate scope, and convenience of amplification. Mechanistic investigations, including cyclic voltammetry (CV), electron paramagnetic resonance (EPR), and radical trapping reactions, support the electrochemical nickel catalytic cycle and formation of alkyl radical species from alkyl iodides.

Dehydroxylative Arylation of Alcohols via Paired Electrolysis.

Nonactivated alcohols along with arene compounds are used in electrochemical dehydroxylative arylation for constructing C(sp3)-C(sp2) bonds. The PIII reagent undergoes single-electron anodic oxidation to form its radical cation, which reacts with the alcohol to produce an alkoxytriphenylphosphine radical. Through spontaneous β-scission of the phosphoranyl radical, the C-O bond is cleaved to form an alkyl radical species, which couples with the radical anion generated by cathodic reduction of the electron-poor arene to afford the dehydroxylative arylated product.

A Facile Approach to Produce Star Polymers Based on Coordination Polymerization

AbstractMany efforts have been devoted to preparing star polymers. Research into coordination polymerization, the most powerful stereoselective process to endow polymers with superb properties, lags far behind those achieved by radical polymerization and ionic polymerization. Herein, we propose a facile strategy to prepare star polymers with regular arms based on coordination polymerization via an insertion reaction between the carbon–heteroatom unsaturated bond and the metal–alkyl species. Terminating a livingcis‐1,4‐selective isoprene polymerization by using isocyanate as cross‐linker (CL), a star polyisoprene with low polydispersity was obtained in high yield (91.8 %). A kinetic study showed the star polymer was formed via a step‐growth procedure. The types ofCLand the ratio of [CL]0 : [Cat.]0are key factors to determine the arm number and the yield of star polymer. Finally, synthetic IR rubber with a green strength up to 1.99 MPa superior to natural rubber (1.43 MPa) was prepared for the first time.

Electrochemical Deoxygenative Barbier-Type Reaction.

An effective deoxygenative C(sp3)-C(sp3) bond formation reaction is achieved through electrochemical reduction of alcoholic phosphates or sulfonates with aldehydes or ketones. Alcohol derivatives of phosphates undergo single-electron reduction under electrochemical conditions followed by a spontaneous cleavage of the C-O bond with the exothermic loss of phosphate resulting in an alkyl radical species. Subsequently, radical intermediates are further reduced to carbanions at the cathode, which are in situ trapped by carbonyl compounds, thus accomplishing a deoxygenative Barbier-type reaction.

Photo-induced trifunctionalization of bromostyrenes via remote radical migration reactions of tetracoordinate boron species

Tetracoordinate boron species have emerged as radical precursors via deboronation by photo-induced single electron transfer (SET) pathway. These reactions usually produce an alkyl radical and boron-bound species, and the valuable boron species are always discarded as a by-product. Given the importance of boron species, it will be very attractive if the two parts could be incorporated into the eventual products. Herein we report a photo-catalyzed strategy in which in situ generated tetracoordinated boron species decomposed into both alkyl radicals and boron species under visible light irradiation, due to the pre-installation of a vinyl group on the aromatic ring, the newly generated alkyl radical attacks the vinyl group while leaving the boron species on ipso-position, then both radical part and boron moiety are safely incorporated into the final product. Tertiary borons, secondary borons, gem-diborons as well as 1,2-diborons, and versatile electrophiles are all well tolerated under this transformation, of note, ortho-, meta- and para-bromostyrenes all demonstrated good capabilities. The reaction portraits high atom economy, broad substrate scope, and diversified valuable products with tertiary or quaternary carbon center generated, with diborons as substrates, Csp2-B and Csp3-B are established simultaneously, which are precious synthetic building blocks in chemical synthesis.

Hydrogenation and isomerization of propenylbenzene isomers over Pt/alumina

The hydrogenation and isomerization of the three isomeric propenylbenzenes, allylbenzene (AB), trans-β-methylstyrene (TBMS) and cis-β-methylstyrene (CBMS), in the liquid phase, was investigated over a 1% Pt/alumina catalyst at 313 K and 1 barg. When reacted individually, the cis-isomer gave the fastest rate of hydrogenation followed by AB, with the trans-isomer having the slowest rate giving a ratio of rates of CBMS:AB:TBMS of 57:19:1. All isomers gave high selectivity to phenylpropane, with isomerization controlled by thermodynamic constraints. Competitive hydrogenation revealed that AB adsorbed on a different site from CBMS and TBMS and that AB inhibited hydrogenation of the other two isomers. In contrast, isomerization was unaffected. These results indicate that AB adsorption limits the supply of hydrogen to the other isomers such that reductive elimination of the half-hydrogenated alkyl species to the alkane is depressed while β-elimination of the alkyl to give an olefin is not affected.

Catalytic cleavage and functionalization of bulky and inert Csp3–Csp3 bonds via a relayed proton-coupled electron transfer strategy

Catalytic cleavage and functionalization of unstrained carbon–carbon bonds represent a formidable challenge for synthetic chemistry. Despite tremendous advances in transition-metal catalysis and photoredox radical chemistry, methods for the cleavage of sterically crowded inert C sp3 –C sp3 bonds remain underdeveloped. Here we describe the direct, photoredox cleavage of hindered C sp3 –C sp3 bonds of alcohols under neutral conditions. A relayed proton-coupled electron transfer (PCET) strategy is employed that overcame the previous requirement of a Brønsted base. Heavily branched alcohols with a high oxidation potential ( E ox½ > +2 V versus saturated calomel electrode) are cleaved and functionalized with remarkable efficiency and versatility. A simple, non-substituted phenyl group can promote a relayed PCET process to deliver primary, secondary, and tertiary alkyl radicals under neutral conditions. • Proton-coupled electron transfer • C–C cleavage of alcohols • Alkyl radicals • Various radicalophiles Liao et al. report a Fukuzumi acridinium salt as a catalyst for the C–C bond cleavage of linear primary, secondary, and tertiary carbinols under neutral conditions. The resulting transient alkyl radical species can be intercepted using various radicalophiles, including electron-deficient alkenes, an electrophilic SCF 3 reagent, and a range of heteroaryls.

Ligand and solvent effects on CO2 insertion into group 10 metal alkyl bonds.

The insertion of carbon dioxide into metal element σ-bonds is an important elementary step in many catalytic reactions for carbon dioxide valorization. Here, the insertion of carbon dioxide into a family of group 10 alkyl complexes of the type (RPBP)M(CH3) (RPBP = B(NCH2PR2)2C6H4−; R = Cy or tBu; M = Ni or Pd) to generate κ1-acetate complexes of the form (RPBP)M{OC(O)CH3} is investigated. This involved the preparation and characterization of a number of new complexes supported by the unusual RPBP ligand, which features a central boryl donor that exerts a strong trans-influence, and the identification of a new decomposition pathway that results in C–B bond formation. In contrast to other group 10 methyl complexes supported by pincer ligands, carbon dioxide insertion into (RPBP)M(CH3) is facile and occurs at room temperature because of the high trans-influence of the boryl donor. Given the mild conditions for carbon dioxide insertion, we perform a rare kinetic study on carbon dioxide insertion into a late-transition metal alkyl species using (tBuPBP)Pd(CH3). These studies demonstrate that the Dimroth–Reichardt parameter for a solvent correlates with the rate of carbon dioxide insertion and that Lewis acids do not promote insertion. DFT calculations indicate that insertion into (tBuPBP)M(CH3) (M = Ni or Pd) proceeds via an SE2 mechanism and we compare the reaction pathway for carbon dioxide insertion into group 10 methyl complexes with insertion into group 10 hydrides. Overall, this work provides fundamental insight that will be valuable for the development of improved and new catalysts for carbon dioxide utilization.