Artículos de revistas: "C-N bond forming processes"

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Valdés, Carlos, Raquel Barroso y María Cabal. "Pd-catalyzed Auto-Tandem Cascades Based on N-Sulfonylhydrazones: Hetero- and Carbocyclization Processes". Synthesis 28, n.º 19 (10 de agosto de 2017): 4434–47. http://dx.doi.org/10.1055/s-0036-1588535.

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The Pd-catalyzed cross-coupling between N-tosylhydrazones and organic halides is a powerful method for the creation of C–C bonds. This transformation has been included recently in cascade processes in which the same catalyst promotes various independent catalytic steps, a process known as auto-tandem catalysis. This strategy proves to be very useful for the construction of relatively complex carbo- and heterocyclic structures, as well as for the generation of molecular diversity. This short review will cover the different Pd-catalyzed auto-tandem reactions involving N-tosylhydrazones organized by the bond-forming sequence: C–C/C–N and C–C/C–C. Some examples of related tandem reactions leading to acyclic compounds are also highlighted.1 Introduction2 Auto-Tandem C–C/C–N Bond-Forming Reactions3 Auto-Tandem C–C/C–C Bond-Forming Reactions4 Tandem Reactions for the Synthesis of Linear Molecules5 Summary and Outlook

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Buchspies, Jonathan, Md Mahbubur Rahman y Michal Szostak. "Transamidation of Amides and Amidation of Esters by Selective N–C(O)/O–C(O) Cleavage Mediated by Air- and Moisture-Stable Half-Sandwich Nickel(II)–NHC Complexes". Molecules 26, n.º 1 (2 de enero de 2021): 188. http://dx.doi.org/10.3390/molecules26010188.

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The formation of amide bonds represents one of the most fundamental processes in organic synthesis. Transition-metal-catalyzed activation of acyclic twisted amides has emerged as an increasingly powerful platform in synthesis. Herein, we report the transamidation of N-activated twisted amides by selective N–C(O) cleavage mediated by air- and moisture-stable half-sandwich Ni(II)–NHC (NHC = N-heterocyclic carbenes) complexes. We demonstrate that the readily available cyclopentadienyl complex, [CpNi(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), promotes highly selective transamidation of the N–C(O) bond in twisted N-Boc amides with non-nucleophilic anilines. The reaction provides access to secondary anilides via the non-conventional amide bond-forming pathway. Furthermore, the amidation of activated phenolic and unactivated methyl esters mediated by [CpNi(IPr)Cl] is reported. This study sets the stage for the broad utilization of well-defined, air- and moisture-stable Ni(II)–NHC complexes in catalytic amide bond-forming protocols by unconventional C(acyl)–N and C(acyl)–O bond cleavage reactions.

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3

Correa, Arkaitz y Marcos Segundo. "Cross-Dehydrogenative Coupling Reactions for the Functionalization of α-Amino Acid Derivatives and Peptides". Synthesis 50, n.º 15 (25 de junio de 2018): 2853–66. http://dx.doi.org/10.1055/s-0037-1610073.

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The functionalization of typically unreactive C(sp3)–H bonds holds great promise for reducing the reliance on existing functional groups while improving atom-economy and energy efficiency. As a result, this topic is a matter of genuine concern for scientists in order to achieve greener chemical processes. The site-specific modification of α-amino acid and peptides based upon C(sp3)–H functionalization still represents a great challenge of utmost synthetic importance. This short review summarizes the most recent advances in ‘Cross-Dehydrogenative Couplings’ of α-amino carbonyl compounds and peptide derivatives with a variety of nucleophilic coupling partners.1 Introduction2 C–C Bond-Forming Oxidative Couplings2.1 Reaction with Alkynes2.2 Reaction with Alkenes2.3 Reaction with (Hetero)arenes2.4 Reaction with Alkyl Reagents3 C–Heteroatom Bond-Forming Oxidative Couplings3.1 C–P Bond Formation3.2 C–N Bond Formation3.3 C–O and C–S Bond Formation4 Conclusions

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4

Youn, So Won. "Transition-Metal-Catalyzed Annulative Coupling Cascade for the Synthesis of 3-Methyleneisoindolin-1-ones". Synthesis 52, n.º 06 (15 de enero de 2020): 807–18. http://dx.doi.org/10.1055/s-0039-1690046.

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This short review describes the recent progress made on transition-metal-catalyzed annulative couplings for the synthesis of 3-methyleneisoindolin-1-ones, which are useful intermediates for the synthesis of numerous alkaloids and can be often found in a wide range of natural products and pharmaceuticals. In particular, new one-pot multiple C–C/C–N bond-forming processes for the construction of the 5-methylenepyrrol-2-one nucleus of such compounds are summarized.1 Introduction2 Intramolecular Cyclization Reactions: C3–N or C3–C3a and C–C Bond Formation3 Intermolecular Annulative Coupling Reactions3.1 C3–C3a and C3–N Bond Formation3.2 C1–C7a and C3–N Bond Formation3.3 C1–C7a and C1–N Bond Formation3.4 C1–C7a, C1–N and C3–N Bond Formation3.5 C3–C3a, C1–C7a, C1–N and C3–N Bond Formation: A Pd-Catalyzed One-Pot Sonogashira Coupling–Carbonylation–Amination–Cyclization Cascade4 Conclusion

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Martín, Cristina del Mar García, José Ignacio Hernández García, Sebastián Bonardd y David Díaz Díaz. "Lignin-Based Catalysts for C–C Bond-Forming Reactions". Molecules 28, n.º 8 (16 de abril de 2023): 3513. http://dx.doi.org/10.3390/molecules28083513.

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Carbon–carbon (C–C) bond formation is the key reaction in organic synthesis to construct the carbon framework of organic molecules. The continuous shift of science and technology toward eco-friendly and sustainable resources and processes has stimulated the development of catalytic processes for C–C bond formation based on the use of renewable resources. In this context, and among other biopolymer-based materials, lignin has attracted scientific attention in the field of catalysis during the last decade, either through its acid form or as a support for metal ions and metal nanoparticles that drive the catalytic activity. Its heterogeneous nature, as well as its facile preparation and low cost, provide competitive advantages over other homogeneous catalysts. In this review, we have summarized a variety of C–C formation reactions, such as condensations, Michael additions of indoles, and Pd-mediated cross-coupling reactions that were successfully carried out in the presence of lignin-based catalysts. These examples also involve the successful recovery and reuse of the catalyst after the reaction.

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6

McNally, Andrew, Ryan Dolewski y Michael Hilton. "4-Selective Pyridine Functionalization Reactions via Heterocyclic Phosphonium Salts". Synlett 29, n.º 01 (12 de diciembre de 2017): 08–14. http://dx.doi.org/10.1055/s-0036-1591850.

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Pyridines are widely used across the chemical sciences in applications ranging from pharmaceuticals, ligands for metal complex and battery technologies. Direct functionalization of pyridine C–H bonds is an important strategy to make useful pyridine derivatives, but there are few ways to selectively transform the 4-position of the scaffold. We recently reported that pyridines can be converted into heterocyclic phosphonium salts that can serve as generic handles for multiple subsequent bond-forming processes. Reactions with nucleophiles and transition-metal cross-couplings will be described to make C–O, C–S, C–N, and C–C bonds in a diverse range of pyridines including those embedded in complex pharmaceuticals.1 Introduction2 Direct, Regioselective Functionalization of Pyridines3 4-Position Selectivity via Metal Catalysis4 Versatile Functional Groups versus Specific Bond Constructions5 Phosphonium Salts as Reagents for Pyridine Functionalization6 Conclusions

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Daoust, Benoit, Nicolas Gilbert, Paméla Casault, François Ladouceur y Simon Ricard. "1,2-Dihaloalkenes in Metal-Catalyzed Reactions". Synthesis 50, n.º 16 (9 de julio de 2018): 3087–113. http://dx.doi.org/10.1055/s-0037-1610174.

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1,2-Dihaloalkenes readily undergo simultaneous or sequential difunctionalization through transition-metal-catalyzed reactions, which makes them attractive building blocks for complex unsaturated motifs. This review summarizes recent applications of such transformations in C–C and C–heteroatom bond forming processes. The facile synthesis of stereodefined alkene derivatives, as well as aromatic and heteroatomic compounds, from 1,2-dihaloalkenes is thus outlined.1 Introduction2 Synthesis of 1,2-Dihaloalkenes3 C–C Bond Forming Reactions4 C–Heteroatom Bond Forming Reactions5 Conclusion

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Todd, David P., Benjamin B. Thompson, Alex J. Nett y John Montgomery. "Deoxygenative C–C Bond-Forming Processes via a Net Four-Electron Reductive Coupling". Journal of the American Chemical Society 137, n.º 40 (5 de octubre de 2015): 12788–91. http://dx.doi.org/10.1021/jacs.5b08448.

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Liu, Jialin, Xiaoyu Xiong, Jie Chen, Yuntao Wang, Ranran Zhu y Jianhui Huang. "Double C–H Activation for the C–C bond Formation Reactions". Current Organic Synthesis 15, n.º 7 (16 de octubre de 2018): 882–903. http://dx.doi.org/10.2174/1570179415666180720111422.

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Background: Among the numerous bond-forming patterns, C–C bond formation is one of the most useful tools for building molecules for the chemical industry as well as life sciences. Recently, one of the most challenging topics is the study of the direct coupling reactions via multiple C–H bond cleavage/activation processes. A number of excellent reviews on modern C–H direct functionalization have been reported by Bergman, Bercaw, Yu and others in recent years. Among the large number of available methodologies, Pdcatalyzed reactions and hypervalent iodine reagent mediated reactions represent the most popular metal and non-metal involved transformations. However, the comprehensive summary of the comparison of metal and non-metal mediated transformations is still not available. Objective: The review focuses on comparing these two types of reactions (Pd-catalyzed reactions and hypervalent iodine reagent mediated reactions) based on the ways of forming new C–C bonds, as well as the scope and limitations on the demonstration of their synthetic applications. Conclusion: Comparing the Pd-catalyzed strategies and hypervalent iodine reagent mediated methodologies for the direct C–C bond formation from activation of C-H bonds, we clearly noticed that both strategies are powerful tools for directly obtaining the corresponding pruducts. On one hand, the hypervalent iodine reagents mediated reactions are normally under mild conditions and give the molecular diversity without the presence of transition-metal, while the Pd-catalyzed approaches have a broader scope for the wide synthetic applications. On the other hand, unlike Pd-catalyzed C-C bond formation reactions, the study towards hypervalent iodine reagent mediated methodology mainly focused on the stoichiometric amount of hypervalent iodine reagent, while few catalytic reactions have been reported. Meanwhile, hypervalent iodine strategy has been proved to be more efficient in intramolecular medium-ring construction, while there are less successful examples on C(sp3)–C(sp3) bond formation. In summary, we have demonstrated a number of selected approaches for the formation of a new C–C bond under the utilization of Pd-catalyzed reaction conditions or hyperiodine reagents. The direct activations of sp2 or sp3 hybridized C–H bonds are believed to be important strategies for the future molecular design as well as useful chemical entity synthesis.

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10

Todd, David P., Benjamin B. Thompson, Alex J. Nett y John Montgomery. "ChemInform Abstract: Deoxygenative C-C Bond-Forming Processes via a Net Four-Electron Reductive Coupling." ChemInform 47, n.º 12 (marzo de 2016): no. http://dx.doi.org/10.1002/chin.201612061.

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11

Gray, Vincent James y Jonathan D. Wilden. "The chemistry of ynol and thioynol ethers". Organic & Biomolecular Chemistry 14, n.º 41 (2016): 9695–711. http://dx.doi.org/10.1039/c6ob01776b.

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12

Buzzetti, Luca, Alexis Prieto, Sudipta Raha Roy y Paolo Melchiorre. "Radical-Based C−C Bond-Forming Processes Enabled by the Photoexcitation of 4-Alkyl-1,4-dihydropyridines". Angewandte Chemie 129, n.º 47 (24 de octubre de 2017): 15235–39. http://dx.doi.org/10.1002/ange.201709571.

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13

Buzzetti, Luca, Alexis Prieto, Sudipta Raha Roy y Paolo Melchiorre. "Radical-Based C−C Bond-Forming Processes Enabled by the Photoexcitation of 4-Alkyl-1,4-dihydropyridines". Angewandte Chemie International Edition 56, n.º 47 (24 de octubre de 2017): 15039–43. http://dx.doi.org/10.1002/anie.201709571.

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14

Chiummiento, Lucia, Rosarita D’Orsi, Maria Funicello y Paolo Lupattelli. "Last Decade of Unconventional Methodologies for the Synthesis of Substituted Benzofurans". Molecules 25, n.º 10 (16 de mayo de 2020): 2327. http://dx.doi.org/10.3390/molecules25102327.

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This review describes the progress of the last decade on the synthesis of substituted benzofurans, which are useful scaffolds for the synthesis of numerous natural products and pharmaceuticals. In particular, new intramolecular and intermolecular C–C and/or C–O bond-forming processes, with transition-metal catalysis or metal-free are summarized. (1) Introduction. (2) Ring generation via intramolecular cyclization. (2.1) C7a–O bond formation: (route a). (2.2) O–C2 bond formation: (route b). (2.3) C2–C3 bond formation: (route c). (2.4) C3–C3a bond formation: (route d). (3) Ring generation via intermolecular cyclization. (3.1) C7a-O and C3–C3a bond formation (route a + d). (3.2) O–C2 and C2–C3 bond formation: (route b + c). (3.3) O–C2 and C3–C3a bond formation: (route b + d). (4) Benzannulation. (5) Conclusion.

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15

Higham, Joe I. y James A. Bull. "Transient imine directing groups for the C–H functionalisation of aldehydes, ketones and amines: an update 2018–2020". Organic & Biomolecular Chemistry 18, n.º 37 (2020): 7291–315. http://dx.doi.org/10.1039/d0ob01587c.

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This review describes recent advances in C–H functionalisation using transient directing groups. Advances in directing group design, new bond forming methodologies, regio- and stereoselective processes, and new mechanistic insights are discussed.

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Nie, Siyuan, Wei Shen, Shengnan Shen, Hui Li, Yuanhui Pan, Yuechang Sun, Yinghua Chen y Haiqin Qi. "Effects of Vacancy and Hydrogen on the Growth and Morphology of N-Type Phosphorus-Doped Diamond Surfaces". Applied Sciences 11, n.º 4 (22 de febrero de 2021): 1896. http://dx.doi.org/10.3390/app11041896.

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Phosphorus is regarded as the best substitutional donor for n-type diamonds. However, because of vacancy-related complexes, H-related complexes, and other defects in P-doped diamonds, obtaining n-type diamonds with satisfying properties is challenging. In this report, PV and PVH complexes are studied in detail using density function theory (DFT). The formation energy reveals the possibility of emergency of these complexes when doping a single P atom. Although vacancies have difficulty forming on the surface alone, the presence of P atoms benefits the formation of PV and PVH complexes and significantly increases crystal vacancies, especially in (111) diamond surfaces. Compared to (111) surfaces, PV and PVH complexes more easily form on (001) surfaces. However, the formation energies of these complexes on (001) surfaces are higher than those of doping P atoms. Studying the structural deformation demonstrated that both constraints of the upper and lower C layers and forces caused by structural deformation prevented doping P atoms. By analyzing the bond population around these dopants, it finds that the bond populations of P–C bonds of PVH complexes are larger than those of PV complexes, indicating that the PV complexes are not as stable as the PVH complexes.

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Valdés, Carlos, Miguel Paraja y Manuel Plaza. "Transition-Metal-Free Reactions Between Boronic Acids and N-Sulfonylhydrazones or Diazo Compounds: Reductive Coupling Processes and Beyond". Synlett 28, n.º 18 (22 de agosto de 2017): 2373–89. http://dx.doi.org/10.1055/s-0036-1590868.

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The metal-free reaction between diazo compounds and boronic acids has been established in recent years as a powerful C(sp3)–C bond-forming reaction. This account covers the recent advances in this area. First, the various synthetic applications of reactions with N-sulfonylhydrazones as a convenient source of diazo compounds is discussed. These transformations can be regarded as reductive couplings of carbonyl compounds. Also covered is the incorporation of other mild sources of diazo compounds in these reactions: diazotization of amines and oxidation of hydrazones. Finally, the development of sequential and cascade processes is presented.1 Introduction2 Early Work: Reactions Between Alkylboranes and Diazo Compounds or N-Sulfonylhydrazones2.1 Reactions Between Alkylboranes and Diazo Compounds2.2 Reactions Between Alkylboranes and N-Sulfonylhydrazones3 Reactions of N-Sulfonylhydrazones and Diazo Compounds with Aryl and Alkylboronic Acids3.1 Reactions of Arylboroxines with Diazo Compounds3.2 Reductive Couplings of N-Sulfonylhydrazones with Aryl- and Alkylboronic Acids3.3 Three-Component Reactions Between α-Halotosylhydrazones, Boronic Acids and Indoles4 Reactions of N-Tosylhydrazones with Alkenylboronic Acids5 Synthesis of Allenes by Reactions with Alkynyl N-Nosylhydrazones6 Reactions with Diazo Compounds Generated by Diazotization of Primary Amines7 Reactions with Diazo Compounds Generated by Oxidation of Hydrazones8 Reactions with Trimethylsilyldiazomethane9 Cascade Cyclization Reactions with γ- and δ-Cyano-N-tosylhydrazones10 Summary and Outlook

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18

Huang, Xiaohua, Kevin W. Anderson, Danilo Zim, Lei Jiang, Artis Klapars y Stephen L. Buchwald. "Expanding Pd-Catalyzed C−N Bond-Forming Processes: The First Amidation of Aryl Sulfonates, Aqueous Amination, and Complementarity with Cu-Catalyzed Reactions". Journal of the American Chemical Society 125, n.º 22 (junio de 2003): 6653–55. http://dx.doi.org/10.1021/ja035483w.

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19

Vinogradova, Ekaterina V. "Organometallic chemical biology: an organometallic approach to bioconjugation". Pure and Applied Chemistry 89, n.º 11 (26 de octubre de 2017): 1619–40. http://dx.doi.org/10.1515/pac-2017-0207.

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AbstractThis review summarizes the history and recent developments of the field of organometallic chemical biology with a particular emphasis on the development of novel bioconjugation approaches. Over the years, numerous transformations have emerged for biomolecule modification with the use of organometallic reagents; these include [3+2] cycloadditions, C–C, C–S, C–N, and C–O bond forming processes, as well as metal-mediated deprotection (“decaging”) reactions. These conceptually new additions to the chemical biology toolkit highlight the potential of organometallic chemistry to make a significant impact in the field of chemical biology by providing further opportunities for the development of chemoselective, site-specific and spatially resolved methods for biomolecule structure and function manipulation. Examples of these transformations, as well as existing challenges and future prospects of this rapidly developing field are highlighted in this review.

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20

Martínez-García, Lucas, Rubén Lobato, Gustavo Prado, Pablo Monje, F. Javier Sardina y M. Rita Paleo. "C–C Bond-Forming and Bond-Breaking Processes from the Reaction of Diesters with Me3SnLi. Synthesis of Complex Bridged Polycycles and Dialkyl Aromatic Compounds". Journal of Organic Chemistry 84, n.º 4 (21 de enero de 2019): 1887–97. http://dx.doi.org/10.1021/acs.joc.8b02891.

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21

LI, Y. y T. J. MARKS. "ChemInform Abstract: Organolanthanoid-Catalyzed Intra- and Intermolecular Tandem C-N and C-C Bond-Forming Processes of Aminodialkenes, Aminodialkynes, Aminoalkeneynes, and Aminoalkynes. New Regiospecific Approaches to Pyrrolizidine, Indolizidine, Pyrrole",. ChemInform 29, n.º 27 (21 de junio de 2010): no. http://dx.doi.org/10.1002/chin.199827135.

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22

Suárez-Pantiga, Samuel y José M. González. "Electrophilic activation of unsaturated systems: Applications to selective organic synthesis". Pure and Applied Chemistry 85, n.º 4 (13 de marzo de 2013): 721–39. http://dx.doi.org/10.1351/pac-con-12-10-24.

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Selected examples from previous work on iodonium-triggered approaches for the functionalization of unsaturated systems, which summarize innovative transformations, are presented. This section is mostly focused on C–C bond-forming processes from alkynes that are directly bonded to relevant heteroatoms, such as iodine, silicon, or sulfur. Besides, recent advances related to iodonium-promoted C–H functionalization reactions are briefly outlined. A second section shows representative examples of our current research activity on electrophilic reactions aimed at the activation of unsaturated systems, which now are built upon the potential offered by the so-called carbophilic catalysis. More specifically, a new catalytic cyclopentannulation sequence from N-tosylimines and propargyl tosylates and novel C–H functionalization processes from related tosylates are studied. Likewise, representative examples for the intermolecular Au(I)-catalyzed [2 + 2] cycloaddition reaction of sulfonylallenamides with activated alkenes are given, including the first enantioselective reaction of this type, which is also among the first examples of an intermolecular asymmetric gold-catalyzed reaction. The discussion of the reported iodonium and gold chemistry emphasizes a search for new intermolecular processes, although intramolecular reactions are also pursued and developed.

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23

Kamanna, Kantharaju y Santosh Y. Khatavi. "Microwave-accelerated Carbon-carbon and Carbon-heteroatom Bond Formation via Multi-component Reactions: A Brief Overview". Current Microwave Chemistry 7, n.º 1 (23 de junio de 2020): 23–39. http://dx.doi.org/10.2174/2213346107666200218124147.

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Multi-Component Reactions (MCRs) have emerged as an excellent tool in organic chemistry for the synthesis of various bioactive molecules. Among these, one-pot MCRs are included, in which organic reactants react with domino in a single-step process. This has become an alternative platform for the organic chemists, because of their simple operation, less purification methods, no side product and faster reaction time. One of the important applications of the MCRs can be drawn in carbon- carbon (C-C) and carbon-heteroatom (C-X; X = N, O, S) bond formation, which is extensively used by the organic chemists to generate bioactive or useful material synthesis. Some of the key carbon- carbon bond forming reactions are Grignard, Wittig, Enolate alkylation, Aldol, Claisen condensation, Michael and more organic reactions. Alternatively, carbon-heteroatoms containing C-N, C-O, and C-S bond are also found more important and present in various heterocyclic compounds, which are of biological, pharmaceutical, and material interest. Thus, there is a clear scope for the discovery and development of cleaner reaction, faster reaction rate, atom economy and efficient one-pot synthesis for sustainable production of diverse and structurally complex organic molecules. Reactions that required hours to run completely in a conventional method can now be carried out within minutes. Thus, the application of microwave (MW) radiation in organic synthesis has become more promising considerable amount in resource-friendly and eco-friendly processes. The technique of microwaveassisted organic synthesis (MAOS) has successfully been employed in various material syntheses, such as transition metal-catalyzed cross-coupling, dipolar cycloaddition reaction, biomolecule synthesis, polymer formation, and the nanoparticle synthesis. The application of the microwave-technique in carbon-carbon and carbon-heteroatom bond formations via MCRs with major reported literature examples are discussed in this review.

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24

Li, Yanwu y Tobin J. Marks. "Organolanthanide-Catalyzed Intra- and Intermolecular Tandem C−N and C−C Bond-Forming Processes of Aminodialkenes, Aminodialkynes, Aminoalkeneynes, and Aminoalkynes. New Regiospecific Approaches to Pyrrolizidine, Indolizidine, Pyrrole, and Pyrazine Skeletons". Journal of the American Chemical Society 120, n.º 8 (marzo de 1998): 1757–71. http://dx.doi.org/10.1021/ja972643t.

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25

Yeagley, Andrew A., Melissa A. Lowder y Jason J. Chruma. "Tandem C−C Bond-Forming Processes: Interception of the Pd-Catalyzed Decarboxylative Allylation of Allyl Diphenylglycinate Imines with Activated Olefins". Organic Letters 11, n.º 17 (3 de septiembre de 2009): 4022–25. http://dx.doi.org/10.1021/ol901745x.

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Li, Ningbo, Qi Fan, Li Xu, Rong Ma, Shitang Xu, Jie Qiao, Xinhua Xu, Rui Guo y Kemin Yun. "Air-stable Organoantimony (III) Perfluoroalkyl(aryl)sulfonate complexes as highly efficient, selective, and recyclable catalysts for C–C and C–N bond-forming reactions". Molecular Catalysis 511 (julio de 2021): 111727. http://dx.doi.org/10.1016/j.mcat.2021.111727.

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Wang, Yuefei, Kunji Chen, Xinye Qian, Zhonghui Fang, Wei Li y Jun Xu. "The role of biasing electric field in intrinsic resistive switching characteristics of highly silicon-rich a-SiOx films". Canadian Journal of Physics 92, n.º 7/8 (julio de 2014): 589–92. http://dx.doi.org/10.1139/cjp-2013-0569.

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The resistive switching behaviors are investigated in highly silicon-rich SiOx (x = 0.73) films, which are deposited using the plasma enhanced chemical vapor deposition method. For the Pt/SiO0.73/Pt structures, after the forming process the reset voltages (∼0.7 V) are lower than the set voltages (∼1.7 V). The metal-free structures N+-Si/SiO0.73/N++-Si/Pt show almost the same switching behaviors as those of Pt/SiO0.73/Pt structures, demonstrating an intrinsic resistive switching mechanism. We use the silicon dangling bonds (Si-DBs) percolation model to explain this. It is based on the biasing electric field decreasing the bond strength and leading to the breakage of Si–O bonds in SiOx films. Consequently the new Si-DBs are created and will contribute to form the dangling bonds percolation path. The temperature dependence of forming voltages is investigated. The forming voltages show no obvious changes and the forming process will occur as soon as the sweeping voltage reaches ∼10.5 V, even if the temperature decreases to 5.5 K. It indicates that the electric field plays an important role during the forming processes. Moreover, through the analysis of X-ray photoelectron spectroscopy and electron spin resonance signals, it can be concluded that the •Si≡Si3 and •Si≡Si2O DBs centers are the main components in Si-DBs percolation path of SiO0.73 films.

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Gaona, Aidé, Urbano Díaz y Avelino Corma. "Functional Acid and Base Hybrid Catalysts Organized by Associated (Organo)aluminosilicate Layers for C–C Bond Forming Reactions and Tandem Processes". Chemistry of Materials 29, n.º 4 (14 de febrero de 2017): 1599–612. http://dx.doi.org/10.1021/acs.chemmater.6b04563.

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Popov, Stasik, Brian Shao, Alex L. Bagdasarian, Tyler R. Benton, Luyi Zou, Zhongyue Yang, K. N. Houk y Hosea M. Nelson. "Teaching an old carbocation new tricks: Intermolecular C–H insertion reactions of vinyl cations". Science 361, n.º 6400 (26 de julio de 2018): 381–87. http://dx.doi.org/10.1126/science.aat5440.

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Vinyl carbocations have been the subject of extensive experimental and theoretical studies over the past five decades. Despite this long history in chemistry, the utility of vinyl cations in chemical synthesis has been limited, with most reactivity studies focusing on solvolysis reactions or intramolecular processes. Here we report synthetic and mechanistic studies of vinyl cations generated through silylium–weakly coordinating anion catalysis. We find that these reactive intermediates undergo mild intermolecular carbon-carbon bond–forming reactions, including carbon-hydrogen (C–H) insertion into unactivated sp3 C–H bonds and reductive Friedel-Crafts reactions with arenes. Moreover, we conducted computational studies of these alkane C–H functionalization reactions and discovered that they proceed through nonclassical, ambimodal transition structures. This reaction manifold provides a framework for the catalytic functionalization of hydrocarbons using simple ketone derivatives.

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Guerra, Walter D., María E. Budén, Silvia M. Barolo, Roberto A. Rossi y Adriana B. Pierini. "Intra- vs inter-molecular electron transfer processes in C N bond forming reactions. Photochemical, photophysical and theoretical study of 2′-halo-[1,1′-biphenyl]-2-amines". Tetrahedron 72, n.º 48 (diciembre de 2016): 7796–804. http://dx.doi.org/10.1016/j.tet.2016.08.051.

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Lopat’eva, Elena R., Igor B. Krylov, Dmitry A. Lapshin y Alexander O. Terent’ev. "Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field". Beilstein Journal of Organic Chemistry 18 (9 de diciembre de 2022): 1672–95. http://dx.doi.org/10.3762/bjoc.18.179.

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Organocatalysis is widely recognized as a key synthetic methodology in organic chemistry. It allows chemists to avoid the use of precious and (or) toxic metals by taking advantage of the catalytic activity of small and synthetically available molecules. Today, the term organocatalysis is mainly associated with redox-neutral asymmetric catalysis of C–C bond-forming processes, such as aldol reactions, Michael reactions, cycloaddition reactions, etc. Organophotoredox catalysis has emerged recently as another important catalysis type which has gained much attention and has been quite well-reviewed. At the same time, there are a significant number of other processes, especially oxidative, catalyzed by redox-active organic molecules in the ground state (without light excitation). Unfortunately, many of such processes are not associated in the literature with the organocatalysis field and thus many achievements are not fully consolidated and systematized. The present article is aimed at overviewing the current state-of-art and perspectives of oxidative organocatalysis by redox-active molecules with the emphasis on challenging chemo-, regio- and stereoselective CH-functionalization processes. The catalytic systems based on N-oxyl radicals, amines, thiols, oxaziridines, ketone/peroxide, quinones, and iodine(I/III) compounds are the most developed catalyst types which are covered here.

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Cera, Gianpiero, Michel Chiarucci y Marco Bandini. "Accessing chemical diversity by stereoselective gold-catalyzed manipulation of allylic and propargylic alcohols". Pure and Applied Chemistry 84, n.º 8 (3 de febrero de 2012): 1673–84. http://dx.doi.org/10.1351/pac-con-11-09-05.

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The combined use of asymmetric Au(I) catalysis with allylic as well as propargylic alcohols proved to be a competent synthetic tool, toward the realization of complex molecular organic architectures in a stereochemically defined manner. In particular, allylic alcohols have been utilized as alkylating agents in the synthesis of tetrahydrocarbazoles/carbolines and morpholines by means of new C–C and C–X bond-forming processes. Analogously, the direct activation of indole-propargylic alcohols with cationic Au complexes opened a direct access to tetracyclic fused indolines in a highly stereoselective manner.

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Crochet, Pascale y Victorio Cadierno. "Arene-Osmium(II) Complexes in Homogeneous Catalysis". Inorganics 9, n.º 7 (12 de julio de 2021): 55. http://dx.doi.org/10.3390/inorganics9070055.

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Although the application of arene-osmium(II) complexes in homogeneous catalysis has been much less studied than that of their ruthenium analogues, different works have shown that, in some instances, a comparable or even superior effectiveness can be achieved with this particular class of compounds. This review article focuses on the catalytic applications of arene-osmium(II) complexes. Among others, transfer hydrogenation, hydrogenation, oxidation, and nitrile hydration reactions, as well as different C-C bond forming processes, are comprehensively discussed.

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Soengas, Raquel G. y Humberto Rodríguez-Solla. "Modern Synthetic Methods for the Stereoselective Construction of 1,3-Dienes". Molecules 26, n.º 2 (6 de enero de 2021): 249. http://dx.doi.org/10.3390/molecules26020249.

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The 1,3-butadiene motif is widely found in many natural products and drug candidates with relevant biological activities. Moreover, dienes are important targets for synthetic chemists, due to their ability to give access to a wide range of functional group transformations, including a broad range of C-C bond-forming processes. Therefore, the stereoselective preparation of dienes have attracted much attention over the past decades, and the search for new synthetic protocols continues unabated. The aim of this review is to give an overview of the diverse methodologies that have emerged in the last decade, with a focus on the synthetic processes that meet the requirements of efficiency and sustainability of modern organic chemistry.

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Protti, Stefano, Daniele Dondi, Maurizio Fagnoni y Angelo Albini. "Photochemistry in synthesis: Where, when, and why". Pure and Applied Chemistry 79, n.º 11 (1 de enero de 2007): 1929–38. http://dx.doi.org/10.1351/pac200779111929.

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A series of photochemical reactions are assessed under the environmental aspect by using Eissen and Metzger's EATOS (environmental assessment tool for organic syntheses) method and are compared with strictly analogous thermal processes. These include C-C bond-forming reactions (arylation and alkylation) and selective oxidation and reduction reactions. In most cases, the photochemical method is experimentally simpler and less expensive than the thermal alternative. A disadvantage is that photochemical reactions are carried out in rather dilute solution, and this factor gives by far the main contribution to the assessment. However, if the solvent is recovered, the photochemical reaction is more environment-friendly.

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36

Luong, Truc Thanh, Reyhaneh Tirgar, Melissa E. Reardon-Robinson, Andrzej Joachimiak, Jerzy Osipiuk y Hung Ton-That. "Structural Basis of a Thiol-Disulfide Oxidoreductase in the Hedgehog-Forming ActinobacteriumCorynebacterium matruchotii". Journal of Bacteriology 200, n.º 9 (12 de febrero de 2018): e00783-17. http://dx.doi.org/10.1128/jb.00783-17.

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ABSTRACTThe actinobacteriumCorynebacterium matruchotiihas been implicated in nucleation of oral microbial consortia leading to biofilm formation. Due to the lack of genetic tools, little is known about basic cellular processes, including protein secretion and folding, in this organism. We report here a survey of theC. matruchotiigenome, which encodes a large number of exported proteins containing paired cysteine residues, and identified an oxidoreductase that is highly homologous to theCorynebacterium diphtheriaethiol-disulfide oxidoreductase MdbA (MdbACd). Crystallization studies uncovered that the 1.2-Å resolution structure ofC. matruchotiiMdbA (MdbACm) possesses two conserved features found in actinobacterial MdbA enzymes, a thioredoxin-like fold and an extended α-helical domain. By reconstituting the disulfide bond-forming machinein vitro, we demonstrated that MdbACmcatalyzes disulfide bond formation within the actinobacterial pilin FimA. A new gene deletion method supported thatmdbAis essential inC. matruchotii. Remarkably, heterologous expression of MdbACmin theC. diphtheriaeΔmdbAmutant rescued its known defects in cell growth and morphology, toxin production, and pilus assembly, and this thiol-disulfide oxidoreductase activity required the catalytic motif CXXC. Altogether, the results suggest that MdbACmis a major thiol-disulfide oxidoreductase, which likely mediates posttranslocational protein folding inC. matruchotiiby a mechanism that is conserved inActinobacteria.IMPORTANCEThe actinobacteriumCorynebacterium matruchotiihas been implicated in the development of oral biofilms or dental plaque; however, little is known about the basic cellular processes in this organism. We report here a high-resolution structure of aC. matruchotiioxidoreductase that is highly homologous to theCorynebacterium diphtheriaethiol-disulfide oxidoreductase MdbA. By biochemical analysis, we demonstrated thatC. matruchotiiMdbA catalyzes disulfide bond formationin vitro. Furthermore, a new gene deletion method revealed that deletion ofmdbAis lethal inC. matruchotii. Remarkably,C. matruchotiiMdbA can replaceC. diphtheriaeMdbA to maintain normal cell growth and morphology, toxin production, and pilus assembly. Overall, our studies support the hypothesis thatC. matruchotiiutilizes MdbA as a major oxidoreductase to catalyze oxidative protein folding.

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Yamada, Tsuyoshi, Jing Jiang, Naoya Ito, Kwihwan Park, Hayato Masuda, Chikara Furugen, Moeka Ishida, Seiya Ōtori y Hironao Sajiki. "Development of Facile and Simple Processes for the Heterogeneous Pd-Catalyzed Ligand-Free Continuous-Flow Suzuki–Miyaura Coupling". Catalysts 10, n.º 10 (19 de octubre de 2020): 1209. http://dx.doi.org/10.3390/catal10101209.

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The Suzuki–Miyaura coupling reaction is one of the most widely utilized C–C bond forming methods to create (hetero)biaryl scaffolds. The continuous-flow reaction using heterogeneous catalyst-packed cartridges is a practical and efficient synthetic method to replace batch-type reactions. A continuous-flow ligand-free Suzuki–Miyaura coupling reaction of (hetero)aryl iodides, bromides, and chlorides with (hetero)aryl boronic acids was developed using cartridges packed with spherical resin (tertiary amine-based chelate resin: WA30)-supported palladium catalysts (7% Pd/WA30). The void space in the cartridge caused by the spherical catalyst structures enables the smooth flow of a homogeneously dissolved reaction solution that consists of a mixture of organic and aqueous solvents and is delivered by the use of a single syringe pump. Clogging or serious backpressure was not observed.

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38

Dominguez, Beatriz, Beatriz Iglesias y Angel R. de Lera. "ChemInform Abstract: A Comprehensive Survey of Stille-Type C(sp2)-C(sp2) Single Bond Forming Processes in the Synthesis of Retinoic Acid and Analogues". ChemInform 31, n.º 12 (9 de junio de 2010): no. http://dx.doi.org/10.1002/chin.200012272.

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39

Meng, Qingyan, Syed G. A. Moinuddin, Sung-Jin Kim, Diana L. Bedgar, Michael A. Costa, Dennis G. Thomas, Robert P. Young et al. "Pterocarpan synthase (PTS) structures suggest a common quinone methide–stabilizing function in dirigent proteins and proteins with dirigent-like domains". Journal of Biological Chemistry 295, n.º 33 (21 de junio de 2020): 11584–601. http://dx.doi.org/10.1074/jbc.ra120.012444.

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The biochemical activities of dirigent proteins (DPs) give rise to distinct complex classes of plant phenolics. DPs apparently began to emerge during the aquatic-to-land transition, with phylogenetic analyses revealing the presence of numerous DP subfamilies in the plant kingdom. The vast majority (>95%) of DPs in these large multigene families still await discovery of their biochemical functions. Here, we elucidated the 3D structures of two pterocarpan-forming proteins with dirigent-like domains. Both proteins stereospecifically convert distinct diastereomeric chiral isoflavonoid precursors to the chiral pterocarpans, (–)- and (+)-medicarpin, respectively. Their 3D structures enabled comparisons with stereoselective lignan– and aromatic terpenoid–forming DP orthologs. Each protein provides entry into diverse plant natural products classes, and our experiments suggest a common biochemical mechanism in binding and stabilizing distinct plant phenol–derived mono- and bis-quinone methide intermediates during different C–C and C–O bond–forming processes. These observations provide key insights into both their appearance and functional diversification of DPs during land plant evolution/adaptation. The proposed biochemical mechanisms based on our findings provide important clues to how additional physiological roles for DPs and proteins harboring dirigent-like domains can now be rationally and systematically identified.

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40

Byrne, Paul G., M. Esther Garcia, John C. Jeffery, Paul Sherwood y F. Gordon A. Stone. "Reactions between µ-alkylidyne iron–molybdenum complexes and but-2-yne: unusually facile C–C bond forming processes accompanied by hydrogen migration between carbon centres". J. Chem. Soc., Chem. Commun., n.º 2 (1987): 53–55. http://dx.doi.org/10.1039/c39870000053.

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41

Huang, Xiaohua, Kevin W. Anderson, Danilo Zim, Lei Jiang, Artis Klapars y Stephen L. Buchwald. "Expanding Pd-Catalyzed C−N Bond-Forming Processes: The First Amidation of Aryl Sulfonates, Aqueous Amination, and Complementarity with Cu-Catalyzed Reactions [J. Am. Chem. Soc.2003,125, 6653−6655]." Journal of the American Chemical Society 125, n.º 35 (septiembre de 2003): 10767. http://dx.doi.org/10.1021/ja033450a.

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42

Stepanenko, D. O., O. M. Grishin y A. I. Belkova. "Analitical and experimental studies of properties of slag and slag-forming mixtures of steelmaking production". Fundamental and applied problems of ferrous metallurgy 37 (2023): 260–70. http://dx.doi.org/10.52150/2522-9117-2023-37-260-270.

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The aim of the study is to analyze and generalize the properties of slags within the CaO-SiO2-Al2O3-MgO-CaF2 system in different ratios of components and their concentrations, which is the basis of refining slags in modern steelmaking. To ensure the technological functions, the slag melt should have a set of optimal values of physical and chemical properties, in particular: viscosity, surface tension, electrical conductivity, melting temperature (beginning and end), enthalpy, density and others, which significantly affect the kinetics of heat and mass transfer processes in the "metal-slag" system. The information resource of researches is provided by own experimental data and data of databases "Slag" and "SFM" containing information about technological properties of melts of slag and oxide systems. The analysis of the data on the dependence of the properties of oxide systems on their chemical composition and temperature was performed. Oxide systems within the chemical composition CaO-SiO2-Al2O3-MgO-CaF2 are considered. The connection of the chemical composition of slag systems with the properties of their melts from the point of view of the concept of directed chemical bonding using integral parameters is established: ρ is the stoichiometry index; ∆e is the average number of electrons localized in the direction of the cation-anion (K-A) bond; d is the average inter-nuclear distance K-A; tgα is the change in the electron density in the direction of the K-A bond; ZA(A-A), ZK(K-A), ZK(K-K) are the weighted average values of cation and anion charges in the A-A, K-A, K-K bonds. Based on the results of experimental and analytical studies, predictive models of the properties of the considered oxide systems were obtained, namely for the calculation of viscosity, electrical conductivity, crystallization temperature and density of slag melts in the range of their temperatures from 1200°C to 1800°C. The presented method of predicting the properties of refining slags can be used to evaluate the use of slags of different composition in the ladle, for example, in ladle-furnace installations.

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Tetteh, Samuel. "A Computational and Structural Database Study of the Metal-Carbene Bond in Groups IA, IIA, and IIIA Imidazol-2-Ylidene Complexes". Journal of Chemistry 2019 (24 de diciembre de 2019): 1–9. http://dx.doi.org/10.1155/2019/5675870.

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Imidazol-2-ylidenes are important N-heterocyclic carbenes which have become universal ligands in organometallic and coordination chemistry. Generally classified as σ-donor ligands, these compounds have been used to stabilize various metal complexes which hitherto were less stable in their catalytic processes. Herein, the number and distribution of group IA, group IIA, and group IIIA metal-imidazol-2-ylidene complexes retrieved from the Cambridge Structural Database (CSD) are assessed. The data showed that the mean M-Ccarbene bond length increases with increasing ionic size but is similar across each diagonal. Dominant factors such as Lewis acidity and electrostatic attractions were found to control the bonding modes of the respective ions. Generally, the metal ions show preference for tetrahedral coordination with larger cations forming complexes with higher coordination numbers. For their high number of entries (101), tetrahedrally coordinated boron complexes with various electron withdrawing and electron donating groups were studied computationally at the DFT/B3LYP level of theory. The strength of the B-Ccarbene bond was found to depend on steric interactions between bulky groups on the borenium atom and substituents on the N-positions of the imidazol-2-ylidene ligand. This observation was further confirmed by estimation of the binding energy, natural charge, and the electron distribution in the B-Ccarbene bond.

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Teichert, Johannes F. y Lea T. Brechmann. "Catch It If You Can: Copper-Catalyzed (Transfer) Hydrogenation Reactions and Coupling Reactions by Intercepting Reactive Intermediates Thereof". Synthesis 52, n.º 17 (13 de julio de 2020): 2483–96. http://dx.doi.org/10.1055/s-0040-1707185.

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The key reactive intermediate of copper(I)-catalyzed alkyne semihydrogenations is a vinylcopper(I) complex. This intermediate can be exploited as a starting point for a variety of trapping reactions. In this manner, an alkyne semihydrogenation can be turned into a dihydrogen-mediated coupling reaction. Therefore, the development of copper-catalyzed (transfer) hydrogenation reactions is closely intertwined with the corresponding reductive trapping reactions. This short review highlights and conceptualizes the results in this area so far, with H2-mediated carbon–carbon and carbon–heteroatom bond-forming reactions emerging under both a transfer hydrogenation setting as well as with the direct use of H2. In all cases, highly selective catalysts are required that give rise to atom-economic multicomponent coupling reactions with rapidly rising molecular complexity. The coupling reactions are put into perspective by presenting the corresponding (transfer) hydrogenation processes first.1 Introduction: H2-Mediated C–C Bond-Forming Reactions2 Accessing Copper(I) Hydride Complexes as Key Reagents for Coupling Reactions; Requirements for Successful Trapping Reactions 3 Homogeneous Copper-Catalyzed Transfer Hydrogenations4 Trapping of Reactive Intermediates of Alkyne Transfer Semihydrogenation Reactions: First Steps Towards Hydrogenative Alkyne Functionalizations 5 Copper(I)-Catalyzed Alkyne Semihydrogenations6 Copper(I)-Catalyzed H2-Mediated Alkyne Functionalizations; Trapping of Reactive Intermediates from Catalytic Hydrogenations6.1 A Detour: Copper(I)-Catalyzed Allylic Reductions, Catalytic Generation of Hydride Nucleophiles from H2 6.2 Trapping with Allylic Electrophiles: A Copper(I)-Catalyzed Hydroallylation Reaction of Alkynes 6.3 Trapping with Aryl Iodides7 Conclusion

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Hölscher, Markus, Christoph Gürtler, Wilhelm Keim, Thomas E. Müller, Martina Peters y Walter Leitner. "Carbon Dioxide as a Carbon Resource – Recent Trends and Perspectives". Zeitschrift für Naturforschung B 67, n.º 10 (1 de octubre de 2012): 961–75. http://dx.doi.org/10.5560/znb.2012-0219.

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With the growing perception of industrialized societies that fossil raw materials are limited resources, academic chemical research and chemical industry have started to introduce novel catalytic technologies which aim at the development of economically competitive processes relying much more strongly on the use of alternative carbon feedstocks. Great interest is given world-wide to carbon dioxide (CO2) as it is part of the global carbon cycle, nontoxic, easily available in sufficient quantities anywhere in the industrialized world, and can be managed technically with ease, and at low cost. In principle carbon dioxide can be used to generate a large variety of synthetic products ranging from bulk chemicals like methanol and formic acid, through polymeric materials, to fine chemicals like aromatic acids useful in the pharmaceutical industry. Owing to the high thermodynamic stability of CO2, the energy constraints of chemical reactions have to be carefully analyzed to select promising processes. Furthermore, the high kinetic barriers for incorporation of CO2 into C-H or C-C bond forming reactions require that any novel transformation of CO2 must inevitably be associated with a novel catalytic technology. This short review comprises a selection of the most recent academic and industrial research developments mainly with regard to innovations in CO2 chemistry in the field of homogeneous catalysis and processes.

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46

Zhou, Ru Jin, Min Huang y Song Shan Qiu. "Study of Interior Wall Coating Based on Metakaolinand Modified Starch". Advanced Materials Research 239-242 (mayo de 2011): 1030–35. http://dx.doi.org/10.4028/www.scientific.net/amr.239-242.1030.

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In order to reduce the emission of volatile organic compounds (VOCs) and save the non-renewable resource, a novel interior wall coating with high bond strength based on metakaolin and modified starch was developed. The process on researches includes three steps. Firstly, cassava starch was reformed including etherification, oxidation, conjugate crosslinking and drying to gain natural polymer glue powder which can be used as forming agent, and a dispensation in producing environment friendly paint for interior wall coating was preliminarily obtained. The dispensation consists of forming agent, calcium carbonate, French chalk, chitosan and mildew preventive. Secondly, the process on metakaolin was studied. Metakaolin shows hydration Characteristics and can make interior wall coating have bond strength and resistance to water. At last, the dispensations and processes in obtaining starch glue, metakaolin and paint powder were decided respectively, and the data in gauging bonding force, resistance to water and the performance of interior wall coating were gained. The research on forming agent was as following: the mixture of cassava starch and NaOH was stirred, and pulverized to be sieved by100 mesh. After reacted stirringly with chloroacetic acid for 1.5h at room temperature, the mixture was oxidized by oxidant for 2h and crosslinked by crosslinking agent for 1h respectively to obtain forming agent. The mass fraction of NaOH, chloroacetic acid, oxidant and crosslinking agent to cassava starch were 6%, 5%, 6% and 0.8%, respectively. The Kaolin selected must contain high percents of Al2O3 and SiO2 , and was calcined at 700°C for 5h to have metakaolin as additive for interior wall coating to improve bond strength and resistance to water. The composition of interior wall coating optimized by orthogonal test is about: 4% of starch glue, 6% of metakaolin, 80% of calcium carbonate, 9.7% of French chalk, 0.1% of chitosan and 0.2% of mildew preventive. The interior wall coating is environmental benign material in building industry.

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Wang, Shuai, Iker Agirrezabal-Telleria, Aditya Bhan, Dante Simonetti, Kazuhiro Takanabe y Enrique Iglesia. "Catalytic routes to fuels from C1 and oxygenate molecules". Faraday Discussions 197 (2017): 9–39. http://dx.doi.org/10.1039/c7fd00018a.

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This account illustrates concepts in chemical kinetics underpinned by the formalism of transition state theory using catalytic processes that enable the synthesis of molecules suitable as fuels from C₁ and oxygenate reactants. Such feedstocks provide an essential bridge towards a carbon-free energy future, but their volatility and low energy density require the formation of new C–C bonds and the removal of oxygen. These transformations are described here through recent advances in our understanding of the mechanisms and site requirements in catalysis by surfaces, with emphasis on enabling concepts that tackle ubiquitous reactivity and selectivity challenges. The hurdles in forming the first C–C bond from C₁ molecules are illustrated by the oxidative coupling of methane, in which surface O-atoms form OH radicals from O₂ and H₂O molecules. These gaseous OH species act as strong H-abstractors and activate C–H bonds with earlier transition states than oxide surfaces, thus rendering activation rates less sensitive to the weaker C–H bonds in larger alkane products than in CH₄ reactants. Anhydrous carbonylation of dimethyl ether forms a single C–C bond on protons residing within inorganic voids that preferentially stabilize the kinetically-relevant transition state through van der Waals interactions that compensate for the weak CO nucleophile. Similar solvation effects, but by intrapore liquids instead of inorganic hosts, also become evident as alkenes condense within MCM-41 channels containing isolated Ni²⁺ active sites during dimerization reactions. Intrapore liquids preferentially stabilize transition states for C–C bond formation and product desorption, leading to unprecedented reactivity and site stability at sub-ambient temperatures and to 1-alkene dimer selectivities previously achieved only on organometallic systems with co-catalysts or activators. C₁ homologation selectively forms C₄ and C₇ chains with a specific backbone (isobutane, triptane) on solid acids, because of methylative growth and hydride transfer rates that reflect the stability of their carbenium ion transition states and are unperturbed by side reactions at low temperatures. Aldol condensation of carbonyl compounds and ketonization of carboxylic acids form new C–C bonds concurrently with O-removal. These reactions involve analogous elementary steps and occur on acid–base site pairs on TiO₂ and ZrO₂ catalysts. Condensations are limited by α-H abstraction to form enolates via concerted interactions with predominantly unoccupied acid–base pairs. Ketonization is mediated instead by C–C bond formation between hydroxy-enolates and monodentate carboxylates on site pairs nearly saturated by carboxylates. Both reactions are rendered practical through bifunctional strategies, in which H₂ and a Cu catalyst function scavenge unreactive intermediates, prevent sequential reactions and concomitant deactivation, and remove thermodynamic bottlenecks. Alkanal–alkene Prins condensations on solid acids occur concurrently with alkene dimerization and form molecules with new C–C bonds as skeletal isomers unattainable by other routes. Their respective transition states are of similar size, leading to selectivities that cannot sense the presence of a confining host. Prins condensation reactions benefit from weaker acid sites because their transition states are less charged than those for oligomerization and consequently less sensitive to conjugate anions that become less stable as acids weaken.

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Kochetova, Ludmila B. y Tatiana P. Kustova. "Kinetics and mechanism of acyl transfer reactions. Part 16. Quantum chemical simulation of mechanism of N-methylaniline sulfonation in aqueous 1,4-dioxane". Butlerov Communications 61, n.º 1 (31 de enero de 2020): 1–8. http://dx.doi.org/10.37952/roi-jbc-01/20-61-1-1.

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The RHF/6-31G(d) quantum chemical simulation of the mechanism of the secondary fatty aromatic amine N-methylaniline interaction with benzenesulfonyl chloride under conditions of N-methylaniline specific solvation by one water molecule and one 1,4-dioxane molecule, and under conditions of N-methylaniline specific solvation by two water molecules and one 1,4-dioxane molecule. Three-dimensional potential energy surfaces of the processes pointed out are computed. It is shown that in the both cases a single route of the reactions is realized, starting as an axial nucleophilic attack, which goes further with decreasing of the attack angle as reagent molecules approach each other. It was established that both simulated reactions proceed in accordance with bimolecular concerted mechanism of nucleophilic substitution SN2, which implies the formation of a single transition state in the reaction path. It was found that geometrical configuration of the reaction center in the transition states of the reactions is medium between the trigonal-bipyramidal and tetragonal-pyramidal, which is associated with the change in the angle of N-methylaniline attack as the reactant molecules approach each other. In the benzenesulfonyl chloride reaction with N-methylaniline, solvated by one water molecule and one 1,4-dioxane molecule, the transition state is solvated only by 1,4-dioxane molecule, while water molecule moves away from the reaction center, whereas in the benzenesulfonyl chloride reaction with N-methylaniline, solvated by two water molecule and one 1,4-dioxane molecule the transition state is solvated by 1,4-dioxane molecule and one water molecule that forms hydrogen bond with chlorine atom and promote the S–Cl-bond loosening. The activation energies of the reactions were calculated; it is shown that specific solvation increases the reactions energetic barrier as compared with the reaction in gaseous phase, that is caused by the partial dehydratation of N-methylaniline molecule before the transition state formation. A decrease of the activation energy of the reaction with participation of N-methylaniline, solvated by two water molecule and one 1,4-dioxane molecule as compared with the cases of non-specific solvation of the reactants and N-methyl-aniline solvation by one water molecule and one 1,4-dioxane molecule is caused by the existence of the second water molecule in the system, forming a bond with amine group and facilitating N–H bond break.

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49

Sun, Chang Q. "Origin and Processes of O-Cu(001) and the O-Cu(110) Biphase Ordering". International Journal of Modern Physics B 12, n.º 09 (10 de abril de 1998): 951–64. http://dx.doi.org/10.1142/s0217979298000533.

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From the perspective of bond forming, origin of phase-formation on the O-Cu(001) and the O-Cu(110)is analyzed. It is suggested that the formation of the O -1 and the hybridized- O -2 gives in nature the c (2 × 2)-O and subsequently, the [Formula: see text]phase, on the Cu(001). The re-ordering of the primary Cu2O units transforms the Cu(110)-(2×1)-O into the c (6 × 2)-O. As consequences of the O-2 -hybridization, the Cu(001)-[Formula: see text] differs from the Cu(110)-(2×1)-O in origin by nothing more than that the -O-Cu-chain rotates 45° to fit itself to the coordination-surrounding. It proposed that one metal atom may donate more than one-electron to different oxygen atoms. However, one oxygen, with two directional bonding orbitals and two nonbonding orbitals, can never get more than one-electron from a specific metal atom. The sp-hybridization of oxygen cannot occur before its two bonding orbitals are fully occupied. Besides the ionization of oxygen and metal atoms, the polarization of the metal and the hybridization of O -2 dominate the processes of oxidation and the behavior of the oxides. Further considerations are required regarding how the O-coverage reversibly varies the valence-state of oxygen, and how the coverage and temperature reassemble the Cu2O on the Cu(110).

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DELGADO, G. E., Asiloé J. MORA, T. GONZÁLEZ, I. SANTOS, P. RIVAS y L. E. SEIJAS. "SOLVENT-FREE SYNTHESIS AND CRYSTAL STRUCTURE OF rac-2-THIOHYDANTOIN-VALINE". Periódico Tchê Química 16, n.º 31 (20 de enero de 2019): 347–52. http://dx.doi.org/10.52571/ptq.v16.n31.2019.353_periodico31_pgs_347_352.pdf.

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Thiohydantoins have been used in the manufacture of medicines and in industrial processes. Depending on the nature and type of substitution on the heterocyclic ring, these compounds may display pharmaceutical and biological activity with a variety of applications as antiepileptic, antitumoral, antiinflammatory, and principally for the treatment of prostate cancer. In this study, a new thiohydantoin was synthetized from the valine amino acid and structurally characterized. The title compound, C6H10N2O2S, with systematic name rac-5-isopropyl-2-tioxoimidazolidin-4-one, has been synthetized by a solvent-free synthesis. The heterocyclic compound was characterized by spectroscopic infrared (FTIR) and nuclear magnetic resonance (NMR) techniques, powder and single-crystal X-ray diffraction analysis (XRD). This material crystallizes in the monoclinic space group P21/c. In the supramolecular structure, the molecules are joined by N- --H···O and N---H···S hydrogen bonds, forming centrosymmetric R2 2(8) dimers and C2 2(9) chains that run along the [001] direction in an infinite one-dimensional network.

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