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Synthesis Gas Chemistry
Published in Saeed Sahebdelfar, Maryam Takht Ravanchi, Ashok Kumar Nadda, 1 Chemistry, 2022
Saeed Sahebdelfar, Maryam Takht Ravanchi, Ashok Kumar Nadda
Recently, developing efficient and regioselective catalysts for the production of linear aldehydes are receiving interest as research topics (Gehrtz et al., 2016). The tuning of regioselectivity, controlling side reactions (such as hydrogenation and isomerization, i.e., chemoselectivity) and enhancing reaction rate can be achieved by a combination of metal center and ligand (Kämper et al., 2016). In the commercial hydroformylation of aliphatic olefins, high n/iso ratios can be obtained by modification of the catalysts by phosphine ligands. The ratio of normal/branched isomers also depends on operating condition, especially partial pressure of CO and temperature. High partial pressures of CO and low temperatures favor higher n/iso products ratio from aliphatic olefins (Mika and Ungváry, 2003).
Heterogeneous Catalysis in Organic Synthesis
Published in Mike G. Scaros, Michael L. Prunier, Catalysis of Organic Reactions, 2017
R. L. Augustine, L. K. Doyle, S. Malhotra, L. S. Posner, S. T. O’Leary, S. A. Roberto, S. K. Tanielyan
We have examined both the Heck arylation reaction11 and the Pd catalyzed allylation in more detail and have verified that both reactions are heterogeneously catalyzed and that they take place on the 3M sites on the Pd catalyst. In the corresponding homogeneously catalyzed reactions the regioselectivity could be modified by changing the electronic character of the ligands on the catalyst. As the data in Schemes 1 and 2 show we have observed a similar regiodirecting effect induced by the electronic character of the support material. Basic MgO, being electron donating, promotes a product formation in the Heck arylation and a slight excess of terminal carbon attack in the allylation. With the acidic, electron withdrawing, SiO2 support, β isomer formation is preferred in the Heck arylation and attack on the secondary carbon in the allylation. With a Pd on graphite electrode as the catalyst, a positive polarity favors β product formation while a negative polarity leads to more α product formation.
Atom Economy
Published in Aidé Sáenz-Galindo, Adali Oliva Castañeda-Facio, Raúl Rodríguez-Herrera, Green Chemistry and Applications, 2020
Kunnambeth M. Thulasi, Sindhu Thalappan Manikkoth, Manjacheri Kuppadakkath Ranjusha, Padinjare Veetil Salija, Nisha Vattakkoval, Shajesh Palantavida, Baiju Kizhakkekilikoodayil Vijayan
In regioselective reactions, one of the positional isomer is preferentially formed. The question of regioselectivity arises when a reagent can approach a particular reactive site through different regions or positions. A regioselective reagent is required to obtain the desired product. A simple example is addition of HX over an unsymmetrical olefin.
Non-heme iron coordination complexes for alkane oxidation using hydrogen peroxide (H2O2) as powerful oxidant
Published in Journal of Coordination Chemistry, 2022
Low catalyst loading, mild reaction condition, higher regioselectivity, unusual site selectivity and satisfactory yield of a diverse range of products made the reaction profile of interest. Previously, oxidation at the unusual site of this complex moiety had been accomplished using biological methods with higher reaction times or very low-temperature condition.
Transition-metal-free electrochemical-induced active C(sp3)-H functionalization
Published in Green Chemistry Letters and Reviews, 2023
Xiaolong Ma, Jinfeng Wei, Xu Yang, Huajin Xu, Yi Hu
In 2018, a modified Hofmann–Löffler–Freytag (HLF) reaction via employing electrochemical oxidation without using halogenated solvents and either prefunctionalized starting materials or a (super)stoichiometric oxidant to realize site-Selective intramolecular C(sp3)-H amination disclosed by Lei group (Scheme 28) (89). In this case, this protocol offers a broad substrate scope including benzylic C(sp3)-H, inert tertiary, secondary, as well as primary C(sp3)-H, which can entirely achieve intramolecular amination to synthesize various functionalized nitrogen-containing heterocycles (86) with great synthetic values. Similarly, Rueping’s group combined N-radicals generated electrochemically with a subsequent 1,5-HAT to achieve intramolecular C(sp3)-H amination (Scheme 29a) (91). It is worth mentioning that this reaction could be implemented for large-scale synthetic applications. On the one hand, this method employed both an industrially acceptable and retrievable solvent-electrolyte system and low-cost graphite and stainless-steel electrodes. On the other hand, an extremely broad variety of functional groups were tolerated in these developed electrochemical conditions. Notably, the corresponding products could be provided with excellent regioselectivity. A possible reaction mechanism shown in Scheme 27b was proposed by authors according to CV studies and experiments. Firstly, the electrooxidation of bromide (Br-) provides the formation of bromine (Br2), which is immediately captured by Br- to generate Br3- anion. Then Br3- anion reacts with methoxy anion (MeO-) to form methyl hypobromite (MeOBr). Subsequently, N-bromo species II generated at electrode, which formed N-centered radical I by SET event on the cathode. Finally, intermediate A is converted to C-centered radical III via 1,5-HAT process, which could easily convert to the target product.
Picolinimidoamide-Cu(II) complex anchored on Fe3O4@SiO2 core–shell magnetic nanoparticles: an efficient reusable catalyst for click reaction
Published in Journal of Coordination Chemistry, 2018
Maryam Zirak, Elham Jamali Garegeshlagi
1,2,3-Triazoles, one of the most important classes of N-heterocyclic compounds, have applications in pharmaceutical chemistry, materials science and coordination chemistry [1–4]. These heterocycles as a bioisoester of the amide linkage resist enzymatic degradation [5], oxidation, reduction and hydrolysis reactions [6]. 1,2,3-Triazole moieties exhibited a wide range of biological activities, such as anti-HIV, antiviral, anticancer, antibiotic, kinase inhibitors, etc. [7–13]. Also, they can function as dyes, agrochemicals, corrosion inhibitors, photo stabilizers, and photographic materials [14, 15]. There are several methods to prepare 1,2,3-triazoles, but the general method is cycloaddition of azides with alkynes in the presence of Cu(I) salts [16–19], known as a click reaction, reported by Sharpless and Meldal in 2001 [20, 21]. Despite the efficiency of the reported homogeneous catalyst, Cu(I) salts are instable thermodynamically and formation of undesired alkyne-alkyne coupling products have been observed in the presence of homogeneous catalysts [22–24]. In addition, these homogeneous catalysts are generally non-recyclable, have low regioselectivity and need long reaction times. Heterogeneous catalysts have several advantages such as easy recovery and recycling, and enhanced stability [25, 26]. Therefore, different heterogeneous copper catalysts such as charcoal, zeolites, montmorillonite, N-heterocyclic carbene (NHC)-modified silica, alumina, silica gel, polystyrene, and chitosan-supported copper catalysts have been reported for the preparation of 1,2,3-triazoles [25, 27–32]. For example, Mahdavinia et al. reported Cu(II) ions immobilized on magnetic chitosan–laponite RD system and used it as an efficient catalyst in click reactions [30]. Among heterogeneous catalysts, magnetic nanoparticles (MNPs) have seen much attention due to their easy separation and high surface-to-volume ratio, which enhances their activity and selectivity [33, 34]. Because of magnetic properties and biocompatibility of MNPs, they are widely used in adsorption of proteins, heavy metals, and dyes, drug delivery, and biosensors [35–42]. According to the importance of 1,2,3-triazoles in pharmaceuticals and industry and also easy separation of MNPs, herein we report the synthesis of a new Cu heterogeneous catalyst based on MNPs and its use in click reactions.