Anion effect controlling the selectivity in the zinc-catalysed copolymerisation of CO₂ and cyclohexene oxide

• Sait Elmas,
• Muhammad Afzal Subhani,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 42–49, doi:10.3762/bjoc.11.7

• heterogeneous catalysts are known to catalyse the copolymerisation reaction [5][11][12][13]. One lead structure (Scheme 1) for catalysing the reaction is based on binuclear complexes with a macrocyclic ligand framework (Type I) [14][15][16]. The macrocyclic ligand L is a 22-membered Robson-type ligand with four

Pd/C-catalyzed aerobic oxidative esterification of alcohols and aldehydes: a highly efficient microwave-assisted green protocol

• Marina Caporaso,
• Giancarlo Cravotto,
• Spyros Georgakopoulos,
• George Heropoulos,
• Katia Martina and
• Silvia Tagliapietra

Beilstein J. Org. Chem. 2014, 10, 1454–1461, doi:10.3762/bjoc.10.149

• Selective oxidations of alcohols are some of the most important transformations in organic synthesis. Therefore, reactions that employ reusable heterogeneous catalysts and molecular oxygen are highly desirable from atom economy and environmental impact point of view [1][2][3]. A number of methods have been

Integration of enabling methods for the automated flow preparation of piperazine-2-carboxamide

• Richard J. Ingham,
• Claudio Battilocchio,
• Joel M. Hawkins and
• Steven V. Ley

Beilstein J. Org. Chem. 2014, 10, 641–652, doi:10.3762/bjoc.10.56

• pyrazine 2 to piperazine 1 (Figure 2b). Both of these steps involve flowing through heterogeneous catalysts, a metal oxide for the hydration of the nitrile and a supported precious metal for the hydrogenation of the heteroaromatic ring. Furthermore, both steps involve the addition of a volatile small

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• [Au(III)salen] [20] and [Au(III)(2-phenylpyridine)Cl2] [21] complexes, immobilized heterogeneous catalysts [22], and gold nanoparticles (Au NP) [23][24][25][26] have been reported until 2010, as well as recognized in two recent exhaustive reviews by Li [2] and Van der Eycken [3]. In the past three

• years the development of new and effective nanostructured catalytic systems dominated the gold-catalyzed approach to A3-coupling. For example, ultrasmall gold(0) nanoparticles embedded in a mesoporous carbon nitride stabilizer [27] proved to be a highly active, selective and recyclable heterogeneous

• catalysts for coupling arylaldehydes, piperidine and phenylacetylene in toluene at 100 °C. One year later, the same research group obtained comparable results under identical reaction conditions by using gold(0) nanoparticles stabilized by nanocristalline magnesium oxide [28]. In this work, the scope was

Continuous-flow Heck synthesis of 4-methoxybiphenyl and methyl 4-methoxycinnamate in supercritical carbon dioxide expanded solvent solutions

• Phei Li Lau,
• Ray W. K. Allen and
• Peter Styring

Beilstein J. Org. Chem. 2013, 9, 2886–2897, doi:10.3762/bjoc.9.325

• cost and product contamination [3]. Further efforts have focused on the development of heterogeneous catalysts or immobilised homogeneous catalysts, particularly for use in continuous flow reactor systems [3][4][5][6]. The yield and selectivity of Heck reactions are profoundly influenced by a number of

• possible, for example the catalyst can present as nanoparticles, ligand-less, unsupported or supported among other forms [16]. Practically speaking, heterogeneous catalysts provide benefits such as ease of separation and recovery from the reaction mixture. In general, heterogeneous catalysts tend to be

• several mesoporous materials [20], and a palladium bipiyridyl complex anchored on nanosized MCM-41 [21]. Furthermore, a myriad of zeolites have been applied in Heck reactions, with examples including: modernite, HY or beta [22][23], montmorillonite [24], layered double hydroxides (LDH) [25]. Heterogeneous

Practical synthesis of indoles and benzofurans in water using a heterogeneous bimetallic catalyst

• Cybille Rossy,
• Eric Fouquet and
• François-Xavier Felpin

Beilstein J. Org. Chem. 2013, 9, 1426–1431, doi:10.3762/bjoc.9.160

• role of copper is twofold since it acts not only as a cocatalyst for the alkynylation reaction but also as a Lewis acid for the cyclization step. Procedures involving heterogeneous catalysts have been much less explored and essentially limited to the use of heterogeneous Pd catalysts in the presence of

A³-Coupling catalyzed by robust Au nanoparticles covalently bonded to HS-functionalized cellulose nanocrystalline films

• Jian-Lin Huang,
• Derek G. Gray and
• Chao-Jun Li

Beilstein J. Org. Chem. 2013, 9, 1388–1396, doi:10.3762/bjoc.9.155

• large-scale industrial settings because of challenges associated with recovery and reuse of the catalysts from the reaction system, which may also increase the cost and cause environmental pollution by metallic ions. Heterogeneous catalysts could overcome the above problems [21]; however, they usually

• catalysis are still very limited. This paper describes the use of HS-functionalized CNCs decorated with gold nanoparticles as a novel class of heterogeneous catalysts for greener organic reactions. AuNPs were formed and deposited on the surface of HS-functionalized CNCs by coordination with the free HS

• for CNCs include nanocomposite formulation, polymer reinforcement, drug delivery [27], enzyme immobilization [28], biomedical applications [29] and as templates for the synthesis of nanomaterials [30]. The deposition of metal nanoparticles onto the surface of CNCs can lead to new nano-heterogeneous

Efficient and selective chemical transformations under flow conditions: The combination of supported catalysts and supercritical fluids

• M. Isabel Burguete,
• Eduardo García-Verdugo and
• Santiago V. Luis

Beilstein J. Org. Chem. 2011, 7, 1347–1359, doi:10.3762/bjoc.7.159

• has increased significantly over the past few years [31]. Different approaches to the immobilization of catalysts in order to design flow processes in scFs can be mentioned: a) Solid heterogeneous catalysts: Hydrogenation processes, in particular those based on solid heterogeneous catalysts derived

• obtained (l/b selectivity). In general, the linear aldehydes are the desired final products for industrial applications. On the other hand, dimerization products can also be obtained along with the desired aldehydes (aldehyde selectivity). a) Solid heterogeneous catalysts An initial example was provided by

• approach is attractive because it combines acid heterogeneous catalysts, as an environmentally and economically acceptable alternative to conventional homogeneous catalysts such as H2SO4 and HF, with the advantages of scFs. Thus, simple fixed-bed reactors can be developed for carrying out continuous flow

Nano copper oxide catalyzed synthesis of symmetrical diaryl sulfides under ligand free conditions

• K. Harsha Vardhan Reddy,
• V. Prakash Reddy,
• A. Ashwan Kumar,
• G. Kranthi and
• Y.V.D. Nageswar

Beilstein J. Org. Chem. 2011, 7, 886–891, doi:10.3762/bjoc.7.101

• , especially under ligand-free conditions, for the synthesis of such highly useful organic compounds. In the past few years, considerable efforts have been made in the area of heterogeneous catalysis for various organic transformations. In general, heterogeneous catalysts offer higher surface area and lower

Continuous flow hydrogenation using polysilane-supported palladium/alumina hybrid catalysts

• Hidekazu Oyamada,
• Takeshi Naito and
• Shū Kobayashi

Beilstein J. Org. Chem. 2011, 7, 735–739, doi:10.3762/bjoc.7.83

• . Heterogeneous catalysts including Pd/C, Pt/C and Pd/SiO2 are commonly used in reduction reactions both in research and industrial environments because of the ease of separation of the catalysts and products. However, the contamination of products as a result of leaching of metals from supports as well as the

• decreased catalytic activity, are both serious problems with the use of conventional heterogeneous catalysts. To address these problems, we recently developed novel methods for the immobilization of metal and non-metal catalysts on supports. This involved the development of microencapsulated (MC) and

Unusual behavior in the reactivity of 5-substituted-1H-tetrazoles in a resistively heated microreactor

• Bernhard Gutmann,
• Toma N. Glasnov,
• Tahseen Razzaq,
• Walter Goessler,
• Dominique M. Roberge and
• C. Oliver Kappe

Beilstein J. Org. Chem. 2011, 7, 503–517, doi:10.3762/bjoc.7.59

• pronounced reactor wall effects and unexpected/undesired side and degradative reactions [33]. The stainless steel reactor contains a variety of metals and the reactor walls could possibly act as heterogeneous catalysts (surface catalysis) [34]. Furthermore, the surface can potentially be considered as a

Air-stable, recyclable, and time-efficient diphenylphosphinite cellulose-supported palladium nanoparticles as a catalyst for Suzuki–Miyaura reactions

• Qingwei Du and
• Yiqun Li

Beilstein J. Org. Chem. 2011, 7, 378–385, doi:10.3762/bjoc.7.48

• ], N-heterocyclic carbenes [13][14][15], P,O-based ligands [16], bis(thiourea) ligands [17], and thiosemicarbazone [18], etc. However, the separation of the catalyst and ligands from the final product is problematic. In this regard, studies on heterogeneous catalysts have drawn much attention because

Hoveyda–Grubbs type metathesis catalyst immobilized on mesoporous molecular sieves MCM-41 and SBA-15

• Hynek Balcar,
• Tushar Shinde,
• Naděžda Žilková and
• Zdeněk Bastl

Beilstein J. Org. Chem. 2011, 7, 22–28, doi:10.3762/bjoc.7.4

• catalysts was reported [20]. A second generation Hoveyda–Grubbs catalyst was immobilized on silica without any linkers by simply placing the Ru complex in contact with silica in a suspension. Heterogeneous catalysts (loading from 0.05 to 0.6 wt % Ru) were prepared, which were active in ring-opening

• heterogeneous catalysts 3/MCM-41 and 3/SBA-15. The immobilization proceeded almost quantitatively: 97% and 94% of the Ru complex was transferred from the solution onto the MCM-41 and SBA-15 surface, respectively. The established catalyst loading was 0.98 wt % and 0.93 wt %, for 3/MCM-41 and 3/SBA-15

• . Heterogeneous catalysts prepared in this way exhibited high activity and 100% selectivity in the RCM of 1,7-octadiene and diethyl diallylmalonate, in the metathesis of methyl oleate and methyl 10-undecenoate, and in the ROMP of cyclooctene. Ru leaching was found to depend on the polarity of substrate and

Stereoselectivity of supported alkene metathesis catalysts: a goal and a tool to characterize active sites

• Christophe Copéret

Beilstein J. Org. Chem. 2011, 7, 13–21, doi:10.3762/bjoc.7.3

• tool to characterize active sites of heterogeneous catalysts and finally to propose strategies to improve catalysts based on the current state of the art. Keywords: active sites; metathesis; stereoselectivity; supported catalysts; Introduction Achieving high selectivity and, in particular

• (styrenyl systems or alkenes with electron withdrawing substituents) [19][20][21]. Here the discussion will focus on the stereoselectivity of alkene metathesis in order to delineate the current state of the art in the case of heterogeneous catalysts and show how it can be used to characterize active sites

• understand the structure and the modification of structures of catalysts under working conditions, whether homogeneous or heterogeneous. Ru-based heterogeneous catalysts are E-selective (60–70%) when transforming (Z)-alkenes such as ethyl oleate, as their homogeneous equivalents. In contrast, the Re-based

C-Arylation reactions catalyzed by CuO-nanoparticles under ligand free conditions

• Mazaahir Kidwai,
• Saurav Bhardwaj and
• Roona Poddar

Beilstein J. Org. Chem. 2010, 6, No. 35, doi:10.3762/bjoc.6.35

• oxide nanoparticles have been used as heterogeneous catalysts for various organic transformations [23][24][25][26][27][28]. The high reactivity of CuO-nanoparticles (CuO-np) is due to the high surface area of nanoparticles combined with unusual reactive morphologies. Moreover, heterogeneous catalysts

Hydroxyapatite supported caesium carbonate as a new recyclable solid base catalyst for the Knoevenagel condensation in water

• Monika Gupta,
• Rajive Gupta and
• Medha Anand

Beilstein J. Org. Chem. 2009, 5, No. 68, doi:10.3762/bjoc.5.68

• catalyst (HAP–Cs2CO3) makes the method very cost-effective. Heterogeneity and recyclability of the catalyst When using supported heterogeneous catalysts, there are two important points to consider: heterogeneity and recyclability. To rule out the possibility of homogeneous catalysis, a reaction between 4

Zeolite catalyzed solvent- free one-pot synthesis of dihydropyrimidin- 2(1H)-ones – A practical synthesis of monastrol

• Mukund G. Kulkarni,
• Sanjay W. Chavhan,
• Mahadev P. Shinde,
• Dnyaneshwar D. Gaikwad,
• Ajit S. Borhade,
• Attrimuni P. Dhondge,
• Yunnus B. Shaikh,
• Vijay B. Ningdale,
• Mayur P. Desai and
• Deekshaputra R. Birhade

Beilstein J. Org. Chem. 2009, 5, No. 4, doi:10.3762/bjoc.5.4

• ][18][19][20]. To overcome this problem, various homogeneous as well as heterogeneous catalysts have been utilized. Typical examples of the various homogeneous catalysts employed are polyphosphate ester [18], LaCl3·7H2O [21] and LiClO4 [22]. Recently Lewis acid catalyzed Biginelli reactions have been

• has also been used recently for this purpose [35]. The Brønsted acid mediated Biginelli reactions using p-TSA [36], H2SO4/SiO2 [37], and KHSO4 [38] are known in the literature. The heterogeneous catalysts used in this reaction involve the use of KSF (montmorillonite) [39], bentonitic clay [40], and

• zeolites like HZSM-5, Hy, MCM–41 [41]. The limitations in using the above mentioned catalysts were elevated reaction temperatures, solvent mediated reactions and moderate yields of the products. Apart from these, the heterogeneous catalysts were required in stoichiometric amounts. Furthermore, when