Efficient Assays for Combinatorial Methods for the Discovery of Catalysts

Bein, Thomas

doi:10.1002/(sici)1521-3773(19990201)38:3<323::aid-anie323>3.0.co;2-4

Cited by 96 publications

(24 citation statements)

References 18 publications

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“…One approach employs carbohydrate coupling partners with identical anomeric latent leaving groups; the reactivities of each of the leaving groups are differentiated by varying the electronic nature of proximal protective groups. [2] The success of this approach to oligosaccharide synthesis thus relies on intricate selection of protective groups to establish a suitable reactivity hierarchy among the carbohydrate building blocks. [2e] In an alternative strategy, the anomeric latent leaving groups in the carbohydrate coupling partners are mutually distinct, possessing chemically orthogonal reactivities; successive glycosylations are performed with a number of different reagents that are specific for a certain latent leaving group.…”

Section: Methodsmentioning

confidence: 99%

“…Bowl-Shaped Tris(2,6-diphenylbenzyl)tin Hydride: A Unique Reducing Agent for Radical and Ionic Chemistry** Kouji Sasaki, Yuichiro Kondo, and Keiji Maruoka* Trialkyltin hydrides (R 3 SnH) are widely utilized in numerous radical reactions including reductive dehalogenations, [1,2] desulfurizations, [3] and radical cyclizations. [4] Among several R 3 SnH (R Me, Bu, Ph), Bu 3 SnH is the most popular reagent in radical chemistry.…”

mentioning

confidence: 99%

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Bowl-Shaped Tris(2,6-diphenylbenzyl)tin Hydride: A Unique Reducing Agent for Radical and Ionic Chemistry

Sasaki

Kondo

Maruoka

2001

Angew. Chem. Int. Ed.

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Section: Methodsmentioning

confidence: 99%

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confidence: 99%

Bowl-Shaped Tris(2,6-diphenylbenzyl)tin Hydride: A Unique Reducing Agent for Radical and Ionic Chemistry

Sasaki

Kondo

Maruoka

2001

Angew. Chem. Int. Ed.

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“…After the reaction mixture had been stirred at À 78 8C for 2.5 h, it was poured into an aqueous saturated solution of NaHCO 3 and then extracted with diethyl ether. [2] The success of this approach to oligosaccharide synthesis thus relies on intricate selection of protective groups to establish a suitable reactivity hierarchy among the carbohydrate building blocks. Evaporation of solvents and purification of the residue by column chromatography on silica gel (diethyl ether/hexane (1/20)) gave 4 as a colorless oil and a small amount of 3 which was recovered (4: 60.8 mg, 0.292 mmol, 97 % yield; 3: 0.008 mmol, 3 % yield).…”

Section: Methodsmentioning

confidence: 99%

Bowl-Shaped Tris(2,6-diphenylbenzyl)tin Hydride: A Unique Reducing Agent for Radical and Ionic Chemistry

Sasaki¹,

Kondo²,

Maruoka³

2001

Angew. Chem.

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Trialkyltin hydrides (R 3 SnH) are widely utilized in numerous radical reactions including reductive dehalogenations, [1,2] desulfurizations, [3] and radical cyclizations. [4] Among several R 3 SnH (R Me, Bu, Ph), Bu 3 SnH is the most popular reagent in radical chemistry. The Bu 3 SnH-mediated radical reactions exhibit high regio-and stereoselectivity by changing radical initiators (azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), hn, Et 3 B, etc.) and/or the reaction conditions. [5] Alternatively, such stereoselectivity is also achievable by replacing Bu 3 SnH or Ph 3 SnH [6] with the sterically more hindered (Me 3 Si) 3 SiH. [7] However, it is apparent that there vertically provided uniform wetting of the substrate in the well area and favored heterogeneous film growth. The films prepared by parallel synthesis were shown to have similar morphology to those synthesized under conventional conditions but their X-ray diffraction patterns indicate lesser orientation of crystallites. Parallel synthesis was used to screen the composition space of organic-free clear synthesis solution for ZSM-5 film growth. The composition SiO 2 :(0.5 ± 0.7) NaOH:(1/300 ± 1/700) Al 2 O 3 :80 H 2 O resulted in continuous ZSM-5 films of Si/Al $ 20:1. Experimental SectionTwo types of silicon sources were used: sodium silicate solution (14 % NaOH and 27 % SiO 2 ), and tetraethylorthosilicate (TEOS). Sodium silicate was filtered by using a Buchner funnel with a coarse fritted disc immediately before use. When TEOS was used as the silicon source, it was first dissolved in tetrapropylammonium hydroxide (TPAOH) to form a clear solution of composition TEOS:0.15 TPAOH:0.7 NaOH:98 H 2 O, which was then filtered before use with a PTFE filter (0.45 mm). Tetrapropylammonium bromide (TPABr) solution (25 wt %) was prepared and filtered with 0.45 mm cellulose acetate membranes.The synthesis mixture was prepared by mixing a measured amount of chemicals in a transparent LDPE vial of volume 1 mL (Nalgene). When sodium silicate solution was used, H 2 SO 4 (5 n, VWR) was added to adjust the alkalinity of the final solution. After thorough shaking, a clear synthesis solution was formed and aged for one day at room temperature without stirring before being introduced into the well for reaction. Occasionally, the synthesis mixtures turned turbid immediately after mixing, but the solution became clear after standing for several hours.The substrates employed were nonporous a-alumina disks of diameter 2.5 cm. Prior to seeding the substrates were cleaned by a procedure described in reference [22]. Seeding of the entire substrate surface with a monolayer of silicalite particles was carried out using a previously developed protocol. [12,33] The seeds about 0.4 mm in size were finer than the substrate roughness and did not cause problems in sealing under pressure against the Teflon surfaces.

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“…Mechanization and computerization, now becoming more readily available and efficient, can help with all these goals. Combinatorial chemistry [4][5][6][7], together with rapid catalyst screening [8,9], has potential value in identification and optimization. The latest methods of computational and theoretical chemistry can give very valuable mechanistic information in ruling out otherwise plausible pathways and predicting structural information for transient species and transition states [10].…”

Section: Meoh + Co = Mecoohmentioning

confidence: 99%

Rapid screening and combinatorial methods in homogeneous organometallic catalysis

Loch

Crabtree

2001

Pure and Applied Chemistry

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Methods are discussed for rapid screening of soluble and polymer-bound homogeneous catalysts for activity. A polymer-bound phosphine library is synthesized, and a modular tridentate pincer CNC bis-carbene Pd complex is described. The possibility of C-bound His in metalloenzymes is raised.Homogeneous catalysis has much to offer Green Chemistry. By allowing reactions to occur at lower temperature and pressure, energy is saved. By enhancing selectivity, waste is avoided. Waste can even be essentially eliminated if catalysis allows atom-economic processes to be used. These are reactions like eq. 1 in which all the atoms of the reagents are incorporated into the product [1,2]. This particular rhodium-catalyzed reaction-the Monsanto Process-is a commercially important route to acetic acid [3]. In contrast, much conventional industrial chemistry still goes via reactions that produce stoichiometric amounts of inorganic salts or tainted water as byproducts. MeOH + CO = MeCOOH(1)For each new application, new homogeneous catalysts may well need to be identified and optimized, then understood mechanistically. Mechanization and computerization, now becoming more readily available and efficient, can help with all these goals. Combinatorial chemistry [4][5][6][7], together with rapid catalyst screening [8,9], has potential value in identification and optimization. The latest methods of computational and theoretical chemistry can give very valuable mechanistic information in ruling out otherwise plausible pathways and predicting structural information for transient species and transition states [10]. Here, we naturally discuss only the title topic, although by doing so we do not intend to detract from the importance of mechanistic understanding.The principles of combinatorial chemistry have been covered in several recent monographs and reviews [11][12][13][14][15][16]. In summary, the concept involves creating a large number of chemically distinct species-called a library-in a controlled way. This library is then assayed by a suitable rapid screening protocol to see if a desired response is elicited. The library members showing a good response, termed "hits", are then analyzed to determine the chemical structure responsible for the desired response.The field has its intellectual roots in an understanding of how the immune system works and in Merrifield's [17] approach to polypeptide synthesis. The immune system has the task of tagging foreign biomolecules to label them for attack. To do this, it creates a library of polypeptides of variable structure, then senses when one of these peptides by chance binds strongly to a foreign target, such as the surface of an invading bacterium, for example. The successful immune system peptide is then synthesized on a large scale to carry out its defense role in the body.

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Efficient Assays for Combinatorial Methods for the Discovery of Catalysts

Cited by 96 publications

References 18 publications

Bowl-Shaped Tris(2,6-diphenylbenzyl)tin Hydride: A Unique Reducing Agent for Radical and Ionic Chemistry

Bowl-Shaped Tris(2,6-diphenylbenzyl)tin Hydride: A Unique Reducing Agent for Radical and Ionic Chemistry

Bowl-Shaped Tris(2,6-diphenylbenzyl)tin Hydride: A Unique Reducing Agent for Radical and Ionic Chemistry

Rapid screening and combinatorial methods in homogeneous organometallic catalysis

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