Katsuomi Takehira

Bio: Katsuomi Takehira is an academic researcher from Hiroshima University. The author has contributed to research in topics: Catalysis & Diphenylphosphine. The author has an hindex of 15, co-authored 30 publications receiving 744 citations.

Manganese-containing MCM-41 for epoxidation of styrene and stilbene

Abstract: Mn-MCM-41 is found to be the most effective heterogeneous catalyst for the epoxidation of styrene with tert-butyl hydroperoxide (TBHP) among several metal ion-containing mesoporous molecular sieves including Mn-, V-, Cr-, Fe-, and Mo-MCM-41. ESR, XANES, diffuse reflectance UV–VIS, UV–Raman and XPS are used to characterize the Mn-MCM-41 synthesized by both direct hydrothermal (DHT) and template ion exchange (TIE) methods. The results suggest that Mn2+ and Mn3+ coexist in the Mn-MCM-41 samples synthesized by both methods and a large part of manganese atoms could be incorporated into the framework of MCM-41 obtained by the DHT method. The oxidation of either styrene or stilbene with TBHP as the oxidant over the Mn-MCM-41 produces corresponding epoxide as the main product; the reaction probably proceeds through a radical intermediate. The TIE catalyst shows higher activity, while the DHT catalyst gives higher TBHP efficiency for the epoxidation reactions.

Intermolecular Hydrophosphination of Alkynes and Related Carbon−Carbon Multiple Bonds Catalyzed by Organoytterbiums

Abstract: Intermolecular hydrophosphination of alkynes with diphenylphosphine is catalyzed by a Yb−imine complex, [Yb(η2-Ph2CNPh)(hmpa)3], to give alkenylphosphines and phosphine oxides after oxidative workup in good yields under mild conditions. This reaction is also applicable to various carbon−carbon multiple bonds such as conjugated diynes and dienes, allenes, and styrene derivatives. Regio- and stereoselectivity and the scope and limitation of the present reaction clearly differ from those of the corresponding radical reaction. Instead, the reaction takes place through insertion of alkynes to a Yb−PPh2 species, followed by protonation. In fact, the Yb−phosphido complex, [Yb(PPh2)2(hmpa)3], is obtained from the imine complex and phosphine, which exhibits similar catalyst activity for the hydrophosphination. The empirical rate law is ν = k[catalyst]2 [alkyne]1[phosphine]0 at least under the standard conditions.

Rare-earth silylamide-catalyzed selective dimerization of terminal alkynes and subsequent hydrophosphination in one pot.

Abstract: Rare-earth silylamides, Ln[N(SiMe3)2]3 (Ln = Y, La, Sm), catalyzed regio- and stereoselective dimerization of terminal alkynes in the presence of amine additives to give conjugated enynes in high yields. The additives played a crucial role to depress the oligomerization and to control the regio- and stereochemistry of the dimerization. Thus, the selectivity for (Z)-head-to-head enynes was increased in the order of tertiary < secondary < primary amine additives. On the other hand, the reversed order was observed for the formation of head-to-tail dimers. When α,ω-diynes were subjected to the dimerization, very novel cyclic bisenyne compounds were given through double-dimerization in satisfactory yields. In addition, an application of the system allowed subsequent hydrophosphination of the enynes generated in situ with diphenylphosphine, giving rise to 1-phosphinyl-1,3-dienes as the sole products in excellent yields after oxidative workup.

Dehydrogenative Silylation of Amines and Hydrosilylation of Imines Catalyzed by Ytterbium−Imine Complexes

Abstract: Dehydrogenative silylation of primary and secondary amines with triphenylsilane was catalyzed by ytterbium−imine complexes, [Yb(η2-Ph2CNAr)(hmpa)n], to give aminosilanes in good yields. In the reaction with diphenyl- and phenylsilanes, diaminosilanes were formed as major products. Whereas n- and sec-alkylamines were readily silylated, tert-alkylamines and aromatic amines exhibited lower reactivities. Moreover, hydrosilylation of imines has been achieved by using phenylsilane and the imine complexes (Ar = Ph, C6H4F-4), giving rise to mono- and diaminosilanes. The two reactions were in agreement as regards the product selectivities and yields.

Synthesis of V-MCM-41 by template-ion exchange method and its catalytic properties in propane oxidative dehydrogenation

Abstract: Vanadium has been introduced to MCM-41 without collapse of the mesoporous structure by exchanging VO2+ ions in the aqueous solution with the template cations in the uncalcined MCM-41. This template-ion exchange (TIE) method provides tetrahedrally coordinated vanadyl species dispersed in the channel of MCM-41. Such synthesized V-MCM-41 shows higher catalytic activity in the oxidative dehydrogenation of propane than that prepared by direct hydrothermal method.

Aerobic Copper-Catalyzed Organic Reactions

Abstract: The chemistry of copper is extremely rich because it can easily access Cu0, CuI, CuII, and CuIII oxidation states allowing it to act through one-electron or two-electron processes. As a result, both radical pathways and powerful two-electron bond forming pathways via organmetallic intermediates, similar to those of palladium, can occur. In addition, the different oxidation states of copper associate well with a large number of different functional groups via Lewis acid interactions or π-coordination. In total, these feature confer a remarkably broad range of activities allowing copper to catalyze the oxidation and oxidative union of many substrates. Oxygen is a highly atom economical, environmentally benign, and abundant oxidant, which makes it ideal in many ways.1 The high activation energies in the reactions of oxygen require that catalysts be employed.2 In combination with molecular oxygen, the chemistry of copper catalysis increases exponentially since oxygen can act as either a sink for electrons (oxidase activity) and/or as a source of oxygen atoms that are incorporated into the product (oxygenase activity). The oxidation of copper with oxygen is a facile process allowing catalytic turnover in net oxidative processes and ready access to the higher CuIII oxidation state, which enables a range of powerful transformations including two-electron reductive elimination to CuI. Molecular oxygen is also not hampered by toxic byproducts, being either reduced to water, occasionally via H2O2 (oxidase activity) or incorporated into the target structure with high atom economy (oxygenase activity). Such oxidations using oxygen or air (21% oxygen) have been employed safely in numerous commodity chemical continuous and batch processes.3 However, batch reactors employing volatile hydrocarbon solvents require that oxygen concentrations be kept low in the head space (typically <5–11%) to avoid flammable mixtures, which can limit the oxygen concentration in the reaction mixture.4,5,6 A number of alternate approaches have been developed allowing oxidation chemistry to be used safely across a broader array of conditions. For example, use of carbon dioxide instead of nitrogen as a diluent leads to reduced flammability.5 Alternately, water can be added to moderate the flammability allowing even pure oxygen to be employed.6 New reactor designs also allow pure oxygen to be used instead of diluted oxygen by maintaining gas bubbles in the solvent, which greatly improves reaction rates and prevents the build up of higher concentrations of oxygen in the head space.4a,7 Supercritical carbon dioxide has been found to be advantageous as a solvent due its chemical inertness towards oxidizing agents and its complete miscibility with oxygen or air over a wide range of temperatures.8 An number of flow technologies9 including flow reactors,10 capillary flow reactors,11 microchannel/microstructure structure reactors,12 and membrane reactors13 limit the amount of or afford separation of hydrocarbon/oxygen vapor phase thereby reducing the potential for explosions. Enzymatic oxidizing systems based upon copper that exploit the many advantages and unique aspects of copper as a catalyst and oxygen as an oxidant as described in the preceding paragraphs are well known. They represent a powerful set of catalysts able to direct beautiful redox chemistry in a highly site-selective and stereoselective manner on simple as well as highly functionalized molecules. This ability has inspired organic chemists to discover small molecule catalysts that can emulate such processes. In addition, copper has been recognized as a powerful catalyst in several industrial processes (e.g. phenol polymerization, Glaser-Hay alkyne coupling) stimulating the study of the fundamental reaction steps and the organometallic copper intermediates. These studies have inspiried the development of nonenzymatic copper catalysts. For these reasons, the study of copper catalysis using molecular oxygen has undergone explosive growth, from 30 citations per year in the 1980s to over 300 citations per year in the 2000s. A number of elegant reviews on the subject of catalytic copper oxidation chemistry have appeared. Most recently, reviews provide selected coverage of copper catalysts14 or a discussion of their use in the aerobic functionalization of C–H bonds.15 Other recent reviews cover copper and other metal catalysts with a range of oxidants, including oxygen, but several reaction types are not covered.16 Several other works provide a valuable overview of earlier efforts in the field.17 This review comprehensively covers copper catalyzed oxidation chemistry using oxygen as the oxidant up through 2011. Stoichiometric reactions with copper are discussed, as necessary, to put the development of the catalytic processes in context. Mixed metal systems utilizing copper, such as palladium catalyzed Wacker processes, are not included here. Decomposition reactions involving copper/oxygen and model systems of copper enzymes are not discussed exhaustively. To facilitate analysis of the reactions under discussion, the current mechanistic hypothesis is provided for each reaction. As our understanding of the basic chemical steps involving copper improve, it is expected that many of these mechanisms will evolve accordingly.

Cobalt-Catalyzed Cross-Coupling Reactions

Abstract: 3.1.2. From Vinylic Grignard Reagents 1437 3.1.3. From Aryl Halides and Alkenyl Acetates 1438 3.2. Aryl-Aryl Cross-coupling 1438 3.2.1. From Aromatic Organometallic Reagents 1438 3.2.2. From Two Aromatic Halides 1440 4. Csp2-Csp3 Cross-coupling Reactions 1440 4.1. Alkenylation 1440 4.1.1. From Aliphatic Organometallic Reagents 1440 4.1.2. From Aliphatic Halides 1442 4.2. Arylation 1442 4.2.1. From Aliphatic Halides 1442 4.2.2. From Aromatic Halides 1445 4.3. Allylation of Aromatic Organometallics 1446 5. Alkynylation 1446 5.1. Pioneering Works 1446 5.2. Benzylation of Acetylenic Grignard Reagents 1446 5.3. Alkylation of Acetylenic Grignard Reagents 1447 5.4. Alkenylation of Acetylenic Grignard Reagents 1447 6. Csp3-Csp3 Cross-coupling 1448 6.1. Allylation 1448 6.1.1. Allylation of Aliphatic Organozinc Compounds 1448

From limestone to catalysis: application of calcium compounds as homogeneous catalysts.

Abstract: 5. Hydrosilylation 3862 5.1. Alkene Hydrosilylation 3863 5.2. Ketone Hydrosilylation 3865 6. Alkene Hydrogenation 3866 7. Aldol-, Mannich-, and Michael-Type Reactions 3867 7.1. Enantioand Diastereoselective Conversions 3867 7.2. Remarks on Stereoselective Induction 3869 8. Miscellaneous Conversions 3869 9. Analogies between Yb2+ and Ca2+ Chemistry 3871 10. Conclusions and Perspectives 3872 11. References 3873