The Experts below are selected from a list of 180 Experts worldwide ranked by ideXlab platform
Yoshihiko Ito - One of the best experts on this subject based on the ideXlab platform.
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asymmetric hydrosilylation of ketones using trans chelating chiral peralkylbisphosphine ligands bearing primary alkyl substituents on phosphorus Atoms
Bulletin of the Chemical Society of Japan, 2000Co-Authors: Ryoichi Kuwano, Masaya Sawamura, Junya Shirai, Masatoshi Takahashi, Yoshihiko ItoAbstract:Asymmetric hydrosilylation of simple ketones with diphenylsilane proceeded at -40 °C in the presence of a Rhodium complex (0.001—0.01 molar amount) coordinated with a trans-chelating chiral bisphosphine ligand bearing linear alkyl substituents on the phosphorus Atoms, (R,R)-(S,S)-Et-, Pr-, or BuTRAP, giving the corresponding optically active (S)-secondary alcohols with up to 97% ee. The asymmetric hydrosilylation using TRAP ligands with bulkier P-substituents resulted in much lower enantioselectivities. The EtTRAP-Rhodium catalyst was also effective for asymmetric hydrosilylation of keto esters with a coordination site for a Rhodium Atom (up to 98% ee). Optically active symmetrical diols were obtained with up to 99% ee from the corresponding diketones via the asymmetric reduction using 2.5 molar amounts of diphenylsilane.
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Synthesis of a trans-chelating chiral diphosphine ligand with only planar chirality and its application to asymmetric hydrosilylation of ketones
Tetrahedron Letters, 1999Co-Authors: Ryoichi Kuwano, Takashi Uemura, Makoto Saitoh, Yoshihiko ItoAbstract:Abstract Optically active diphosphine (S,S)-2,2″-bis[(diethylphosphino)methyl]-1,1″-biferrocene (abbreviated to (S,S)-EtTRAP-H) was synthesized from ferrocenyloxazoline derived from l -valinol in 47% overall yield. The new chiral ligand, (S,S)-EtTRAP-H, which coordinates to a Rhodium Atom in a trans-chelating manner, was effective for asymmetric hydrosilylation of ketones to give optically active secondary alcohols with up to 94% ee.
Ryoichi Kuwano - One of the best experts on this subject based on the ideXlab platform.
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asymmetric hydrosilylation of ketones using trans chelating chiral peralkylbisphosphine ligands bearing primary alkyl substituents on phosphorus Atoms
Bulletin of the Chemical Society of Japan, 2000Co-Authors: Ryoichi Kuwano, Masaya Sawamura, Junya Shirai, Masatoshi Takahashi, Yoshihiko ItoAbstract:Asymmetric hydrosilylation of simple ketones with diphenylsilane proceeded at -40 °C in the presence of a Rhodium complex (0.001—0.01 molar amount) coordinated with a trans-chelating chiral bisphosphine ligand bearing linear alkyl substituents on the phosphorus Atoms, (R,R)-(S,S)-Et-, Pr-, or BuTRAP, giving the corresponding optically active (S)-secondary alcohols with up to 97% ee. The asymmetric hydrosilylation using TRAP ligands with bulkier P-substituents resulted in much lower enantioselectivities. The EtTRAP-Rhodium catalyst was also effective for asymmetric hydrosilylation of keto esters with a coordination site for a Rhodium Atom (up to 98% ee). Optically active symmetrical diols were obtained with up to 99% ee from the corresponding diketones via the asymmetric reduction using 2.5 molar amounts of diphenylsilane.
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Synthesis of a trans-chelating chiral diphosphine ligand with only planar chirality and its application to asymmetric hydrosilylation of ketones
Tetrahedron Letters, 1999Co-Authors: Ryoichi Kuwano, Takashi Uemura, Makoto Saitoh, Yoshihiko ItoAbstract:Abstract Optically active diphosphine (S,S)-2,2″-bis[(diethylphosphino)methyl]-1,1″-biferrocene (abbreviated to (S,S)-EtTRAP-H) was synthesized from ferrocenyloxazoline derived from l -valinol in 47% overall yield. The new chiral ligand, (S,S)-EtTRAP-H, which coordinates to a Rhodium Atom in a trans-chelating manner, was effective for asymmetric hydrosilylation of ketones to give optically active secondary alcohols with up to 94% ee.
Yu Lan - One of the best experts on this subject based on the ideXlab platform.
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probing enantioselectivity in Rhodium catalyzed si c bond cleavage to construct silicon stereocenters a theoretical study
Catalysis Science & Technology, 2019Co-Authors: Tao Zhang, Ruopeng Bai, Yu LanAbstract:The Rhodium-catalyzed asymmetric synthesis of dibenzooxasilines developed by Hayashi and co-workers provides an efficient method to construct tetraorganosilicon stereocenters. In the present study, density functional theory (DFT) calculations were performed to investigate the mechanism and enantioselectivity of this reaction. Theoretical calculations indicate that the mechanism involves the initial formation of an aryloxoRhodium complex followed by Rh–Si exchange to afford an arylRhodium complex. The favorable oxidative addition/reductive elimination to cleave one Si–C(phenyl) bond from the arylRhodium complex determines the enantioselectivity. The enantioselectivity originates from the silyl moiety extruding from the phenyl ring on the Rhodium Atom in the reductive elimination transition state.
Karin Ruhlandt-senge - One of the best experts on this subject based on the ideXlab platform.
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Interaction of Rh(I) with meso-arylsapphyrins and -rubyrins: first structural characterization of bimetallic hetero-rubyrin complex.
Inorganic chemistry, 2001Co-Authors: Seenichamy Jeyaprakash Narayanan, Bashyam Sridevi, Tavarekere K. Chandrashekar, Ulrich Englich, Karin Ruhlandt-sengeAbstract:The ligational behavior of meso-arylsapphyrins and rubyrins toward Rh(I) is investigated. Sapphyrins form monometallic complexes with coordination of one imine and amine type nitrogens of the bipyrrole unit in an η2 fashion. The Rh(I) coordination is completed by the presence of two ancillary carbon monoxide ligands. Rubyrins form both monometallic and bimetallic complexes. Two types of bimetallic complexes have been isolated. In the first type, both Rhodium Atoms are projected above the mean rubyrin plane, while in the second type, one Rhodium Atom is projected above and the other below the mean plane. Detailed 1H and 2D NMR spectral analyses along with IR and UV−visible spectra of the complexes confirm the proposed binding modes for the Rhodium complexes. Furthermore, the single-crystal X-ray analysis of one of the bimetallic complexes of rubyrin shows a bowl-shaped symmetric structure where both Rh(I) Atoms are projected above the mean rubyrin plane at an angle of 71.73°. The geometry around each rhodi...
Masahiro Yamanaka - One of the best experts on this subject based on the ideXlab platform.
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Mechanism of C-H Bond Activation/C-C Bond Formation Reaction between Diazo Compound and Alkane catalyzed by DiRhodium Tetracarboxylate
Journal of the American Chemical Society, 2002Co-Authors: Eiichi Nakamura, Naohiko Yoshikai, Masahiro YamanakaAbstract:The B3LYP density functional studies on the diRhodium tetracarboxylate-catalyzed C-H bond activation/C-C bond formation reaction of a diazo compound with an alkane revealed the energetics and the geometry of important intermediates and transition states in the catalytic cycle. The reaction is initiated by complexation between the Rhodium catalyst and the diazo compound. Driven by the back-donation from the Rh 4d(xz) orbital to the C[bond]N sigma*-orbital, nitrogen extrusion takes place to afford a Rhodium[bond]carbene complex. The carbene carbon of the complex is strongly electrophilic because of its vacant 2p orbital. The C[bond]H activation/C[bond]C formation proceeds in a single step through a three-centered hydride transfer-like transition state with a small activation energy. Only one of the two Rhodium Atoms works as a carbene binding site throughout the reaction, and the other Rhodium Atom assists the C[bond]H insertion reaction. The second Rh Atom acts as a mobile ligand for the first one to enhance the electrophilicity of the carbene moiety and to facilitate the cleavage of the Rhodium[bond]carbon bond. The calculations reproduce experimental data including the activation enthalpy of the nitrogen extrusion, the kinetic isotope effect of the C[bond]H insertion, and the reactivity order of the C[bond]H bond.
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mechanism of c h bond activation c c bond formation reaction between diazo compound and alkane catalyzed by diRhodium tetracarboxylate
Journal of the American Chemical Society, 2002Co-Authors: Eiichi Nakamura, Naohiko Yoshikai, Masahiro YamanakaAbstract:The B3LYP density functional studies on the diRhodium tetracarboxylate-catalyzed C-H bond activation/C-C bond formation reaction of a diazo compound with an alkane revealed the energetics and the geometry of important intermediates and transition states in the catalytic cycle. The reaction is initiated by complexation between the Rhodium catalyst and the diazo compound. Driven by the back-donation from the Rh 4d(xz) orbital to the C[bond]N sigma*-orbital, nitrogen extrusion takes place to afford a Rhodium[bond]carbene complex. The carbene carbon of the complex is strongly electrophilic because of its vacant 2p orbital. The C[bond]H activation/C[bond]C formation proceeds in a single step through a three-centered hydride transfer-like transition state with a small activation energy. Only one of the two Rhodium Atoms works as a carbene binding site throughout the reaction, and the other Rhodium Atom assists the C[bond]H insertion reaction. The second Rh Atom acts as a mobile ligand for the first one to enhance the electrophilicity of the carbene moiety and to facilitate the cleavage of the Rhodium[bond]carbon bond. The calculations reproduce experimental data including the activation enthalpy of the nitrogen extrusion, the kinetic isotope effect of the C[bond]H insertion, and the reactivity order of the C[bond]H bond.
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mechanism of c h bond activation c c bond formation reaction between diazo compound and alkane catalyzed by diRhodium tetracarboxylate
Journal of the American Chemical Society, 2002Co-Authors: Eiichi Nakamura, Naohiko Yoshikai, Masahiro YamanakaAbstract:The B3LYP density functional studies on the diRhodium tetracarboxylate-catalyzed C−H bond activation/C−C bond formation reaction of a diazo compound with an alkane revealed the energetics and the geometry of important intermediates and transition states in the catalytic cycle. The reaction is initiated by complexation between the Rhodium catalyst and the diazo compound. Driven by the back-donation from the Rh 4dxz orbital to the C−N σ*-orbital, nitrogen extrusion takes place to afford a Rhodium−carbene complex. The carbene carbon of the complex is strongly electrophilic because of its vacant 2p orbital. The C−H activation/C−C formation proceeds in a single step through a three-centered hydride transfer-like transition state with a small activation energy. Only one of the two Rhodium Atoms works as a carbene binding site throughout the reaction, and the other Rhodium Atom assists the C−H insertion reaction. The second Rh Atom acts as a mobile ligand for the first one to enhance the electrophilicity of the ...