- New Class of Chiral Diphosphine Ligands for Highly Efficient Transition Metal-Catalyzed Stereoselective Reactions: The Bis(diphenylphosphino) Five-membered Biheteroaryls
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The synthesis and application of three examples of a new class of chiral (C2) atropisomeric diphosphines characterized by two interconnected five-membered heteroaromatic rings, with hindered rotation around the interanular bond, are described.Optically pure (+)- and (-)-2,2'-bis(diphenylphosphino)-4,4',6,6'-tetramethyl-3,3'-bibenzothiophene (tetraMe-bitianp) (1a) and the parent unsubstituted system (+)- and (-)-bitianp (1b) were synthesized.They were found to be optically stable at 100 deg C and were successfully employed as ligands in the Ru(II)-catalyzed hydrogenation of α- and β-oxo esters to the corresponding α- and β-hydroxy esters and in the hydrogenation of olefinic substrates.The optical and chemical yields were comparable with those reported for the same Ru(II)-binap-catalyzed reactions carried out under the same experimental conditions.The 2,2'-bis(diphenylphosphino)-3,3'-bibenzofuran (1c), the oxygenated analogue of bitianp, was found to be configurationally unstable at room temperature.Complete structural X-ray elucidation of the Pd complexes of 1a-c is reported.The advantages of these biheteroaromatic ligands over the classical biaryl systems are discussed.
- Benincori, Tiziana,Brenna, Elisabetta,Sannicolo, Franco,Trimarco, Licia,Antognazza, Patrizia,et al.
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p. 6244 - 6251
(2007/10/03)
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- Cationic BINAP-Ru(II) Halide Complexes: Highly Efficient Catalysts for Stereoselective Asymmetric Hydrogenation of α- and β-Functionalized Ketones
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Cationic ruthenium-BINAP complexes 5, 7, and 10 of the formula Y, where X = Cl, Br, I; Y = Cl, Br, I, BF4, B(C6H5)4; arene = benzene, p-cymene, ethyl benzoate, and their enantiomers have been prepared by the reaction of arene-ruthenium halide complexes 4, 6, and 9 with (S)-BINAP or (R)-BINAP.Structures of the complexes were established by spectroscopy, conductivity, and a single-crystal X-ray analysis (5d: orthorhombic, P21212; a=20.141(2) Angstroem, b=18.504(1) Angstroem, c=12.241(1) Angstroem, V=4562.0(7) Angstroem3, Z=4, R=0.078 for unique 4177 reflections).BINAP derivatives with various substituents at the para and meta positions of four phenyl rings on phosphorus atoms and their cationic Ru(II) complexes have also been synthesized.These BINAP-Ru(II) complexes have been used as catalysts for the asymmetric hydrogenation of various unsaturated organic compounds such as α- and β-keto esters, allylic alcohols, and α,β-unsaturated carboxylic acids in excellent diastereo- and/or enantioselectivities.Catalytic activities and stereoselectivities depend highly on reaction conditions such as solvent, temperature, and additives.Variation of halogen ligands bound to ruthenium atom and substituents on four phenyl rings of BINAP also have exerted remarkable effects on the efficiency of the catalysis.Asymmetric hydrogenation of methyl (+/-)-2-(benzamidomethyl)-3-oxobutanoate catalyzed by the species derived from 9c and 3,5-(t-Bu)2-BINAP afforded the corresponding syn-(2S,3R)-17 in 98percent de and 99percent ee.
- Mashima, Kazushi,Kusano, Koh-hei,Sato, Naomasa,Matsumura, Yoh-ichi,Nozaki, Kyoko,et al.
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p. 3064 - 3076
(2007/10/02)
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- Synthesis and Characterization of Mono- and Tri-nuclear Ruthenium Complexes of 2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl and Their Catalytic Activity
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The structures of ruthenium(II) complexes formed in solution from Y (S)-3 (X, Y = halide and/or BF4-; binap = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl; arene = benzene or p-cymene) depend on the solvent.In acetonitrile-methanol (1:1) dicationic complexes X(Y) (S)-4 (X = Y = Cl a; X = Cl, Y = BF4 b; X = Y = Br c; or X = Y = I d) are predominantly formed, while monocationic species X (S)-6 (X = Cl a, Br b or I c) were observed in acetonitrile.These mono- and di-cationic species could not be isolated pure, while (S)-5 was isolated from (S)-4a or (S)-6a upon concentration of the reaction mixture.In methanol without donor molecules such as acetonitrile, cationic trinuclear complexes Y (S)-7 (X = Y = Cl a; X = Cl, Y = BF4 b or X = Y = Br c) were exclusively formed by heating at 60 deg C or UV irradiation of a solution of (S)-3.The structure of (S)-7 was characterized by spectral data and an X-ray crystallographic analysis of (S)-7b 12121, a = 26.328(5), b = 18.140(3), c = 26.374(4), Z = 4, R'= 0.083>.The relationship between the structure of the RuII(binap) complexes and their catalytic activities for asymmetric hydrogenation of methyl 3-oxobutanoate has been investigated.
- Mashima, Kazushi,Hino, Takahiro,Takaya, Hidemasa
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p. 2099 - 2108
(2007/10/02)
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- Synthesis of New Cationic BINAP-Ruthenium(II) Complexes and their Use in Asymmetric Hydrogenation
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Reaction of 2 (1) and (S)-BINAP gives cationic BINAP-ruthenium complexes of the formula Y (2) (X = Cl, Br, and I; Y = Cl, Br, I, BF4, and BPh4; arene = C6H6 and p-MeC6H4CHMe2) which are efficient catalyst precursors for enantioselective hydrogenation of various prochiral alkenic and ketonic substrates ; a crystal structure of (2) (with X = Cl, Y = BF4) was obtained.
- Mashima, Kazushi,Kusano, Koh-hei,Ohta, Tetsuo,Noyori, Ryoji,Takaya, Hidemasa
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p. 1208 - 1210
(2007/10/02)
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