Highly Effective Chiral Dipyridylphosphine Ligands:  Synthesis, Structural Determination, and Applications in the Ru-Catalyzed Asymmetric Hydrogenation Reactions

Pai, Cheng‐Chao; Lin, Ching‐Wen; Lin, Cheng‐Kun; Chen, and Chih-Chiang; Chan, Albert S. C.; Wong, Wing Tak

doi:10.1021/ja000163n

Cited by 206 publications

(60 citation statements)

References 22 publications

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“…Optical rotations were measured on a PerkinElmer model 341 polarimeter in a 10-cm cell. Optically pure P-Phos (1a) and Xyl-P-Phos (1b) were synthesized according to our previously reported procedures (46,48). Copper f luoride, phenylsilane, polymethylhydrosiloxane, and ketone substrates were purchased from Aldrich or Acros (Hong Kong) and used as received without further purification unless otherwise stated.…”

Section: Methodsmentioning

confidence: 99%

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A remarkably effective copper(II)-dipyridylphosphine catalyst system for the asymmetric hydrosilylation of ketones in air

Chan

2005

Proc. Natl. Acad. Sci. U.S.A.

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102

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The combination of catalytic amounts of optically active dipyridylphosphine and CuF 2 along with hydride donor PhSiH3 generated in situ a remarkably reactive catalyst system (substrate-toligand molar ratio up to 100,000) for the highly enantioselective hydrosilylation of a broad spectrum of aryl alkyl ketones (up to 97% enantiomeric excess) in normal atmosphere and at mild conditions (ambient temperature to ؊20°C, compatible with traces of moisture) in the absence of base additives. Furthermore, a highly effective catalytic asymmetric hydrosilylation of unsymmetrical diarylketones using this catalyst system was also realized (up to 98% enantiomeric excess). The introduction of the dipyridylphosphine ligands in the air-accelerated and inexpensive metal-mediated asymmetric hydrosilylation of ketones makes the present system highly attractive and thus provides an excellent opportunity for practical applications.asymmetric catalysis C onsiderable efforts have been devoted to the development of efficient methods for the preparation of enantiomerically pure secondary alcohols because of the significance of these intermediates for the manufacture of pharmaceuticals and advanced materials. The catalytic asymmetric reduction of prochiral ketones as a direct route to enantiomeric alcohols is among the most attractive, and various strategies have been developed accordingly (1-5). Although intensive studies have been focused on the asymmetric hydrogenation that shows excellent enantioselectivities for a wide range of simple ketones (refs. 6 and 7 and references therein and refs. 8 -18), asymmetric hydrosilylation as a desirable alternative has also attracted much attention, owing to the mild reaction conditions used and technical simplicity (1d). Since the early reports three decades ago (19 -23), the asymmetric hydrosilylations of prochiral simple ketones mediated by catalysts of rhodium(I) (4, 24 -28) and ruthenium(II) (29, 30) as well as some less expensive metals such as titanium (31-34), zinc (35), tin (36), and copper(I) (37) have been extensively explored. However, most of these reactions were routinely conducted at a low substrate-to-ligand (S͞L) ratio (50 to 500). The high cost of catalyst and the low substrate-to-catalyst ratio rendered the previous hydrosilylation work unattractive commercially. More recently, a significant breakthrough in this area was achieved by , who developed a very effective catalyst system formed in situ from CuCl and nonracemic bidentate phosphines [e.g., (6,6Ј-dimethoxybiphenyl-2,2Ј-diyl)bis[di(3,5-dimethylphenyl)phosphine] (41, 42) or (4,4Ј-bi-1,3-benzodioxol)-5,5Ј-diylbis(di(3,5-di-tert-4-methoxyphenyl)phosphane) (43)] along with t-BuONa. This system allowed for highly active and enantioselective hydrosilylations of both aryl alkyl and heteroaromatic ketones in the presence of an inexpensive stoichiometric reductant polymethylhydrosiloxane (44) even at a S͞L molar ratio up to 100,000, which approached the levels achieved in related ruthenium-based asymmetric hydrogenations (ref. 6 and ...

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Section: Methodsmentioning

confidence: 99%

“…1 and ref. 46) and its analogues (47,48) and have established their effectiveness for many catalytic asymmetric hydrogenation reactions (46 -49), especially the utility of 2,2Ј,6,6Ј-tetramethoxy-4,4Ј-bis[di(3,5-dimethylphenyl)phosphino]-3,3Ј-bipyridine (Xyl-P-Phos) (1b, Fig. 1 and ref.…”

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A remarkably effective copper(II)-dipyridylphosphine catalyst system for the asymmetric hydrosilylation of ketones in air

Chan

2005

Proc. Natl. Acad. Sci. U.S.A.

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102

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“…Atropisomeric, C 2 -symmetric diphosphine ligands have played a particularly crucial role in the development of asymmetric catalysis (1)(2)(3)(4). Therefore, it is not surprising that considerable efforts have been taken for the design and synthesis of atropisomeric ligands based on the biphenyl, binaphthyl, or other biaryl backbones (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). Enantiomerically pure biaryls can be obtained by aryl-aryl coupling followed by a classical resolution of the resulting atropisomers.…”

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“…Herein, we report an example of essentially complete atropdiastereoselectivity in the synthesis of diphosphine dioxide by means of intramolecular Ullmann coupling (27,34,40,41) or Fe(III)-promoted oxidative coupling (42)(43)(44)(45) with central-to-axial chirality transfer, resulting in a concomitant eight-membered ring closure. The introduction of the chiral bridge restricted the conformational rotation of the diphosphine and made it more rigid than other biaryl diphosphine ligands (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)46). The diphosphine ligand was found to be highly effective in the asymmetric hydrogenation of ␣-and ␤-ketoesters, 2-(6Ј-methoxy-2Ј-naphthyl)propenoic acid, ␤-alkyl-substituted ␤-(acylamino)acrylates, and enol acetates.…”

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Remarkably diastereoselective synthesis of a chiral biphenyl diphosphine ligand and its application in asymmetric hydrogenation

Qiu

Chan

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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Essentially complete atropdiastereoselectivity was realized in the preparation of biaryl diphosphine dioxide by asymmetric intramolecular Ullmann coupling and oxidative coupling with central-toaxial chirality transfer. A bridged C2-symmetric biphenyl phosphine ligand possessing additional chiral centers on the linking unit of the biphenyl groups was synthesized. No resolution step was required for the preparation of the enantiomerically pure chiral ligand. These findings offer a general and practical tool for the development of previously uninvestigated atropdiastereomeric biaryl phosphine ligands. The diphosphine ligand was found to be highly effective in the asymmetric hydrogenation of ␣-and ␤-ketoesters, 2-(6-methoxy-2-naphthyl)propenoic acid, ␤-(acylamino)acrylates, and enol acetates.A xially chiral biaryls are not only common structural motifs in many natural products, but they are also the core of many highly effective chiral ligands for asymmetric reactions. Atropisomeric, C 2 -symmetric diphosphine ligands have played a particularly crucial role in the development of asymmetric catalysis (1-4). Therefore, it is not surprising that considerable efforts have been taken for the design and synthesis of atropisomeric ligands based on the biphenyl, binaphthyl, or other biaryl backbones (5-15). Enantiomerically pure biaryls can be obtained by aryl-aryl coupling followed by a classical resolution of the resulting atropisomers. The disadvantage of the path by resolution is that the maximum yield of the desired atropisomer is only 50% and the enantiomeric excesses (ee's) are usually Ͻ100%, not to mention that resolution procedures are frequently tedious. From a practical standpoint, it is desirable to develop efficient atroposelective methodologies for the synthesis of biaryls ligands to expand the scope of the useful catalysts. Various approaches, including desymmetrization of prochiral biaryls (16), kinetic resolution of racemic substrates (17), asymmetric catalytic coupling (18-23), and chirality transfer from central, axial, and planar asymmetry have been reported (24-38). Oxazolinemediated asymmetric Ullmann coupling was studied by Meyers and coworkers (28-30) to produce diastereomerically pure bis(oxazoline)s and corresponding enantiomerically pure biphenols and binaphthols. Previously, most of the research was focused on the syntheses of biphenols and binaphthols; in contrast, less attention was paid to the atroposelective syntheses of biaryl diphosphine oxides, the precursors of widely used diphosphine ligands. Recently, we successfully developed two diastereomeric diphosphine ligands for use in asymmetric hydrogenation reactions by stereoselective intermolecular Ullmann coupling of two chiral phosphine oxide precursors with moderate atropdiastereoselectivity (39). However, very careful separation of the diastereomers by column chromatography on silica gel was still needed. Herein, we report an example of essentially complete atropdiastereoselectivity in the synthesis of diphosphine dioxide by means of int...

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“…4 By preventing the coordination of the pyridyl groups via the use of bulky substituents, we found that the resulting rhodium(I) complex was effective for the hydrogenation of aldehydes, olefins, and imines. Inspired by the success of the modified pyridylphosphine ligand, we have developed a chiral dipyridylphosphine ligand 2,2',6,6'-tetramethoxy-4,4'-bis(diphenylphosphino)-3,3'-bipyridine (P-Phos), 6 which was found to be very effective in the Ru catalyzed asymmetric hydrogenation of 2-(6'-methoxy-2'-naphthyl)propenoic acid to give the nonsteroidal anti-inflammatory drug naproxen. 6,7 In this paper, we report the synthesis, characterization and application of a new dipyridylphosphine ligand, 2,2',6,6'-tetramethoxy-4,4'-bis[di(p-tolyl)phosphino]-3,3'-bipyridine (Tol-P-Phos).…”

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Synthesis and Structural Characterization of a Highly Effective Chiral Dipyridylphosphine Ligand and Its Application in the Ru-Catalyzed Asymmetric Hydrogenation of β-Ketoesters

Wu¹,

Chen²,

Zhou³

et al. 2001

Synlett

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Abstract:A new chiral dipyridylphosphine ligand Tol-P-Phos has been synthesized and the structure of the complex of (R)-Tol-PPhos oxide with (-)-dibenzoyl-L-tartaric acid [(-)-DBT] was determined by single crystal X-ray diffraction. The ruthenium complex of Tol-P-Phos, Ru(R-Tol-P-Phos)(C 6 H 6 )Cl 2 , has been found to be a highly active and enantioselective catalyst in the asymmetric hydrogenation of b-ketoesters (up to 98.2% e.e.). The catalyst is also found to be air-stable even in solution.Key words: asymmetric catalysis, hydrogenation, dipyridylphosphine ligands, ruthenium complex, b-ketoesterThe search for new chiral ligands is an ongoing process in the field of asymmetric synthesis.1 Although more than a thousand chiral nonracemic diphosphines have been synthesized and the efficiency of catalysts derived from these ligands have been established, 1,2 the possibility of discovering catalysts with improved utility, activity, and selectivity by designing new ligands remains to be an area of active research.Over the past two decades, tremendous success has been achieved in the use of chiral arylphosphine ligands such as BINAP, BIPHEP, MeO-BIPHEP, and DuPhos, etc. in Rhor Ru-catalyzed asymmetric hydrogenation reactions.1 As an effort to expand the scope of the arylphosphine ligands and their application in homogeneous catalysis, transition-metal complexes containing pydridylphosphine ligands have been synthesized and tested in homogeneous catalysis.3 Unfortunately, the tested complexes were found to be inactive in the homogeneous hydrogenations owing to the pyridyl group which coordinated to the metal center and rendered the complex coordinately saturated. 4 By preventing the coordination of the pyridyl groups via the use of bulky substituents, we found that the resulting rhodium(I) complex was effective for the hydrogenation of aldehydes, olefins, and imines.

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Highly Effective Chiral Dipyridylphosphine Ligands: Synthesis, Structural Determination, and Applications in the Ru-Catalyzed Asymmetric Hydrogenation Reactions

Cited by 206 publications

References 22 publications

A remarkably effective copper(II)-dipyridylphosphine catalyst system for the asymmetric hydrosilylation of ketones in air

A remarkably effective copper(II)-dipyridylphosphine catalyst system for the asymmetric hydrosilylation of ketones in air

Remarkably diastereoselective synthesis of a chiral biphenyl diphosphine ligand and its application in asymmetric hydrogenation

Synthesis and Structural Characterization of a Highly Effective Chiral Dipyridylphosphine Ligand and Its Application in the Ru-Catalyzed Asymmetric Hydrogenation of β-Ketoesters

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