"Achiral" benzophenone ligand for highly enantioselective Ru catalysts in ketone hydrogenation

[reaction: see text] The chirality of an "achiral" benzophenone-based complex can be controlled. The benzophenone-based complex thus controlled affords high enantioselectivity in the catalytic asymmetric ketone hydrogenation (up to 99% ee, >99% yield).     

Air-stable catalysts for highly efficient and enantioselective hydrogenation of aromatic ketones

A series of chiral trans-[RuCl(2)(dipyridylphosphine)(1,2-diamine)] complexes have been synthesized and characterized by NMR and single-crystal X-ray diffraction studies. These Ru complexes combined with (CH(3))(3)COK in 2-propanol formed a very effective catalyst system for the hydrogenation of a diverse range of simple aromatic ketones with high activity (substrate-to-catalyst ratio up to 100 000) and excellent enantioselectivity (up to >99.9%). The catalyst system was also found to be stable in solution even under a normal atmosphere.     

Air-stable and phosphine-free iridium catalysts for highly enantioselective hydrogenation of quinoline derivatives

Enantioselective hydrogenation of quinoline derivatives catalyzed by phosphine-free chiral cationic Cp*Ir(OTf)(CF 3TsDPEN) complex (CF 3TsDPEN = N-(p-trifluoromethylbenzenesulfonyl)-1,2-diphenylethylene-diamine) afforded the 1,2,3,4-tetrahydroquinoline derivatives in up to 99% ee. The reaction could be carried out with a substrate-to-catalyst molar ratio as high as 1000 in undegassed methanol and with no need for inert gas protection.     

Self-supported heterogeneous catalysts for enantioselective hydrogenation

"Self-supported" catalysts were prepared by the reaction of bis-MonoPhos ligand with rhodium(I) metallic ion on the basis of molecular assembling through coordination. These polymeric metal-organic assemblies are insoluble in common organic solvents and, as a result, provide an excellent opportunity for running asymmetric catalysis heterogeneously. The application of the self-supported Rh(II) catalysts in the asymmetric hydrogenation of olefin derivatives afforded a variety of enantioenriched amino acid and amine derivatives with high yields and enantioselectivities. This strategy might provide a new direction in asymmetric catalysis, particularly for the development of practical heterogeneous asymmetric synthesis of optically active compounds.     

Studies of copper-nickel catalysts for enantioselective hydrogenation

Studies of the effect of preparation conditions on the activity and enantioselectivity of asymmetric Cu–Ni catalysts have revealed their great dependence and two maxima in the dependence of the optical yield on the pH of the modifying solution. Cu–Ni catalysts are shown to have similar catalytic properties in a wide range of their Cu content.

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, Cu–Ni . pH , Cu–Ni .

     

Mesoporous silica nanoreactors for highly efficient proteolysis

Protein digestion inside the nanoreactor channels of mesoporous silica (SBA-15) is reported, and evaluated by using peptide-mass mapping. Both proteases and substrates were efficiently captured within these biocompatible nanoreactors. After 10 minutes, the mass spectrum of the protein digests released from the mesoporous-silica-based nanoreactors revealed the presence of eight peptides covering 58% of the protein sequence with an intense signal (signal/noise ratio > 70). In comparison, the conventional overnight in-solution digestion of proteins under otherwise identical conditions generated only three peptides (27% sequence coverage). We propose that this order-of-magnitude increase in the proteolytic reaction rate is mainly attributed to two factors: substrate enrichment within mesoporous silica channels and enzyme immobilization. The surface properties and macrostructure of the mesoporous silica were studied to reveal their significant influence on proteolytic reactions.     

Studies of Cu?Ni supported catalysts for enantioselective hydrogenation

The effect of support content and composition of supported metal phase on the crystallite size, phase composition and catalytic properties of supported Ni and Cu–Ni catalysts has been investigated. It has been established that with increasing metal content, crystallite sizes and enantioselectivity increase. Copper added to Ni catalysts decreases metal phase dispersity and enantioselectivity.

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Mesoporous silica-supported zirconocene catalysts for highly isotactic polypropylene

A new bis(indenyl)zirconocene bearing a pendant Si-Cl anchor has been grafted onto MCM-41, SBA-15, MCM-48 and a disordered mesoporous silica for the polymerisation of ethylene and propylene, producing polymers with very high molecular weights, low polydispersities and, in the case of polypropylene, higher levels of isotacticity than obtainable with analogous homogeneous systems.     

Activation of ruthenium on silica hydrogenation catalysts

Activation of RuCl₃-impregnated silica by nitrogen-hydrogen tratment at high temperature, up to 700 °C, is superior to calcination of the material prior to reduction. Sintering hardly occurs. In addition, activity measurements, based on the liquid phase hydrogenation of benzene, and thermogravimetric analysis suggest a favorable (chemical) interaction between ruthenium and silica.

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, RuCl₃ 700°C . . , , () .

     

Novel phosphine-phosphite and phosphine-phosphinite ligands for highly enantioselective asymmetric hydrogenation

Two novel phosphine-phosphite (S,R)-o-BINAPHOS and phosphine-phosphinite (S)-o-BIPNITE ligands based on ortho phenyl substituted (S)-BINOL have been synthesized. Extremely high enantioselectivity (over 99% ee in most cases) has been achieved for the Rh-catalyzed asymmetric hydrogenation of α-dehydroamino acid derivatives.     

Development of 4,4'-substituted-XylBINAP ligands for highly enantioselective hydrogenation of ketones

[reaction: see text] A family of 4,4'-substituted-xylBINAPs was synthesized in multistep sequences and characterized by NMR spectroscopy and mass spectrometry. Ru(diphosphine)(diamine)Cl(2) complexes based on these 4,4'-substituted-xylBINAPs and chiral diamines (DPEN and DAIPEN) were synthesized by treatment of [(benzene)RuCl(2)](2) with 4,4'-substituted-xylBINAP followed by chiral diamine, and characterized by (1)H and (31)P NMR spectroscopy and mass spectrometry. These Ru complexes were used for asymmetric hydrogenation of aromatic ketones in a highly enantioselective manner with complete conversion. With 0.1% catalyst loading, complete conversion and enantioselectivity greater than 99% were obtained for most of the aromatic ketones examined. These Ru catalysts thus gave the highest ee for asymmetric hydrogenation of aromatic ketones among all of the catalysts reported in the literature. A single-crystal X-ray diffraction study of Ru[(R)-L(4)()][(R,R)-DPEN]Cl(2) indicated that the 4-methyl group of the naphthyl ring and the methyl groups of the two xylyl moieties form a fence on the opposite side of the DPEN ligand of the Ru center. These three methyl groups will have significant repulsive interactions with the bulky aryl ring of the hydrogen-bonded aromatic ketone in the disfavored transition state. These results support our hypothesis of combining dual modes of enantiocontrol (i.e., the substituents on 4,4'-positions of the binaphthyl framework and the methyl groups on the bis(xylyl)phosphino moieties) to achieve higher stereoselectivity in the hydrogenation of aromatic ketones.     

Scaffolding catalysts: highly enantioselective desymmetrization reactions

Ex-changing places: a highly enantioselective desymmetrization of 1,2-diols has been developed in which the catalyst utilizes reversible covalent bonding to the substrate to achieve both high selectivity and rate acceleration (see scheme, PMP=pentalmethylpiperidine, TBS=tert-butyldimethylsilyl). Induced intramolecularity is responsible for the enhanced rate, thus allowing the reaction to be performed at room temperature.