- A Practical and Stereoselective In Situ NHC-Cobalt Catalytic System for Hydrogenation of Ketones and Aldehydes
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Homogeneous catalytic hydrogenation of carbonyl groups is a synthetically useful and widely applied organic transformation. Sustainable chemistry goals require replacing conventional noble transition metal catalysts for hydrogenation by earth-abundant base metals. Herein, we report how a practical in situ catalytic system generated by easily available pincer NHC precursors, CoCl2, and a base enabled efficient and high-yielding hydrogenation of a broad range of ketones and aldehydes (over 50 examples and a maximum turnover number [TON] of 2,610). This is the first example of NHC-Co-catalyzed hydrogenation of C=O bonds using flexible pincer NHC ligands consisting of a N-H substructure. Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized by fine-tuning of the steric bulk of pincer NHC ligands. Additionally, a bis(NHCs)-Co complex was successfully isolated and fully characterized, and it exhibits excellent catalytic activity that equals that of the in-situ-formed catalytic system. Catalytic hydrogenation is a powerful tool for the reduction of organic compounds in both fine and bulk chemical industries. To improve sustainability, more ecofriendly, inexpensive, and earth-abundant base metals should be employed to replace the precious metals that currently dominate the development of hydrogenation catalysts. However, the majority of the base-metal catalysts that have been reported involve expensive, complex, and often air- and moisture-sensitive phosphine ligands, impeding their widespread application. From a mixture of the stable CoCl2, imidazole salts, and a base, our newly developed catalytic system that formed easily in situ enables efficient and stereoselective hydrogenation of C=O bonds. We anticipate that this easily accessible catalytic system will create opportunities for the design of practical base-metal hydrogenation catalysts. A practical in situ catalytic system generated by a mixture of easily available pincer NHC precursors, CoCl2, and a base enabled highly efficient hydrogenation of a broad range of ketones and aldehydes (over 50 examples and up to a turnover number [TON] of 2,610). Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized in high selectivities. Moreover, the preparation of a well-defined bis(NHCs)-Co complex via this pincer NHC ligand consisting of a N-H substructure was successful, and it exhibits equally excellent catalytic activity for the hydrogenation of C=O bonds.
- Zhong, Rui,Wei, Zeyuan,Zhang, Wei,Liu, Shun,Liu, Qiang
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supporting information
p. 1552 - 1566
(2019/06/14)
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- Synthesis and reactions of enantiopure substituted benzene cis-hexahydro-1,2-diols
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Enantiopure dis-dihydro-1,2-diol metabolites, obtained from toluene dioxygenase-catalysed dis-dihydroxylation of six monosubstituted benzene substrates, have been converted to their corresponding dis-hexahydro-1,2-diol derivatives by catalytic hydrogenation via their dis-tetrahydro-1,2-diol intermediates. Optimal reaction conditions for total catalytic hydrogenation of the dis-dihydro-1,2-diols have been established using six heterogeneous catalysts. The relative and absolute configurations of the resulting benzene dis-hexahydro-1,2-diol products have been unequivocally established by X-ray crystallography and NMR spectroscopy. Methods have been developed to obtain enantiopure dis-hexahydro-1,2diol diastereoisomers, to desymmetrise a meso-cishexahydro-1,2-diol and to synthesise 2-substituted cyclohexanols. The potential of these enantiopure cyclohexanols as chiral reagents was briefly evaluated through their application in the synthesis of two enantiomerically enriched phosphine oxides from the corresponding racemic phosphine precursors.
- Boyd,Sharma,Berberian,Dunne,Hardacre,Kaik,Kelly,Malone,McGregor,Stevenson
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experimental part
p. 855 - 868
(2010/07/05)
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- Hydrolysis of Alkenyl Esters and Ethers Catalyzed by Metal Complexes
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(Equation presented) Various kinds of transition metals catalyzed the hydrolysis of alkenyl esters and ethers under buffer-free, high concentration conditions compared to usual biocatalysts. Hydrolytic kinetic resolution of cis-2-tert-butylcyclohexyl vinyl ether was achieved by chiral (salen)Co complexes with good selectivity (krel = 10.0).
- Aoyama, Hiroshi,Tokunaga, Makoto,Hiraiwa, Shin-Ichiro,Shirogane, Yuki,Obora, Yasushi,Tsuji, Yasushi
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p. 509 - 512
(2007/10/03)
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- Chiral Sulfur Compounds. Part 25. Diastereoselective 1,2-Additions of Lithiated (+)-(S)-N-tert-Butyldiphenylsilyl-S-methyl-S-phenylsulfoximine to Ketones
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Lithiated (+)-(S)-N-tert-butyldiphenylsilyl-S-methyl-S-phenylsulfoximine 2f reacts with prochiral ketones to give a mixture of diastereomeric β-hydroxy sulfoximine adducts with a diastereoselection ranging from 79:21 to 98:2 depending upon the steric demand of the ketone.Racemic chiral cyclic ketones react with 2f to give a mixture of diastereoisomeric β-hydroxy sulfoximine adducts which could be separated by a combination of column chromatography and recrystallization.Thermolysis of the diastereoisomerically pure adducts gave 2-alkylcyclohexanones in high enantiomeric purity.The relative stereochemistries of four of the β-hydroxy sulfoximine adducts have been unequivocally determined from single-crystal X-ray structural analysis.The stereochemical outcome of these 1,2-additions can best be rationalized by invoking competing boat transition states.
- Pyne, Stephen G.,Dong, Zemin,Skelton, Brian W.,White, Allan H.
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p. 2607 - 2614
(2007/10/02)
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