566-66-5Relevant articles and documents
A Practical and Stereoselective In Situ NHC-Cobalt Catalytic System for Hydrogenation of Ketones and Aldehydes
Zhong, Rui,Wei, Zeyuan,Zhang, Wei,Liu, Shun,Liu, Qiang
supporting information, p. 1552 - 1566 (2019/06/14)
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.
Preparation of a Polymer-supported Diol and Its Use in isolating Aldehydes and Ketones from Mixtures and as a Protecting Group for Aldehydes and Ketones
Hodge, Philip,Waterhouse, Janette
, p. 2319 - 2323 (2007/10/02)
Reaction of cross-linked chloromethylated polystyrenes with 3-mercaptopropane-1,2-diol and sodium hydroxide under phase-transfer conditions gave polymers containing diol residues.A range of aldehydes and ketones were successfully bound to these polymers via acetal formation.The aldehydes and ketones were released by treating the products with aqueous dioxane in the presence of toluene-p-sulphonic acid.The polymer-supported diol could be used to isolate aldehydes or ketones from mixtures with other compounds and to separate a 3-oxosteroid from a 17- or a 20- oxosteroid.The supported diol was successfully used to protect the aldehyde group of undec-10-enal whilst the terminal vinyl group was transformed into -CH2CH2OCOPh.Attempts to monoprotect dicarbonyl compounds were unsuccessful.
METAL-ASSISTED REACTIONS-12. UNUSUAL SELECTIVITY IN THE REDUCTION OF KETONES WITH ZINC OR CADMIUM BIS-TETRAHYDROBORATE/DIMETHYLFORMAMIDE COMPLEX
Hussey, Brendan J.,Johnstone, Robert A. W.,Boehm, Peter,Entwistle, Ian D.
, p. 3769 - 3774 (2007/10/02)
Zinc bis-tetrahydroborate forms a solid complex with dimethylformamide (DMF) of composition, Zn(BH4)2*1.5DMF.Unlike zinc bis-tetrahydroborate itself, the complex with DMF can be stored as a solid at room temperature.Ketones and aldehydes are reduced to the corresponding alcohols by the complex but the mechanism of reduction appears to be different from that using zinc bis-tetrahydroborate itself and from other tetrahydroborates in that only one hydride equivalent from each BH4- unit is utilized and not four.Further, although saturated aliphatic ketones are reduced rapidly to alcohols, aromatic ketones react much more slowly and α,β-unsaturated ketones react very slowly so that the complex appears to have selective reducing potential with regard to different classes of ketones.It is also apparent that the zinc bis-tetrahydroborate/DMF complex reduces sterically hindered saturated ketones much more slowly than it does unhindered ketones.An analogous cadmium bis-tetrahydroborate/DMF complex can be prepared in solution and reacts with ketones similarly to the zinc complex.
