Aerobic Dehydrogenation of Cyclohexanone to Cyclohexenone Catalyzed by Pd(DMSO)2(TFA)2: Evidence for Ligand-Controlled Chemoselectivity

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• 作者：Tianning Diao ; Doris Pun ; Shannon S. Stahl
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：June 5, 2013
• 年：2013
• 卷：135
• 期：22
• 页码：8205-8212
• 全文大小：555K
• 年卷期：v.135,no.22(June 5, 2013)
• ISSN：1520-5126

文摘

The dehydrogenation of cyclohexanones affords cyclohexenones or phenols via removal of 1 or 2 equiv of H₂, respectively. We recently reported several Pd^II catalyst systems that effect aerobic dehydrogenation of cyclohexanones with different product selectivities. Pd(DMSO)₂(TFA)₂ is unique in its high chemoselectivity for the conversion of cyclohexanones to cyclohexenones, without promoting subsequent dehydrogenation of cyclohexenones to phenols. Kinetic and mechanistic studies of these reactions reveal the key role of the dimethylsulfoxide (DMSO) ligand in controlling this chemoselectivity. DMSO has minimal kinetic influence on the rate of Pd(TFA)₂-catalyzed dehydrogenation of cyclohexanone to cyclohexenone, while it strongly inhibits the second dehydrogenation step, conversion of cyclohexenone to phenol. These contrasting kinetic effects of DMSO provide the basis for chemoselective formation of cyclohexenones.