title: Aerobic dehydrogenation of cyclohexanone to cyclohexenone catalyzed by Pd(DMSO)2(TFA)2: evidence for ligand-controlled chemoselectivity.
abstract: 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.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors.forename: Tianning
authors.initials: T
authors.lastname: Diao
authors.forename: Doris
authors.initials: D
authors.lastname: Pun
authors.forename: Shannon S
authors.initials: SS
authors.lastname: Stahl
mesh_terms: D002384:Catalysis; D003512:Cyclohexanones / Q000737:chemistry*; D053138:Cyclohexenes / Q000138:chemical synthesis* / Q000737:chemistry; D006865:Hydrogenation; D008024:Ligands; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D010636:Phenols / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: D003512:Cyclohexanones; D053138:Cyclohexenes; D008024:Ligands; D009942:Organometallic Compounds; D010636:Phenols; D010165:Palladium