title: Diamine-catalyzed addition of ZnEt2 to PhC(O)CF3 : two mechanisms and autocatalytic asymmetric enhancement.
abstract: NMR spectroscopic studies of the catalytic addition reaction of ZnEt2 to PhC(O)CF3 in the presence of three very efficient catalysts [TMEDA, tBuBOX, and L; where L is a chiral diamine synthesized from optically pure (R,R)-1,2-diphenylethylenediamine and (S)-2,2'-bis-(bromomethyl)-1,1'-binaphthalene] reveal large differences in their behavior. For the ligands TMEDA and tBuBOX, the catalysis shows no unusual features and proceeds via [(NN)Zn(Et){OC(CF3 )(Et)Ph}]. For NNL, the observation of autocatalytic asymmetric enhancement during the catalysis, and unusual inverse concentration dependence on the reaction rate, indicate the participation of an additional novel catalytic cycle that goes through a dinuclear intermediate containing one ZnEt2 and one ZnEt fragment connected by NN and OR bridges. Interestingly, the (19) F NMR signals of the main product of the reaction ([Zn(Et){OC*(CF3 )(Et)Ph}]2 ) allowed us to assess the enantioselectivity of the processes in situ without the assistance of chiral chromatography.
authors.affiliation: IU CINQUIMA/Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, Paseo Belén 5, 47011 Valladolid (Spain), Fax: (+34) 983423013.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Calvillo-Barahona
authors.forename: Juan A
authors.initials: JA
authors.lastname: Casares
authors.forename: Carlos
authors.initials: C
authors.lastname: Cordovilla
authors.forename: Miroslav N
authors.initials: MN
authors.lastname: Genov
authors.forename: Jesús M
authors.initials: JM
authors.lastname: Martínez-Ilarduya
authors.forename: Pablo
authors.initials: P
authors.lastname: Espinet
mesh_terms: D000098:Acetophenones / Q000737:chemistry*; D002384:Catalysis; D005617:Chlorofluorocarbons, Methane / Q000737:chemistry*; D003959:Diamines / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D009942:Organometallic Compounds / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000098:Acetophenones; D005617:Chlorofluorocarbons, Methane; D003959:Diamines; D009942:Organometallic Compounds; C454811:diethylzinc; C009554:fluoroform
keywords: alkylation; asymmetric catalysis; autocatalysis; ligand effects; zinc