title: Optimization of catalyst enantioselectivity and activity using achiral and meso ligands.
abstract: The optimization of asymmetric catalysts for enantioselective synthesis has conventionally revolved around the synthesis and screening of enantiopure ligands. In contrast, we have optimized an asymmetric reaction by modification of a series of achiral ligands. Thus, employing (S)-3,3'-diphenyl BINOL [(S)-Ph(2)-BINOL] and a series of achiral diimine and diamine activators in the asymmetric addition of alkyl groups to benzaldehyde, we have observed enantiomeric excesses between 96% (R) and 75% (S) of 1-phenyl-1-propanol. Some of the ligands examined have low-energy chiral conformations that can contribute to the chiral environment of the catalyst. These include achiral diimine ligands with meso backbones that adopt chiral conformations, achiral diimine ligands with backbones that become axially chiral on coordination to metal centers, achiral diamine ligands that form stereocenters on coordination to metal centers, and achiral diamine ligands with pendant groups that have axially chiral conformations. Additionally, we have structurally characterized (Ph(2)-BINOLate)Zn(diimine) and (Ph(2)-BINOLate)Zn(diamine) complexes and studied their solution behavior.
authors.affiliation: P. Roy and Diane T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, USA.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Costa
authors.forename: Ciril
authors.initials: C
authors.lastname: Jimeno
authors.forename: Jason
authors.initials: J
authors.lastname: Gavenonis
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Carroll
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Walsh
mesh_terms: D001547:Benzaldehydes / Q000737:chemistry*; D001592:Benzyl Alcohols / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray; D003959:Diamines / Q000737:chemistry*; D007097:Imines / Q000737:chemistry*; D008024:Ligands; D008968:Molecular Conformation; D009284:Naphthols / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry; D013237:Stereoisomerism; D015032:Zinc / Q000737:chemistry
chemical_list: C406944:BINOL, naphthol; D001547:Benzaldehydes; D001592:Benzyl Alcohols; D003959:Diamines; D007097:Imines; D008024:Ligands; D009284:Naphthols; D009942:Organometallic Compounds; C007656:alpha-ethylbenzyl alcohol; D015032:Zinc; C032175:benzaldehyde