title: NMR spectroscopic characterization and DFT calculations of zirconium(IV)-3,3'-Br2-BINOLate and related complexes used in an enantioselective Friedel-Crafts alkylation of indoles with α,β-unsaturated ketones.
abstract: Experimental and theoretical studies on the structure of several complexes based on (R)-3,3'-Br(2)-BINOL ligand and group (IV) metals used as catalysts in an enantioselective Friedel-Crafts alkylation of indoles with α,β-unsaturated ketones have been carried out. NMR spectroscopic studies of these catalysts have been performed, which suggested that at room temperature the catalysts would form a monomeric structure in the case of Ti(IV) and a dimeric structure in the cases of Zr(IV) and Hf(IV). Density functional theory (DFT) calculations clearly corroborate the conclusions of these experimental spectroscopic studies. The dimeric structure with a doubly bridged motif [Zr(IV)(2)(μ-(R)-3,3'-Br(2)-BINOL)(2)] where each binaphthol ligand acts as bridge between the metal centers (Novak's model) is more stable than the dimeric structure with a doubly bridged motif [Zr(IV)(2)(μ-O(t)Bu)(2)] where the tert-butoxide groups act as bridging ligands (Kobayashi's model). The scope of the Friedel-Crafts alkylation with regard to the indole structure has been studied. Finally a plausible mechanism for the Friedel-Crafts reaction and a stereomodel for the mode of action of the catalyst that explain the observed stereochemistry of the reaction products have been proposed.
authors.affiliation: Departament de Química Orgànica, Facultat de Química, Universitat de València, Dr. Moliner 50, E-46100-Burjassot, València, Spain.
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Blay
authors.forename: Joan
authors.initials: J
authors.lastname: Cano
authors.forename: Luz
authors.initials: L
authors.lastname: Cardona
authors.forename: Isabel
authors.initials: I
authors.lastname: Fernández
authors.forename: M Carmen
authors.initials: MC
authors.lastname: Muñoz
authors.forename: José R
authors.initials: JR
authors.lastname: Pedro
authors.forename: Carlos
authors.initials: C
authors.lastname: Vila
mesh_terms: D000478:Alkylation; D007211:Indoles / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009284:Naphthols / Q000737:chemistry*; D013237:Stereoisomerism; D015040:Zirconium / Q000737:chemistry*
chemical_list: C406944:BINOL, naphthol; D007211:Indoles; D007659:Ketones; D009284:Naphthols; C030374:indole; D015040:Zirconium