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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

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

Gonzalo Blay, Joan Cano, Luz Cardona, Isabel Fernández, M Carmen Muñoz, José R Pedro, Carlos Vila

J Org Chem. 2012 Dec 7;77(23):10545-56.

PMID: 23126442

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.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP2081121	Zirconium(IV) tert-butoxide		2081-12-1	Price

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