Date of Award

4-19-2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Irina P. Smoliakova

Abstract

Cyclopalladated complexes constitute a fair portion of species in the organometallic family. They have interesting properties and potential applications in a variety of areas. Optically-active cyclopalladated complexes can serve as catalysts or pre-catalysts in asymmetric synthesis, reagents for chiral resolution, chiral derivatizing agents for optical purity determination, and starting materials for preparation of more complex enantiopure compounds. This dissertation focuses on preparation and characterization of new optically-active cyclopalladated and Pd(II) coordination complexes of monodentate oxazolines. New and previously reported optically-active oxazolines were synthesized from commercially available chiral α-amino alcohols using published procedures. Regioselectivity of oxazoline cyclopalladation was studied using (S)-2-tert-butyl-4-phenyl-2-oxazoline. Direct metalation of this preligand using Pd(OAc)2 in CH3CO 2H or MeCN provided a mixture of the endo palladacycle with a (sp 3)C–Pd bond and the exo derivative with a (sp2)C–Pd bond. Hybridization of the carbon atom to be palladated and other factors affecting regioselectivity were investigated. A possibility of forming six-membered palladacycles from oxazolines was studied. Direct palladation of (S)-4-benzyl-2-methyl-2-oxazoline and (S)-2-benzyl-4-tert-butyl-2-oxazoline using Pd(OAc)2 in MeCN afforded the corresponding μ-acetato-dimeric complexes with six-membered exo and endo palladacycles, respectively. The same complexes were obtained by reacting the corresponding Pd(OAc)2(HL) 2 coordination complexes with Pd(OAc)2 in MeCN. Metalation of (S)-2,4-dibenzyl-2-oxazoline with Pd(OAc)2 in AcOH, MeCN or CH2Cl2 resulted in the regiospecific formation of a six-membered endo palladacycle. The desired exo and endo six-membered palladacycles with the aliphatic (sp3)C–Pd bond could not be obtained from (S)-4-isobutyl-2-methyl-2-oxazoline and (S)-2-(2,2-dimethylpropyl)-4-isopropyl-2-oxazoline, respectively. Diastereoselectivity in the direct palladation of enantiopure oxazolines, having a prochiral CMe2 fragment in the substituent at the 2-position of the heterocycle, was investigated using (R)-4-ethyl-2-(1,1-dimethylpropyl)-2-oxazoline, (S)-4-tert-butyl-2-(1,1-dimethylbutyl)-2-oxazoline, and (S)-2-(1-adamantyl-1-methylethyl)-4-isobutyl-2-oxazoline. Cyclopalladation of the heterocycles under different conditions occurred with low diastereoselectivity. Pd(II) coordination complexes of substituted oxazolines were synthesized. The majority of the complexes obtained exist in solution as a mixture of trans and cis isomers with the former isomer being major. The composition and purity of new oxazolines and their cyclopalladated and coordination complexes were confirmed by elemental analysis. The structures of the oxazolines and Pd(II) complexes were supported by IR and NMR spectroscopy and X-ray crystallographic studies in some cases.

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