Design, Synthesis and Characterization of Chiral CCC-NHC Transition Metal Complexes and Catalytic Activity

Design, Synthesis and Characterization of Chiral CCC-NHC Transition Metal Complexes and Catalytic Activity
Author: Gopalakrishna Akurathi
Publisher:
Total Pages: 177
Release: 2016
Genre:
ISBN:

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The first stable "free" N-heterocyclic carbene (NHC) was isolated in 1991, since then many classes of NHCs were synthesized and isolated. N-heterocyclic carbene ligands have become a common ligand in the synthesis of metal complexes, due to their strong [Sigma]-donation with poor [pi]-acceptor ability. Among all the NHC metal complexes, Hollis group was interested in exploring CCC-NHC pincer complexes. In 2005, Hollis and co-workers synthesized and isolated first achiral CCC-NHC zirconium pincer amido complex and studied its catalytic ability to perform intramolecular hydroamination of aminoalkenes. Later, Hollis group designed and developed new NHCs with a saturated chiral backbone, and used these new ligands to generate a new series of metal complexes. This dissertation is focused on the design, synthesis and characterization of several chiral bi-dentate NHC ligands with varying substituents on the backbone. These NHC ligands were used to synthesize several chiral mono, bis and tris amido CCC-NHC zirconium pincer complexes. Further, transmetallation to cobalt complexes were achieved. Intramolecular hydroamination was measured for several chiral bis and tris amido CCC-NHC pincer zirconium catalysts. Variants of these catalytic systems were generated with differing steric hinderance and electronic structure. The enantioselectivity of these novel new molecules were studied.

Chiral Ferrocenes in Asymmetric Catalysis

Chiral Ferrocenes in Asymmetric Catalysis
Author: Li-Xin Dai
Publisher: John Wiley & Sons
Total Pages: 433
Release: 2010-02-01
Genre: Science
ISBN: 3527322809

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This book meets the long-felt need for a reference on ferrocenes with the focus on catalysis. It provides a thorough overview of the synthesis and characterization of different types of chiral ferrocene ligands, their application to various catalytic asymmetric reactions, and versatile chiral materials as well as drug intermediates synthesized from them. Written by the "who's who" of ferrocene catalysis, this is a guide to the design of new ferrocene ligands and synthesis of chiral synthetic intermediates, and will thus be useful for organic, catalytic and synthetic chemists working in academia, industrial research or process development.

Synthesis of Chiral Nonracemic C2-symmetric 2,2'-bipyridines and Their Evaluation as Ligands in Copper-catalyzed Asymmetric Reactions

Synthesis of Chiral Nonracemic C2-symmetric 2,2'-bipyridines and Their Evaluation as Ligands in Copper-catalyzed Asymmetric Reactions
Author: Brendan John Whelan
Publisher:
Total Pages: 528
Release: 2010
Genre: Asymmetric synthesis
ISBN:

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This thesis concerns the synthesis and evaluation of a series of new chiral nonracemic C2-symmetric 2,2'-bipyridines for use as ligands in catalytic asymmetric reactions. The 2,2'-bipyridines were prepared using a divergent synthetic strategy which employed an asymmetric dihydroxylation reaction of a 2-chloropyrindine as the key step. The resultant chiral diol was condensed with a series of symmetrical ketones to afford chiral acetals which were converted into the requisite ligand series. These ligands were evaluated in the asymmetric copper(I)-catalyzed cyclopropanation reaction of styrene and ethyldiazoacetate. The major Trans-cyclopropane products were isolated in good yield and very high enantioselectivities were achieved (up to 94% ee). These are amongst the highest enantioselectivities reported for chiral 2,2'-bipyridyl ligands. The most effective ligand, an adamantanone derivative, was evaluated in the copper(I)-catalyzed asymmetric allylic oxidation of cyclic alkenes with Tert-butyl peroxybenzoate. High enantioselectivities were also obtained in these reactions (up to 91% ee).

Studies Toward the Synthesis of a Novel Diastereomerically Pure Cyclopropyl N-heterocyclic Carbene Ligand for Asymmetric Catalysis

Studies Toward the Synthesis of a Novel Diastereomerically Pure Cyclopropyl N-heterocyclic Carbene Ligand for Asymmetric Catalysis
Author: Brandon T. Milliken
Publisher:
Total Pages: 146
Release: 2014
Genre: Asymmetric synthesis
ISBN:

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"This M.S. Thesis research objective is designed towards the racemic synthesis of a novel diastereoselectively pure, sterically bulky, cyclopropyl-containing, N-heterocyclic carbene (NHC) ligand. It is hypothesized that introduction of the sterically bulky cyclopropyl moiety at the N-substituent position of the imidazolium backbone will cause the self-assembly to develop a well defined C2-symmetric N-heterocyclic ligand, thereby limiting the free rotation about the C-N bond and creating a well-defined chiral pocket. It was discovered through utilizing classic synthetic methods that a diastereomeric imidazolium salt product was yielded, which can be attributed to the racemic synthesis of a diastereomeric cyclopropane starting material."--Abstract.