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Macrocyclic N-Heterocyclic Carbenes (NHC) for Size-Selective Nucleophilic Catalysis and Olefin Metathesis.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Macrocyclic N-Heterocyclic Carbenes (NHC) for Size-Selective Nucleophilic Catalysis and Olefin Metathesis./
Author:	Zhang, Yutong.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
Description:	294 p.
Notes:	Source: Dissertations Abstracts International, Volume: 82-09, Section: B.
Contained By:	Dissertations Abstracts International82-09B.
Subject:	Organic chemistry. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28257761
ISBN:	9798582509110

Macrocyclic N-Heterocyclic Carbenes (NHC) for Size-Selective Nucleophilic Catalysis and Olefin Metathesis.
Zhang, Yutong.

Macrocyclic N-Heterocyclic Carbenes (NHC) for Size-Selective Nucleophilic Catalysis and Olefin Metathesis. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 294 p.

Source: Dissertations Abstracts International, Volume: 82-09, Section: B.

Thesis (Ph.D.)--State University of New York at Buffalo, 2021.

This item must not be sold to any third party vendors.

One of the most challenging problems in organic synthesis is selectivity among the same functional group. A size-selective catalyst that could differentiate substrates based on their aggregate size would provide a new perspective towards solving this problem. In this dissertation, synthesis of a series of macrocyclic N-heterocyclic carbenes (NHC) and their application in nucleophilic catalysis as well as olefin metathesis will be discussed. The well-defined macrocyclic environment provided a unique size-selectivity, that is, displayed different reactivity between substrates that carry different steric bulk that's remote from the reaction center, but similar in electronic property.In Chapter 1, synthesis of three novel macrocyclic NHC is described. X-ray single crystal structure indicated the NHC points slightly outside the cavity, which is different from our original hypothesis. In the intramolecular Michael-Stetter reaction of salicylaldehyde derivatives, these catalysts exhibited significantly higher reactivity on sterically small reactants over bulky reactants. A DFT calculation (collaboration with Dr. Travis Dudding and Rozhin Rowshanpour from Brock University) revealed that in the case of the bulky di-t-butyl substrate, formation of the Breslow intermediate was energetically disfavored. In cross-benzoin condensation between substituted benzaldehydes, our catalyst displayed preference towards formation of the unsubstituted homo-benzoin over the diisopropyl or di-t-butyl homo-benzoin, which indicated that the smaller aldehyde is more readily activated by the free carbene.In Chapter 2, synthesis of two ruthenium carbene complexes YZ-1 and YZ-2 using macrocyclic NHC is reported. Benchmark performance tests revealed significantly lower reactivity of these complexes in comparison to the commercial Hoveyda-Grubbs second generation catalyst (HG II). Homo-dimerization of traditional type 1 olefins in the Grubbs model was performed using the structurally more rigid catalyst YZ-1, which displayed different reactivity that's correlated to aggregate size of the olefins. Competitive cross metathesis of olefin pairs (small and bulky) with t-butyl acrylate, a type 2 olefin in Grubbs classification, displayed significant preference towards formation of the small cross product when YZ-1 was employed. In two separated cases, we demonstrated that selective cross metathesis between two type 1 olefins toward formation of the cross dimer was practical using YZ-1. A working selectivity model was proposed, in which the ruthenium alkylidene resulting from pre-catalyst activation with the smaller olefin is favored due to less steric interaction with the macrocyclic framework, which could be turned over with another molecule of the smaller olefin to yield small homo-dimer, or with the bulkier olefin to give the cross dimer. Formation of the former product is believed to be reversible while the latter is not, due to increased steric hindrance. Thus, the desired cross dimer was formed as the major product in satisfactory yield.In Chapter 3, the size-selectivity principle was extended to intermolecular ene-yne metathesis with our catalysts. Competitive ene-yne metathesis of olefin pairs with terminal alkyne using commercial HG II surprisingly showed size-selectivity in some cases, which has not been documented in literature, to the best of our knowledge. The selectivity was improved with macrocyclic catalyst YZ-1. Kinetic study confirmed the existence of secondary metathesis under the reaction condition. A crossover experiment indicated that the bulky diene produced through ene-yne metathesis is formed reversibly. Reaction with internal alkyne showed higher size-selectivity than terminal alkyne using both HG II and YZ-1.Different modification strategies of current macrocycle system are discussed in Chapter 4. Efforts were made towards obtaining structural variety through backbone functionalization. Three new ruthenium complexes (YZ-3, YZ-4 and YZ-5) with substituted Hoveyda chelate were synthesized in order to improve catalysis reactivity by inducing steric interaction with the macrocycle scaffold. However, these attempts were not successful possibly due to an unexpected conformational change. Replacing the tetrafluoroborate in YZ-1 catalyst with other anions revealed that the counter ion played an important role in catalyst performance, although an accurate explanation cannot be provided at this point. Further, a new phenanthroline macrocycle was successfully synthesized with expanded dimension, which is expected to better accommodate the metal complex. Rigidification strategies aiming to lock the NHC inside the cavity is currently under investigation. The phenanthroline moiety can be further utilized to coordinate first row transition metals. Synthesis of a series of metal complexes using this novel ligand system and study of their reactivity and/or selectivity is foreseeable.

ISBN: 9798582509110Subjects--Topical Terms:

523952
Organic chemistry.
Subjects--Index Terms:

Macrocycle

Macrocyclic N-Heterocyclic Carbenes (NHC) for Size-Selective Nucleophilic Catalysis and Olefin Metathesis.
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245 1 0 $a Macrocyclic N-Heterocyclic Carbenes (NHC) for Size-Selective Nucleophilic Catalysis and Olefin Metathesis.
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506 $a This item must not be sold to any third party vendors.
520 $a One of the most challenging problems in organic synthesis is selectivity among the same functional group. A size-selective catalyst that could differentiate substrates based on their aggregate size would provide a new perspective towards solving this problem. In this dissertation, synthesis of a series of macrocyclic N-heterocyclic carbenes (NHC) and their application in nucleophilic catalysis as well as olefin metathesis will be discussed. The well-defined macrocyclic environment provided a unique size-selectivity, that is, displayed different reactivity between substrates that carry different steric bulk that's remote from the reaction center, but similar in electronic property.In Chapter 1, synthesis of three novel macrocyclic NHC is described. X-ray single crystal structure indicated the NHC points slightly outside the cavity, which is different from our original hypothesis. In the intramolecular Michael-Stetter reaction of salicylaldehyde derivatives, these catalysts exhibited significantly higher reactivity on sterically small reactants over bulky reactants. A DFT calculation (collaboration with Dr. Travis Dudding and Rozhin Rowshanpour from Brock University) revealed that in the case of the bulky di-t-butyl substrate, formation of the Breslow intermediate was energetically disfavored. In cross-benzoin condensation between substituted benzaldehydes, our catalyst displayed preference towards formation of the unsubstituted homo-benzoin over the diisopropyl or di-t-butyl homo-benzoin, which indicated that the smaller aldehyde is more readily activated by the free carbene.In Chapter 2, synthesis of two ruthenium carbene complexes YZ-1 and YZ-2 using macrocyclic NHC is reported. Benchmark performance tests revealed significantly lower reactivity of these complexes in comparison to the commercial Hoveyda-Grubbs second generation catalyst (HG II). Homo-dimerization of traditional type 1 olefins in the Grubbs model was performed using the structurally more rigid catalyst YZ-1, which displayed different reactivity that's correlated to aggregate size of the olefins. Competitive cross metathesis of olefin pairs (small and bulky) with t-butyl acrylate, a type 2 olefin in Grubbs classification, displayed significant preference towards formation of the small cross product when YZ-1 was employed. In two separated cases, we demonstrated that selective cross metathesis between two type 1 olefins toward formation of the cross dimer was practical using YZ-1. A working selectivity model was proposed, in which the ruthenium alkylidene resulting from pre-catalyst activation with the smaller olefin is favored due to less steric interaction with the macrocyclic framework, which could be turned over with another molecule of the smaller olefin to yield small homo-dimer, or with the bulkier olefin to give the cross dimer. Formation of the former product is believed to be reversible while the latter is not, due to increased steric hindrance. Thus, the desired cross dimer was formed as the major product in satisfactory yield.In Chapter 3, the size-selectivity principle was extended to intermolecular ene-yne metathesis with our catalysts. Competitive ene-yne metathesis of olefin pairs with terminal alkyne using commercial HG II surprisingly showed size-selectivity in some cases, which has not been documented in literature, to the best of our knowledge. The selectivity was improved with macrocyclic catalyst YZ-1. Kinetic study confirmed the existence of secondary metathesis under the reaction condition. A crossover experiment indicated that the bulky diene produced through ene-yne metathesis is formed reversibly. Reaction with internal alkyne showed higher size-selectivity than terminal alkyne using both HG II and YZ-1.Different modification strategies of current macrocycle system are discussed in Chapter 4. Efforts were made towards obtaining structural variety through backbone functionalization. Three new ruthenium complexes (YZ-3, YZ-4 and YZ-5) with substituted Hoveyda chelate were synthesized in order to improve catalysis reactivity by inducing steric interaction with the macrocycle scaffold. However, these attempts were not successful possibly due to an unexpected conformational change. Replacing the tetrafluoroborate in YZ-1 catalyst with other anions revealed that the counter ion played an important role in catalyst performance, although an accurate explanation cannot be provided at this point. Further, a new phenanthroline macrocycle was successfully synthesized with expanded dimension, which is expected to better accommodate the metal complex. Rigidification strategies aiming to lock the NHC inside the cavity is currently under investigation. The phenanthroline moiety can be further utilized to coordinate first row transition metals. Synthesis of a series of metal complexes using this novel ligand system and study of their reactivity and/or selectivity is foreseeable.
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