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Investigation of Kinetically Labile Supramolecu-lar System Addressing Substrate Selectivity in the Catalytic Epoxidations of Olefins

Odille, Fabrice LU (2006)
Abstract (Swedish)
Popular Abstract in Swedish

Inom kemin kan uppbyggnaden av molekylära aggregat styras genom att använda sig av kovalenta bindningar eller genom att utnyttja svaga växelverkningar. Den moderna kemin baseras på många års grundforskning på reaktionsförlopp där bildningen av en kovalent bindning stått i fokus vilket har gjort det möjligt att förutsäga utfallet av en sådan reaktion. Däremot är det betydligt svårare att förutsäga vad för sorts aggregat olika molekyler kommer att bilda sinsemellan, när svaga växelverkningar är den enda formen av interaktion som står till buds. Sedan den supramolekulära kemin föddes på 1960-talet, har kemister kunnat börja förstå och formgiva system som bildar denna typen av aggregat på ett... (More)
Popular Abstract in Swedish

Inom kemin kan uppbyggnaden av molekylära aggregat styras genom att använda sig av kovalenta bindningar eller genom att utnyttja svaga växelverkningar. Den moderna kemin baseras på många års grundforskning på reaktionsförlopp där bildningen av en kovalent bindning stått i fokus vilket har gjort det möjligt att förutsäga utfallet av en sådan reaktion. Däremot är det betydligt svårare att förutsäga vad för sorts aggregat olika molekyler kommer att bilda sinsemellan, när svaga växelverkningar är den enda formen av interaktion som står till buds. Sedan den supramolekulära kemin föddes på 1960-talet, har kemister kunnat börja förstå och formgiva system som bildar denna typen av aggregat på ett kontrollerat sätt. Det är mycket viktigt att studera sådana system eftersom många livsviktiga processer i naturen sker genom sådana svaga växelverkningar.



Alla levande celler innehåller katalysatorer som går under benämningen enzymer. Dessa ämnen vars egenskaper naturen utvecklat och förfinat under miljarder år har förmågan att katalysera en specifik reaktion på ett specifikt substrat miljontals gånger utan att enzymet degraderas. Genom att använda sig av de kunskaper som supramolekylära kemister har skaffat sig under årens lopp är det idag möjligt att fantisera om att en dag kunna skapa konstgjorda enzymsystem med liknande eller nya egenskaper.



Syftet med denna avhandlingen är att lämna ett litet bidrag till det redan mycket omfattande supramolekylära katalysfältet. Vi har därför skapat en katalysator som består av två separata enheter: den ena enheten består av en Jacobsen-Katsuki katalysator som kan epoxidera dubbelbindningar och den andra består av en receptorenhet som kan välja bland olika substrat och föra dem i närkontakt med katalysatorn. Båda enheterna har modifierats på så sätt att de kan interagera med varandra genom svaga vätebindningar. Systemet har visat sig kunna diskriminera mellan substrat som kan binda till receptorenheten och sådana som inte kan binda till receptorenheten. Tyvärr var inte resultaten lika bra som vi hade hoppats på men vi har lyckats identifiera problemen vilket gör att vi är i stånd att omorganisera vårt system på ett sådant sätt att vi kan öka substratselektiviteten. (Less)
Abstract
This thesis is devoted to the development and investigation of a supramolecular system used to catalyze Jacobsen-Katsuki epoxidations with the aim to attain substrate selectivity without product inhibition.



The supramolecular catalyst is composed of two well-defined entities or units: a catalytic and a receptor. The keyword for the design was flexibility. The interactions foming the supramolecular catalyst were designed to give the system enough flexibility for it to be able to release the product as soon as it is formed avoiding product inhibition. This could be obtained by using the 2-pyridone hydrogen-bonding motif. The catalyst unit is a derivative of Jacobsen's (Salen)MnIII, where 2-quinolones are attached to the 5-... (More)
This thesis is devoted to the development and investigation of a supramolecular system used to catalyze Jacobsen-Katsuki epoxidations with the aim to attain substrate selectivity without product inhibition.



The supramolecular catalyst is composed of two well-defined entities or units: a catalytic and a receptor. The keyword for the design was flexibility. The interactions foming the supramolecular catalyst were designed to give the system enough flexibility for it to be able to release the product as soon as it is formed avoiding product inhibition. This could be obtained by using the 2-pyridone hydrogen-bonding motif. The catalyst unit is a derivative of Jacobsen's (Salen)MnIII, where 2-quinolones are attached to the 5- and 5´-positions of the salen ligand. The receptor unit is a zinc-porphyrin with 2-pyridone groups attached to it. The spatial arrangement of the 2-pyridone motifs was designed to favor the formation of a cavity between the catalyst and the receptor unit. The receptor can select a pyridine-appended olefin via coordination to its zinc-porphyrin core. The supramolecular catalyst was shown to be partly selective for such olefins over phenyl appended one. Three different substrates were synthesized and investigated pairwise. Two substrates contained the pyridine required for it to be selected by the supramolecular catalyst. These substrates were differentiated by their size. The third one lacks the anchor; the pyridyl group is exchanged for a phenyl group.



The synthesis of the receptor and investigation of the substrate selectivity is discussed. The epoxidations were run at different concentrations of receptor and catalytic units, varying the composition of the system like the presence of different substrates and additives. The effect of both the receptor and substrate on the stability, reactivity, substrate- and enantio-selectivity of the catalyst unit were addressed and are presented in addition to the above-mentioned substrate selectivity. A complete mathematical model is also presented which helped us to estimmate the association constants characterizing the system. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Professor Rebek Jr., Julius, The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 N. Torrey Pines Roa
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Naturvetenskap, Natural science, enantioselectivity, (Salen)Mn(III), substrate selectivity, porphyrin, Jacobsen-Katsuki epoxidation, supramolecular catalysis, Hydrogen-bond, 2-pyridone
pages
107 pages
publisher
Organic Chemistry, Lund University
defense location
Kemicentrum room K:B Getingevägen 60 Lund
defense date
2006-02-24 13:15
ISBN
91-7422-104-3
language
English
LU publication?
yes
id
e572ccea-cc84-4f03-9dbb-82e3ce600341 (old id 546231)
date added to LUP
2007-10-13 11:25:34
date last changed
2016-09-19 08:45:11
@misc{e572ccea-cc84-4f03-9dbb-82e3ce600341,
  abstract     = {This thesis is devoted to the development and investigation of a supramolecular system used to catalyze Jacobsen-Katsuki epoxidations with the aim to attain substrate selectivity without product inhibition.<br/><br>
<br/><br>
The supramolecular catalyst is composed of two well-defined entities or units: a catalytic and a receptor. The keyword for the design was flexibility. The interactions foming the supramolecular catalyst were designed to give the system enough flexibility for it to be able to release the product as soon as it is formed avoiding product inhibition. This could be obtained by using the 2-pyridone hydrogen-bonding motif. The catalyst unit is a derivative of Jacobsen's (Salen)MnIII, where 2-quinolones are attached to the 5- and 5´-positions of the salen ligand. The receptor unit is a zinc-porphyrin with 2-pyridone groups attached to it. The spatial arrangement of the 2-pyridone motifs was designed to favor the formation of a cavity between the catalyst and the receptor unit. The receptor can select a pyridine-appended olefin via coordination to its zinc-porphyrin core. The supramolecular catalyst was shown to be partly selective for such olefins over phenyl appended one. Three different substrates were synthesized and investigated pairwise. Two substrates contained the pyridine required for it to be selected by the supramolecular catalyst. These substrates were differentiated by their size. The third one lacks the anchor; the pyridyl group is exchanged for a phenyl group.<br/><br>
<br/><br>
The synthesis of the receptor and investigation of the substrate selectivity is discussed. The epoxidations were run at different concentrations of receptor and catalytic units, varying the composition of the system like the presence of different substrates and additives. The effect of both the receptor and substrate on the stability, reactivity, substrate- and enantio-selectivity of the catalyst unit were addressed and are presented in addition to the above-mentioned substrate selectivity. A complete mathematical model is also presented which helped us to estimmate the association constants characterizing the system.},
  author       = {Odille, Fabrice},
  isbn         = {91-7422-104-3},
  keyword      = {Naturvetenskap,Natural science,enantioselectivity,(Salen)Mn(III),substrate selectivity,porphyrin,Jacobsen-Katsuki epoxidation,supramolecular catalysis,Hydrogen-bond,2-pyridone},
  language     = {eng},
  pages        = {107},
  publisher    = {ARRAY(0x9e6a288)},
  title        = {Investigation of Kinetically Labile Supramolecu-lar System Addressing Substrate Selectivity in the Catalytic Epoxidations of Olefins},
  year         = {2006},
}