N-heterocyclic Carbene Copper-Catalyzed Carboxylation of Alkynes with Carbon Dioxide

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http://urn.fi/URN:NBN:fi:hulib-202003161557
Title: N-heterocyclic Carbene Copper-Catalyzed Carboxylation of Alkynes with Carbon Dioxide
Author: Hiltunen, Otto-Matti
Contributor: University of Helsinki, Faculty of Science
Publisher: Helsingin yliopisto
Date: 2020
Language: eng
URI: http://urn.fi/URN:NBN:fi:hulib-202003161557
http://hdl.handle.net/10138/313405
Thesis level: master's thesis
Degree program: Kemian ja molekyylitieteiden maisteriohjelma
Master's Programme in Chemistry and Molecular Sciences
Magisterprogrammet i kemi och molekylära vetenskaper
Specialisation: ei opintosuuntaa
no specialization
ingen studieinriktning
Discipline: none
Abstract: Copper complexes are versatile catalysts for different fixations of carbon dioxide. Copper-catalyzed carboxylations of unsaturated hydrocarbons with CO2 provide access to valuable carboxylic acids. Generally, the formation of Cu-C species from the substrate and the catalyst is followed by carbon dioxide insertion across the Cu-C bond which produces copper carboxylate RCOO-Cu via C-C bond formation. Moreover, copper complexes can undergo transmetallation with less-nucleophilic organoboron reagents to afford Cu-C species. Copper-catalyzed reductive carboxylations of C-C unsaturated bonds with CO2 entail hydrogenative, alkylative and heterocarboxylation methodologies. This thesis elaborates a protocol for the N-heterocyclic carbene copper (I)-catalyzed synthesis of carboxylic acids from alkynes with carbon dioxide. The main interest lies in a regioselective hydrocarboxylation of alkynes catalyzed by NHC-copper hydrides and copper-catalyzed carboxylation of alkylboranes with CO2. The literature review focuses on the catalytic activity of N-heterocyclic copper (I) complexes in organometallic chemistry, especially within a range of reductive carboxylation reactions. Alkynes insert readily into the copper hydride bond constituting C-Cu species prior to the CO2 insertion. The regioselectivity of this carboxylation reaction derives from the syn addition of Cu-H species to the alkyne. Correspondingly, the alkylboranes can be carboxylized in a regiospecific fashion due to the regioselective manner of the initial hydroboration. In the experimental part, two different catalytic hydrocarboxylation pathways were carried out with in situ- copper (I) catalysts. The use of mild base additive CsF was necessary for the catalyst formation. The first pathway was catalyzed by a NHC-copper(I)-hydride complex in the presence of hydrosilane as the reducing agent. In the second pathway, a tandem hydroboration carboxylation sequence was utilized, catalyzed by copper(I) fluoride species. Both pathways furnished carboxylic acids from terminal and internal alkynes.


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