Chemistry and Biochemistry
Bayer School of Natural and Environmental Sciences
Atom transfer radical addition, ATRA, Copper complexes, Kharasch, Reducing agents, TPMA
The focus of this dissertation was to improve the atom transfer radical addition (ATRA) by decreasing the amount of copper catalyst needed to achieve good yields of the monoadduct. This is a fundamental organic reaction in which an alkyl halide is added to the carbon-carbon double bond of an alkene via a free radical mechanism. Previously, ATRA required between 5 and 30 mol% of a copper catalyst relative to alkene in order to achieve good yields of the desired monoadduct due to the accumulation of copper(II) as a result of unavoidable radical termination reactions. The solution to this problem was found for the mechanistically similar atom transfer radical polymerization where the addition of a reducing agent served to continuously regenerate copper(I) in situ, allowing for the significant decrease in the amount of copper catalyst.
We utilized tris(2-pyridylmethyl)amine (TPMA) as a complexing ligand, due to its high activity in ATRA. Free radial initiator, 2, 2'-azobis(isobutyronitrile), was used as a reducing agent and were able to show that polyhalogenated methanes could be efficiently added across a variety of alkenes. Very low catalyst loadings were required for alkenes that do not readily undergo free radical polymerization such as α-olefins. However, significantly higher concentrations of copper catalyst were required for highly active alkenes such as styrene and methyl acrylate. In order to achieve better control of monoadduct formation in these systems, we utilized low temperature free radical initiator 2, 2'-azobis(4-methoxy-2, 4-dimethyl-valeronitrile), which was successful in providing good control over ATRA of methyl acrylate, methyl methacrylate, vinyl acetate and styrene with very low catalyst loadings.
To better understand the correlation between the structure of the copper complex and its activity in ATRA, copper complexes with the TPMA ligand were isolated and characterized with a variety of anions and auxiliary ligands. We observed that copper(I) TPMA complexes contained coordinated halide anions, which raised questions as to how coordinatively saturated complexes such as these could have such a high activity in an inner sphere electron transfer process such as ATRA. It was determined that ATRA with copper TPMA complexes most likely operates by partial ligand dissociation.
Eckenhoff, W. (2010). Structural and Mechanistic Aspects of Copper Catalyzed Atom Transfer Radical Addition Reactions in the Presence of Reducing Agents (Doctoral dissertation, Duquesne University). Retrieved from https://dsc.duq.edu/etd/514