Solid Phase Synthesis of M-Phenylene Ethynylene Oligomer Heterosequences
Ray, Christian R.
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Permalink
https://hdl.handle.net/2142/84215
Description
Title
Solid Phase Synthesis of M-Phenylene Ethynylene Oligomer Heterosequences
Author(s)
Ray, Christian R.
Issue Date
2005
Doctoral Committee Chair(s)
Moore, Jeffrey S.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Polymer
Language
eng
Abstract
The synthesis of m-phenylene ethynylene (mPE) oligomers is currently a tedious process. To address this, two methods for the solid-phase synthesis of mPE oligomers (including heterosequences) have been developed. The first strategy employs a silyl-acetylene linker attached to ArgoGel(TM) solid support, and uses palladium-catalyzed cross-coupling reactions to form the desired mPE backbone in a monomer-by-monomer fashion. In order to rapidly access hexameric oligomers in a period of one to two days, efforts were taken to limit the need for deprotection steps and ensure cross-coupling conditions were complete within two hours. This led to the ability to produce mPE heterosequence hexamers with aryl bromide and terminal acetylene endgroups in good yields (typically 55-75%), in twelve hours. To increase the diversity of mPE oligomer endgroups available from solid-phase methods, a new strategy based on a triazene linker and Merrifield resin was also investigated. In this approach the mPE backbone was constructed in the same fashion as used in the silyl-acetylene linker approach. However, due to differences in resin swelling, some modification of reaction conditions were required. These new conditions allowed mPE heterosequences with aryl iodide and TMS-acetylene endgroups to be produced in 45-65% yields in forty-eight hours. Both solid-phase methods were able to produce oligomers of up to nine or ten repeat units. A method for obtaining longer-length oligomers was, however, necessary. To achieve this, a method of on-resin fragment coupling was investigated. This strategy employed previously established synthetic conditions to couple oligomer fragments onto a solid support through a silyl-acetylene linker. The on-resin mPE fragments were then subjected to a sequence of deprotection and coupling steps in order to access the desired length mPE oligomers in low, but acceptable yields. Aggregation of resin-bound oligomers may be attributed to the lack of conversion observed for the room temperature on-resin fragment coupling. Disruption of on-resin aggregates was achieved by elevating the temperature of coupling reactions.
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