Simple and efficient
methods are a key consideration for small
molecule and polymer syntheses. Direct arylation polymerization (DArP)
is of increasing interest for preparing conjugated polymers as an
effective approach compared to conventional cross-coupling polymerizations.
As DArP sees broader utilization, advancements are needed to access
materials with improved properties and different monomer structures
and to improve the scalability of conjugated polymer synthesis. Presented
herein are considerations for developing new methods of conjugated
polymer synthesis from small molecule transformations, exploring how
DArP has successfully used this approach, and presenting how emerging
polymerization methodologies are developing similarly. While it is
common to adapt small molecule methods to polymerizations, we demonstrate
the ways in which information gained from studying polymerizations
can inform and inspire greater advancements in small molecule transformations.
This circular approach to organic synthetic method development underlines
the value of collaboration between small molecule and polymer-based
synthetic research groups.
Direct arylation is an appealing method for preparing π-conjugated materials, avoiding the prefunctionalization required for traditional cross-coupling methods. A major effort in organic electronic materials development is improving the environmental and economic impact of production; direct arylation polymerization (DArP) is an effective method to achieve these goals. Room-temperature polymerization would further improve the cost and energy efficiencies required to prepare these materials. Reported herein is new mechanistic work studying the underlying mechanism of room temperature direct arylation between iodobenzene and indole. Results indicate that room-temperature, Pd/Ag-catalyzed direct arylation systems are radical-mediated. This is in contrast to the commonly proposed two-electron mechanisms for direct arylation and appears to extend to other substrates such as benzo[b]thiophene and pentafluorobenzene.
A robust method of room temperature
direct arylation for benzofuran
is reported. This discovery allows for mild arylation by commercially
available aryl iodides with complete C-2 regioselectivity and tolerates
a range of functional groups, including heat sensitive groups. Mechanistically,
a Heck-type oxyarylation product from a direct arylation process is
reported as a key piece of evidence for a carbopalladation intermediate.
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