Room-temperature Pd/Ag direct arylation enabled by a radical pathway

Abstract

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.

Efficient room temperature catalytic synthesis of alternating conjugated copolymers via C-S bond activation

“…Nevertheless, the high reaction temperatures of these polymerizations not only consume energy, but can also compromise chemoselectivity by producing inseparable structural defects in the product polymers 7 – 10 . Up until now, the polymerizations that can be performed at room temperature or lower in short reaction times have primarily utilized methodologies such as controlled/living polymerization or radical polymerization 11 , 12 . However, the major limitation of these approaches is lack of regioselectivity, hence unsuitability for creating device-quality alternating conjugated polymers 13 .…”

Advances in applying C–H functionalization and naturally sourced building blocks in organic semiconductor synthesis

“…In this study, we synthesized a low molecular weight and branched semiconducting homopolymer from 5-iodo-1-octylindole monomer using room-temperature DArP as shown in Scheme 10. 76 Notably, the mechanistic study indicated that this polymerization was governed by a lightmediated radical process, which was a significant discovery that can inspire future developments of mild reaction conditions for DArP. Also, the aforementioned polyaddition via a cobalt-catalyzed hydroarylation of alkynes reported by Kanbara group is another example of near room temperature synthesis of OSMs.…”

Room Temperature C–H Arylation of Benzofurans by Aryl Iodides

“…Our preliminary investigations were informed by our previous work on room temperature direct arylation of indole, alongside reports of room temperature conditions for indole and benzothiophene arylation. − The previously known indole conditions did not afford any of the desired product 3a (Scheme , entry 1). Similarly, when the reported benzothiophene room temperature arylation conditions were tried, a small amount of 3a was produced (Scheme , entry 2).…”

“…Our preliminary investigations were informed by our previous work on room temperature direct arylation of indole, 18 alongside reports of room temperature conditions for indole and benzothiophene arylation. 15−17 The previously known indole conditions did not afford any of the desired product 3a (Scheme 1, entry 1).…”

“…Previous work from our group demonstrates that indole proceeds under a photomediated mechanism under similar conditions. 18 We hypothesize that this is due to differences in relative aromaticity of the five membered ring on these heterobiaryl scaffolds, where benzofuran and benzothiophene show reduced aromatic character compared to indole in the five-membered ring, allowing for pseudoalkene reactivity. 30−32 Benzofuran in particular is well-documented to behave as (Z)-styryl phenyl ether in ring cleavages, 33 accounting for the mechanistic change between indole and benzofuran under similar conditions.…”