Smith ML, Leone AK, Zimmerman PM, McNeil AJ. Impact of Preferential π-Binding in Catalyst-Transfer Polycondensation of Thiazole Derivatives.
ACS Macro Lett 2016;
5:1411-1415. [PMID:
35651203 DOI:
10.1021/acsmacrolett.6b00886]
[Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Polymerizing electron-deficient arenes in a controlled, chain-growth fashion remains a significant challenge despite a decade of research on catalyst-transfer polycondensation. The prevailing hypothesis is that the chain-growth mechanism stalls at a strongly associated metal-polymer π-complex, preventing catalyst turnover. To evaluate this hypothesis, we performed mechanistic studies using thiazole derivatives and identified approaches to improve their chain-growth polymerization. These studies revealed a surprisingly high barrier for chain-walking toward the reactive C-X bond. In addition, a competitive pathway involving chain-transfer to monomer was identified. This pathway is facilitated by ancillary ligand dissociation and N-coordination to the incoming monomer. We found that this chain-transfer pathway can be attenuated by using a rigid ancillary ligand, leading to an improved polymerization. Combined, these studies provide mechanistic insight into the challenges associated with electron-deficient monomers as well as ways to improve their living, chain-growth polymerization. Our mechanistic studies also revealed an unexpected radical anion-mediated oligomerization in the absence of catalyst, as well as a surprising oxidative addition into the thiazole C-S bond in a model system.
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