Insights into the radical-radical and radical-substrate dimerization processes for substituted phenylmethylenepyrans

Laurianne Wojcik 1 Isidoro López 1 Sebastien Gauthier 2 Nolwenn Cabon 2 Pascal Le Poul 2 Frederic Gloaguen 1 Nicolas Le Poul 1
1 CEMCA - Chimie, Electrochimie Moléculaires et Chimie Analytique
2 ISCR - Institut des Sciences Chimiques de Rennes
Abstract : The electrochemically-induced CC bond making/breaking for six differently R-substituted phenylmethylenepyrans has been investigated by voltammetry in organic media. All compounds display an irreversible oxidation peak whose potential is fully dependent on the electrophilic property of the substituent R. The electrochemical oxidation yields bis-pyrylium compounds by σ-σ CC bond formation. The initial methylenepyrans are recovered by cleavage of the CC bond through electrochemical reduction of the bis-pyrylium species. According to the voltammetric analysis, the mechanistic pathway, radical-radical or radical-substrate, for the intermolecular dimerization is fully R-dependent. Electronic structure calculations show that the spin population in the radical cation and the strength of the σ-σ CC bond in the dimer strongly depend on the nature of R. In addition, low-temperature electrochemical voltammetry (175 K), and room-temperature high scan rate cyclic voltammetry have been used to unravel the kinetics of the CC bond formation.
Keywords : methylenepyran ab initio calculations C-C bond making low-temperature voltammetry radical dimerization
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Laurianne Wojcik, Isidoro López, Sebastien Gauthier, Nolwenn Cabon, Pascal Le Poul, et al.. Insights into the radical-radical and radical-substrate dimerization processes for substituted phenylmethylenepyrans. Electrochimica Acta, Elsevier, 2019, 305, pp.304-311. ⟨10.1016/j.electacta.2019.03.046⟩. ⟨hal-02096108⟩

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