Activation of Aryl and Vinyl Triflates by Palladium and Electron Transfer – Electrosynthesis of Aromatic and α,β-Unsaturated Carboxylic Acids from Carbon Dioxide

Abstract

The electrochemical reduction of aryl and vinyl triflates in the presence of CO2 and a catalytic amount of palladium results in the formation of aromatic and α,β‐unsaturated carboxylic acids. Aryl and vinyl triflates usually undergo palladium‐catalysed cross‐coupling reactions with nucleophiles. Their reactivity has been reversed in the presence of an electron source, so that they react with electrophiles such as CO2. The reaction proceeds through an activation of the C–O bond of the aryl or vinyl triflate by oxidative addition to a palladium(0) complex, followed by an activation by electron transfer of the thus formed aryl‐ or vinylpalladium(II) complexes.

A Toolbox Approach To Construct Broadly Applicable Metal-Free Catalysts for Photoredox Chemistry: Deliberate Tuning of Redox Potentials and Importance of Halogens in Donor–Acceptor Cyanoarenes

“…With respect to the impressive reductive properties as determined for catalyst 3DPA2FBN , we finally set out to investigate its performance in a highly challenging detriflation of unactivated aryl triflates (typical range of E 1/2 (red): –2.65 V to −1.95 V vs SCE) …”

“…To finally compare the reductive power of our best reducing catalyst 3DPA2FBN ( E 1/2 (PC/PC • – ) = −1.92 V vs SCE) to such protocols, we chose the simple, but challenging defunctionalization of naphthol triflate 9 , whose detriflation would require high reduction potentials ( E 1/2 (red) = −2.01 V vs SCE for 9 ) …”

Carboxylation of Aryl Triflates with CO2 Merging Palladium and Visible-Light-Photoredox Catalysts

“…Previously, the group of Nielsen and Jutand reported palladium-catalyzed electrosynthesis of aromatic and α,β-unsaturated carboxylic acids from the corresponding triflates with CO 2 . Deleterious homocoupling, hydrolysis to phenol, and reduced product formation at elevated temperatures lead to the carboxylation products in moderate yields.…”

Organic thermally activated delayed fluorescence (TADF) compounds used in photocatalysis

“…p-CN-benzene derivatives). 355 The defunctionalisation of naphthyl triflate (E red = À2.01 V vs. SCE) 356 was considered, with both 3DPA2FBN and fac-Ir(ppy) 3 under investigation owing to their very negative ground state reduction potentials (E red = À1.92 V and À2.19 V, respectively). Both photocatalysts proved successful in this reaction with comparable yields of 86% and 90%; the slightly higher yield obtained by the iridium photocatalyst correlates with its more negative reduction potential.…”