Palladium-Catalyzed Decarboxylative Cross-Coupling of 2,4-Dienoic Acids and Aryl Halides: Access to Fluorescence Active (<i>E,E</i>)-1,4-Diarylbutadienes

A range of (<i>E</i>,<i>E</i>)-1,4-diarylbutadienes has been efficiently achieved through a Pd-catalyzed decarboxylative cross-coupling of various 2,4-dienoic acids with diverse (hetero)aryl halides, such as bromides, chlorides, and iodides. This protocol successfully produces the corresponding 1,4-diarylbutadiene cross-coupled products in high yields across a large range of substrates (68 examples), demonstrating compatibility with various sensitive functional groups, including heterocycles. A catalytic amount of silver salt was used as a cocatalyst in this approach, replacing the stoichiometric amounts utilized in earlier reports. A sequence of spectroscopic experiments, were performed for the first time to investigate and identify the catalytically active species' oxidation state. Furthermore, steady-state and time-resolved spectroscopic studies of selected compounds revealed promising luminescence characteristics featuring excellent fluorescence emission efficiency (quantum yields). These findings pave the way for the potential use of (<i>E,E</i>)-1,4-diarylbutadiene derivatives as functional organic materials.