Dithienylethene-based photoswitchable phosphines for light-controlled palladium-catalyzed Stille coupling reaction

Homogeneous transition metal catalysis is a constantly developing field of the chemical sciences. A growing interest in this area is photoswitchable catalysis, which pursues in-situ modulation of catalyst activity through non-invasive light irradiation. Phosphorus ligands are excellent targets to accomplish this goal by introducing photoswitchable moieties; however, only a limited number of examples has been reported so far. In this work we have developed a series of palladium complexes capable of catalyzing the Stille coupling reaction that contain photoisomerizable phosphine ligands based on dithienylethene switches. Incorporation of electron-withdrawing substituents into these dithienylethene moieties allows to vary the electron density on the phosphorus atom of the ligands upon light irradiation, which in turn leads to a modulation of the catalytic properties of the formed complexes and their activity in a model Stille coupling reaction. These results are supported by theoretical computations, which show that the energy barriers for the rate-determining steps of the catalytic cycle decrease when the photoswitchable phosphine ligands are converted to their closed state.