Dithienylethene-Based Photoswitchable Phosphines for the Palladium-Catalyzed Stille Coupling Reaction

TL;DR

Scientists created light-sensitive phosphine ligands that can control the activity of palladium catalysts in a chemical reaction using light.

Contribution

The novel contribution is the development of dithienylethene-based photoswitchable phosphines for modulating Stille coupling catalysis with light.

Findings

Photoswitchable phosphine ligands based on dithienylethene were synthesized and integrated into palladium complexes.

Light irradiation modulates the electron density of the phosphine ligands, affecting the catalytic activity in Stille coupling reactions.

Theoretical computations confirm that the energy barriers for key catalytic steps decrease when ligands switch to their closed state.

Abstract

Homogeneous transition metal catalysis is a constantly
developing
field in chemical sciences. A growing interest in this area is photoswitchable
catalysis, which pursues in situ modulation of catalyst
activity through noninvasive light irradiation. Phosphorus ligands
are excellent targets to accomplish this goal by introducing photoswitchable
moieties; however, only a limited number of examples have 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 variation of 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.

Two photoisomerizable phosphine ligands
were synthesized
based on dithienylethenes, whose electronic communication with strong
electron-withdrawing groups was switched on and off upon light irradiation.
As a result, the σ-donating ability of these phosphines can
be efficiently light-controlled. This behavior was transferred to
palladium(II) catalytic complexes and exploited to photomodulate the
reaction rate of a model Stille reaction

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