Acridine PNP-Pincer Ligands Enabling Transition Metal-Catalyzed Photoreactions

Transition metal-catalyzed reactions are developed together
with
ligands. While transition metal-catalyzed photoreactions have been
extensively reported in recent years, the development of ligands for
photoreactions is limited to only a few cases. Therefore, establishing
ligands that shed light on transition metal-catalyzed photoreactions
is an important research goal. We successfully synthesized four acridine-containing
PNP-pincer ligands and formed transition metal complexes with Ni,
Pd, Pt, Cu, and Co. We found that the platinum complex induced photoreactions
of olefins under visible light irradiation: transfer hydrogenation,
which required only a stoichiometric amount of hydrogen source, and
hydroxy/alkoxy alkylation of olefins. These reactions did not proceed
with existing well-known ligands, demonstrating that the development
of photoreaction-oriented ligands reveals unknown reactivities of
transition metals.