A highly active and recyclable homogeneous NHC–palladium catalyst with pH- and light-sensitive tags for the Suzuki–Miyaura coupling reactions of aryl halides with arylboronic acids

Abstract

The design and synthesis of a stable, highly active, and recyclable homogeneous palladium catalyst for Suzuki–Miyaura coupling reactions is of great interest. A well-defined N-heterocyclic carbene (NHC) Pd(II) complex with pH- and light-sensitive nitrobenzospiropyran (SP) tags has been synthesized in good yields via a series of simple steps. This complex is a homogeneous catalyst which has excellent reactivities for the Suzuki–Miyaura coupling of aryl bromides and aryl chlorides with arylboronic acids. Significantly, at a low loading (0.2 mol%), this catalyst has very good recyclability in an i-PrOH–H₂O solvent system (1 : 1 v/v), under mild conditions. By making use of the pH- and light-sensitive SP tags, the catalyst can be recovered and reused seven times.