PEPPSI-Type Pd(II)—NHC Complexes on the Base of <i>p-tert</i>-Butylthiacalix[4]arene: Synthesis and Catalytic Activities

Abstract

The creation of effective catalytic systems for cross-coupling reactions, reduction, etc., capable of working in water-organic or pure aqueous media is in great demand. The article presents the synthesis of NHC-palladium complexes of the PEPPSI type based on monoimidazolium derivatives of thiacalix[4]arene. The structure of the imidazolium precursors, obtained in 81–88% yields and the complexes themselves, obtained in 40–50% yields, is established using modern methods, including X-ray structural analysis and high-resolution mass spectrometry. It is shown that the obtained complex with bulk substituents near the palladium atom is not inferior to the well-known PEPPSI-type Organ’s catalyst in the catalysis of Suzuki-Miyaura coupling and is four times superior to the latter in the p-nitrophenol reduction reaction. Given the presence of free phenolic hydroxyl groups in the macrocycle, the obtained complexes are of interest for further post-modification or for immobilization on a carrier.

Keywords

• thiacalix[4]arene
• NHC
• palladium
• cross-coupling
• PEPPSI complex