Amphiphilic Pd^II-NHC Complexes on 1,3-Alternate p-tert-Butylthiacalix[4]arene Platform: Synthesis and Catalytic Activities in Coupling and Hydrogenation Reactions

Abstract

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Herein we report the first example of amphiphilic PdII–NHC complexes on the thiacalix[4]arene backbone in 1,3-alternate configuration. Relative catalytic activity of synthesized PdII–NHC complexes in Suzuki–Miyaura coupling of haloarenes with phenylboronic acid was studied. A combination of micellar and metallocomplex catalysis was observed in Suzuki–Miyaura coupling upon going from pure DMF to water/DMF 3:1: the 2-fold increase of conversion of 4-bromoanisole unlike pure DMF was found. Interesting feature was found using chloroarene in DMF/water: the reaction selectivity changed from heterocoupling to homo coupling of phenylboronic acid. PdII–NHC complexes demonstrated a high activity in model hydrogenation reaction of p-nitrophenol using sodium borohydride. The most lipophilic PdII–NHC complex was found to be most active, which can be attributed with additional p-nitrophenol preconcentration in the aggregates due to larger hydrophobic capacity of macrocycle.