Applicability of Pyridinium Polymer as a Support in Heck Reaction in Water

Abstract

Quaternarization of poly(4-vinylpyridine) (1: M_n = 8.8 × 10⁴, M_w/M_n = 1.98) or poly(4-vinylpyridine-co-styrene) (2: M_n = 1.3 × 10⁵, M_w/M_n = 1.92, styrene content: 10%) with iodoethane was performed in DMF at 60 ℃ for 20 h to give partially quaternarized polymer supports (3 or 4, respectively). The content of pyridinium unit in 3 or 4 was estimated from ¹H NMR spectra. The structure of the polymer supports was found to influence the catalytic activity. When the Heck reaction of 4-iodotoluene with styrene was carried out in 1.5 mol·L^-1 KOH aqueous solution using 4b (pyridinium unit content: 40%) as a polymer support, coupling product was obtained in 81% yield. The effect of base on the reaction and recycling of polymer supported palladium catalyst were thoroughly investigated.