Base-free efficient palladium catalyst of Heck reaction in molten tetrabutylammonium bromide

Phosphine-free palladium precursors (PdCl2, PdCl2(PhCN)2 and Pd(OAc)2) in molten [nBu4N]Br as the reaction medium and without addition of base were used as components for efficient catalytic systems for Heck coupling of bromobenzene with butyl acrylate. In all the systems under studies the yield of product, butyl cinnamate 1, strongly depends on the concentration of palladium. The maximum yield of 1 was obtained for PdCl2(PhCN)2 at 0.09 mol% and for PdCl2 and Pd(OAc)2 at ca. 0.4 mol%. Lower yields were obtained below and over that concentration. Addition of bases (NaHCO3, NaHCO2, Et3N or Bu3N) caused an increase of acrylate conversion and formation of butyl β-phenyl cinnamate 2. During recycling experiments the change of selectivity was observed with increase of 1/2 products ratio.

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