New palladium-bis(oxazoline)-phosphine complexes: Synthesis, characterization and catalytic application in alkoxycarbonylation of alkynes

New cationic palladium-bis(oxazoline)-phosphine (Pd-BOX-PR₃) complexes (Pd-BOX-B and Pd-BOX-C) have been synthesized and characterized using ¹H, ¹³C and ³¹P NMR, FTIR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The new complexes were used as catalysts in the alkoxycarbonylation of alkynes with various alcohols as nucleophiles. The carbonylation has produced the gem-α,β-unsaturated ester isomer (3) in high regioselectivity and excellent yields. The catalyst systems have been optimized by screening the type of palladium complexes and also by varying the reaction parameters including the reaction time, solvent, and temperature. A mechanism of the catalytic cycle based on a N-protonated palladium bis(oxazoline) phosphine active species was proposed for the alkoxycarbonylation reaction. (Figure Presented.).