Catalytic activity of Pd dithiolate complexes with large-bite-angle diphosphines in Heck coupling reactions

Palladium(II) complexes of aryl dithiolates and wide-bite-angle diphosphines Xantphos and dppf have been developed as efficient catalysts in Suzuki and Suzuki carbonylation reactions. The catalytic activity of these highly stable, discrete and charged complexes was investigated in Heck coupling reactions of styrene and a variety of aryl bromides. Under optimized reaction conditions these palladium complexes showed excellent activity with high turnover number (6 × 10⁶) and high turnover frequency (4 × 10⁵ h^?1). The effect of bite angle of diphosphines on the catalytic activity of the complexes Pd₂(P^∩P)₂(SC₁₂H₈S)]₂(OTf)₄ followed the trend P^∩P = Xantphos > dppf > dppe as the order of their bite angles. The catalyst could be reused, and after three cycles the formation of significant amount of Pd nanoparticles was noticed, which were characterized using powder X-ray diffraction, energy-dispersive X-ray analysis and transmission electron microscopy. The high catalytic activity has been attributed to the Pd nanoparticles.