MCM-41-supported poly-gamma-mercaptopropylsiloxane palladium (0,II) complexes were easily prepared from poly-gamma-mercaptopropylsiloxane and MCM-41 in chloroform, followed by coordination to palladium chloride in ethane at room temperature. These catalysts are highly active and stereoselective for vinylation of aryl iodides with olefins, and give a variety of trans substituted products in high yields at 70 degrees C, and can be reused without loss in activity.