There is provided processes for metal mediated reactions, particularly cross coupling and carbometallation reactions, wherein the metal is present as a catalyst system comprising a catalyst microencapsulated within a permeable polymer microcapsule shell and the reaction is carried out under super-critical or near super-critical conditions. Preferred metal-mediated cross coupling reactions include Heck, Suzuki, Sonogashira and Stille reactions. Preferred carbometallation reactions include hydroformylations.