Phosphonium ionic liquid (IL)-trihexyl-tetradecylphosphonium bis(trifluoromethylsulfonyl)imide, has been tested as the medium in the Diels-Alder reaction between cyclopentadiene and dienophiles from the group of alpha,beta-unsaturated esters, aldehydes and ketones. Catalytic activities of a few metal chlorides, triflates and bis-triflimides in this reaction have been compared. The recycling of the catalyst with phosphonium IL was studied.