Solvents play a very important role in organic chemistry. Most reactions must be carried out in solvents, thus for chemists, they have to deal with huge volumes of solvents everyday. Solvents can be highly damaging chemicals for two simple reasons: (1 ) they are used on a large scale, (2 ) they are often volatile which makes them difficult to contain. For the reason of environmental protection and reduction of damage to human being, clean technologies have become a major concern throughout both industry and academia. Therefore, search for the replacement of the damaging solvents has became a high priority. Based on such ideas, we have investigated some catalytic reactions in room temperature ionic liquids 1,3-dialkylimidazolium, which are potentially a new type of variety of solvent system to replace the conventional solvents. We have also studied the applications of ionic liquids in several different fields. In this respect, the ambient temperature ionic liquid 1,3-dialkylimidazolium systems [BMIM]PF6 or [BMIM] BF4 were employed for coupling reactions with nickel (0) complexes as catalyst (Chapter 2); to support the bioreduction with immobilised baker’s yeast in the presence of water (Chapter 3); for the studies of diaryl etherfomiation reaction catalysed by palladium with ligand in ionic liquid (Chapter 4); and for the indium-catalysed Sakurai reaction in ionic liquid (Chapter 5).