Organometallic reactions in ionic liquids : formation and reaction of organoindium, organozinc and organomagnesium reagents with imines and carbonyl compounds

Abstract

Because of concern for the environment, there has been extensive recent research into the use of environmentally benign reaction media to replace volatile organic solvents. The most extensively studied alternatives are water, supercritical carbon dioxide, and ionic liquids (IL). However, water and supercritical carbon dioxide are well known to react with some reactive organometallic reagents, such as Grignard or organozinc reagents which are very useful in chemical synthesis. Alternative reagents or solvent media must be sought for solving this dilemma. We have explored the possibility of metal-mediated allylation and alkylation reactions in IL systems. The challenge, under such reaction conditions, is to seek base-stable ILs which favor the in-situ generation of reactive organometallic reagents. The study of organometallic reactions in room-temperature ionic liquids (RTILs) has thus far been limited to the less-reactive allylmetal reagents or their variations. This is because the commonly used imidazolium-based RTILs react with reactive organometallic reagents to give imidazol-2-ylidenes (W-heterocyclic carbenes, NHCs). Recently, we found that the RTIL N-butylpyridinium tetrafluoroborate, [bpy][BF4], is stable toward diethylzinc and preformed diethylzinc could be used to react with aldehydes in [bpy][BF4] to give the adducts in high yields. We are therefore interested in the possibility of generating organometallic reagents directly from metal (zinc, magnesium and indium) and organohalides (alkyl and allyl) in RTILs. In this thesis, we demonstrate that (1) allylindium reagents can react with imines in IL and the mechanism of the reaction was investigated; (2) alkylzinc and functionalized alkylzinc reagents can be formed in IL and their reactions with carbonyl compounds were studied; (3) alkylmagnesium reagents can be formed in IL and their reactions with carbonyl compounds were found to be different from that in organic solvents.