Imidazolium and Imidazolinium Salts as Carbene Precursors or Solvent for Ruthenium-Catalysed Diene and Enyne Metathesis

Abstract

This review reports the utilisation of catalytic systems prepared in situ from a source of ruthenium, a precursor of 1,3-diaminocarbene, and a base to perform enyne ring-closing metathesis. Silylated enynes and allyl propargyl ethers have been rearranged into cyclic derivatives bearing a conjugated diene structure in the presence of [(p-cymene)RuCl2]2, an imidazolium or imidazolinium chloride, and cesium carbonate. From 1,6-dienes, the dichotomous behaviour of the catalytic system generated from imidazolinium salts makes possible the preparation of cycloisomerisation products, or metathesis compounds when the reaction is carried out in the presence of acetylene. Finally, the possibility of performing ring-closing metathesis in imidazolium salts as an ionic solvent with an ionic catalyst of the type [(p-cymene)RuCl(PCy3)CCCPh2][X] is demonstrated.