Progresses of Ring Expansion Reaction of Small Transitional Metallacyclic Compounds

Metallacycles, especially those small rings, play an important role in the field of organometallic and coordination chemistry. They are considered as reactive intermediates in metal promoted or catalyzed reactions including olefin metathesis reactions and alkyne polymerization reactions. Due to the high ring strain, small metallacycles can easily react with unsaturated compounds to produce ring expansion products with lower ring strain. To further understand the importance of small metallacycle intermediates in the catalytic reactions and synthesis methodology, the ring expansion reactions of several typical three-, fourand five-membered metallacycles is summarize.