Ethylene rhodium cyclopentadienyl complex

The first report of rhodium-catalyzed [2 - - 2 - - 2] cycloaddition of alkynes with nitriles involves intermolecular reactions catalyzed by a cyclopentadienyl rhodium(I) ethylene complex, which was reported in 1987 (Scheme 4.52) [54a,b]. These reactions required excess nitriles and high temperature. 

The cyclopentadienyl rhodium(I) ethylene complex was able to catalyze partially intramolecular [2 + 2 + 2] cycloaddition of 1,7-diyne with propionitrile, while the yield of the bicyclic pyridine desired was low (Scheme 4.55) [54a],... 

---