Metall acyclobutane

Metallacyclobutanes, fomed upon addition of olefin to the metal carbene, were proposed as intermediates or transition states for olefin metathesis. Metal-acyclobutanes are also known to undergo reductive and p-hydride elimination [27] to produce cyclopropanes, Eq. (8 a), and olefins, Eq. (8 b), respectively. These reactions are termination reactions for olefin metathesis. 

The living polymerization prindples developed using the titanacene metall-acyclobutane catalysts have been extended to ROMP reactions catalyzed by other transition-metal complexes. These new systems include tantalacyclobutane complexes and preformed tungsten(VI) carbene complexes. 

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