Acetylene metathesis reaction, transition-metal

Metallacycles have been suggested as intermediates in many transition-metal catalyzed reactions of olefins, acetylenes, and cyclopropanes. Metallacyclobutane complexes are invoked in olefin and cyclopropane isomerization schemes (Scheme as well as in olefin metathesis schemes. Metallacyclopentane, -pentene, and -pentadiene complexes can all be invoked in olefin and acetylene dimerization and polymerization (Scheme Many of these involve early transition metals and do not include phosphine ligands. 

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