The metathesis reactions of cycloolefins results in a ring‐chain equilibrium of cyclic oligomers and an acyclic polymer. The distribution of the polymer can be described by a most probable molecular weight distribution. The oligomer distribution differs in the kinetically controlled regime of the reaction from the equilibrium situation. The particular cases of norbornene and norbornadiene are discussed. Carbene complexes may be used as initiators. The more stable the carbene the more strained the cycloolefin has to be in order to be polymerizable. With increasing strain the cis‐stereoselectivity is significantly attenuated. (CO)5CRCR′R″ may initiate the metathesis reaction of cyclic and acyclic vinylethers. The reaction proceeds in a structurally uniform manner, i.e. only vinylethers are formed, and yields the equilibrium ratio of cis and trans double bonds.

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Some new divinylidene compounds, 1,3-bis[4-(B-styryl)phenyl]propane (2 b), 1,6-bis[4-@styryl)phenyl]hexane (2d), 2,6-bis(B-styryl)pyridine (1 b), and 1,5-bis@-styryl)naphthalene (1 c), were prepared. Their reaction with electron transfer agents was investigated and compared with that of homologous divinylidene compounds. The cyclic oligomers formed after protonation were separated and characterized spectroscopically. In general, no preferential formation of isomers is observed. The cyclic dimer, however, is the main product of the electron transfer reaction of l b and lc.