Cycloocta-1,5-diene cyclic oligomers

Fig. 3.1 Routes A, B, C, D to equilibrium E between cycloocta-1,5-diene, cyclic oligomers, and linear high polymer, starting from monomer M, polymer P, oligomers O, or a mixture F of monomer and oligomer, respectively. Starting concentration in all cases equivalent to 2.7 mol C4H6 units litre . Catalyst W[=C(OMe)Ph](CO)4(PPh3)/TiCl4. Solvent O = chloro-benzene = benzene, 30°C (Chauvin 1977, 1978).

The relative proportions of cyclic oligomers, c-M , both initially and at equilibrium, form a continuously declining series for values of x larger than 3 or 4. In the case of cycloocta-1,5-diene, the series of cyclic oligomers have the formula (C4He) c with no tendency for the even-numbered members of the series to predominate see Fig. 3.2(a) (Kelly 1975 Kumobayashi 1976 Chauvin 1977, 1978). 

With cycloocta-1,5-diene, reaction (10) can take place at any double bond in the chain, so accounting for the continuous series of cyclic oligomers of formula (C4He). At the beginning of the reaction, alternate double bonds in the chain P will have cis configuration (being pre-formed in the monomer) but the other double bonds may be cis or trans. It appears that this is not a significant factor in... 

Fig. 12.4 The proportion of extractable cyclic oligomers as a function of the reciprocal initial monomer concentration [M]o for the ROMP of (A) cw-cyclooctene, and (B) cis,cis-cycloocta-1,5-diene. Catalyst WCl6/EtAlCl2/EtOH (1/4/1) in benzene (Scott 1969)...

It was first observed in 1969 that the ROMP of cycloocta-1,5-diene and cyclooctene produced not only linear polymer but also a series of cyclic oligomers, detectable by GC [67]. These are the products of back-biting metathesis reactions in competition with the propagation reaction. Eqn. (10) is an example of the formation of cyclic tetramer during the ROMP of cyclopentene, [68]. The back-biting reaction is thus the reverse of the propagation step for the cyclic oligomer itself. 

The synthesis of a,co-difunctional telomers by cross-metathesis between cyclic olefins and acyclic functionalized olefins is possible in the presence of functional-group-tolerant catalysts. Thus, cross-metathesis of dimethyl hex-3-enedioate with cycloocta-1,5-diene (Pinazzi 1980 Reyx 1982b, 1990), cyclopentene (Reyx 1986, 1987), or norbomene (Cramail 1991a) in the presence of the catalyst system WCV Mc4Sn allows the synthesis of a,m-difunctional oligomers, e.g. reaction (2). 

---