Cyclic strained olefins

Ring opening polymerization of strained cyclic olefins, discussed previously, might exemplify such a system. The metalla-carbene, Met=CHR, is the active, and presumably labile form, while the ring species,... 

ROMP is without doubt the most important incarnation of olefin metathesis in polymer chemistry [98]. Preconditions enabling this process involve a strained cyclic olefinic monomer and a suitable initiator. The driving force in ROMP is the release of ring strain, rendering the last step in the catalytic cycle irreversible (Scheme 3.6). The synthesis of well-defined polymers of complex architectures such as multi-functionaUsed block-copolymers is enabled by living polymerisation, one of the main benefits of ROMP [92, 98]. 

Scheme 14.10. Reaction of titanocene-methylidene with strained cyclic olefins.

Table 8.6 ROMP of low-strained cyclic olefins using catalysts XXVIIIa, XXVIIId in toluene at RT. Substrate Catalyst Monomer/Catalyst Time Conversion %) 10 xM M /M ...

Olefin metathesis catalysts based on ruthenium have been shown to exhibit a quite good tolerance to a variety of functional groups. The ring opening metathesis polymerization of strained, cyclic olefins initiated by group VIII salts and coordination complexes in aque-... 

Even highly strained cyclic olefins can thus be obtained [38] ... 

Strained cyclic olefins like cyclobutene, cyclopentene, and norbonene can be used as monomers and comonomers in a wide variety of polymers. Generally... 

The reaction is applied in industrial processes (Phillips triolefin process. Shell higher olefin process) and has importance in ring opening-metathesis polymerization (ROMP) in polymer chemistry [1]. In the past, olefin metathesis was not commonly applied in organic synthesis [2] because of the reversibility of the reaction, leading to olefin mixtures. In contrast, industrial processes often handle product mixtures easily. In ROMP, highly strained cyclic olefins allow the equilibrium of the reaction to be shifted towards the product side. 

The first example of fully aqueous metal catalysis of olefin isomerization was reported by Grubbs et al. in 1994 [2]. These authors adopted [Ru(H20)6](tos)2 (tos = p-toluenesulfonate) [8] as a catalyst, which is highly active for the ring-opening polymerization of strained cyclic olefin. Both allylic alcohol and allylic ethers undergo isomerization in the presence of [Ru(H20)6](tos)2. 

On the contrary, if a highly strained cyclic olefin such as the cyclopropene 16 [20] or the norbomene derivative 17 [21] is employed, the titanacyde is deaved to form the corresponding titanocene-alkylidene 18 or 19. This reaction is dearly enhanced by the concomitant release of intrinsic strain energy (Scheme 14.10). 

Asymmetric Codimerizations. The use of Ni catalysts modified by an optically active phosphine in catalytic asymmetric syntheses, e.g., of the type [ NiX(rj -C3Hs) ij]/ Al2Cl3Et3/PR3, is important . Phosphines bearing the optical activity in the substituents such as 7 are most effective. Particularly high optical yields occur in the codimerization of C2H4 with a strained cyclic olefin such as norbomene [equation (a)] ... 

Although these reactions are quite impressive, kinetic measurements have shown that 32 and 42 are less reactive dienophiles than other comparably strained cyclic olefins [35b, 35 c]. It can be concluded that the inherent high reactivity of the strained double bonds in 32 and 42 is partially compensated by the steric hindrance which the ortho-hydrogen atoms on the phane-arene units exert on the approach of the cycloaddend. 

Cationic and radical polymerizations of norbornene yield only low molecular weight oligomers [169,170]. Ring-opening metathesis polymerization (ROMP) of strained cyclic olefins was first reported in the 1950s [171] and is of industrial importance. Attempts were made to prepare 193 nm resist polymer by ROMP of functionalized norbornenes and tetracyclododecenes (Fig. 75) [168,251]. Hydrogenation of the unsaturated backbone was necessary to afford ther-mooxidative stability and to reduce OD at 193 nm. Use of tetracyclododecene... 

Carbon-13 n.m.r. studies may be used to investigate strain effects in cyclic olefins.The values of the chemical shifts in some strained cyclic olefins are shown in Table II. 

Carbon-13 chemical shifts, p.p.m. from CS2, in some strained cyclic olefins... 

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