Cyclic norbomene

The most commonly studied olefins are naturally the least expensive ethylene and propylene. Higher a-olefins have been studied mostly as comonomers since the homopolymers are usually not crystalline thermoplastics like PE and isotaaic polypropylene. More exotic olefin monomers have been investigated in the academic realm but some, such as cyclic norbomene (see Chapter 3.26), have also received industrial attention. 

Substituted and unsubstituted bi- or multi-cyclic mono-, di- or multi-olefins, i.e. containing condensed rings at least one of which contains a double bond. Norbomene is homopolymerised commercially whilst, as previously mentioned, ethylidenenorbomene and dicyclopentadiene are used as the cure site monomer in EPDM rubbers. 

New kinds of living polymer systems result from the reactions of transition metals with cyclic, strained olefins 16). These polymerizations proceed through the intermediacy of metal carbenes and are exemplified by the polymerization of norbomene initiated by bis(cyclopentadienyl)-titane-cyclobutane described recently by Grubbs17>. 

In anti addition to a cyclic substrate, the initial attack by the electrophile is also from the less-hindered face. However, many (though not all) electrophilic additions to norbomene and similar strained bicycloalkenes are syn additions." In these cases attack is always from the exo side, for example," ... 

The results of the olefin oxidation catalyzed by 19, 57, and 59-62 are summarized in Tables VI-VIII. Table VI shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbomene) are selectively oxidized to epoxides. Cyclopentene shows exceptional behavior, it is oxidized exclusively to cyclopentanone without any production of epoxypentane. This exception would be brought about by the more restrained and planar pen-tene ring, compared with other larger cyclic nonplanar olefins in Table VI, but the exact reason is not yet known. Linear inner olefin, 2-octene, is oxidized to both 2- and 3-octanones. 2-Methyl-2-butene is oxidized to 3-methyl-2-butanone, while ethyl vinyl ether is oxidized to acetaldehyde and ethyl alcohol. These products were identified by NMR, but could not be quantitatively determined because of the existence of overlapping small peaks in the GC chart. The last reaction corresponds to oxidative hydrolysis of ethyl vinyl ether. Those olefins having bulky (a-methylstyrene, j8-methylstyrene, and allylbenzene) or electon-withdrawing substituents (1-bromo-l-propene, 1-chloro-l-pro-pene, fumalonitrile, acrylonitrile, and methylacrylate) are not oxidized. 

It has been reported by R.Scheiner that phenylazide forms triazoline compounds by 1,3-cyclic addition to unsaturated olefines such as n-butylethylene and norbornen(9 ). These triazolines are decomposed photochemically or thermally to give imine compounds and aziridine as is shown in scheme 1. These facts suggest that phenylazide may react with 3-methyl-1-butene to give triazoline in a similar reaction to that with norbomen. 

The most common alkenes employed in the Pd-catalysed synthesis of alternating polyketones are ethene, styrene, propene and cyclic alkenes such as norbomene and norbornadiene. Even though the mechanism does not vary substantially with the alkene, the reactions of the various co-monomers are here reported and commented on separately, starting with the ethene/CO copolymerisation, which is still the most studied process. As a general scheme, the proposed catalytic cycles are presented first, then the spectroscopic experiments that have allowed one to elucidate each single mechanistic step. 

The metathesis route opens up new opportunities for the synthesis of new copolymers by copolymerizing 6,7-dihydro-2(3//)-oxepinone with other cyclic olefins such as norbomene, even though this approach has barely been exploited until now [121]. 

As is true for most reagents, there is a preference for approach of the borane from the less hindered side of the molecule. Because diborane itself is a relatively small molecule, the stereoselectivity is not high for unhindered molecules. Table 4.6 gives some data comparing the direction of approach for three cyclic alkenes. The products in all cases result from syn addition, but the mixtures result both from the low regioselectivity and from addition to both faces of the double bond. Even the quite hindered 7,7-dimethyl-norbomene shows only modest preference for endo addition with diborane. The selectivity is enhanced with the bulkier reagent 9-BBN. 

Some typical epoxidations are listed in Table 3.1. The first Ru-catalysed epoxida-tion was reported in 1983 by James et al., in which RuBrlPPh XOEPl/PhlO/CHjClj was used to epoxidise styrene, norbomene and c/x-stilbene in low yields trans-stilbene was not oxidised [588]. It was later noted that tranx-RulOl lTMPl/Oj/C H aerobically oxidised cyclic alkenes, and a catalytic cycle involving Ru 0(TMP) was proposed, in which there is disproportionation of Ru(0)(TMP) to Ru(TMP) and fran -Ru(0)2(TMP), the latter epoxidising the alkene and the former being oxidised back to the latter by (Fig. 1.26) [46, 583]. Stilbene, tranx-styrene and norbomene were efficiently epoxidised by trani-RulOl lTMPl/lCl pyNOl/CgH [589], as was epoxidation of exo-norbomenes catalysed by trani-RulOl lTMPl/Oj/ CgHg [590]. 

Copolymers of ethylene and norbomene exhibit excellent transparency, high moisture barrier, high strength and stiffness, and low shrinkage. In comparison to poly(ethylene) (PE) and polypropylene) (PP), they show a very low gas permeability. They are used for blister packaging in pharmacy applications and for flexible films for food packaging. Multilayer films consisting of PP outer layers and a cyclic olefin copolymer are in use. 

The glass transition temperature varies with monomer composition. It can readily exceed 150°C. It increases with increasing norbomene content (22). A linear relationship between cyclic monomer content and glass transition temperature has been reported (6). 

Hydrocyanation is also catalyzed by [Pd(PPh3)4] (103) and [Pd P(OPh), 4] (132), again in both cases in the presence of excess ligand.604 Complex (132) is an effective catalyst for the addition of hydrogen cyanide to cyclic monoenes and dienes such as norbomene and norbornadiene 605-606 ethylene also reacted readily. The product obtained from norbornene was the exo isomer (equation 165). When norbornadiene was the substrate, some of the endo product was formed.605... 

The reaction of norbomene yields the cis exo diester (equation 66).93 This exo isomer is not obtained directly by Diels-Alder chemistry. Other cyclic alkenes such as cyclopentene yield cis diesters, but isomers are obtained as a result of (3-hydride elimination-readdition from intermediates such as (23) prior to CO insertion (equation 67). Thus the palladium walks around the ring to some extent, but always stays on the same face. The extent of rearrangement can be minimized by higher CO pressures since CO insertion becomes more competitive with (3-elimination. This rearrangement becomes a critical problem in the dicarboxylation of 1-alkenes, since a variety of diesters are formed and the reaction is not particularly useful. These reactions were carried out with catalytic amounts of palladium and stoichiometric amounts of copper chloride. 

Figure 5.50 shows three related molecules, the 7-methyl substituted (the visual orbital progression explained here is not quite as smooth for the unsubstituted molecules) derivatives of the 7-norbomyl cation (a), the neutral alkene norbomene (b), and the 7-norbomenyl cation (c). For each species an orbital is shown as a 3D region of space, rather than mapping it onto a surface as was done in Fig. 5.49. In (a) we see the LUMO, which is as expected essentially an empty p atomic orbital on C7, and in (b) the HOMO, which is, as expected, largely the n molecular orbital of the double bond. The interesting conclusion from (c) is that in this ion the HOMO of the double bond has donated electron density into the vacant orbital on C7 forming a three-center, two-electron bond. Two n electrons may be cyclically delocalized, making the cation a bishomo (meaning expansion by two carbons) analogue of the aromatic cyclopropenyl cation [326], This delocalized bishomocyclopropenyl structure for 7-norbomenyl cations has been controversial, but is supported by NMR studies [327].

COC cyclic olefin copolymer amorphous copolymer of 2-norbomene and ethylene (Zeonor)... 

Amino acid-based norbomene random and block copolymers have been synthesized by Sanda, Masuda et al. [178]. The blocks were constructed with monomers containing either the ester or carboxyl amino acid forms, and C4 was used. While the random copolymers were partially soluble in acetone, the block copolymers were soluble through formation of reverse micelles (Scheme 24). Moreover, the diameter of these aggregates was around 100 nm as measured by DLS and AFM. Amino acid-based ROMP monomers with a different cyclic core, i.e., cyclobutenecarbonyl glycine methyl esters, were polymerized by Sampson et al., leading to head-to-tail-ordered polymers without stereocenters [179]. C6 was used and polydispersities between 1.2 and 1.6 were obtained. 

In asymmetric hydrocyanation reactions the desired isomers are the chiral branched products only. Good regioselectivity toward the branched product (>98%) is limited to vinylarenes. Hydrocyanation of 1,3-dienes gives a variety of mixtures depending on the catalyst and conditions 1-alkenes give the linear nitrile as major product [34]. Both are seen in the adiponitrile process in which the unwanted branched 2M3BN (hydrocyanation product from 1,3-butadiene) is isomerized to the linear product 3-pentenenitrile, which is then hydrocyanated by in-situ isomerization to 4-pentenenitrile, resulting in the linear adiponitrile. Thus vinylarenes and cyclic alkenes (mainly norbomene) are usually the substrates of choice for the asymmetric hydrocyanation. Hopefully 1,3-dienes will become feasible substrates in the near future. 

PiccineUi [5] used (tricyclopentylphosphine)dichloro(3-methyl-butenylidene), (VI), or related cyclic derivatives, (VII), to prepared anti-fog agents, (Vlll), by coupling 2-norbomene and aUyl-terminated ohgomeric ethylene oxide using ring opening metathesis polymerization as illustrated in (VIII) below. 

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