Branched terminal dienes

The reactivity of 3-methyl-1-hexene was explored to determine the steric effect of the allylic methyl group. It was found that the olefin undergoes no reaction with [W]2 but undergoes nearly complete dimerization with [Mo]2 [56]. NMR studies revealed that the tungsten catalyst s lack of activity was due to the exclusive formation of the a,a -disubstituted tungstacyclobutane [8bj. 

Schrock s [Mo]2 catalyst gives quantitative conversion to the dimer of vinyl cyclohexane. This result was extended to the successful polymerization of 1,2-divinylcyclohexane to the corresponding ADMET polymer with an of 7.8 X 10 gmol , a PDI of 1.9, and with 88% cis content [56]. 

Courchay et al. [57] conducted a series of NMR spectroscopy experiments to better understand the effect of allylic methyl groups in CM. Under both ADMET and CM conditions, [Mo]2, [Ru]l, and [Ru]2 showed significantly reduced conversion with substrates containing an adylic methyl group. In the case of [Mo]2, an accumulation of the nonproductive metallacyclobutane was observed, while both Grubbs catalysts coordinated the substrate only to yield nonproductive metathe- 

A series of methyl-substituted polymers, with varying numbers of methylene units between the terminal olefin and the branch point [58], demonstrated that, when there are at least two methylene units separating the olefin and branch point, there is little effect on the catalysis of the reaction. A series of poly(l,4-alkylenephenylene)s have also been prepared by ADMET with Schrock s molybdenum, Grubbs first-generation, and classical catalysts [59]. This series demonstrated that hydrocarbon dienes containing aromatic groups are readily polymerizable by ADMET, even when there is only one methylene unit between the olefin and the aromatic group. 

Because ADMET polymerization of allylic-substituted dienes was not possible with Schrock s tungsten catalysts, and only somewhat successful with [Mo]2 and 

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Terminal dienes gave slightly different results. Both cyclic and linear enol silyl ethers were produced in the reaction of 1,5-hexadiene, whereas for 1,7-octadiene only the straight chain E and Z isomers were produced. In neither case is the branched product observed.106... 

Cyclization to form 6-membered rings competes more favorably with hydride shift. Linear hexadienes with terminal CFl2-groups (expected products of equation 18) are recovered in a yield of 0.6 pmol/A-s for the case = 3, while cyclohexene constitutes a yield of 0.35 pmol/A-s 1-methylcyclopentene 0.08 pmol/A-s and the other methylcyclopentenes 0.06 pmol/A-s. Products characteristic of free CeHn cations that rearrange to the most stable allylic structures—2,4-hexadienes and branched CeHio dienes—are recovered in a yield of 0.15 pmol/A-s. As in the n = 2 case, the products from cations produced in ion-neutral complexes greatly exceed those from free cations produced by simple bond fission, just as the 70 eV mass spectrum would predict. 

In ADMET, comonomers comprising terminal dienes with no branching or functionality within three methylene units of the double bond are assumed to have roughly equal reactivities. 

Unlike the case of the Ni-catalyzed reaction, which afforded the branched thioester (Eq. 7.1), the PdCl2(PPh3)3/SnCl2-catalyzed reaction with 1-alkyne and 1-alkene predominantly provided terminal thioester 6 in up to 61% yield in preference to 7. In 1983, a similar hydrothiocarboxylation of an alkene was also documented by using a Pd(OAc)2/P( -Pr)3 catalyst system with t-BuSH to form 8 in up to 79% yield (Eq. 7.6) [16]. It was mentioned in the patent that the Pt-complex also possessed catalyhc activity for the transformation, although the yield of product was unsatisfactory. In 1984, the hydrothiocarboxylation of a 1,3-diene catalyzed by Co2(CO)g in pyridine was also reported in a patent [17]. In 1986, Alper et al. reported that a similar transformation to the one shown in Eq. (7.3) can be realized under much milder reaction conditions in the presence of a 1,3-diene [18], and the carboxylic ester 10 was produced using an aqueous alcohol as solvent (Eq. 7.7) [19]. 

Raising the temperature of a radical chain reaction causes an increase in the overall rate of polymerization since the main effect is an increase in the rate of decomposition of the initiator and hence the number of primary radicals generated per unit time. At the same time the degree of polymerization falls since, according to Eq. 3.3, the rate of the termination reaction depends on the concentration of radicals (see Example 3-2). Higher temperatures also favor side reactions such as chain transfer and branching, and in the polymerization of dienes the reaction temperature can affect the relative proportions of the different types of CRUs in the chains. 

Ruthenium vinylidene intermediates have also been proposed in the mechanism of the coupling of unactivated alkenes with terminal alkynes to afford 1,3-dienes as a mixture of two isomers, linear and branched derivatives. The linear one was favored [56] (Eq. 42). The same system has allowed the ruthenium-catalyzed alkenylation of pyridine [57]. 

This process is generally applicable to cyclic and acyclic alkenes, and can be used to obtain branched, internal acyclic 1,3-dienes, 1,2-bismethylenecycloalkanes, and 3-meth-ylene-l-cycloalkenes, as well as terminal 1,3-dienes. ... 

The regioselectivity of the allylation depends on the presence of an adjacent free hydroxyl group the predominant formation of linear 1,4-dienes (awti-Markovnikov products) is achieved from propargylic alcohols whereas simple terminal alkynes wifh a protected hydroxyl group give fhe corresponding branched 1,4-dienes (Markovnikov products) (Tab. 8.9) [57c]. 

Alkenes such as norbomene and styrene, and also 1,3-dienes add alkynylsilanes, the latter at the terminal double bond to afford branched skipped enynes. Cyanoalkynes split and add to alkynes and allenes to generate conjugated enynes. ... 

Allenes and alkynes are regarded as impurities whose concentration cannot exceed certain minimum levels in monomer feed streams [112]. However, these same compounds, especially 1,2-butadiene, are also added as modifiers in alkyllithium-initiated diene polymerizations to prevent thermal branching at higher temperatures via chain termination and/or chain transfer reactions [3, 112-114]. Although these carbon acids can terminate chain growth, the ability of the resulting metalated chain transfer product to reinitiate chain growth has only been demonstrated for... 

Scandium and Ytrium A new a-alkylation of pyridines via C—H addition to terminal alkenes RCH=CH2, styrenes, and conjugated dienes has been attained, with cationic Sc and Y half-sandwich complexes as catalysts in conjunction with (QH5)3B. The method provides a straightforward access to alkylated pyridine derivatives, namely the branched a-PyCH(R)Me with Cp ScX2 as catalyst, and linear PyCH2CH2Ar using styrenes and Cp YX2. ... 

Shell employs the oligomerization process at their Geismar plant in Louisiana and Stanlow plant in England. This process is part of the Shell Higher Olefins Process (SHOP). The linear terminal olefins can then be used to produce detergent alcohols. The quality of the Shell olefins is shown in Table 6.2. The olefins are extremely low in aromatics, dienes, paraffins, internal olefins, and branched olefins. 

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