Olefins and Dienes

Organolithium reagents have been used to prepare random, block, and graft copolymers. Much work has been done on the copolymerization of diene and olefin monomers, especially 1,3-butadiene and styrene. In this review, we shall emphasize the copolymerization of these two monomers. 

When butadiene and styrene are mixed in the presence of an organolithium initiator, the resulting copolymerization process and product will be governed by the reaction conditions. The rate of copolymerization, the relative composition of the copolymer, and the distribution of monomer units (i.e., block, random, etc.) will be determined by such factors as solvent, temperature, and monomer feed ratio. 

As in the case of olefin or diene homopolymerization by RLi, copolymerization is particularly sensitive to solvent effects. Initial-charge (all monomers added together) copolymerization of butadiene and styrene tends to result in a tapered block copolymer (a block of butadiene with increasing levels of styrene, followed by a block of styrene) in hydrocarbon solvents and a random copolymer (a uniform distribution of butadiene and styrene) in polar media. 

In hydrocarbon solvents, butadiene is preferentially polymerized until 

Two explanations have been advanced for such copolymerization behavior in hydrocarbon solvents. Korotkov (67) suggested that selective complexation or solvation of the lithium chain ends by butadiene causes an increase in the concentration of butadiene about the growing chain ends. In turn, this monomer dominates the early phases of the copolymerization. Consistent with this notion are the high entropies of activation for this copolymerization noted by Morton (68). The work of Oliver and co-workers (64, 65) adds further suggestive support to the concept of preferential solvation. They observed the interaction between the lithium and the double bond of the model compound 3-butenyllithium by 7Li-NMR, UV, and IR spectroscopy. Similar observations were made by Glaze et al. (52) and Halasa el al. (37). 

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Intramolecular D-A rxn which form large rings are often favorable reactions with the diene and olefin portions act as if they were seperate molecules... 

Alternating isoprene-ethylene copolymers (IER) were prepared with the same catalyst. Due to the strictly alternating sequences of diene and olefin units and the absence of chiral carbon atoms IER shows strain-induced crystallization, but at lower temperatures compared to natural rubber. 

The copolymers consist of strictly alternating sequences of diene and olefin. C-NMR measurements Showed the microstructure of the butadiene units in BPR to be exclusively of the trans-1,4 configuration (Figure 8). The isoprene units in isoprene-ethylene copolymer (IER) contain 84 % trans-1,4, 15 % cis-1,4, and 1 % 3,4 structures (Figure 9). Spontaneous crystallization in unstretched BPR samples was detected by dilatometry and confirmed by X-ray diffraction and DSC measurements. The extrapolated equilibrium melting point is about -10 °C. 

This behavior is illustrated in Table I by the linear oligomerization of dienes, and the cooligomerization of dienes and olefins (examples 27-35). The H transfer may also lead to a cyclic structure (reaction 29, compared with examples 3, 5, and 6 in Table I). 

The term Diels-Alder reaction in a general sense refers to the reaction between a diene and a dienophile. Retro Diels-Alder reaction is a process that, under certain conditions, produces diene and olefin or a compound containing a C=C bond. The application of flash vacuum pyrolysis to effect the retro Diels-Alder reaction, as shown in Schemes 5-46 and 5-47, has become the standard procedure since the introduction of the method by Stork et al.74 in the 1970s. Therefore, alkenes that are difficult to access by conventional methods may be obtained via retro Diels-Alder reactions.75 In particular, this reaction allows the preparation of thermodynamically less stable compounds such as 4,5-dialkyl cyclopenta-2-en-one. In this case, the alkene functional group can be regarded as being protected by cyclopentadiene (as shown in 154 or 157), which, after subsequent reaction, can easily be removed through quick pyrolysis. 

Bicyclic derivatives. Polyhydroxylated carbo-bicyclic derivatives may be regarded as carbasugars with the rigid structure resulting from the presence of the additional carbocyclic ring. The most convenient way for construction of the bicyclic skeleton consists of the Diels-Alder reaction of properly functionalized trienes (intramolecular version) or dienes and olefins (intermolecular). 

Until recently, the hypothesis that the termination reaction of type II photooxygenation reactions occurs between the substrate and an excited light absorber-oxygen complex seemed to be well established. The typical products obtained from cyclic 1,3-dienes and olefins (see Fig. 1 and Sect. IV) could only be made by photochemical reactions. 

Anionic polymerization of conjugated dienes and olefins retains its lithium on the chain ends as being active moities and capable of propagating additional monomer. This distinguishing feature has an advantage over other methods of polymerization such as radical, cationic and Ziegler polymerization. Many attempts have been made to prepare block copolymers by the above methods, but they were not successful in preparing the clear characterized block copolymer produced by anionic technique. 

The formation of new bonds in file Diels-Alder reaction requires that file n electrons in file individual diene and olefin n systems become reorganized and shared in file new bonding pattern of the cyclic product. It follows that for this bonding change to occur, file two n systems must overlap so that electrons can move into new orbitals. The most straightforward way file needed orbital overlap can occur is for one n system to function as an electron donor and file other r system to function as an electron acceptor. Therefore file bonding changes in file Diels-Alder reaction result from a donor-acceptor interaction between the diene and olefin jt systems. 

This review is limited to the polymerization of hydrocaibon dienes and olefins by means of organolithium initiators. It is not intended to include activated olefins or dienes that can be polymerized by bases of far lower reactivity or that do not involve direct caibon-lithium bonding. 

This review will feature the kinetics and mechanism of RLi-initiated, homo- and copolymerization of hydrocarbon diene and olefin monomers, with and without polar ligands. Hydrocarbon olefin homopolymerization in nonpolar media will not be discussed per se because simple olefins such as ethylene do not polymerize under such conditions, and such reactive, hydrocarbon a-olefins as styrene behave similarly to dienes in... 

The products formed by the co-oligomerization of acrylic esters with butadiene (102,106) provide useful information concerning the nature and configuration of the intermediates involved. Naked-nickel, methyl acrylate, and butadiene do not react together.7 However, reaction does occur if the nickel-ligand system is used. The formation of the Diels-Alder adduct between the diene and olefin (a cyclohexene derivative) can be suppressed by adding the reactants dropwise to the catalyst (Table XVI footnote C). 

Functionalising of Low-Molecular, Oligomer Dienes and Olefins with S, O-Containing Compounds... 

As antiscuff, anti-wear properties of additives depend on the covalent-bonded sulfur contents, the selection of optimum conditions to effect sulfuring processes has been set with introducing the greatest amount possible of covalent sulfur. For this purpose functionalizing of diene and olefin hydrocarbons was conducted on a wide time-temperature mode. Considering that the temperature of boiling pipeiylene fraction low (42-44°C), sulfuring was carried out in a constantly temperature-controlled autoclave in the presence of the catalyst cobalt phthalocyanine [3], in the medium of non-polar solvents (for example, heptane). Under... 

The absolute stereochemical selectivities achieved in these reactions can be explained in terms of the nnf/-exo-transition-state models 16, 17, and 18, which are analogous to those previously proposed for the reaction of dienes and olefinic dienophiles (Fig. 8) [12,27d]. These transition-state models are based on three assumptions (i) the substituent in the chiral ligand blocks the same enantiofacial side of the carbonyl in the Diels-Alder reactions of acetylenic and olefinic aldehydes (ii) exo-transition structures predominate and (hi) anh-coordination of the bulky chiral Lewis acid to carbonyl is preferred in the transition state. 

Measurements of competitive hydrogenation of butadiene into butenes on palladium and platinum catalysts supported on silica [30] allowed the determination of the relative adsorption coefficients of dienes and olefins. 

Many transition metals catalyze oligomerization reactions between dienes and olefins or alkynes. Possible reaction products are legion. But it is almost exclusively with zerovalent nickel that cyclic products are formed. Addition of olefins or alkynes to catalysts mentioned in the previous section suppresses the cyclooligomerization and instead gives cyclo-co-oligomerization products. 

Cooligomerization of 1,3-dienes with an olefin on a Ni° template leads, depending upon the nature of the ligand, either to linear 1 1 products (1,4-hexadienes) or to cyclic 2 1 products (rran5,m-l,5-cyclodecadienes) (Scheme 5) [6, 31-33]. A wide variety of dienes and olefins have been studied the reaction appears to be limited to strained or monosubstituted olefins or to intramolecular reactions [49, 50] (eqs. (8)-(10)). 

In polymer production the water content in the starting monomer and in solvents is of great importance with respect to product quality. The proposed method was used to determine water in some diene and olefin monomers (isoprene, styrene, heptene, vinylcyclohexane, etc.), which are normally inert with respect to lithium aluminium hydride solutions. The method was also apphed to the determination of water in ethers and cyclic esters. 

As has been noted already in Section IV.B.3, Smart and Middleton103 generated bis(trifluoromethyl)sulfene (126) in solution by treating [(Me2N)3S + C(CF3)2S02F with silicon tetrafluoride or boron trifluoride. This sulfene adds to various dienes and olefins to give [4 + 2] and [2 + 2] adducts in moderate to good yields (equations 113-117). 

This leads us to propose a theoretically verified, refined catalytic cycle for production of linear and cycHc CiQ-olefin products (cf. Scheme 3). Furthermore, a detailed comparison of crucial mechanistic aspects of the catalytic reaction course for co-oligomerization of butadiene and ethylene and for cyclooligomerization of butadiene promoted by zerovalent bare nickel complexes was undertaken. These contribute (first) to a more detailed understan(fing of mechanistic aspects of the [Ni"]-mediated co-oHgomerization of 1,3-dienes and olefins and (second) to a deeper insight into the catalytic structure reactivity relationships in the transition-metal-assisted co-oHgomerization and oligomerization reactions of 1,3-dienes. 

Metal-containing polymers are also applied to the catalysis of other processes such as polymerization and copolymerization of butadiene and isoprene (see, e.g., ref. (64)), oopolymerization of diene and olefin monomers and polymerization conversions of acetylene-type monomers (65). Such investigations are likely to be oriented both theoretically and practically. Metallopolymers can be used as advantage in some other catalytic processes (54), among them hydrogenation of imsaturated carpounds, oxidative conversions of hydrocarbons, in hydroformylation, polycondensation and other processes, etc. (Table 4). Catalysis of almost all reactions obeys the same or similar principles as in the case of polymerization. The position of metallopolymers in catalysis and their links with traditional catalysts can be illustrated as follows ... 

Sheng, M. N. Zajacek, J. G. Hydroperoxide oxidations catalyzed by metals. III. Epoxidation of dienes and olefins with functional groups. J. Org. Chem., 1970, 35,1839. 

Ten-Membered Ring Formation from Dienes and Olefins or Acetylenes... 

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