Butadiene, catalyzed reactions polymerization

Reaction between oxygen and butadiene in the liquid phase produces polymeric peroxides that can be explosive and shock-sensitive when concentrated. Ir(I) and Rh(I) complexes have been shown to catalyze this polymerization at 55°C (92). These peroxides, which are formed via 1,2- and 1,4-addition, can be hydrogenated to produce the corresponding 1,2- or 1,4-butanediol [110-63-4] (93). Butadiene can also react with singlet oxygen in a Diels-Alder type reaction to produce a cyclic peroxide that can be hydrogenated to 1,4-butanediol. 

Many solvents form dangerous levels of peroxides during storage e.g., dipropyl ether, divinylacetylene, vinylidene chloride, potassium amide, sodium amide. Other compounds form peroxides in storage but concentration is required to reach dangerous levels e.g., diethyl ether, ethyl vinyl ether, tetrahydrofuran, p-dioxane, l,l-diethox) eth-ane, ethylene glycol dimethyl ether, propyne, butadiene, dicyclopentadiene, cyclohexene, tetrahydronaphthalenes, deca-hydrona-phthalenes. Some monomeric materials can form peroxides that catalyze hazardous polymerization reactions e.g., acr) lic acid, acr)Ionitrile, butadiene, 2-chlorobutadiene, chlorotrifluoroethylene, methyl methacrylate, styrene, tetrafluoroethylene,... 

It was discovered that the addition of 1,3-cyclohexadiene to the Rh -catalyzed reactions increased the rate of butadiene polymerization by a factor of over 20 [20]. Considering the reducing properties of 1,3-cyclohexadiene, this effect could be due to the reduction of Rh to Rh and stabilization of this low oxidation state by the diene ligands. With neat 1,3-cyclohexadiene, Rh is reduced to the metallic state. These emulsion polymerizations are sensitive to the presence of Lewis basic functional groups. A stoichiometric amount of amine (based on Rh) is sufficient to inhibit polymerization completely. It was also discovered that styrene could be polymerized using the Rh catalyst. However, the atactic nature of the polymer, along with the kinetic behavior of the reaction, indicated that a free-radical process, rather than a coordination-insertion mechanism, was operative. 

Computational studies have been carried out to map the reaction mechanisms involved in the polymerization of butadiene catalyzed by complexes of the type NiCp( -phenyl)( 7 -butadiene). This study has probed the crucial steps of insertion, allylic isomerization, and if (a) — rearrangement. Variable-energy photoelectron spectroscopy... 

Addition of butadiene to ethene polymerizations gives cross-linked material, but dienes are themselves important substrates for polymerization reactions. Natural rubber is an all-ds polymer of isoprene (Figure 21.10), which we encountered in Chapter 11, as an important precursor of the terpenes. Synthetic rubber made by radical polymerization is a mixture of cis- and trans-polyisoprene, (21.10). The material produced by metal-catalyzed polymerization is, however, all-ds and essentially identical to natural rubber. 

Copper-catalyzed monoaddition of hydrogen cyanide to conjugated alkenes proceeded very conveniently with 1,3-butadiene, but not with its methyl-substituted derivatives. The most efficient catalytic system consisted of cupric bromide associated to trichloroacetic acid, in acetonitrile at 79 °C. Under these conditions, 1,3-butadiene was converted mainly to (Z )-l-cyano-2-butene, in 68% yield. A few percents of (Z)-l-cyano-2-butene and 3-cyano-1-butene (3% and 4%, respectively) were also observed. Polymerization of the olefinic products was almost absent. The very high regioselectivity in favor of 1,4-addition of hydrogen cyanide contrasted markedly with the very low regioselectivity of acetic acid addition (vide supra). Methyl substituents on 1,3-butadiene decreased significantly the efficiency of the reaction. With isoprene and piperylene, the mononitrile yields were reduced... 

Dupont and co-workers studied the Pd-catalyzed dimerization [108] and cyclodimerization [109] of butadiene in non-chloroaluminate ionic liquids. The biphasic dimerization of butadiene is an attractive research goal since the products formed, 1,3,5-octatriene and 1,3,6-octatriene, are sensitive towards undesired polymerization, so that separation by distillation is usually not possible. These octa-trienes are of some commercial relevance as intermediates for the synthesis of fragrances, plasticizers, and adhesives. Through the use of PdCl2 with two equivalents of the ligand PPhj dissolved in [BMIM][Pp6], [BMIM][Bp4], or [BMIM][CF3S03], it was possible to obtain the octatrienes with 100 % selectivity (after 13 % conversion) (Scheme 5.2-23) [108]. The turnover frequency (TOP) was in the range of 50 mol butadiene converted per mol catalyst per hour, which represents a substantial increase in catalyst activity in comparison to the same reaction under otherwise identical conditions (70 °C, 3 h, butadiene/Pd = 1250) in THF (TOP = 6 h ). 

Butadiene) Group 4 metal complexes and (allyl) complex systems derived thereof have also been suggested as reactive intermediates at various homogeneous Group 4 metal complex-catalyzed conjugated diene polymerization reactions.151... 

Heterogcnized complexes have been used to catalyze a great number of reactions, such as hydrogenation [18], hydroformylation [19], ethylene oligomerization [20], hydrosilylation [21, 22], polymerization [23], telo-merization [24], oxidation [25], oligomerization of monoalkenc [26], methanol carbonylation [27], butadiene oligomerization [28], synthesis gas chemistry [29], and isomerization [30],... 

Metallo-ene reactions involving the transfer of palladium and nickel have been described since the early 1960s, mostly in cormection with their crucid role in the Pd- and Ni-catalyzed polymerization of butadiene." Hence, insertions of 1,3-dienes into allylpalladium compounds were extensively studied. Thus preformed allylic complexes (49) underwent the metallo-ene reactions (49) —> (51) at 20 C (20 h) or 35 °C (<5 min) or 70 °C 0 h) the reaction rate depended on the substituents R and as well as on the ligand L and decreased in the order R = Cl > H > Me R = H > Me L = Feacac > acac > Cl. Further diene insertion into the resulting allylpalladium product (51) (polymerization) was generally slower than the initial step (49) —> (51) and again relies on the nature of the ligand L (Scheme 11). ... 

The strong Lewis acids HC(py)3M (NO)2 (M = Mo, W) (see also Section 14.3.1), with Lewis acidities comparable with that of BF3, were shown by Faller et al. to coordinate and activate a,/8-unsaturated carbonyl compounds via formation of an M-O a-bond. These complexes, in nitromethane, catalyze Diels-Alder reactions with dienes (e.g. butadiene). They also readily polymerize butadiene when a less basic dienophile com-... 

---