Transition metal catalysts, butadiene

Coupling of butadiene with CO2 under electrochemically reducing conditions produces decadienedioic acid, and pentenoic acid, as weU as hexenedioic acid (192). A review article on diene telomerization reactions catalyzed by transition metal catalysts has been pubUshed (193). 

Between the 1920s when the initial commercial development of mbbery elastomers based on 1,3-dienes began (5—7), and 1955 when transition metal catalysts were fkst used to prepare synthetic polyisoprene, researchers in the U.S. and Europe developed emulsion polybutadiene and styrene—butadiene copolymers as substitutes for natural mbber. However, the tire properties of these polymers were inferior to natural mbber compounds. In seeking to improve the synthetic material properties, research was conducted in many laboratories worldwide, especially in the U.S. under the Rubber Reserve Program. 

This paper is concerned with some of our experiments in this field. Our purpose was to obtain polymers with extremely high stereoregularity. In the first part we will report on the homopolymerization of butadiene with f-transition metal catalysts. 

Polybutadiene and polyisoprene are produced and used mainly as synthetic rubber on an industrial scale by using transition metal catalysts, especially titanium- and nickel-based ones. By contrast, only minor attention has been paid to the palladium-catalyzed polymerization of butadiene. A mixture of 1,2-polybutadiene and trans- and c/s-l, 4-polybutadiene was obtained by using PdCl2 as a catalyst (7, 2). 

Typical Isomer Distributions in 1 1 Codimerization of Ethylene and Butadiene by Various Transition Metal Catalysts... 

More synthetic interest is generated by the potentially very useful hydration of dienes. As shown on Scheme 9.6, methylethylketone (MEK) can be produced from the relatively cheap and easily available 1,3-butadiene with combined catalysis by an acid and a transition metal catalyst. Ruthenium complexes of several N-N chelating Hgands (mostly of the phenanthroline and bipyridine type) were found active for this transformation in the presence of Bronsted acids with weakly coordinating anions, typically p-toluenesulfonic acid, TsOH [18,19]. In favourable cases 90 % yield of MEK, based on butadiene, could be obtained. 

As discussed in connection with olefin-coupling reactions and shown in Fig. 4, the coupling of vinyl Grignard reagents is stereospecific and dependent upon the transition metal catalyst used (32, 33). The dimerization of ethylene, shown in Fig. 6, was also shown to produce primarily the terminal olefin 1-butene (35). The size of the metal has also been shown to influence the course of the catalyzed oligomerization reactions of butadiene. When bis-(ir-allyl) metal complexes are used as... 

Several cyclic oligomers 1-5 are prepared from butadiene using transition metal catalysts. The preparation of 1,5-cyclooctadiene (3 1,5-COD) by a catalyst prepared from Ni(CO)4 and phosphine is the first report on cyclooligomerzation of butadiene [1], However, the activity of this catalyst is low due to strong coordination of CO. Catalyst prepared from TiCU and EtjAl has higher catalytic activity for the formation of 1,5-COD and 1,5,9-cyclododecatriene (1,5,9-CDT 4). Also Ni(0) catalysts are active for the preparation of COD and CDT. In addition to COD and CDT, the cyclic... 

Transition Metal Catalyst Systems for Polymerizing Butadiene and Isoprene... 

Kohnlc and his co-workers reported the influence of CO2 on the catalytic properties of transition metal catalysts in the dimerization of butadiene. In the presence of (PPhj). in an atmosphere of argon, the Diels-Alder product 4-vinyM-cyclohexenc 1 formed in yields up to 97% with small amounts of 1, 3, 7-octatricne as a by-product. When argon is replaced by COj, only trans-1.3, 7-octatriene is obtained. The authors do not discuss the mechanism of the action of CO2 but they suggest that unstable CO3 complexes are formed during the reaction 297, 298], Attempts to isolate such complexes were, however, unsuccessful. 

This process (hetero Diels-Alder reaction leading to a dihydropyran system) may be also conducted in an asymmetric version application of chiral transition-metal catalysts based on BINOL, BDMAP, bisoxazolines, etc. provides adducts in very high optical purity (ee up to 99%) [1,6], In a series of papers Jurczak reported recently a highly enantioselective cycloaddition of 1-methoxy-1,3-butadiene and butyl glyoxylate catalyzed with chiral salen complexes [21],... 

The f-transition metal catalysts were first described by von Dohlen [98] in 1963, Tse-chuan [99] in 1964 and later by Throckmorton [100]. In the 1980s Bayer [14] and Enichem [101] developed manufacturing processes based on neodymium catalysts. The catalyst system consists of three components [102] a carboxylate of a rare earth metal, an alkylaluminum and a Lewis acid containing a halide. A typical catalyst system is of the form neodymium(III) neodecanoate/diisobutylaluminum hydride/butyl chloride [103]. Neodymium(III) neodecanoate has the advantage of very high solubility in the nonpolar solvents used for polymerization. The molar ratio Al/Nd/Cl = 20 1 3. Per 100 g of butadiene, 0.13 mmol neodymium(III) neodecanoate is used. With respect to the monomer concentration, the kinetics are those of a first-order reaction. 

Polymerization of cis, cis-1,4-dideuterio-l, 3-butadiene by several transition metal catalysts has been studied. The existence of non-stereo-specific bond forming events is postulated to signal the involvement of allyl isomerization in the polymerization mechanism. Trans-1,4-polymers are accompanied by complete scrambling of deuterium stereochemistry, contrasting with a more specific process to form cis polymers. Allyl isomerization is thus implicated as a key event in the formation of trans, but not cis, polymer. 

Unless otherwise noted, the following general procedure was used to effect pol)anerization of butadiene with transition metal catalysts. 

The addition of HCN to C=C double bonds can be effected in low yields to produce Markovnikov addition products. However, through the use of transition metal catalysts, the selective anti-Markovnikov addition of HCN to alkenes can take place. The most prominent example of the use of aqueous media for transition metal-catalyzed alkene hydrocyanation chemistry is the three-step synthesis of adi-ponitrile from butadiene and HCN (Eqs. 5-7). First discovered by Drinkard at DuPont [14], this nickel-catalyzed chemistry can use a wide variety of phosphorus ligands [15] and is practiced commercially in nonaqueous media by both DuPont and Butachimie, A DuPont/Rhone-Poulenc joint venture. Since the initial reports of Drinkard, first Kuntz [16] and, more recently, Huser and Perron [17, 18] from Rhone-Poulenc have explored the use of water-soluble ligands for this process to facilitate catalyst recovery and recycle from these high-boiling organic products. 

Most unsaturated substances such as alkenes, alkynes, aldehydes, acrylonitrile, epoxides, isocyanates, etc., can be converted into polymeric materials of some sort—either very high polymers, or low-molecular-weight polymers, or oligomers such as linear or cyclic dimers, trimers, etc. In addition, copolymerization of several components, e.g., styrene-butadiene-dicyclo-pentadiene, is very important in the synthesis of rubbers. Not all such polymerizations, of course, require transition-metal catalysts and we consider here only a few examples that do. The most important is Ziegler-Natta polymerization of ethylene and propene. 

Dienes such as butadiene and isoprene are important feedstock for production of polymer materials as well as low molecular weight compounds. Of particular synthetic importance is manufacturing synthetic rubbers using transition metal catalysts. Diene polymers can be prepared by successive insertions of dienes into transition metal alkyls or metal hydrides. 

It is well known that oxiranes react with carbon dioxides yielding organic carbonates. Several transition metal catalysts permit very mild conditions and give high yields and selectivities in this reaction [63-65], but palladium catalysts proved to be particularly effective [66]. The question arose which reaction occurs when both butadiene and an oxirane are possible reaction partners of CO2. 

Organosilicon compounds are largely produced by the hydrosilylation of unsaturated organic substrates [47]. Various transition metal catalysts have been used to obtain alkyl-SiR products from the reaction of H-SiRj with an alkene. Alkene insertion into an M-Si bond is recognized as a fairly common process which plays a key role in catalytic hydrosilylation processes. The reaction of 1,3-butadiene (3-6) with triethylsilane in the presence of [Cr(CO)g] under photochemical condition yields exclusively the ds-1,4-adduct, ds-l-(triethylsilyl)-2-butene (7) (Scheme 10.7) [48]. In all cases, 1-4 addition products form in major, however, in some cases 1-2 addition product (9) also forms in minor yield. Formation of product 12 can be rationalized in terms of double bond migration subsequent to the initial hydrosilylation (Scheme 10.7). 

Polybutadiene (transition metal catalyst) Polyisoprene (transition metal catalyst) Polybutadiene and styrene butadiene rubber —alkyl-lithium initiation... 

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