Acetylene polymerization catalytic

FIGURE 3.7 Schematic representation of plausible mechanism for acetylene polymerization in the chiral nematic LC. The helical polyacetylene with counterclockwise (left-handed) screw direction blue arrow) grows up starting from catalytic species in the clockwise (right-handed) chiral nematic LC. 

Figure 2.7 Schematic representation of mechanism for acetylene polymerization in the N -LC. The H-PA with left-handed screw direction grows starting from the catalytic species in the right-handed N -LC.

There are many opportunities for modifying the catalytic system for acetylene polymerization, and the authors [38] found that one of the most effective methods is the introduction of long alkyl chains into alkyl aluminates and alkyl titanates as Ziegler catalysts, which suppressed the polymerization rate. PA was synthesized... 

Akagi, K., Sakamaki, K., and Shirakawa, H., Intrinsic nonsolvent polymerization method for synthesis of polyacetylene films, Synth. Med., 55, 779-784 (1993). Catellani, M., Destri, S., and Bolognesi, A., New catalytic systems for acetylene polymerization, MakromoL Chem., 187, 1345-1349 (1986). 

The removal of C4-acetylenes may be effected by catalytic gas-phase hydrogenation in a gas-particle operation by a process similar to that widely used for removing acetylene from ethylene streams. However, in view of the strong polymerization tendency of the C4-fractions, it is desirable in this case to work at the lowest possible temperature. 

The electronic properties of germanium have led to an interest in incorporating the element into extended polymeric chains due to the intrinsic properties of the polymers themselves or in their use as precursors for material synth-esis. Catalytic co-polymerization of the germylene Ge[N(SiMe3)2]2 with various substituted acetylenes leads to... 

When alkynes are treated with catalytic amounts of a carbene complex, polymerization instead of metathesis can occur (Figure 3.44) [565,595,597,752-754]. The use of carbene complexes to catalyze alkyne polymerization enables much better control of the reaction than with heterogeneous or multi-component catalysts. Pure acetylene oligomers (n = 3-9) with terminal fcrf-butyl groups have been prepared with the aid of a tungsten carbene complex [755]. 

Week et al. [65] further reported the Co salen complex supported on norbomene polymers (23, 24) with stable phenylene-acetylene linker (Figure 8). The polymer-supported salen catalysts were investigated for HKR of the racemic terminal epoxides that showed outstanding catalytic activities and comparable selectivities to the original catalysts reported by Jacobsen. However, the polymeric catalyst was recycled only once after its precipitation with diethylether as the catalyst became less soluble and less reactive in subsequent catalytic... 

In the metal carbonyl catalysts, the use of a catalytic amount of Ph2CCl2 enables the omission of CGI4. For example, the polymerization of phenylacetylene with W(CO)6 in the presence of Ph2GGl2 in toluene upon photoirradiation proceeds homogeneously to give a polymer with of ca. 2 x 127,128 MW polymers > 10 ) are attainable from sterically bulky aromatic and aliphatic acetylenes. It is also effective to use a catalytic amount of Lewis acids instead of GGI4 in the M(GO)6-based catalysts (M = W, Mo). ... 

Of greater relevance catalytically is that the combined use of l3C enrichment and 13C nutation NMR spectroscopy can distinguish between proposed rival mechanisms for the Ziegler-Natta catalyzed polymerization of acetylene. In the four-center insertion mechanism the enriched acetylene (HC =C H) is incorporated as shown in Scheme 6. It is to be noted that the, 3C—13C bond label is here incorporated into a carbon-carbon double bond, the length of which is significantly smaller than that of a carbon-carbon single bond, which is how the enriched acetylene would be incorporated in the two-center mechanism shown in Scheme 7. The results of nutation experiments leave little doubt that the Ziegler-Natta polymerization of acetylene proceeds by a four-center mechanism. 

The first instance involves the Pt(II) fragment "TpPdMe," used not as a catalyst, but rather as a protecting function for alkynes during catalytic, and indeed stoichiometric, processes, a role that followed from the noted stability of TpPtMe(r 2-RC=CR) complexes, and their capacity to release the alkyne by carbonylation.56 63 Thus, ji-complexes with a series of bis (amide)acetylenes (144-149, Scheme 12, Section III.B.l), formed from the polymeric TpPtMe (126), could be subjected to conditions of catalytic hydrogenation, or basic hydrolysis of the pendant functions, without... 

The hydrides 44b have been found to polymerize ethylene and react with a variety of protic reagents such as terminal alkynes and nitriles. Catalytic effects in the hydroboration of olefins have also been observed [27]. A well-defined /i-ethynyl complex of yttrium is formed by protolysis of the alkyl derivative 38b with acetylene (Eq. 18). Figure 14 shows the dimeric structure of 45b with bridging ethynyl ligands [27, 65]. 

Conversion of an j2-acetylene complex to the hydridoalkynyl complex will lead to linear oligomerization or polymerization. The tendency of some Ilh or Pd complexes to form hydridooalkynyl complexes explains their catalytic activity toward linear oligomerization. Recently, Hagihara et al. 115) examined the reaction of preformed hydrido-alkynyl complexes, MH(insertion into the M—H bond. 

Catalytic conversions were experimentally studied in Russia toward the end of the nineteenth century, and especially in the twentieth century, and regularities were empirically established in a number of cases. The work of A. M. Butlerov (1878) on polymerization of olefins with sulfuric acid and boron trifluoride, hydration of acetylene to acetaldehyde over mercury salts by M. G. Kucherov (1881) and a number of catalytic reactions described by V. N. Ipatieff beginning with the turn of the century (139b) are widely known examples. S. V. Lebedev studied hydrogenation of olefins and polymerization of diolefins during the period 1908-13. Soon after World War I he developed a process for the conversion of ethanol to butadiene which is commercially used in Russia. This process has been cited as the first example of commercial application of a double catalyst. Lebedev also developed a method for the polymerization of butadiene to synthetic rubber over sodium as a catalyst. Other Russian chemists (I. A. Kondakov I. Ostromyslenskif) were previously or simultaneously active in rubber synthesis. Lebedev s students are now continuing research on catalytic formation of dienes. 

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