Isoprene catalyst activity

Polymerization Aliphatic, aromatic and oxygenated monomers Vinyl chloride Isoprene Acrylonitrile Catalyst activation... 

The catalyst activity is so high that uranium concentration lower than 0.1 millimoles per liter allows a complete conversion of butadiene to be obtained in a few hours, at 20°C, The transfer reaction of uranium based catalyst is similar to that of conventional 3d-block elements (titanium, cobalt, nickel) so that the molecular weight of the polymer is affected by polymerization temperature, polymerization time and monomer concentration in the customary way. This is in contrast, as we shall see later on, to some catalysts based on 4 f-block elements. Uranium based catalysts are able to polymerize isoprene and other dienes to high cis polymers the cis content of polyisoprene is 94%, somewhat inferior to titanium based catalysts. In contrast, with 3d-block elements an "all cis", random butadiene-isoprene... 

The catalytic activities of Nb and Ta complexes Cp M() -diene)Cl2 (M = Nb, Ta diene = 1,3-butadiene, isoprene, 2,3-dimethyl-l,3-butadiene) activated by MAO have been compared. They both give polyethylene with very narrow polydispersities at low temperature (Mw/M as low as 1.05). The Nb complexes are superior to the Ta complexes in terms of the catalyst activity and the polydispersity. Cp Ta(o-xylylene)Cl2/MAO is twice as catalytically active and the molecular weight distribution of the polyethylene is much narrower than that using Cp M( -l,3-butadiene)Cl2/MAO as catalysts. ... 

The counterion in these complexes plays a significant role for both catalyst activity and reaction enantioselectivity (eq 5). The hexafluoroantimonate-derived complex is 20 times more reactive in the Diels-Alder reaction than its triflate counterpart. This discovery resulted in a significantly broader scope (e.g. 1,3-cyclohexadiene, furan, isoprene and many other dienes can also be used successfully) of the reaction. The crystalline aquo com-... 

In this paper we have investigated the performance of zeolites Y, EMT, beta and ZSM-5 for the reaction of isoprene (1) with methylvinylketone (2) to 4-acetyl-1-methyl-1-cyclohexene (3) and 4-acetyl-2-methyl-1-cyclohexene (4) shown in fig. 1. Furthermore, we used a silica binder in order to avoid experimental problems which arise when zeolite powder is taken as catalyst. In some cases binders have a significant influence on the catalyst activity and selectivity sometimes the activity can be enhanced, e.g., by additional active sites on the binder surface. Again, a loss of selectivity can be observed, if the spatial restrictions inside the zeolite framework, which are often required for selectivity, are not present on the binder surface. The nature of the binder and its effect on catalyst performance were also a subject of this study. 

A great number of catalysts active in dimerization of isoprene is known. Ziegler-type catalysts prepared by an aluminum compound and a titanium-, cobalt-, zirkonium-, iron- or vanadium compound yield, besides cyclic products [85—87], mostly the linear tail-to-head dimer 2,6-dimethyl-l,3,6-octatriene [88—95]. Only in a few cases, is the tail-to-tail product 2,7-dimethyl-1,3,6-octatriene also formed [86]. Using nickel catalysts, the tail-to-tail dimer 2,7-dimethyl-1,3,7-octatriene is generally the main product [96—98], but also the head-to-tail dimer allocymene can be obtained [99]. 

Lv K, Cui D. CCC-Pincerbis(carbene) lanthanide dibromides. Catalysts on highly cis-1,4-selective polymerization of isoprene and active species. Organometallics. 

A series of complexes 46 was investigated for the polymerization of isoprene after activation of pre-catalysts with AlRj (R = Et, Me, i-Bu) and... 

A mixture of PdBrj/PhONa/PhOH can also be used to generate the required Pd(0) catalyst. The presence of phenol greatly improves catalyst activity and selectivity, favoring the formation of the 1,4-addition product. The reaction could be extended to isoprene, 1,3-pentadiene and 2,4-hexadiene to afford mixtures of 1,2- and 1,4-addition products, albeit in lower yields. In all these reactions, some high-boiling products are also formed [173]. Similar results have been obtained in the hydroamination of isoprene with Et2NH catalyzed by Pdfacaclj/dppe/BFj.OEtj [174]. 

The reaction of dihalocarbenes with isoprene yields exclusively the 1,2- (or 3,4-) addition product, eg, dichlorocarbene CI2C and isoprene react to give l,l-dichloro-2-methyl-2-vinylcyclopropane (63). The evidence for the presence of any 1,4 or much 3,4 addition is inconclusive (64). The cycloaddition reaction of l,l-dichloro-2,2-difluoroethylene to isoprene yields 1,2- and 3,4-cycloaddition products in a ratio of 5.4 1 (65). The main product is l,l-dichloro-2,2-difluoro-3-isopropenylcyclobutane, and the side product is l,l-dichloro-2,2-difluoro-3-methyl-3-vinylcyclobutane. When the dichlorocarbene is generated from CHCl plus aqueous base with a tertiary amine as a phase-transfer catalyst, the addition has a high selectivity that increases (for a series of diolefins) with a decrease in activity (66) (see Catalysis, phase-TRANSFEr). For isoprene, both mono-(l,2-) and diadducts (1,2- and 3,4-) could be obtained in various ratios depending on which amine is used. 

Another group of isoprene polymerization catalysts is based on alanes and TiCl. In place of alkyl aluminum, derivatives of AlH (alanes) are used and react with TiCl to produce an active catalyst for the polymerization of isoprene. These systems are unique because no organometaHic compound is involved in producing the active species from TiCl. The substituted alanes are generally complexed with donor molecules of the Lewis base type, and they are Hquids or soHds that are soluble in aromatic solvents. The performance of catalysts prepared from AlHCl20(C2H )2 with TiCl has been reported (101). 

Another chiral titanium reagent, 11, was developed by Corey et al. [17] (Scheme 1.24). The catalyst was prepared from chiral ris-N-sulfonyl-2-amino-l-indanol and titanium tetraisopropoxide with removal of 2-propanol, followed by treatment with one equivalent of SiCl4, to give the catalytically-active yellow solid. This catalyst is thought not to be a simple monomer, but rather an aggregated species, as suggested by NMR study. Catalyst 11 promotes the Diels-Alder reaction of a-bro-moacrolein with cyclopentadiene or isoprene. 

Supported Lewis acids are an interesting class of catalysts because of their operational simplicity, filterability and reusability. The polymer-bound iron Lewis-acid 53 (Figure 3.8) has been found [52] to be active in the cycloadditions of a, S-unsaturated aldehydes with several dienes. It has been prepared from (ri -vinylcyclopentadienyl)dicarbonylmethyliron which was copolymerized with divinylbenzene and then treated with trimethylsilyltriflate followed by THF. Some results of the Diels-Alder reactions of acrolein and crotonaldehyde with isoprene (2) and 2,3-dimethylbutadiene (4) are summarized in Equation 3.13. 

Figure 3.40 Experimental results for isoprene conversion in metallic and ceramic micro reactors. The metallic micro reactors were operated without catalyst to determine blank activity of the various construction materials. In addition, conversion data were calculated. (0) Calculated values for micro-channel reactor model (full symbols) experimental values for different reactor materials [27].

There has also been some interest in NHC-lanthanide complexes as polymerisation catalysts. Indenyl and fluorenyl functionalised NHC complexes of structures 14 and 15 (Fig. 4.5) were evaluated for isoprene polymerisation following activation... 

Conjugated dienes are among the most significant building blocks both in laboratories and in the chemical industry [1], Especially, 1,3-butadiene and isoprene are key feedstocks for the manufacture of polymers and fine chemicals. Since the discovery of the Ziegler-Natta catalyst for the polymerizations of ethylene and propylene, the powerful features of transition metal catalysis has been widely recognized, and studies in this field have been pursued very actively [2-7]. 

This gives rise to dual valency state (+3 and +4) (23). As to the activity of lanthanide based catalysts we confirm a singular behavior that has been already reported by Chinese scientists (22) and that is summarized in Fig. 9. The activity of lanthanides in promoting the polymerization of butadiene and isoprene shows a large maximum centered on neodymium, the only exception being represented by samarium and europium that are not active, reasonably because they are reduced to bivalent state by aluminum alkyls, as pointed out by Tse-chuan and associates (22). 

The dimerization of isoprene was carried out by a catalyst system of PdBr2/bis(diphenylphosphino)-1,2-ethane (39) sodium phenoxide at 150°C for I hour in benzene (85). Catalytic activity was enhanced by the addition... 

The activity of Ziegler-type systems such as M(acac) -AlEt3 (M = Cr, Mn, Fe, Co, or Ni acac = acetylacetonate) was examined with 1-olefins and triethyl- or triethoxysilanes (55). Systems with nickel or cobalt showed low activity for hydrosilation but isomerized the olefin and were reduced to the metal. The study was extended to dienes and acetylenes (56). Isoprene gave the same products with these catalysts as are made with chloroplatinic acid. Penta-1,3-diene with Pt gave l-methylbut-2-en-ylsilanes. The Ziegler catalysts gave mainly penta-2-enylsilanes... 

The hydrosilation of butadiene, isoprene and other simple conjugated dienes with platinum catalysts has not been intensively studied. It usually occurs by 1,4 addition and only at elevated temperatures (10). Although palladium catalysts are practically ineffective to hydrosilate an alkene, they are very active under mild conditions with conjugated dienes to give two principal products, sometimes in 100% yields. With triethoxy silane, butadiene, and PdCl2(PhC=N)2 (5.5 x 103 moles/mole) at 22°C for 24... 

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