Transition metal complexes oligomerization

Butadiene could be oligomerized to cyclic dienes and trienes using certain transition metal complexes. Commercially, a mixture of TiCU and Al2Cl3(C2H5)3 is used that gives predominantly cis, trans, trans-1,5,9-cyclododecatriene along with approximately 5% of the dimer 1,5-cyclooctadiene ... 

Investigations of silicon-metal systems are of fundamental interest, since stable coordination compounds with low valent silicon are still rare [64], and furthermore, silicon transition-metal complexes have a high potential for technical applications. For instance, coordination compounds of Ti, Zr, and Hf are effective catalysts for the polymerization of silanes to oligomeric chain-silanes. The mechanism of this polymerization reaction has not yet been fully elucidated, but silylene complexes as intermediates have been the subject of discussion. Polysilanes find wide use in important applications, e.g., as preceramics [65-67] or as photoresists [68-83],... 

Coordination-catalyzed ethylene oligomerization into n-a-olefins. The synthesis of homologous, even-numbered, linear a-olefins can also be performed by oligomerization of ethylene with the aid of homogeneous transition metal complex catalysts [26]. Such a soluble complex catalyst is formed by reaction of, say, a zero-valent nickel compound with a tertiary phosphine ligand. A typical Ni catalyst for the ethylene oligomerization is manufactured from cyclo-octadienyl nickel(O) and diphenylphosphinoacetic ester ... 

The catalytic cyclo-oligomerization of 1,3-butadiene mediated by transition-metal complexes is one of the key reactions in homogeneous catalysis.1 Several transition metal complexes and Ziegler-Natta catalyst systems have been established that actively catalyze the stereoselective cyclooligomerization of 1,3-dienes.2 Nickel complexes, in particular, have been demonstrated to be the most versatile catalysts.3... 

Dimerization, oligomerization, and similar reactions of olefins have been reported to be catalyzed by systems involving the majority of the Group VIII metals (3). The reasons for the particular interest in nickel-containing catalysts are their exceptionally high catalytic activity (catalytic reactions have been performed at temperatures as low as - 100°C), the diversity of catalytic reactions of obvious synthetic value, as well as the possibility to direct the course and control the selectivity of a catalytic reaction by tailoring the catalyst which are perhaps without parallel among transition metal complex catalysts. 

The catalytic transformation of olefins by transition metal complexes has received a great deal of attention during the past two decades. These catalytic reactions are important, especially industrially, because they represent some of the most economical ways to synthesize olefinic monomers or polymers. The more common types of these transformation reactions are (a) dimerization or polymerization of a-olefins (b) dimerization, oligomerization, cyclooligomerization, or polymerization of con-... 

These requirements have met using a mixed catalystic system consisting of an iron catalyst complex that can oligomerize ethylene and a zirconium transition metal complex that can copolymerize ethylene and the nonconjugated monomer 5-ethylidene-2-norbomene. Using this catalytic pair nonbrancy poly(ethylene-co5-ethylidene-2-norbomene) and poly (ethylene-col,4-hexadiene) were prepared. 

Another simple oligomerization is the dimerization of propylene. Because of the formation of a relatively less stable branched alkylaluminum intermediate, displacement reaction is more efficient than in the case of ethylene, resulting in almost exclusive formation of dimers. All possible C6 alkene isomers are formed with 2-methyl-1-pentene as the main product and only minor amounts of hexenes. Dimerization at lower temperature can be achieved with a number of transition-metal complexes, although selectivity to 2-methyl-1-pentene is lower. Nickel complexes, for example, when applied with aluminum alkyls and a Lewis acid (usually EtAlCl2), form catalysts that are active at slightly above room temperature. Selectivity can be affected by catalyst composition addition of phosphine ligands brings about an increase in the yield of 2,3-dimethylbutenes (mainly 2,3-dimethyl-1-butene). 

Schuchardt U, Dos Santos EN, Santos Dias F (1989) Butadiene oligomerization and telomerization catalyzed by transition metal complexes supported on organic polymers. J Mol Catal 55 340-352... 

Some unusual complexes that include pentadienyl or related ligands have been obtained from reactions of alkynes with various transition metal complexes. As the main thrust of this work is on oligomerization of alkynes and not toward the preparation and identification of pentadienyls, only a few key papers and results will be mentioned. 

Catalyzed oligomerization and co-oligomerization of conjugated dienes have been performed with a wide range of transition-metal complexes. Catalytic cyclodimerizations of conjugated dienes have also been performed selectively [27]. Thus, a catalytic amount of CpRuCl(diene) and Ag(0S02CF3) led to the formation of 1,5-cyclooctadiene, dimethylcyclooctadienes, and 6-methyl-... 

Compound 35 does not form above 30°C when an aromatic solvent is used instead, two alkynes are dimerized to give a titanacyclopentadiene having the structure of l,l-bis(r 5-cyclopentadienyl)-2,3,4,5-tetraphenylzirconole (36) (Fig. 15). It is an important intermediate in alkyne oligomerization reactions on transition metal complexes. 

The following section describes metal-assisted syntheses of rings and cages from phosphaalkynes. The phosphaalkyne may either become part of a well-defined transition-metal complex, or alternatively react with metal centers in a cocondensation process. Moreover, it is possible for phosphaalkynes to oligomerize or cooligomerize with other molecules in the coordination sphere of a metal complex. Detachment of the newly constructed ligands is not in all cases possible. 

Ionic liquids can be used as replacements for many volatile conventional solvents in chemical processes see Table A-14 in the Appendix. Because of their extraordinary properties, room temperature ionic liquids have already found application as solvents for many synthetic and catalytic reactions, for example nucleophilic substitution reactions [899], Diels-Alder cycloaddition reactions [900, 901], Friedel-Crafts alkylation and acylation reactions [902, 903], as well as palladium-catalyzed Heck vinylations of haloarenes [904]. They are also solvents of choice for homogeneous transition metal complex catalyzed hydrogenation, isomerization, and hydroformylation [905], as well as dimerization and oligomerization reactions of alkenes [906, 907]. The ions of liquid salts are often poorly coordinating, which prevents deactivation of the catalysts. 

Many of the complexes discussed in the previous sections are catalysts for alkyne oligomerization. In fact, alkyne dimerization and trimerization (see Cyclodimerization -tri-merization Reactions) at a cobalt center is recognized as one of the most synthetically useful catalytic reactions mediated by a homogeneous transition metal complex. The cobalt complexes most useful and extensively studied are CpCoL2, where L is CO, alkene, diene, or phosphine. The complex types... 

Recent Developments in Theoretical Organometallic Chemistry. 15, I Redistribution Equilibria of Organometallic Compounds, 6, 171 Redistribution Reactions of Transition Metal Organometallic Complexes, 23, 9S Redistribution Reactions on Silicon Catalyzed by Transition Metal Complexes, 19, 213 Remarkable Features of (7] -Conjugated Diene) zirconocene and -hafnocene Complexes, 24, I Selectivity Control in Nickel-Catalyzed Olefln Oligomerization, 17, lOS Silyl. Germyl, and Stannyl Derivatives of Azenes. N H Part I. Derivatives of Diazene, N,H2, 23, 131... 

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