Alkyl metathesis

Despite the high selectivity of the reaction, the formation of by-products must be thoroughly monitored since severe specifications are usually imposed on the C4 raffinate (the C4 stream leaving the plant after the isobutene elimination) used later on as a feedstock to alkylation, metathesis or 1-butene extraction (where oxygenates act as poisons). 

Although this alkylation/metathesis approach is certainly quite flexible and reasonably short, a one-step route to RTILs would be ideal. (Scheme 3) Several different attempts to achieve this goal have been reported, including one-pot reactions (in which alkylation and metathesis are combined),i alkylations using species other than alkyl halides (such as alkyl sulfonates, eliminating the need for anion metathesis), Michael reactions with reactive Michael acceptors, and simple protonation using strong acids. ... 

Cyclic Polyolefins (GPO) and Gycloolefin Copolymers (GOG). Japanese and European companies are developing amorphous cycHc polyolefins as substrate materials for optical data storage (213—217). The materials are based on dicyclopentadiene and/or tetracyclododecene (10), where R = H, alkyl, or COOCH. Products are formed by Ziegler-Natta polymerization with addition of ethylene or propylene (11) or so-called metathesis polymerization and hydrogenation (12), (101,216). These products may stiU contain about 10% of the dicycHc stmcture (216). 

Tetrakis-Cp uranium complexes are readily prepared via metathesis of UCl and KCp in refluxing benzene. These complexes are a relatively rare example of a pseudotetrahedral complex with four Tj -Cp rings, (rj-ring) (25). The Cp derivative has been shown to react with CO and CO2 to give acyl and carboxylato complexes. This complex also reacts with alkyl haUdes to afford the U(IV) complex, Cp UX (X = halide). 

Other tri alkyl and triaryl compounds of the type R2SbY2, where Y is a pseudohaUde or a group such as NO, CIO, or S SO, have been prepared. They are usually obtained from the dihahdes by metathesis with a silver salt, eg ... 

In addition to the tri alkyl- and triaryldihaloarsoranes there are a number of compounds of the type R2ASY2, where Y is a pseudohalide, nitrate, carboxy, or other negative group. They are usually prepared from tri alkyl- or triaryldibromo- or dichloroarsoranes by metathesis. Thus dia2idotrimethyiarsorane [21121-84-6], C H AsN, has been prepared in the following manner (151) ... 

In addition to the applications reported in detail above, a number of other transition metal-catalyzed reactions in ionic liquids have been carried out with some success in recent years, illustrating the broad versatility of the methodology. Butadiene telomerization [34], olefin metathesis [110], carbonylation [111], allylic alkylation [112] and substitution [113], and Trost-Tsuji-coupling [114] are other examples of high value for synthetic chemists. 

The metathesis of alkyl- or aryl-substituted cycloalkenes provides a route to certain perfectly alternating copolymers. For example, metathesis of 5-methylcyclooctene leads to a polymer that may be considered as a... 

What can ADMET offer in terms of tailoring the properties of a given polymer The answer lies in the clean chemistry of metathesis. If a metathesis active a,co-diene can be synthesized, then a known polymer can be produced. Few other polymerization techniques are so versatile, yet so precise. In recent years, our group has focused attention toward modeling polymers and copolymers made from ethylene in particular, we have been examining the effect of precise placement of alkyl and polar branches sequentially along tire backbone of polyethylene. 

The synthesis, structures, and reactivity of neutral and cationic mono- and bis(guanidinato)zirconium(rV) complexes have been studied in detail. Either salt-metathesis using preformed lithium guanidinates or carbodiimide insertion of zirconium amides can be employed. Typical examples for these two main synthetic routes are illustrated in Schemes 73 and 74. Various cr-alkyl complexes and cationic species derived from these precursors have been prepared and structurally characterized. 

Negishi E, Tan Z (2005) Diastereoselective, Enantioselective, and Regioselective Carbo-alumination Reactions Catalyzed by Zirconocene Derivatives. 8 139-176 Netherton M, Fu GC (2005)Pa]ladium-catalyzed Cross-Coupling Reactions of Unactivated Alkyl Electrophiles with Organometallic Compounds. 14 85-108 Nicolaou KC, King NP, He Y (1998) Ring-Closing Metathesis in the Synthesis of EpothUones and Polyether Natmal Products. 1 73-104 Nishiyama H (2004) Cyclopropanation with Ruthenium Catalysts. 11 81-92 Noels A, Demonceau A, Delaude L (2004) Ruthenium Promoted Catalysed Radical Processes toward Fine Chemistry. 11 155-171... 

Group 14 metal halides also undergo metathesis reactions. For instance, organotin compounds are prepared on an industrial scale using organoaluminum reagents. These reactions take place because tin is a softer Lewis acid than aluminum, and carbon (in an alkyl group, represented by R) is a softer Lewis base than chlorine ... 

Two principle strategies have been employed for the synthesis of siloxide-containing molecular precursors. The first involves a silanolysis, or condensation, reaction of the Si - OH groups with a metal amido, alkyl, hahde, or alkoxide complex. The second method involves salt metathesis reactions of an alkali metal siloxide with a metal hahde. Much of our work has been focused on formation of tris(tert-butoxy)siloxide derivatives of the early transition metals and main group elements. The largely imexplored regions of the periodic table include the lanthanides and later transition metals. 

This catalytic reaction has been named alkane a-bond metathesis since alkyl fragments of alkane mixtures are exchanged. For example, propane is... 

In the course of studying a large nnmber of examples where the side chains of the imidazol- and imidazolidin-2-ylidene were altered, several research groups found that NHCs bearing exclnsively alkyl side chains did not provide catalysts with better characteristics when compared to SIMes- and DVIes-derived systems 14 and 15. While Herrmann and co-workers showed that an unsaturated NHC bearing cyclohexyl wing tips conld be incorporated into a second-generation catalyst that was active in metathesis [20-23], more recent studies showed that similar complexes were either very difficult to prepare or were unstable and showed dramatically decreased catalytic properties [24-26] (complexes 17-19, Fig. 3.4). 

---