Metathetical displacement

The postulated steps that constitute the Suzuki coupling process are shown in Scheme 25. After oxidative addition of the organic halide to the palladium(o) catalyst, it is presumed that a metathetical displacement of the halide substituent in the palladium(ii) complex A by ethoxide ion (or hydroxide ion) takes place to give an alkoxo-palladium(ff) complex B. The latter complex then reacts with the alkenylborane, generating the diorganopalladium complex C. Finally, reductive elimination of C furnishes the cross-coupling product (D) and regenerates the palladium(o) catalyst. 

Gallium trichloride is a solid (mp 78-79°) which reacts with air. It is soluble in both hydrocarbons and ether-type solvents. Both the solid compound and its solutions can be stored in a waterfree environment for relatively long periods. Gallium trichloride undergoes typical metathetical displacement of one, two, or all three chlorine atoms in reactions with one, two, or three molar equivalents of an alkyllithium compound, respectively 4... 

The proposed mechanism of the catalytic reaction involves the formation of the Cu(l) alkoxide 68 by displacement of either the chloride or the NHC from 65-67, followed by conversion to the hydride 69 by metathetical exchange of the tert-butoxide by the H of the silane (Fig. 2.10). 

However, although either chlorine or bromine can displace carbon monoxide from the five-coordinate rhodium(I) cation [Rh(CO) (Me2P)2C2H4 2]+, chlorine forms the cis isomer, whilst bromine forms the trans isomer (equations 235 and 236). Similar complexes can be prepared by metathetical reactions involving the ionic halide (equation 237).229... 

Many industrial processes are driven forward by separation of at least one of the reaction products. For many of the reactions in aqueous solutit ns one of the products has low solubility in the reaction medium. Its precipitation or evaporation pushes the reaction forward. If, on the other hand, all the products are soluble, an equilibrium is reached and a means of separation has to be applied to recover the product and to recycle the reagents (shift the equilibrium). The economics of such processes is strongly affected by the concentration of the product at equilibrium, which determines the load on the separation and the cost of concentrating the separated product. This could be the case in many processes such as acid production through displacement from its salts production of water-soluble salts, e.g., fertilizers, through metathetic ( double decomposition ) reactions and product-inhibited fermentation,... 

The 1 1 complex derived from phenyltungsten trichloride and aluminium trichloride is an effective catalyst for diene-cyclobutane metathetical interconversions. Thus, the tetracyclic compounds (291) and (292) were respectively isomerized to the dienes (293) and (294). Rather more surprising was the virtually quantitative formation of the cyclobutanoid compound (296) from (295). Reaction of norbomadiene with 2,2 -bipyridyl(cyclo-octa-l,5-diene)nickel at 25°C yielded the exo-trans,endo-metal o-carbocyclic (297) which, on treatment with an activated olefin (e.g. maleic anhydride), afforded the cyclo-dimer (298 predominantly exo-trans,endo) in good yield by displacement of the hydrocarbon moiety. Catalytic conversions can also be achieved. 

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