Acid halides homogeneous catalysis

As with carboxylic acids obtained by palladium hydroxycarbonylation, their derivatives esters, amides, anhydrides and acyl halides are synthesized from alkenes, CO and HX (X = OR, NR2 etc.). The Pd-catalyzed methoxycarbonylation is one of the most studied reactions among this type of catalyzed carbonylations and has been reviewed and included in reports of homogeneous catalysis.625, 26 The methoxycarbonylation has been applied to many different substrates to obtain intermediates in organic syntheses as well as specific products. For instance, the reaction has been applied for methoxycarbonylation of alkynes666 Highly efficient homogeneous Pd cationic catalysts have been reported and the methoxycarbonylation of alkynes has been used to develop economically attractive and environmentally benign process for the production of methyl... 

Metalloenzymes contain a bound metal ion as part of their structure. This ion can either partidpate directly in the catalysis, or stabilize the active conformation of the enzyme. In Lewis acid catalysis (typically with zinc, vanadium, and magnesium), the M"+ ion is used instead of H+. Many oxidoreductases use metal centers such as V, Mo, Co, and Fe in much the same way as homogeneous catalysis uses ligand-metal complexes. Figure 5.7 shows a simplified mechanism for the halide oxidation readion catalyzed by vanadium chloroperoxidase. The vanadium atom ads as a Lewis add, activating the bound peroxide [30]. 

MF5 and MCI5 are strongly electrophilic see Electrophile and Electrophilic Reaction) and catalyze Friedel-Crafts reactions. The HF/TaFs system is a superacid catalyst and has been used in the selective acid-catalyzed isomerization and hydrogenolysis of cycloalkanes. Oligomerization and polymerization of alkynes with Nb and Ta halides as catalysts have been reported see Oligomerization Polymerization by Homogeneous Catalysis) ... 

A direct carbonylation reaction demonstrating in an impressive way the potential of homogeneous catalysis is the double carbonylation [9]. Phenyl pyruvic acid derivatives can be prepared directly from benzyl halides. 

The very soluble hexachloroplatinic acid, H2 [PtCl ] nH20, is the most useful precursor for synthetic and catalytic work. For the hydrosilation of unsaturated substrates, the catalyst of choice is chloroplatinic acid, because of its very high activity. There is currently some doubt as to whether the true catalyst is homogeneous or colloidal metal and therefore heterogeneous see Hydrosilation Catalysis). Nearly all halides andpseudohahdes (= X) form salts of the [PtXe] ion and of the [PtX4(NH3)2] type. 

Homogeneous, aqueous tv o-phase catalysis is also of industrial interest for the production of the important intermediate phenylacetic acid (PAA), -which is used in perfume and pesticides syntheses. The previous process (benzyl chloride to benzyl cyanide -with hydrolysis of the latter) suffered from the formation of large amounts of salt (1400 kg per kg of PAA). The new carbonylation method reduces the amount of salt by 60% and makes use of the great cost difference between —CN and —CO [79-81]. Finally, the Suzuki coupling of aryl halides and arylboronic acids, substituting Pd/TPPMS with Pd/TPPTS catalysts, should be also mentioned. 

---