Aryl halides amines with additives

The palladium(O) complex undergoes first an oxydative addition of the aryl halide. Then a substitution reaction of the halide anion by the amine occurs at the metal. The resulting amino-complex would lose the imine with simultaneous formation of an hydropalladium. A reductive elimination from this 18-electrons complex would give the aromatic hydrocarbon and regenerate at the same time the initial catalyst. 

Several studies were performed in order to establish the mechaiusm (5-7). The currently accepted mechartism, presented in Scheme 26.1 for the Pd(BINAP) catalyzed amination, involves the formation of a complex, Pd(BINAP)2 from a catalyst precursor (usually Pd(OAc)2 or Pd2(dba)3) and ligand this complex lies outside the catalytic cycle and undertakes dissociation of one BINAP to form Pd(BINAP) the following steps are the oxidative addition of the aryl halide to the Pd(BINAP), reaction with amine and base, and the reductive elimination of the product to reform Pd(BlNAP). 

There are a number of procedures for coupling of terminal alkynes with halides and sulfonates, a reaction that is known as the Sonogashira reaction.161 A combination of Pd(PPh3)4 and Cu(I) effects coupling of terminal alkynes with vinyl or aryl halides.162 The reaction can be carried out directly with the alkyne, using amines for deprotonation. The alkyne is presumably converted to the copper acetylide, and the halide reacts with Pd(0) by oxidative addition. Transfer of the acetylide group to Pd results in reductive elimination and formation of the observed product. 

In addition, complexes of P(/-Bu)3 have been shown to catalyze the formation of diaryl heteroarylamines from bromothiophenes.224 Aminations of five-membered heterocyclic halides such as furans and thiophenes are limited because their electron-rich character makes oxidative addition of the heteroaryl halide and reductive elimination of amine slower than it is for simple aryl halides. Reactions of diarylamines with 3-bromothiophenes occurred in higher yields than did reactions of 2-bromothiophene, but reactions of substituted bromothiophenes occurred in more variable yields. The yields for reactions of these substrates in the presence of catalysts bearing P(/-Bu)3 as ligand were much higher than those in the presence of catalysts ligated by arylphosphines. 

The formation of bonds to aromatic rings is the foundation of much of organic synthesis. There has been much excitement over the past several years around Pd- or Cu-mediated displacement of an aromatic halide or aryl sulfonate with an amine. Paul Knochel of the University of Munich reports (Angew. Chem. Int. Ed. 2004,43, 897) a complementary approach, the addition of an aryl halide-derived Grignard such as 2 to the diazonium derivative 3. Aryl triflates such as 4 are efficient partners for further coupling. 

Elimination-addition reactions of aryl halides with alkali-metal amides are discussed in Section 14-6C high-temperature copper-catalyzed amination, also effective, usually does not lead to rearrangement. 

Aromatic carboxylic acids, a,/f-unsaturated carboxylic acids, their esters, amides, aldehydes and ketones, are prepared by the carbonylation of aryl halides and alkenyl halides. Pd, Rh, Fe, Ni and Co catalysts are used under different conditions. Among them, the Pd-catalysed carbonylations proceed conveniently under mild conditions in the presence of bases such as K2CO3 and Et3N. The extremely high toxicity of Ni(CO)4 almost prohibits the use of Ni catalysts in laboratories. The Pd-catalysed carbonylations are summarized in Scheme 3.9 [215], The reaction is explained by the oxidative addition of halides, and insertion of CO to form acylpalladium halides 440. Acids, esters, and amides are formed by the nucleophilic attack of water, alcohols and amines to 440. Transmetallation with hydrides and reductive elimination afford aldehydes 441. Ketones 442 are produced by transmetallation with alkylmetal reagents and reductive elimination. 

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