Aryl exchange

Finally, the kinetics of the one-aryl exchange reaction, equilibrium (289)... 

Compound (tht)AuC6F5 undergoes random aryl exchange with pentafluorophenylpalladium(ii) complexes, while the 3,5-dichloro-2,4,6-trifluorophenylgold complex specifically catalyzes the trans-cis isomerization of [Ar2Pd(tht)2]. The reaction appears to follow an associative mechanism.1... 

These authors propose as the mechanism for this reaction a reversible oxidative addition of the aryl-phosphido fragments to a low valent rhodium species. A facile aryl exchange has been described for complexes Pd(PPh3)2(C6H4CH3)I. The authors [35] suggest a pathway involving oxidative additions and reductive eliminations. The mechanism outlined below, however, can also explain the results of these two studies. 

Kong, K.-C. Cheng, C.-H. Facile aryl—aryl exchange between the Pd center and phosphine ligands in Pd(ll) complexes./. Am. Chem. Soc. 1991, 113, 6313-6315. 

Another polyhalophenyl gold(I) complex, [Au(3,5-C6Cl2F3)(tht)], has been found to be a very efficient catalyst for the isomerization of fra/w-[Pd(3,5-CftCI2F3)2(tht)21 to c/s-[Pd(3,5-C6Cl2F3)2(tht)2].40 The reaction takes place through a novel reversible aryl exchange between Pd(II) and Au(I). The mechanism involves associative substitution of... 

A second issue is that catalytic aminations are plagued by several notable side reactions. Most prevalent among these is jS-hydride elimination (see -Hydride Elimination) of imine from the intermediate Pd-amido complex (equation 31). This reaction also produces a Pd H species, which can then reduce the substrate to form arene, the generation of which can be considered a second side reaction. Furthermore, aryl-aryl exchange has also been noted in amination reactions, and, for the monoarylation of primary amines, by-products caused by overarylation (equation 32) to form tertiary amines pose an additional difficulty. 

Subsequent work with a Pt11 complex containing a labile triflate ligand showed evidence for the alkyl/aryl exchange labeled as type (c) in Fig. 1. While mechanistic studies were limited, the observation of little positional selectivity in the reaction with toluene argued in favor of the oxidative addition pathway, i.e., via a PtIV intermediate (Eq. 13) [60]. 

Scheme 7.13 Effect of aryl-aryl exchange in polymerization by Suzuki coupling, and modes of incorporation of phosphorus in the polymer.

Alkyl and aryl exchange reactions between trialkyl alanes and trialkyl or triaryl boranes have been very fully investigated (188). The exchange of ligands, which occurs very rapidly even at room temperature, occurs through the association products like ... 

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