Iodonium salts ligand coupling mechanism

The styryl iodonium salt (7 a) reacts slowly with acetic acid to give the E and Z isomeric products (8a) and (9a) in the ratio 85 15.3 The decenyl system (7b) is much more reactive and gives only the inversion product, the Z isomer (9b). It was suggested that the styryl system reacts in a two-step mechanism via the vinylene phenonium ion (10), whereas the decenyl system follows a one-step vinylic. S n2 mechanism, hi contrast, 2-bromo-l-decenyliodonium salt reacts with bromide ion in MeCN with complete retention.4 The observed rate constants show an unexpected dependence on [Br ], in accordance with a mechanism involving ligand coupling within a bromoiodane intermediate. 

Alkenyl(phenyl)iodonium salts are highly reactive in vinylic nucleophilic substitution reactions because of the excellent leaving group ability of the phenyliodonium moiety. Only a few examples of non-catalytic alkenylation of carbon nucleophiles are known [50,51]. In most cases these reactions proceed with predominant retention of configuration via the addition-elimination mechanism or ligand coupling on the iodine [42,50]. 

It is assumed that the mechanism of the palladium-catalyzed cross-coupling reactions of iodonium salts involves the initial oxidative addition step, followed by ligand coupling at the iodine and then at the palladium centers analogously to the mechanism shown in Scheme 31 [63,66]. 

Alkenylations of heteroatom nucleophiles with alkenyl(aryl)iodonium salts occur by a variety of mechanisms, including SN1, SN2, alkylidenecarbene, and addition-elimination pathways [ 126,127]. Reactions that occur with retention of configuration at vinylic carbon are sometimes attributed to a ligand-coupling... 

The mechanism of solvolysis of methoxy-substituted diaryliodonium tetrafluoroborates, Arl+Ph Bp4, in methanoi and 2,2,2-trifluoroethanol has been investigated [893]. The solvolysis products include alkox-ide substitution products (ArOR and PhOR) as well as iodoarenes (Phi and Arl). The ratios of products, ArOR/PhOR, range from 8 2 to 4 6. The results of this study provide experimental evidence against the formation of aryl cation under these conditions and support the pathways via ligand coupling or 5nAt2 mechanisms involving a solvent molecule as a nucleophile in the transition state [893]. If the reaction is performed in inert (not nucleophilic) solvent, various nucleophiles may be involved in the reaction with iodonium salt. 

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