On the regioselectivity of palladium catalyzed cross-coupling reactions of alkenylsilanes: participation of β-cationic organosilicate-palladium species during the transmetallation

Article abstract of DOI:10.1016/0022-328X(94)87042-X

The cross-coupling reaction promoted by a palladium catalyst and fluoride salt of 1-<(fluoro)(dimethyl)silyl>-1-phenylethene (1) with substituted aryl iodides gave the unexpected cine-substitution products (E)-1-aryl-2-phenylethenes (3) along with the normal ipso-substitution product 1-aryl-1-phenylethene (2).The product ratios were strongly dependent on the electronic nature of the substituent on aryl iodides: ipso-substitution products (2) were favoured by an electron-withdrawing substituent, and cine-substitution products (3) by an electron-donating substituent.On the basis of these observations, the following mechanism of transmetallation of alkenyl(fluoro)silicates with arylpalladium is proposed: electrophilic attack of an arylpalladium complex on the olefinic α-carbon of an alkenyl(fluoro)silicate produces a β-cationic organosilicate-palladium species which then transfers the alkenyl group from silicon to the palladium complex. Key words: Silane; Palladium; Transmetallation; Regioselectivity