ON THE REGIOSELECTIVITY OF PALLADIUM-CATALYZED CROSS-COUPLING REACTIONS OF ALKENYLSILANES - PARTICIPATION OF BETA-CATIONIC ORGANOSILICATE-PALLADIUM SPECIES DURING THE TRANSMETALATION

The cross-coupling reaction promoted by a palladium catalyst and fluor ide salt of 1-[(fluoro)(dimethyl)silyl]-1-phenylethen (1) with substit uted aryl iodides gave the unexpected cine-substitution products (E)-1 -aryr-2-phenylethenes (3) along with the normal ipso-substitution prod uct 1-aryl-1-phenylethene (2). The product ratios were strongly depend ent on the electronic nature of the substituent on alyl iodides: ipso- substitution products (2) were favoured by an electron-withdrawing sub stituent, and cine-substitution products (3) by an electron-donating s ubstituent. On the basis of these observations, the following mechanis m of transmetallation of alkenyl(fluoro)silicates with aryrpalladium i s proposed: electrophilic attack of an aryrpalladium complex on the ol efinic alpha-carbon of an alkenyl(fluoro)silicate produces a beta-cati onic organosilicate-palladium species which then transfers the alkenyl group from silicon to the palladium complex.