Studies on fluoroalkylation and fluoroalkoxylation. Part 28. Palladium(0)-induced addition of fluoroalkyl iodides to alkenes: an electron transfer process

Abstract

In the presence of catalytic amounts of tetrakis(triphenylphosphine)palladium, fluoroalkyl iodides react readily with alkenes under mild conditions to give the corresponding adducts in high yields. Dichlorobis(triphenylphosphine)palladium or fluoroalkylbis(triphenylphosphine)palladium iodide fails to induce the reaction under the same conditions. Di-iodobis(triphenylphosphine)palladium, but not the fluoroalkylated complex of palladium, Pdl(PPh₃)₂R_F, is formed in the reaction confirmed by X-ray photoelectron spectroscopy. The reaction can be partially suppressed by radical inhibitors, such as 2-nitro-2-nitrosopropane or di-t-butyl nitroxide, but no effects are observed by the presence of oxygen in air or p-dinitrobenzene [molar ratio p-DNB:Pd⁰= 1:1] unless an excess of p-DNB(10:1) was added. In the presence of diallyl ether, fluoroalkylated tetrahydrofuran derivatives are formed. All these results indicate that a radical-chain process initiated by single electron transfer from palladium(0) to iodide might be involved. Also, the formation of fluoroalkylbis(triphenylphosphine)palladium iodide is proved to proceed through a radical intermediate by e.s.r. trapping techniques.