DEFLUORINATION OF PERFLUOROOLEFINS BY DIVALENT LANTHANOID REAGENTS - ACTIVATING C-F BONDS

Divalent lanthanoid complexes MCp*2·L (M = Yb, Eu, Sm; L = diethyl ether or THF; Cp* = η5-pentamethylcyclopentadienyl) and YbCpʹ2·L (Cpʹ = η5-methylcyclopentadienyl; L = tetrahydrofuran) rapidly abstract fluorine atoms from a variety of perfluoroolefins including perfluoro-2,4-dimethyl-3-ethylpent-2-ene, perfluoro-2,3-dimethylpent-2-ene, and perfluorocyclohexene. A similar abstraction of fluorine atoms from perfluorobenzene is much slower. However, visible light enhances the rate of fluorine abstraction from perfluorobenzene by MCp*2·OEt2 (M = Yb, Eu, Sm). Qualitative observation shows that the relative fluorine abstraction reactivity of the four lanthanoid complexes increases with increasingly negative reduction potential for reasonably unhindered fluoroolefin substrates. The Yb(III)/Yb(II) reduction potential of YbCpʹ2 solvated in acetonitrile is determined here to be ‒1.65 V (relative to ferrocene) by cyclic voltammetry. The fully characterized organometallic products from the fluorine atom abstraction reactions are solvated trivalent lanthanoid fluorides MCp*2F·L (M = Yb, Eu, Sm; L = diethyl ether or THF) and YbCpʹ2F-THF. The molecular structures of YbCp*2F·OEt2 and YbCp*2F·THF determined by X-ray crystallography reveal the first terminal lanthanoid-fluoride bonds. However, three different environments for bridging lanthanoid‒fluoride bonds are seen in the X-ray determined structure of the trivalent pentaytterbium cluster [Yb5Cp*6(µ4-F)(µ3-F)2(µ-F)6], which is a secondary product from the further reaction of YbCp*2F with perfluoroolefins. From the X-ray data of these three trivalent ytterbium compounds the averaged Yb‒F distances are 2.02 Å for the terminal Yb‒F bonding mode, 2.20 Å for an F atom bridging between two Yb atoms, and 2.37 Å for an F atom bridging between three of four Yb atoms. © 1990, American Chemical Society. All rights reserved.