Carbon–fluorine bond activation in perfluorobenzonitrile by LiN(SiMe3)2. Synthesis of (Me3Si)2NC6F4CN-4 and crystal structure of LiN(C6F4CN-4)2·2C4H 8O

Abstract

The reaction of C ₆ F ₅ CN with the dimeric lithium salt [Li(NSiMe ₃ )·Et ₂ O] ₂ yielded a 11∶9 mixture of (Me ₃ Si) ₂ NC ₆ F ₄ CN-4 1 and LiN(C ₆ F ₄ CN-4) ₂ ·2thf, respectively (thf = tetrahydrofuran). The compounds were characterized spectroscopically and complex 2 by crystal structure determination. The central lithium forms a distorted trigonal bipyramid the apical position of which is filled by a nitrile nitrogen of an adjacent molecule, inducing chains running parallel to the b-direction of the crystal. The driving force for the production of 1 and 2 is the elimination of LiF and SiMe ₃ F, respectively. The calculated enthalpy for formation of 2 is more favourable compared to that for formation of 1, although the similar yields indicate that similar enthalpies of activation apply to both systems.