Pentakis(methoxycarbonyl)cyclopentadiene chemistry. VIII. Some onium salts X-ray structure of [Nme₄][C₅(CO₂Me)₅]

Abstract

Reactions between Tl[C₅(CO₂Me)₅] and [R]X [R = NMe₄, NEt₄, NPr₄, NBu₄, AsPh₄, N(PPh₃)₂; X = C1, Br] have given salts [R][C₅(CO₂Me)₅] as white, crystalline solids. The X-ray structure of [NMe₄][C₅(CO₂Me)₅] has been determined; the unit cell contains isolated cations and anions, with no close interactions between them. The anion consists of a planar C₅ ring [C-C 1.406(10) Å] with five CO₂Me substituents whose planes have an essentially random orientation with respect to the C₅ plane. [NMe₄][C₅(CO₂Me)₅] is monoclinic, space group P2₁/c, with a 9.267(4), b 16.249(5), c 14.687(6) ź, β 100.90(3)º, and Z 4; 1610 data with I >3σ (I) were refined to R 0.066 and R' 0.053.