Syntheses and x-ray Structures of Anionic Sodocene Sandwiches.
In: Organometallics, Jg. 15 (1996) ; Nr. 1, S. 118-122
Zeitschriftenaufsatz / Fach: Chemie
While the lithocene anion (Cp2Li-) can simply be generated by reacting 2 equiv of CpLi with PPh4Cl in THF, the attempted synthesis of the sodocene anion under similar reaction conditions results in the crystn. of [PPh4+][Cp-]. The structure consists of naked Cp anions pinched between metaphenyl hydrogens of the phosphonium cations. An ansa-sodocene anion in which the two Cp rings are bridged by a -CMe2CMe2- chain was obtained by reaction of Me4C2(C5H4Na)2 with 1 equiv of PPh4Cl in THF. Its crystal structure shows a disordered ansa-sodocene anion contg. a sandwiched Na cation solvated by a THF mol. Unbridged Cp2Na- was obtained by pushing the (CpNa + Cp-)/Cp2Na- equil. to the sodocene anion side. Cell dimensions, space group symmetry, and the mol. structure of [PPh4+][Cp2Na-] are remarkably similar to that of [PPh4+][Cp2Li-]. The anion can be described as a centrosym. (h5,h5)Cp2Na- sandwich (av. C-Na = 2.630(3) .ANG.) with approx. D5d symmetry.