title: On the structural diversity of [K(18-crown-6)EPh3] complexes (E = C, Si, Ge, Sn, Pb): synthesis, crystal structures and NOESY NMR study.
abstract: A series of homologous potassium triphenylelement complexes [K(18-crown-6)EPh3] 6a-e of group 14 elements (E = C, Si, Ge, Sn, Pb) was synthesised by alkoxide induced heterolytic cleavage of boron-element compounds. The complexes 6a-e are isolated as storable solids possibly useful as sources of nucleophilic [EPh3](-) moieties. The solid state structures of 6a-e were established by X-ray crystal structure determination. Whilst all structures can be described as polymeric chains consisting of alternating [K(18-crown-6)](+) and [EPh3](-) units, the interaction within each chain varies systematically with the coordination properties of E. For Si and Ge, classical E-K coordination along with secondary phenyl-K interactions are characteristic, whilst for Sn and Pb, potassium coordination via the phenyl π-system is observed due to inefficient coordination by the free electron pair localised in an 'inert' s-orbital. The carbon derivative is exceptional as the central sp(2)-hybridised carbon atom gives rise to extensive charge delocalisation and coordination via these partially charged π-systems. A (1)H-(1)H NOESY NMR spectroscopic study in THF-d8 suggests appreciable anion/cation interactions for Si to Pb and hence the presence of contact ion pairs.
authors.affiliation: Institut für Anorganische und Analytischen Chemie der Technischen Universität Carolo-Wilhelmina zu Braunschweig, Hagenring 30, 38106 Braunschweig, Germany. ch.kleeberg@tu-braunschweig.de
authors.forename: Christian
authors.initials: C
authors.lastname: Kleeberg