Insight in cyclopentadienyl metal complexes with superbulky ligands: The crystal structure of [Cp BIGK] ∞

Abstract

Reaction of (4- nBu-C 6H 4) 5CpH (=Cp BIGH) with KH in THF and subsequent recrystallization from hexane/Et 2O gave the solvent-free product Cp BIGK in good crystalline yield (55%). Crystal structure determination revealed the one-dimensional coordination polymer [Cp BIGK] ∞ . Despite the steric bulk of the Cp BIG ligands, the chains are not perfectly linear. They can be pictured as an array of highly symmetric ( Cp BIG ) 2 K - sandwiches bridged by K + ions at an angle of 167.7(2)°. The C–K bond distances are much shorter than those in other cyclopentadienyl potassium complexes. This is explained by networks of attractive C–H⋯C(π) interactions between neighbouring Cp BIG ligands. In all cases the C–H donors and C acceptors are represented by the ortho-CH units in the aryl substituents. The C–H···C(π) networks within the supersandwich are less distinct than those observed in the metallocene sandwich complexes ( Cp BIG ) 2 M (M = Ca, Sr, Ba, Yb, Sm). Significant out-of-plane bending of the aryl substituents indicates that, within the supersandwich chain, pairs of tighter C–H⋯C(π) networks exist. Large displacement factors for the K + ions are explained by assuming induced polarization of these soft metals. This results in enforcement of the Cp BIG–K interactions.