Superbulky metallocene complexes of the heavier alkaline-earth metals strontium and barium

Abstract

Superbulky sandwich complexes with the cyclopentadienyl ligand (4-nBu-C₆H₄)₅Cp (abbreviated here as Cp^BIG) have been prepared by reaction of Cp^BIGH with benzylic strontium or barium reagents. Both metallocenes have been structurally characterized by single crystal X-ray diffraction. Even for the larger metallocene (Cp^BIG)₂Ba a highly symmetric sandwich complex with parallel Cp rings was isolated (Cp_center–Ba = 2.667(1) Å). Both structures show evidence for a C–H⋯C(π) network between the Cp ligands. These attractive forces induce an inward out-of-plane bending of the aryl substituents (Sr 3.4(2)°; Ba 5.3(2)°). A linear correlation between this bending angle and metal size has been found.