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

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Abstract
Superbulky sandwich complexes with the cyclopentadienyl ligand (4-nBu-C6H4)5Cp (abbreviated here as CpBIG) have been prepared by reaction of CpBIGH with benzylic strontium or barium reagents. Both metallocenes have been structurally characterized by single crystal X-ray diffraction. Even for the larger metallocene (CpBIG)2Ba a highly symmetric sandwich complex with parallel Cp rings was isolated (Cpcenter–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.