Abstract
AbstractThe η8‐C8H62− pentalene ligands in the recently discovered sandwich compounds (η8‐C8H6)2M (M = Ti, Zr) can be derived either by transannular ‘pinching’ of the cyclooctatetraene dianion, C8H82−, or by edge‐sharing fusion of two cyclopentadienyl ligands C5H5−. This paper depicts the relationship between the molecular orbitals in C8H62−, C8H82−, and 2C5H5−. In addition, this paper shows that the d orbital of the central metal atom is of suitable symmetry for δ bonding in the D2h complexes (η8‐C8H6)2M (M = Ti, Zr) unlike in the D8h complexes (η8‐C8H8)2M derived from cyclooctatetraene. This can account for the fact that the cyclooctatetraene sandwich compounds of stoichiometry (C8H8)2M have unsymmetrical (η8‐C8H8)(η4‐C8H8)M structures in the case of the d‐block metals titanium and zirconium in contrast to perhapto structures (η8‐C8H8)2An in the case of the actinides (An = Th, Pa, U, Np, Pu) where metal f orbitals are available for metal–ring bonding. Copyright © 2003 John Wiley & Sons, Ltd.
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