Bis-cyclopentadienyl Iron: a Molecular Sandwich

Abstract

Kealy and Pauson¹ have described the preparation of bis-cyclopentadienyl iron, (C₅H₅)₂Fe, which they formulated as (I). More recently, Wilkinson, Rosenblum, Whiting and Woodward² have observed that the compound is diamagnetic, that it has zero dipole moment, and that only one C—H stretching frequency occurs (at 3.25 µ) in the infra-red absorption spectrum; on the basis of these observations they have proposed the very unorthodox structures (II) or (III). In the present communication we wish to present X-ray evidence for the correctness of (II) and also to interpret this unusual structure in terms of electronic structural principles.