Diels−Alder Reactions of 3-Ferrocenyl-2,4,5-triphenylcyclopentadienone:  Syntheses and Structures of the Sterically Crowded Systems C₆Ph₅Fc, C₇Ph₆FcH, and [C₇Ph₆FcH][SbCl₆]

Abstract

Diels-Alder addition of diphenylacetylene or of 1,2,3-triphenylcyclopropene to 3-ferrocenyl-2,4,5-triphenylcyclopentadienone yields, upon thermolysis, C 6 Ph 5 Fc (5) or C 7 Ph 6 FcH (8), respectively. Subsequent treatment of 8 with triethyloxonium hexachloroantimonate results in the formation of the ferricinium complex [C 7 Ph 6 FcH] + [SbCl 6 ] -(13), rather than the anticipated tropylium cation [C 7 Ph 6 Fc] + . The substituted ferrocene derivatives 5, 8, and 13 have been characterized by X-ray crystallography. From the solid-state structure of 5 it is evident that the peripheral aryl substituents do not adopt a regular propeller type conformation, but instead exhibit an incremental progression of twist angles relative to the central ring. The dynamics of peripheral ring rotations in 5 and 8 have been studied by variable-temperature NMR.

Artificial Molecular Rotors

“…This is lower than the value obtained by Gust and co-workers, but it was not possible to tell if this was a result of a stabilization effect on the transition state of destabilization of the ground state. Replacing the phenyl-Cr(CO) 3 unit by a ferrocene group (44), McGlinchey and colleagues 376 found that a propeller conformation was not the lowest energy structure. Instead, as evidenced in the crystal structure, the rings exhibit an incremental progression of twist angle (51°to 120°) with respect to the central benzene ring.…”

Syntheses, Structures and Dynamics of 9‐(Ferrocenylmethyl)anthracene and Related Molecular Gears: Phosphorus to the Rescue!

“…One should emphasise that the development of negative charge at the methylene position upon breakdown of the P ‐hydroxyphosphoranes 14a/b is hampered since α‐ferrocenyl carbanions are strongly disfavoured, as typified by the failure of formylferrocene to undergo benzoin self‐condensation . If a purely carbanion‐mediated mechanism were to operate, the formation of 15 would be expected to prevail, whereby the anion is preferentially located on the anthracene skeleton.…”

A Synthetic, X‐ray, NMR Spectroscopy and DFT Study of β‐Naphthil Dihydrazone, Di(β‐naphthyl)acetylene, Tetra(β‐naphthyl)cyclopentadienone, and Hexa(β‐naphthyl)‐benzene: C6(C10H7)6 Is a Disordered Molecular Propeller

“…The disordered propeller conformation found for 5 is in contrast with the previously reported structures of ferrocenylpenta(β‐naphthyl)benzene and ferrocenylpentaphenylbenzene; neither of which adopt a propeller conformation, but instead both exhibit an incremental progression of dihedral angles (51 to 120°). In those cases, it is tempting to invoke a domino effect, such that rotation of the ferrocenyl group would proceed with correlated rotation of the aryl rings.…”