As far as known, there is no detailed report on the dehydration of perfluoroalkyl-substituted tertiary alcohols. Rising interest in the field of biphasic fluorous catalysis has paved way to a larger spectrum of ligands, that are soluble in fluorine phases [1]. However, the fabrication of fluorous cyclopentadienes, is still an area to explore. Several cyclopentadienes become fluorophobic by connecting to polyfluorinated fluorous ponytails such as (perfluoroalkyl) ethyl chains. Wu and group [2] also fabricated unimolecular cyclopentadienes with one perfluoroalkyl chain, even though they are difficult to use in metallic complexation. Our team made the (perfluoroalkyl) tetramethyl cyclopentadienes which are synthesised in a complicated manner in our group [3, 4, 5]. The electron-withdrawing (inductive) effect of the three methyl groups in the compound cancels the effect of the perfluoroalkyl chain adsorbed directly to the ring, Hence they act as stable ligands with excellent electric and steric properties and as higher homologs of the well-known Gasmann ligand.
The two-step synthesis of (perfluoroalkyl) tetramethyl cyclopentadienes is triggered with the nucleophilic addition of an in situ perfluoroalkyl Grignard reagent to achieve a mixture of perfluoroalkyl tertiary alcohols. This is achieved through an aqueous acidic workup and subjecting the mixture to water elimination with phosphorus trichloride (POCl3)/pyridine, thereby yielding a mixture of endo, exo-compounds deprotonable to only one common substituted cyclopentadienyl anion. To compensate the very low yield (40%), we now investigate the dehydration step in detail including the kinetics of formation of the diene isomers. The destabilizing effect of the electron, attracting perfluoroalkyls on the intermediate carbocation causes interest in this work.
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