Electrochemistry of 1,1′-Bis(2,4-dialkylphosphetanyl)ferrocene and 1,1′-Bis(2,5-dialkylphospholanyl)ferrocene Ligands: Free Phosphines, Metal Complexes, and Chalcogenides

The oxidative electrochemistries of a series of chiral bisphosphinoferrocene ligands, 1,1′-bis(2,4-dialkylphosphetanyl)ferrocene (FerroTANE) and 1,1′-bis(2,5-dialkylphospholanyl)ferrocene (FerroLANE), were examined. The reversibility of the oxidation is sensitive to the steric bulk of the alkyl groups. New transition metal compounds and phosphine chalcogenides of these ligands were prepared and characterized. X-ray crystal structures of 10 of these compounds are reported. The percent buried volume (%Vbur) is a recently developed measurement based on crystallographic data that examines the steric bulk of N-heterocyclic carbene and phosphine ligands. The %Vbur for the FerroTANE and FerroLANE structures with methyl or ethyl substituents suggests these ligands are similar in steric properties to 1,1′-bis(diphenylphosphino)ferrocene (dppf). In addition the %Vbur has been found to correlate well with the Tolman cone angle for phosphine chalcogenides. The oxidative electrochemistries of the transition metal complexes occur at more positive potentials than the free ligands. While a similar positive shift is seen for the oxidative electrochemistries of the phosphine chalcogenides, the oxidation of the phosphine selenides does not occur at the iron center, but rather oxidation occurs at the selenium atoms.