Iron complexes of facially capping triphosphorus macrocycles

Abstract

Primary and secondary phosphine piano-stool complexes of the type [η⁵-CpFeL₃]⁺ (L = phenylphosphine, 3, (α-methyl)vinylphosphine, 4, allylphosphine, 5, (2-methylpropenyl)phosphine, 5b, allyl(phenyl)phosphine, 6) are described. The alkenyl phosphine complexes, 5 and 6, react by intramolecular hydrophosphination to give the corresponding [η⁵-CpFe]⁺ complexes of 1,5,9-triphosphacyclododecane (12-aneP₃R₃, 2, R = H), 9 and 10 respectively. Alkylation of the secondary phosphines in 9 is achieved by hydrophosphinations with ethene to give the 12-aneP₃R₃ (R = Et) derivative 11. These complexes are also obtained by reaction of suitable [η⁵-CpFe]⁺ containing precursor complexes with the corresponding free 12-aneP₃R₃ macrocycle as is the related [η⁵-Cp*Fe]⁺ derivative, 8. Direct substitution of acetonitrile in [Fe(CH₃CN)₆][BF₄]₂ by 12-aneP₃Et₃, leads to the macrocycle piano-stool complex, [(12-aneP₃Et₃)Fe(CH₃CN)₃][BF₄]₂, 7. The crystal structures of selected primary phosphine, η⁵-Cp, η⁵-Cp* complexes and 7, allow a comparison of steric influences upon key macrocycle ring closure reactions and hence an insight into parameters required for the formation of smaller ring sizes by template based methods.