Reactions of metal carbonyl derivatives. Part XV. Oxidation studies of some η-cyclopentadienyl bridging sulphido- and phosphino-derivatives of iron

Abstract

The bridged sulphide- and phosphino-complexes [Fe(cp)(CO)SR]₂(cp =η-C₅H₅; R = Me, Et, Prⁱ, Buⁿ, Bu^t Bz, or Ph) and [Fe(cp)(CO)PPh₂]₂ are readily oxidised by oxygen in aqueous or non-aqueous acidified media, as well as by reagents such as iodine and silver salts, to the paramagnetic species [Fe(cp)(CO)SR]₂⁺ and [Fe(cp)(CO)PPh₂]₂⁺ respectively. This oxidation is reversible with reduction being effected by water under basic conditions and by reducing agents such as sodium amalgam, sodium tetrahydroborate or iodide ions. Further oxidation of the complex [Fe(cp)(CO)SR]₂⁺ to the dicationic species [Fe(cp)(CO)SR]₂²⁺ can be achieved by treatment with an excess of bromine, silver ions, or nitrosyl hexafluorophosphate. Reduction of this dication is readily effected even by weak reducing agents such as the tetraphenylborate anion. These redox reactions are stereoselective. E.s.r. spectra of the monocationic derivative and Mössbauer spectra of the neutral, monocationic, and dicationic derivatives are reported and discussed in terms of a bonding scheme proposed by Mason and Mingos for bridged binuclear systems of this type. Oxidation affects each iron atom to the same extent and results in a decrease in chemical-isomer shift, consistent with removal of an electron from an MO having predominantly metal d-character.