Diphenylphosphide-bridged diiron derivatives of [Fe2(η5-C5H5)2(μ-H)(μ-PPh2)(CO)2]

The complex trans- [Fe2Cp2(mu-H)(mu-PPh2)(CO)(2)] is obtained in 91% Yield by refluxing toluene solutions of [Fe2Cp2(CO)(4)] (Cp = eta(5)-C5H5) and the secondary phosphine PPh2H. This compound isomerizes upon irradiation with visible-UV light under a CO atmosphere to yield cis-[Fe2Cp2(mu-H)(mu-PPh2)(CO)(2)]. The above hydride complexes react under photochemical conditions with 1 equiv of secondary phosphines PR2H (R = Et, Ph) to give the corresponding monocarbonyl compounds [Fe2Cp2(mu-PPh2)(mu-PR2)(mu-CO)] via the hydride intermediates [Fe2Cp2(mu-H)(mu-PPh2)(CO)(PR2H)] (detected and isolated for R = Et). Deprotonation of trans[Fe2Cp2(mu-H)(mu-PPh2)(CO)(2)] with LiBu gives the binuclear anion [Fe2Cp2(mu-PPh2)(CO)(2)](-). This highly nucleophilic carbonylate reacts rapidly with [AuCl((PPr3)-Pr-i)] or MeI to give the corresponding gold diiron cluster [AuFe2Cp2(mu-PPh2)(CO)(2)((PPr3)-Pr-i)] or methyl derivative [Fe2Cp2(Me)(mu-PPh2)(mu-CO)(CO)(2)], respectively. Both hydrides cis- and trans-[Fe2Cp2(mu-H)(mu-PPh2)(CO)(2)] can be reversibly oxidized at low temperature to the corresponding cation radicals cis- and trans-[Fe2Cp2(mu-H)(mu-PPh2)(CO)(2)](+). At room temperature, however, the trans dicarbonyl cation isomerizes to its cis isomer, which in turn experiences a degradation process involving the reductive elimination of the bridging groups. The structures of the new complexes are analyzed on the basis of the corresponding IR and NMR (H-1, P-31 and C-13) spectroscopic data. The nature of the new radical cations is analyzed also on the basis of cyclic voltammetry and ESR measurements.