Diphenylphosphide-Bridged Diiron Derivatives of [Fe₂(η⁵-C₅H₅)₂(μ-H)(μ-PPh₂)(CO)₂]

Abstract

The complex trans-[Fe2Cp2(μ-H)(μ-PPh2)(CO)2] is obtained in 91% yield by refluxing toluene solutions of [Fe2Cp2(CO)4] (Cp = η5-C5H5) and the secondary phosphine PPh2H. This compound isomerizes upon irradiation with visible−UV light under a CO atmosphere to yield cis-[Fe2Cp2(μ-H)(μ-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(μ-PPh2)(μ-PR2)(μ-CO)] via the hydride intermediates [Fe2Cp2(μ-H)(μ-PPh2)(CO)(PR2H)] (detected and isolated for R = Et). Deprotonation of trans-[Fe2Cp2(μ-H)(μ-PPh2)(CO)2] with LiBu gives the binuclear anion [Fe2Cp2(μ-PPh2)(CO)2]-. This highly nucleophilic carbonylate reacts rapidly with [AuCl(PiPr3)] or MeI to give the corresponding gold diiron cluster [AuFe2Cp2(μ-PPh2)(CO)2(PiPr3)] or methyl derivative [Fe2Cp2(Me)(μ-PPh2)(μ-CO)(CO)2], respectively. Both hydrides cis- and trans-[Fe2Cp2(μ-H)(μ-PPh2)(CO)2] can be reversibly oxidized at low temperature to the corresponding cation radicals cis- and trans-[Fe2Cp2(μ-H)(μ-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 (1H, 31P and 13C) spectroscopic data. The nature of the new radical cations is analyzed also on the basis of cyclic voltammetry and ESR measurements.