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

The complex trans -[Fe 2 Cp 2 (μ-H)(μ-PPh 2 )(CO) 2 ] is obtained in 91% yield by refluxing toluene solutions of [Fe 2 Cp 2 (CO) 4 ] (Cp = η 5 -C 5 H 5 ) and the secondary phosphine PPh 2 H. This compound isomerizes upon irradiation with visible−UV light under a CO atmosphere to yield cis -[Fe 2 Cp 2 (μ-H)(μ-PPh 2 )(CO) 2 ]. The above hydride complexes react under photochemical conditions with 1 equiv of secondary phosphines PR 2 H (R = Et, Ph) to give the corresponding monocarbonyl compounds [Fe 2 Cp 2 (μ-PPh 2 )(μ-PR 2 )(μ-CO)] via the hydride intermediates [Fe 2 Cp 2 (μ-H)(μ-PPh 2 )(CO)(PR 2 H)] (detected and isolated for R = Et). Deprotonation of trans -[Fe 2 Cp 2 (μ-H)(μ-PPh 2 )(CO) 2 ] with LiBu gives the binuclear anion [Fe 2 Cp 2 (μ-PPh 2 )(CO) 2 ] - . This highly nucleophilic carbonylate reacts rapidly with [AuCl(P i Pr 3 )] or MeI to give the corresponding gold diiron cluster [AuFe 2 Cp 2 (μ-PPh 2 )(CO) 2 (P i Pr 3 )] or methyl derivative [Fe 2 Cp 2 (Me)(μ-PPh 2 )(μ-CO)(CO) 2 ], respectively. Both hydrides cis - and trans -[Fe 2 Cp 2 (μ-H)(μ-PPh 2 )(CO) 2 ] can be reversibly oxidized at low temperature to the corresponding cation radicals cis- and trans -[Fe 2 Cp 2 (μ-H)(μ-PPh 2 )(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 ( 1 H, 31 P and 13 C) spectroscopic data. The nature of the new radical cations is analyzed also on the basis of cyclic voltammetry and ESR measurements.