Synthesis and electrochemical studies of new ferrocene-labelled dinuclear rhodium(II) complexes. Crystal structures of [Rh2(O2CMe)2{[(C6H4)PhP(C5H4)]Fe(C5H5)}2(HO2CMe)2] and [Rh2(O2CMe)2{[(C6H4)PhP(C5H4)]2Fe}(HO2CMe)]·CH2Cl2

Abstract

The reaction of diphenylphosphinoferrocene and 1,1′-bis(diphenylphosphino)ferrocene with [Rh₂(O₂CMe)₄(MeOH)₂](1:1 and 1:2 molar ratio respectively) yields the monoadducts [Rh₂(O₂CMe)₄{(Ph₂PC₅H₄)Fe(C₅H₅)}]1 and [{Rh₂(O₂CMe)₄(MeOH)}₂{(Ph₂PC₅H₄)₂Fe}]2. By thermal treatment of 1 in refluxing toluene–acetic acid (10:3) the monometallated product [Rh₂(O₂CMe)₃{[(C₆H₄)PhP(C₅H₄)]Fe(C₅H₅)}(HO₂CMe)₂]3 was obtained in practically quantitative yield. Compound 3 reacts with [Fe(C₅H₅)(C₅H₄PPh₂)](1:1 molar ratio) giving the adduct [Rh₂(O₂CMe)₃{[(C₆H₄)PhP(C₅H₄)]Fe(C₅H₅)}{(Ph₂PC₅H₄)Fe(C₅H₅)}]4, which reacts thermally in toluene–acetic acid (10:3) yielding the doubly metallated product [Rh₂(O₂CMe)₂{[(C₆H₄)PhP(C₅H₄)]Fe(C₅H₅)}₂(HO₂CMe)₂]5 as a mixture of conformational isomers. An X-ray determination of 5 has been carried out: space group Pbca(orthorhombic), a= 18.065(3), b= 20.606(4), c= 26.242(5)Å, Z= 8, and R= 0.038. The crystal structure shows that the two metallated phosphines are in a head-to-tail configuration. Thermal treatment of a mixture of [Rh₂(O₂CMe)₄(MeOH)₂] and [Fe(C₅H₄PPh₂)₂](1:1 molar ratio) in acetic acid yields the compound [Rh₂(O₂CMe)₂{[(C₆H₄)PhP(C₅H₄)]₂Fe}(HO₂CMe)]·CH₂Cl₂6 after purification and crystallization from a CH₂Cl₂–hexane–acetic acid mixture. An X-ray diffraction investigation showed that this compound crystallizes in space group P2₁/c(monoclinic) with a= 12.735(4), b= 16.811(5), c= 20.161(8)Å, β= 95.17(4)°, Z= 4 and R= 0.089. The two PPh₂ fragments of the ferrocene ligand act as bridging orthometallated ligands in a head-to-head configuration. Two well defined oxidation processes were detected by cyclic voltammetry for all the complexes in CH₂Cl₂ solution: the first one, in the range 0.6–0.7 V, is due to the couple Fe²⁺–Fe³⁺ while the second one, in the range 0.9–1.32 V, is due to the couple Rh₂⁴⁺–Rh₂⁵⁺.