SYNTHESIS AND ELECTROCHEMICAL STUDIES OF NEW FERROCENE-LABELED 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

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) angstrom, 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)].CH2Cl2 6 after purification and crystallization from a CH2Cl2-hexane-acetic acid mixture. An X-ray diffraction investigation showed that this compound crystallizes in space group P2(1)/c (monoclinic) with a = 12.735(4), b = 16.811(5), c = 20.161(8) angstrom, beta = 95.17(4)degrees, 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 Rh2(4+)-Rh2(5+).