Transition metal dithiolene complexes. Part XVIII. Adducts of cobalt and iron bis-1,2-dithiolenes containing ethyldiphenylphosphine and bis(1,2-diphenylphosphino)ethane

Abstract

The syntheses and spectral characterisation of a series of adducts of iron and cobalt bis-1,2-dithiolenes with ethyldiphenylphosphine and bis(1,2-diphenylphosphino) ethane (diphos) are described. With PEtPh₂, five-co-ordinate species of the type [M(PEtPh₂)–(S–S)₂]^z were obtained, where z =–1 and (S–S)= S₂C₂(CN)₂,S₂C₂(CF₃)₂ or S₂C₆Cl₄, or where z = 0 and (S–S)= S₂C₂Ph₂, S₂C₂(4-MeC₆H₄)₂ or S₂C₂(4-MeOC₆H₄)₂. With diphos, compounds of a similar type were prepared, viz.[M(diphos)–(S–S)₂]^z, where z =–1 or 0 and (S–S) was as shown above. By oxidation of the appropriate monoanion with iodine, [Fe(diphos){S₂C₂(CN)₂}₂]⁰ was prepared and isolated, and [Co(PEtPh₂){S₂C₂(CF₃)₂}₂]⁰ was identified by e.s.r. spectral measurements. Treatment of [Co(diphos)-{S₂C₂(4-MeOC₆H₄)₂}₂]⁰ with AgPF₆ afforded the corresponding monocation, as the [PF₆]^– salt. The majority of the complexes underwent reversible one-electron transfer reactions indicating that they were members of the electron-transfer series [M(L)–(S–S)₂]^z where M = Fe or Co, L = PEtPh₂ or diphos, and z=–2, –1, 0 or +1.

From the spectral and voltammetric data, it appears that in [M(diphos)–(S–S)₂]^z, when z=–1 and (S–S)= S₂C₂(CN)₂ or S₂C₂(CF₃)₂, the diphosphine ligand is bidentate, but when z= 0 and (S–S)= S₂C₂Ph₂, S₂C₂(4-MeC₆H₄)₂ or S₂C₂(4-MeOC₆H₄)₂, it may be monodentate.