The dimerisation of carbon disulfide on Fe centres. Some new tetrathiolene complexes of iron

The thermolysis of [Fe(L)2(CO)2((eta)^2-CS2)] complexes (1) in refluxing benzene gives the blue tetrathiolene derivatives [Fe2(L)4(CO)2(C2S4)](2) when L = P(OPh)3, P(OEt)3, P(OPri)3, PPh(OEt)2, PPh2(OEt). 2 are formed only when the phosphorus(III) ligands L readily dissociate from 1 and have cone angles between 109° and 133°. The two most stable are 2a{L = P(OPh)3, cone angle 128°} and 2c{L = P(OPri)3, cone angle 130°}. 2 have been characterised by IR, electronic and NMR spectroscopy and elemental analyses. Their UV-Vis spectra are dominated by an intense absorption band ((epsilon)= 13000-18000 dm^3 mol^-1 cm^-1) with (lambda)max= 640-690 nm. The labile triphenylphosphite ligands in 2a can be replaced in part by CO. Spectroscopic data confirms that the unstable product, 3a, contains a ligand set similar to that of 2a. Electrochemical studies show that 2a undergoes a one-electron reversible reduction to [2a](bullet)- and a one-electron, irreversible oxidation. The UV-Vis spectrum of [2a](bullet)shows a very low energy absorption band at 2556 nm (3912 cm^-1) with (epsilon)=ca. 3600 dm^3 mol^-1 cm^-1 which is attributed to a charge transfer transition from the SOMO to an orbital with (mu)-C2S4 character. The ESR spectrum of [2a](bullet)x^2-y^2 character which is localised on one Fe atom. Under CO, one-electron reversible transfers are observed in the electrochemistry due to the redox series [3a]-/0/+. 2a is oxidised by halogens to [L2(OC)(X)Fe(S2C2S2) Fe(X)(CO)L2] derivatives.