Département de chimie moléculaire

The synthesis and redox properties are presented for the electron-rich bis(monothiolate)s Fe2(SR)2(CO)2(dppv)2 for R = Me ([1]0) (1), Ph ([2]0) (2) , CH2Ph ([3]0 (3)). Whereas related derivatives adopt C2-sym. Fe2(CO)2P4 cores, [1]0-[3]0 have Cs symmetry resulting from the unsym. steric properties of the axial vs. equatorial R groups. Complexes [1]0-[3]0 (1-3) undergo 1e- oxidation upon treatment with ferrocenium salts to give the mixed valence cations [Fe2(SR)2(CO)2(dppv)2]+ (4-6). As established crystallog., [3]+ adopts a rotated structure, characteristic of related mixed valence diiron complexes. Unlike [1]+ and [2]+ and many other [Fe2(SR)2L6]+ derivatives, [3]+ undergoes C-S bond homolysis, affording the diferrous sulfido-thiolate [Fe2(SCH2Ph)(S)(CO)2(dppv)2]+ ([4]+). According to X-ray crystallog., the first coordination spheres of [3]+ and [4]+ are similar, but the Fe-sulfido bonds are short in [4]+. The conversion of [3]+ to [4]+ follows first-order kinetics, with k = 2.3 × 10-6 s-1 (30°). When the conversion is conducted in THF, the organic products are toluene and dibenzyl. In the presence of TEMPO, the conversion of [3]+ to [4]+ is accelerated ∼10×, the main organic product being TEMPO-CH2Ph. DFT calculations predict that the homolysis of a C-S bond is exergonic for [Fe2(SCH2Ph)2(CO)2(PR3)4]+ but endergonic for the neutral complex as well as less substituted cations. The unsaturated character of [4]+ is indicated by its double carbonylation to give [Fe2(SCH2Ph)(S)(CO)4(dppv)2]+ ([5]+), which adopts a bioctahedral structure.