SYNTHESIS AND CHEMICAL AND ELECTROCHEMICAL CHARACTERIZATION OF FE-S CARBONYL CLUSTERS - X-RAY CRYSTAL-STRUCTURES OF [N(PPH(3))(2)](2)[FE5S2(CO)(14)] AND [N(PPH(3))(2)](2) [FE6S6(CO)(12)]

A reinvestigation of the redox behavior of the [Fe-3(mu(3)-S)(CO)(9)]( 2-) dianion led to the isolation and characterization of the new [Fe5S 2(CO)(14)](2-), as well as the known [Fe6S6(CO)(12)](2-) dianion. As a corollary, new syntheses of the [Fe3S(CO)(9)](2-) dianion are also re ported. The [Fe5S2(CO)(14)](2-) dianion has been obtained by oxidative condensation of [Fe3S(CO)(9)](2-) induced by tropylium and Ag(I) salt s or SCl2, or more straightforwardly through the reaction of [Fe-4(CO) (13)](2-) with SCl2. The [Fe6S6(CO)(12)](2-) dianion has been isolated as a byproduct of the synthesis of [Fe3S(CO)(9)](2-) and [Fe5S2(CO)(1 4)](2-) or by reaction of [Fe-4(CO)(13)](2-) with elemental sulfur. Th e structures of [N(PPh(3))(2)](2)[Fe5S2(CO)(14)] and [N(PPh(3))(2)](2) [Fe6S6(CO)(12)] were determined by single-crystal X-ray diffraction an alyses. Crystal data: for [N(PPh(3))(2)](2)[Fe5S2(CO)(14)], monoclinic , space group P2(1)/c (No. 14), a = 24.060(5), b = 14.355(6), c = 23.8 98(13) Angstrom, beta = 90.42(3)degrees, Z = 4; for [N(PPh(3))(2)](2)[ Fe6S6(CO)(12)], monoclinic, space group C2/c (No. 15), a = 34.424(4), b = 14.081(2), c = 19.674(2) Angstrom, beta = 115.72(1)degrees, Z = 4. The new [Fe5S2(CO)(14)](2-) dianion shows a ''bow tie'' arrangement o f the five metal atoms. The two Fe-3 triangles sharing the central Fe atom are not coplanar and show a dihedral angle of 55.08(3)degrees. Ea ch Fe-3 moiety is capped by a triply bridging sulfide ligand. The 14 c arbonyl groups are all terminal; two are bonded to the unique central atom and three to each peripheral iron atom. Protonation of the [Fe5S2 (CO)(14)](2-) dianion gives reversibly rise to the corresponding [HFe5 S2(CO)(14)](-) monohydride derivative, which shows an H-1-NMR signal a t delta -21.7 ppm. Its further protonation results in decomposition to mixtures of Fe2S2(CO)(6) and Fe3S2(CO)(9), rather than formation of t he expected H2Fe5S2(CO)(14) dihydride. Exhaustive reduction of [Fe5S2( CO)(14)](2-) with sodium diphenyl ketyl progressively leads to fragmen tation into [Fe3S(CO)(9)](2-) and [Fe(CO)(4)](2-), whereas electrochem ical, as well as chemical oxidation with silver or tropylium tetrafluo roborate, in dichloromethane, generates the corresponding [Fe5S2(CO)(1 4)](-) radical anion which exhibits an ESR signal at g = 2.067 at 200 K. The electrochemical studies also indicated the existence of a subse quent one-electron anodic oxidation which possesses features of chemic al reversibility in dichloromethane but not in acetonitrile solution. A reexamination of the electrochemical behavior of the [Fe3S(CO)(9)](2 -) dianion coupled with ESR monitoring enabled the spectroscopic chara cterization of the [Fe3S(CO)(9)](-) radical monoanion and demonstrated its direct involvement in the generation of the [Fe5S2(CO)(14)](n-) ( n = 0, 1, 2) system.