SYNTHESIS, STRUCTURE, AND CHARACTERIZATION OF THE [FE5S4(CO)(12)](2-,-) IONS AND STUDIES ON THE OXIDATIVE CONVERSION OF THE DIANAION TO [FE6S6(CO)(12)](2-)

The compounds (Pr4N)(2)[Fe5S4(CO)(12)] ((Pr4N)(2)IV) and (Pr4N)[Fe5S4(CO)(12)]. 0.5THF ((Pr4N)-V . 0.5THF, THF = tetrahydrofuran) have been prepared and structurally characterized. Crystals of (Pr4N)IV are monoclinic, space group C2/c (a = 34.16(1) Angstrom, b = 19.446(8) Angstrom, c = 17.902(8) Angstrom, beta = 121.40(2)degrees, R = 0.056, R(w) = 0.064, 2368 reflections with I > 3 sigma(I)); crystals of (Pr4N)V . 0.5THF are triclinic, space group P1 (a = 11.745(1) Angstrom, b = 11.807(1) Angstrom, c = 15.198(2) Angstrom, alpha = 68.58(1)degrees, beta = 85.99(1)degrees, gamma = 75.46(1)degrees, R = 0.023, R(w) = 0.038, 5296 reflections with I > 3 sigma(I). The two anions have similar structures, with a central Fe atom (Fe(II) and Fe(III) for IV and V, respectively) coordinated in a distorted tetrahedral geometry by two [Fe2S2(CO)(6)](2-) ligands. Cluster IV undergoes an O-2-specific oxidation to the known cluster [Fe6S6(CO)(12)](2-) (VI) by an undetermined mechanism. Cluster VI can be prepared cleanly by reaction of Fe2S2(CO)(6) (I) with [Fe4S4(CO)(12)](2-) (II), and a mechanism involving oxidative addition of I to II is postulated. (Pr4N)(2)VI has been obtained in crystalline form (orthorhombic, space group Cmc2(1); a = 18.870(8) Angstrom, b = 17.307(13) Angstrom, c = 16.430(3) Angstrom, R = 0.057, R(w) = 0.076, 2689 reflections with I > 3 sigma(I)) and structurally characterized. Oxidative addition of II is also suggested as an important step in the formation of the previously reported cluster [MoOFe5S6(CO)(12)](2-), which insight has resulted in an improved synthesis for the latter cluster. This newly-discovered reactivity of [Fe4S4(CO)(12)](2-) makes the compound a potentially useful reagent in preparing a variety of mixed M-Fe-S clusters having new stoichiometries and structures.