Synthesis, Structure, and Characterization of the [Fe₅S₄(CO)₁₂]²⁻,⁻ Ions and Studies on the Oxidative Conversion of the Dianion to [Fe₆S₆(CO)₁₂]²⁻


The compounds (Pr4N)2[Fe5S4(CO)12] ((Pr4N)2IV) 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) Å, b = 19 446(8) Å, c = 17.902(8) Å, β = 121.40(2)°, R = 0.056, Rw = 0.064, 2368 reflections with I > 3σ(I)); crystals of (Pr4N)V·0.5THF are triclinic, space group P1 (a = 11.745(1) Å, b = 11.807(1)Å, c = 15.198-(2) Å, a = 68.58(1)°, β = 85.99(1)°, R= 75.46(1)°, R = 0.023, Rw = 0.038, 5296 reflections with I > 3σ(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 O2-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)2VI has been obtained in crystalline form (orthorhombic, space group Cmc21; a = 18.870(8) Å, b = 17.307(13) Å, c = 16.430(3) Å, R = 0.057, Rw = 0.076, 2689 reflections with I > 3σ(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)I2]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. © 1995 American Chemical Society.



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© 1995 American Chemical Society (ACS), All rights reserved.