Metal−Metal Bonding in Pentanuclear Bow-Tie Metal Sulfido Clusters. Synthetic and Structural Studies on the Cationic Pentanuclear Clusters [(Cp*Ir)<sub>2</sub>(μ<sub>3</sub>-S)<sub>2</sub>M(μ<sub>3</sub>-S)<sub>2</sub>(IrCp*)<sub>2</sub>]<i><sup>n</sup></i><sup>+</sup> (M = Fe, Co, Ni; <i>n</i> = 1, 2)
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Reactions of [Cp*MCl(μ2-SH)2MCp*Cl] (1, M = Ir; 2, M = Rh; Cp* = η5-C5Me5) with excess FeCl2·4H2O in THF gave the paramagnetic trinuclear clusters [(Cp*M)2(μ3-S)2FeCl2] (3, M = Ir; 4, M = Rh), which were further converted into the dicationic 78e- pentanuclear bow-tie cluster [(Cp*Ir)2(μ3-S)2Fe(μ3-S)2(IrCp*)2]2+ (5) by treatment with NaBPh4. When complex 1 was allowed to react with CoCl2 and NiCl2·6H2O or Ni(cod)2 (cod = cyclooctadiene), the related pentanuclear 79e- and 80e- bow-tie clusters [(Cp*Ir)2(μ3-S)2M(μ3-S)2(IrCp*)2]2+ (6, M = Co; 7, M = Ni) were obtained directly, respectively. Cyclic voltammograms of 5[BPh4]2, 6[BPh4]2, and 7[BPh4]2 showed two reversible reduction waves at −0.25 to −0.43 V and −1.04 to −1.34 V. In both redox couples, the redox potential was in the order Fe < Co < Ni. One-electron reduction of clusters 5[BPh4]2, 6[BPh4]2, and 7[BPh4]2 with Co(η5-C5H5)2 gave the corresponding monocationic pentanuclear 79−81e- bow-tie clusters [(Cp*Ir)2(μ3-S)2M(μ3-S)2(IrCp*)2]+ (8, M = Fe; 9, M = Co; 10, M = Ni). The molecular structures of 3, 4, 5[BPh4]2·CH2Cl2, 6[CoCl3(NCMe)]2, 7[NiCl4]·CH2Cl2, 8[BPh4], 9[BPh4], and 10[BPh4] were unambiguously determined by X-ray diffraction study. The structures of the pentanuclear bow-tie cluster cores remarkably changed stepwise as the core electrons increased from 78 to 81. Two of the M−Ir (M = Fe, Co) bonds in the 79e- clusters 6 and 8 show significant elongation in comparison with the Fe−Ir bonds in the 78e- cluster 5. Two different types of the bow-tie structures were observed for the 80e- clusters 7 and 9. Cluster 7 has a Z-shaped metal core with only two Ni−Ir bonds, while in cluster 9, the six metal−metal bonds in the bow-tie structure are retained with slight elongation of the Co−Ir bonds in comparison with the corresponding dication 6. The 81e- cluster 10 has two normal Ni−Ir bonds and one long Ni−Ir bonding interaction with the fourth nonbonding Ni−Ir contact. This structural variation is interpreted in terms of the total electron counts and molecular orbital calculations of the clusters.
