Sulfido-Persulfido Equilibria in Sulfur-Rich Metal Clusters: The Case of (C5Me5)3RhRu2S4

The reaction of [(C5Me5)M(MeCN)3](PF6)2 with (C5Me5)2Ru2S4 gives the cluster compounds [(C5Me5)3MRu2S4(MeCN)](PF6)2, 1(PF6)2 (M ) Rh) and 3(PF6)2 (M ) Ir). Crystallographic studies of 1(PF6)2 show that the dication consists of an asymmetric RhRu2S4 core containing an isosceles triangle of metal atoms with a Ru-Ru bond of 2.88 Å. The three metal atoms are joined by two μ3-η:η:ηS2 units, each persulfide being monodentate toward Rh. NMR studies show that 12+ is stereochemically nonrigid such that the two Ru(C5Me5) resonances coalesce at higher temperatures. The dynamic processes involving 12+ are unaffected by added (C5Me5)Rh(MeCN)3, ruling out dissociation of the (C5Me5)Rh center. Exchange of the (C5Me5)Ru sites in [(C5Me5)2(C5Me4Et)RhRu2S4(MeCN)](PF6)2, 2(PF6)2, is associated with coalescence of the pairs of C5Me4Et resonances, suggesting that the dynamics in 12+ involve racemization. It is proposed that these dynamics proceed via the “base-free” intermediate [(C5Me5)3RhRu2S4], wherein one S-S bond has been cleaved. Solutions of 12+ react with acetone to give the S-acetonyl derivative [(C5Me5)3RhRu2S3(SCH2COCH3)]PF6, 4(PF6). This species, which is not fluxional on the NMR time scale, is a rare example of a metal sulfido cluster with a trigonal prismatic M3S3 core. There is one metal-metal bond of 2.75 Å between the two Ru atoms, spanned by the acetonylthio ligand. The M-S distances are nearly equivalent at 2.33 Å while the S-S bonding distance is 2.12 Å. This reaction is reversed by acid to give 12+ and acetone.