Electron-Deficient Early−Late Heterobimetallic Sulfido Clusters. Unusual Reactivities of Ti₂Ru₂S₄ Cubane-Type Clusters with Four Cyclopentadienyl Coligands

Treatment of [Cp₂Ti(SH)₂] (1; Cp = η⁵-C₅H₅) with [(Cp*Ru)₄(μ₃-Cl)₄] (2; Cp* = η⁵-C₅Me₅) in a Ti:Ru ratio of 1:1 afforded the hydrosulfido-bridged titanium−ruthenium heterobimetallic complex [Cp₂Ti(μ₂-SH)₂RuClCp*] (3). Complex 3 reacted with an excess of triethylamine to give the early−late heterobimetallic cubane-type sulfido cluster [(CpTi)₂(Cp*Ru)₂(μ₃-S)₄] (4), with a loss of HCl and cyclopentadiene. An X-ray diffraction study and extended Hückel molecular orbital calculations for the 60e^- cluster 4 demonstrated that 4 has four Ru→Ti dative bonds and a weak Ti−Ti interaction. The reaction of 4 with 3 equiv of [Cp₂Fe][PF₆] afforded the dicationic cubane-type cluster [(CpTi)₂(Cp*Ru)₂(μ₃-S)₄][PF₆]₂ (5), which contains an additional Ru−Ru bond. In contrast, oxidation of 4 with an excess of HCl at room temperature resulted in the formation of the neutral dichloride cluster [(CpTiCl₂)(CpTi)(Cp*Ru)₂(μ₃-S)₄] (6). Clusters 5 and 6 were converted into each other by treatment with chloride or hexafluorophosphate anion. Furthermore, substitution of one of the cyclopentadienyl ligands in 6 by a chloride anion took place in boiling 1,2-dichloroethane to give the trichloride cluster [(TiCl₃)(CpTi)(Cp*Ru)₂(μ₃-S)₄] (7). The detailed structures of these oxidized cubane-type clusters 5·2DMF, 6·CH₂Cl₂, and 7·CH₂Cl₂ as well as the hydrosulfido-bridged dinuclear complex 3 have also been determined by X-ray crystallography. The Ti₂Ru₂S₄ cubane-type cores in 5−7 differ considerably in structure from each other, depending upon the ancillary ligands bound to the Ti atoms, although they have a Ru−Ru bond and two Ru→Ti dative bonds in common.