Molecular Design of Cyclopentadienyl Tantalum Sulfide Complexes.

Use of (Me3Si)2S and [Ta(η5-C5Me5)Cl4] (1) in a 4:3 ratio afforded the trimetallic sulfide cluster [Ta3(η5-C5Me5)3Cl3(µ3-Cl)(µ-S)3(µ3-S)] (2) with loss of SiClMe3. A similar reaction between 1, TaCl5, and (Me3Si)2S in a 2:1:4 ratio resulted in the analogous complex [Ta3(η5-C5Me5)2Cl4(µ3-Cl)(µ-S)3(µ3-S)] (3). Single-crystal X-ray diffraction analyses of 2 and 3 showed in all cases trinuclear tantalum sulfide clusters. On the other hand, thermal treatment of 2 with SiH3Ph generated very cleanly the dinuclear tantalum(IV) sulfide complex [Ta2(η5-C5Me5)2Cl2(µ-S)2] (4) in a quantitative way. Likewise, we found that 4 was synthesized more easily by a one-pot reaction of 1, (Me3Si)2S, and SiH3Ph in toluene. Reactions of 4 with a series of alkylating reagents rendered the dinuclear peralkylated sulfide complexes [Ta2(η5-C5Me5)2R2(µ-S)2] (R = Me 5, Et 6, CH2SiMe3 7, C3H5 8, Ph 9). Single-crystal X-ray diffraction analyses of 4, 5, and 9 showed in all cases a trans disposition of the chloro or alkyl substituents. The short Ta-Ta distances (2.918(1)-2.951(1) Å) along with DFT calculations indicate a σ-Ta-Ta interaction. Complexes 5, 6, and 8 undergo trans- cis isomerization, and mechanistic proposals are discussed based on DFT calculations.