A NEW BIS(MU-SULFIDO)DITANTALUM(IV) EDGE-SHARING BIOCTAHEDRAL MOLECULE AND A REASSESSMENT OF SOME EARLIER BIS(MU-CHLORO) MOLECULES

After reduction of TaCl5in toluene with Na/Hg, PhSSPh was added, followed by PMe2Ph. After appropriate workup, orange crystalline Ta2(M-S)2Cl4(PMe2Ph)4was obtained and its crystal structure determined. The compound formed crystals in space group Pl (a= 10.823 (2) Å, b = 10.991 (4)Å, c = 9.782 (3) Å, α = 107.77 (3)°, β = 113.86 (2)°, γ = 86.58(3)°, Z= 1), and the centrosymmetric molecule has a Ta-Ta distance of 2.8757 (4) Å and a mean Ta-S distance of 2.358 [4] Å. Previously reported Nb2Cl6(EtSCH2CH2SEt)2has been obtained in an isomeric form having different relative ring conformations. Crystals in space group P2Ja (a = 14.838 (5) Å, b = 10.396 (5) Å, c = 16.492 (5) Å, β = 95.4 (3)°, Z = 4) contain molecules in which the chelate rings, each with an anti arrangement of ethyl groups, are related by virtual D2symmetry. When the present results as well as several other structures are compared, we are led to propose that three compounds previously reported to be Nb2Cl6(SMe2)4, Ta2Cl6(SMe2)4, and Ta2Cl6(EtSCH2CH2SEt)2should be reformulated as having two μ-S groups rather than two μ-Cl groups. This changes the metal atom oxidation states from III to IV and the M-M bond orders from 2 to 1 and thus rationalizes the apparently long M-M bonds. © 1990, American Chemical Society. All rights reserved.