Synthetic, Structural, and Theoretical Studies on the Electron-Deficient Cubanes (RC₅H₄)₄Ti₄S₄ (RC₅H₄)V₄S₄ and [(RC₅H₄)₄V₄S₄⁺

Treatment of (MeCp)₂V₂S₄ with PBu₃ gives the electron-deficient (56e) cubane (MeCp)₄V₄S₄ (1). Desulfurization of a 1:1 mixture of (MeCp)₂V₂S₄ and Cp₂V₂S₄ gave a mixture of ring-substituted cubanes (MeCp)_4-xCp_xV₄S₄(x = 1–4) while (MeCp)₂V₂S₄ and Cp₂V react to give exclusively (MeCp)₂Cp₂V₄S₄. Compound 1 has a triplet (S = 1) ground state, exhibits Curie-Weiss magnetic behavior, and has a well-resolved isotropically shifted ¹H NMR spectrum. Cyclic voltammetry (vs Ag/AgCl) established the following redox series: 1⁺/1 (772 mV), 1/1^- (176 mV), and 1^-/1^2- (-1281 mV). The salt [1](BF₄) was prepared by the reaction of 1 and Ph₃CBF₄. The diamagnetic 52e cubanes (RCp)₄Ti₄S₄ (R = Me (2), i-Pr) were prepared from (RCp)TiCl₂(THF)_x and (Me₃Si)₂S. The compounds 1, [1](BF₄), and 2 were characterized by single-crystal X-ray diffraction. Compound 1 crystallized in the cubic space group P4̅3n with a = 16.551 (3) Å with Z = 6; 671 unique reflections were processed to a final R(F) = 5.31 (R_w(F) = 5.80). Compound [1](BF₄) crystallized in the tetragonal space group I4̅ with a = 10.600 (3) Å and c = 12.600 (3) Å with Z = 2; 463 unique reflections were processed to a final R = 6.40 (R_W(F) = 6.55). Compound 2 crystallized in the orthorhombic space group Cmca with a = 1.412 (5), b = 17.293 (6), c = 24.503 (9) Å with Z = 8; 558 unique reflections were processed to give R = 10.5 (R_W(F) = 12.6). 1 and [1]⁺ are extremely similar structurally; no bond distances differ by more than 0.03 Å. The structure of 2 revealed two sets of Ti-Ti distances, four distances of 3.00 Å and two of 2.93 Å. Electronic structure calculations of Cp₄V₄S₄ and [Cp₄V₄S₄]⁺ were performed by the scattered wave-Xα method. The ground-state configuration for the Cp₄V₄S₄ metal bonding orbitals is a₁² e⁴ t₂². The t₂ orbital is predicted to be nonbonding, consistent with the structural results. The bonding in 1, 1⁺, and 2 is discussed in light of recent results from other laboratories.