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

Article abstract of DOI:10.1021/ja00209a023

Treatment of (MeCp)2V2S4 with PBu3 gives the electron-deficient (56e) cubane (MeCp)4V4S4 (1).Desulfurization of 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 behaviour, 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-cristal X-ray diffraction.Compound 1 crystallized in the cubic space group p4<*>3n with a = 16.551 (3) Angstroem 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 I4<*> with a = 10.600 (3) Angstroem and c = 12.600 (3) Angstroem 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) Angstroem 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 Angstroem.The structure of 2 revealed two sets of Ti-Ti distances, four distances of 3.00 Angstroem and two of 2.93 Angstroem.Electronic structure calculations of Cp4V4S4 and ⁺ were performed by the scattered wave-Xα method.The ground-state configuration for the Cp4V4S4 metal bonding orbitals is a₁²e⁴t₂².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.