Zirconium Clusters from the Reaction of ZrCl₄ with HSnBu₃ Followed by Addition of Phosphines:  Zr₆Cl₁₄H₄(PR₃)₄ Compounds

The reduction of ZrCl₄ with HSnBu₃ followed by addition of phosphines yields pentanuclear cluster compounds Zr₅Cl₁₂(PR₃)₅H₄ (2) and three types of hexanuclear cluster compounds, Zr₆Cl₁₄(PR₃)₄H₄ (3), as well as [Zr₆Cl₁₈H₅]^3- (4) and a small amount of [Zr₆Cl₁₈H₄]^4- (5). Separation of these compounds has been achieved by using different solvents in which they have different solubilities and stabilities. The presence of hydrogen atoms and their numbers have been established by ¹H NMR spectroscopy. The compounds Zr₆Cl₁₄(PR₃)₄H₄ (3a, R = Me; 3b, R = Et; 3c, R = n-Pr) and [HP(t-Bu)₂Ph]₃[Zr₆Cl₁₈H₅] (4d) have been characterized by X-ray crystallography. In compounds 3a and 3b, four hydrogen atoms distributed on the eight triangular faces of the Zr₆ octahedron were located. Compound 3a·2CH₂Cl₂ crystallized in the monoclinic space group P2₁/n with cell dimensions (−75 °C) of a = 11.149(2) Å, b = 11.049(4) Å, c = 20.666(7) Å, β = 103.42(2)°, V = 2476(1) ų, and Z = 2. Compound 3b·2CH₂Cl₂ crystallized in orthorhombic space group Pbca with cell dimensions (−60 °C) of a = 12.127(3) Å, b = 21.793(5) Å, c = 23.022(4) Å, V = 6084(2) ų, and Z = 4. Compound 3c·2.31C₆H₆ crystallized in triclinic space group P1̄ with cell dimensions (−60 °C) of a = 12.585(1) Å, b = 13.679(2) Å, c = 23.319(4) Å, α = 97.08(2)°, β = 94.77(2)°, γ = 93.30(2)°, V = 3960.6(9) ų, and Z = 2. Compound 4d·2CH₂Cl₂·2C₆H₆ crystallized in monoclinic space group C2/c with cell dimensions (−60 °C) of a = 29.432(4) Å, b = 13.503(1) Å, c = 23.892(3) Å, β = 110.96(1)°, V = 8867(2) ų, and Z = 4. In compounds 3a−c, six zirconium atoms are arranged in a slightly elongated octahedron with four phosphine ligands at the equatorial positions. The distance of Zr_eq−Zr_ax (3.359(8) Å) is slightly longer that of Zr_eq−Zr_eq (3.308(6) Å), but both of them are shorter than that found in compound 4d (3.416(2) Å).