Characterization and Reactions of [PPh₄]₃[Zr₆Cl₁₈H₅] and Its Deprotonation Products

Abstract

The octahedral hexazirconium cluster compound [PPh4]3[Zr6Cl18H5] has been structurally characterized by both neutron and X-ray single-crystal diffraction studies. The compound [PPh4]3[Zr6Cl18H5]·3CH2Cl2 crystallizes in the triclinic space group P1̄ with unit cell parameters of a = 15.993(3), b = 22.237(3), and c = 14.670(4) Å, α = 95.31(1), β = 112.07(2), and γ = 82.06(2)°, V = 4784(2) Å3, and Z = 2 at ambient temperature and a = 15.780(6), b = 21.96(3), and c = 14.521(7) Å, α = 94.96(8), β = 111.59(4), and γ = 81.72(5)°, V = 4627(11) Å3, and Z = 2 at T = 15 K. The hydrogen atoms in the cluster anion, [Zr6Cl18H5]3-, were found to be distributed at the centers of the eight triangular faces of the Zr6 octahedron from neutron diffraction data. The occupancy parameters of the sites range from 0.32 to 0.92 with a total of 5.3(1) hydrogen atoms per cluster, close to the value from 1H NMR measurement (5.0). The average Zr−H distance is 1.96(4) Å. A variable temperature 1H NMR study indicated that the cluster hydrogen atoms undergo rapid movement at room temperature. One of the five hydrogen atoms in the cluster [Zr6Cl18H5]3- was readily removed as a proton with primary linear amines with formation of the corresponding ammonium cations, while the cluster anion, [Zr6Cl18H5]3-, was thus converted into a new cluster anion, [Zr6Cl18H4]4-. The feasibility of such a deprotonation reactions is controlled by the size of both the Lewis base and the cavity available on the Zr3 triangular faces of the Zr6 clusters, and also by the basicity of the deprotonating reagents. Two products, [PPh4]4[Zr6Cl18H4]·4CH2Cl2 and [H3NEt]4[Zr6Cl18H4]·4MeCN from the deprotonation reactions were characterized by X-ray crystallography