Synthesis, Structure, and Reactivity of [Zr6Cl18H5]2-, the First Paramagnetic Species of Its Class

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Abstract
Reaction of [Zr6Cl18H5]3- (1) with 1 equiv of TiCl4 yields a new cluster anion, [Zr6Cl18H5]2- (2), which can be converted back into [Zr6Cl18H5]3- (1) upon addition of 1 equiv of Na/Hg. Cluster 2 is paramagnetic and unstable in the presence of donor molecules. It undergoes a disproportionation reaction to form 1, some Zr(IV) compounds, and H2. It also reacts with TiCl4 to form [Zr2Cl9]- (4) and a tetranuclear mixed-metal species, [Zr2Ti2Cl16]2- (3). The oxidation reaction of 1 with TiCl4 is unique. Oxidation of 1 with H+ in CH2Cl2 solution results in the formation of [ZrCl6]2- (5) and H2, while in py solution the oxidation product is [ZrCl5(py)]- (6). There is no reaction between 1 and TiI4, ZrCl4, [TiCl6]2-, [ZrCl6]2-, or CrCl3. Compounds [Ph4P]2[Zr6Cl18H5] (2a), [Ph4P]2[Zr2Ti2Cl16] (3a), [Ph4P]2[Zr2Cl9] (4a), [Ph4P]2[ZrCl6]·4MeCN (5a·4MeCN), and [Ph4P][ZrCl5(py)] (6a) were characterized by X-ray crystallography. Compound 2a crystallized in the trigonal space group R3̄ with cell dimensions (20 °C) of a = 28.546(3) Å, b = 28.546(3) Å, c = 27.679(2) Å, V = 19533(3) Å3, and Z = 12. Compound 3a crystallized in the triclinic space group P1̄ with cell dimensions (−60 °C) of a = 11.375(3) Å, b = 13.357(3) Å, c = 11.336(3) Å, α = 106.07(1)°, β = 114.77(1)°, γ = 88.50(1)°, V = 1494.8(7) Å3, and Z = 1. Compound 4a crystallized in the triclinic space group P1̄ with cell dimensions (−60 °C) of a = 12.380(5) Å, b = 12.883(5) Å, c = 11.000(4) Å, α = 110.39(7)°, β = 98.29(7)°, γ = 73.12(4)°, V = 1572(1) Å3, and Z = 2. Compound 5a·4MeCN crystallized in the monoclinic space group P21/c with cell dimensions (−60 °C) of a = 9.595(1) Å, b = 19.566(3) Å, c = 15.049(1) Å, β = 98.50(1)°, V = 2794.2(6) Å3, and Z = 2. Compound 6a crystallized in the monoclinic space group P21/c with cell dimensions (20 °C) of a = 10.3390(7) Å, b = 16.491(2) Å, c = 17.654(2) Å, β = 91.542(6)°, V = 3026.4(5) Å3, and Z = 4.