COORDINATION CHEMISTRY OF ZIRCONIUM TETRACHLORIDE - CRYSTAL-STRUCTURE OF THE 1-2 ADDUCT WITH PINACOLONE

Studies of adducts 1–4 of zirconium tetrachloride with acetone, pinacolone, 3-pentanone, and tetrahydrofuran by infrared spectroscopy in solution and in the solid state, and by low-temperature 1H NMR spectroscopy in solution, suggest that all four bases form octahedral 1:2 complexes. This conclusion is supported by the results of an X-ray crystallographic study of the 1:2 pinacolone adduct 2, which crystallizes in the orthorhombic space group P212121 with a = 9.660 (3) Ǻ, b = 11.935 (4) Ǻ, c = 16.813 (7) Ǻ, V = 1938.4 Ǻ3, and Z = 4. Refinement of 3259 reflections yielded R = 0.18. The structure shows that the ketones are cis and σ-bound with an average C-O-Zr angle of 151°. In solution, bound and free acetone exchange by dissociation of complex 1 with ΔC* = 12.4 kcal/mol. Syn-anti isomerization is rapid in acetone adduct 1 and 3-pentanone adduct 3 even at -120 °C in CHF2Cl, possibly because significant oxygen-p-zirconium-d π-bonding or an important electrostatic contribution to the energy of complexation facilitates inversion at oxygen. © 1990, American Chemical Society. All rights reserved.