The formation, crystal and molecular structure of (η 5-pentamethylcyclopentadienyl)(η 7-cycloheptatrienyl)titanium and (η 5-pentamethylcyclopentadienyl)(η 8-cyclooctatetraene)titanium

Abstract

(η 5-C 5Me 5)(η 8-C 8H 8)Ti was prepared in 34% yield from a reaction between (η 5-C 5Me 5)TiCl 3 and K 2C 8H 8 in THF solution, and in 31% yield from reduction of (η 5-C 5Me 5)TiCl 3 in THF solution by magnesium metal in the presence of cyclooctatetraene. The latter synthesis could be extended to the synthesis of (η 5-C 5H 5)(η 8-C 8H 8)Ti in 38% yield. Reduction of (η 5-C 5Me 5TiCl 3 in THF solution by metallic magnesium in the presence of cycloheptatriene produced (η 5-C 5Me 5)(η 7-C 7H 7)Ti in 68% yield. The structure of (η 5-C 5Me 5)(η 8-C 8H 8)Ti, at room temperature, was examined. This compound crystallizes in the orthorhombic space group Pnma with unit cell constants, a 9.946(7), b 13.597(4), c 11.513(9) Å and D(calc) 1.23 g cm −3 for Z = 4. Full matrix least-squares refinement using 915 independent observed reflections resulted in a final R value of 0.032. The titanium atom is located on a crystallographic mirror plane which bisects the two aromatic rings. The eight membered ring is disordered into two orientations. The average TiC(η 8) and TiC(η 5) distances are 2.34(2) and 2.338(5) Å, respectively. A low temperature (−90°C) X-ray diffraction study of (η 5-C 5Me 5)(η 7-C 7H 7)Ti resolved the disorder problem found for the C 8H 8 analogue. (η 5-C 5Me 5)(η 7-C 7H 7)Ti crystallizes in the orthorhombic space group Pnma with a 10.327(2), b 12.441(3), c 11.025(1) Å (at −90±2°C) and D(calc) 1.29 g cm −3 for Z = 4. A final R value of 0.048 was obtained from full matrix least-squares refinement based on 1143 independent observed reflections. The titanium atom resides on a crystallographic mirror plane which bisects the two aromatic rings. The TiC(η 7) distances average 2.21(1) Å, the TiC(η 5) separations average 2.32(1) Å, and the Cent(η 5)TiCent(η 7) angle is 176.2°.