Isodicyclopentadienes and related molecules : LVII. Solid state structural studies of the diastereomeric exo- and endo-(η -cyclopentadienyl)( η -( 1S,8R)-9,9-dimethyltricyclo[6.1.1.0]deca-2,5-dienyl) dichlorotitaniums and a stereopure exo-(η-pentamethyl-cyclopentadienyl) congener

The lithium salt of optically pure (1S,8R)-9,9-dimethyltricyclo6.1.1.0^2,6]deca-2,5-diene (9) has been transformed in highly stereoselective fashion to the dichlorotitanium complexes 5–7. Temperature and reaction conditions can be suitably controlled to attain proper ρ-facial selectivity in those condensations involving CpTiCl₃. Direct condensation with CpTiCl₃, on the other hand, leads only to 7 in a more sluggish reaction. A stereochemical crossover to arrive at 8 was attempted by taking advantage of the inversion of configuration that operates during condensation of silane 10 with TiCl₄. Unfortunately, steric hindrance precluded the successful reaction of 11 with Cp^*M (M = Li, K, Tl, SiMe₃ SnMe₃) to provide 8. Crystal structure analyses of the three available complexes were completed and detailed comparison of their structural features are presented. The absolute configurational assignments rest securely on the synthetic pathway developed earlier for gaining access to 9.