IMPORTANCE OF STERIC REQUIREMENTS RELATIVE TO ELECTRONIC CONTRIBUTIONS IN BICYCLOALKYL-SUBSTITUTED TITANOCENE DICHLORIDES

A group of bicycloalkyl-substituted titanocene dichlorides was examined by X-ray photoelectron spectroscopy in order to gauge if the rather large steric requirements of these ligands exert greater or lesser impact on the binding energy of the titanium center relative to the electronic effect of alkyl substitution. Simpler model systems were likewise evaluated. X-ray crystallographic data were available for many of the norbornyl-, bornyl-, and pinanyl-fused titanocenes. The solid-state structure of 3 has been established by X-ray crystallographic analysis: space group C2/c, a = 12.456(5), b = 6.695(3), c = 16.591(8) angstrom; beta = 98.37(3)-degrees; Z = 4. The structure refined to R and R(w) values of 0.067 and 0.079, respectively, with use of 1357 reflections. This information and associated Fenske-Hall calculations revealed that, although heightened levels of ring slippage were in effect, the inductive contributions of substituents directly bonded to the Cp rings dominate over the steric contributions of the space-demanding ligands in controlling the electronic changes at the core titanium atom.