Enantio‐ and Diastereomerically Pure Titanocenes by Dynamic Conformational Locking

The synthesis of enantiomerically pure titanocenes is limited to cases with enantiomerically pure substituents at the cyclopentadienyl ligands and to ansa‐titanocenes. For the latter complexes, the use of achiral ligands requires a resolution of enantiomers and frequently also a separation of the diastereoisomers obtained after metalation. Here, we introduce a new synthetic method that relies on the use of enantiomerically pure camphorsulfonate (CSA) ligands as control elements for the absolute and relative configuration of titanocene complexes. Starting from the conformationally flexible (RC5H4)2TiCl2, the desired conformationally locked and hence enantio‐ and diastereomerically pure complexes (RC5H4)2Ti(CSA)2 are obtained in just two steps. According to X‐ray crystallography the (RC5H4)2Ti fragment is essentially C2‐symmetric and nuclear magnetic resonance displays overall C2‐symmetry. We applied density functional theory methods to unravel the dynamics of the complexes and the mechanisms and selectivities of their formation. Conformational locking of unbridged substituted titanocenes is achieved by the introduction of chiral anionic ligands. A novel method for the synthesis of monosubstituted, enantio‐ and diastereomerically pure titanocenes with C2‐symmetry in the (RC5H4)2Ti fragment by reacting the methylated complexes with camphorsulfonic acid is presented. This study encompasses data from NMR and X‐ray analysis as well as a mechanistic investigation with the aid of state of the art DFT calculations.