Titanocene catalysts with modifiable C2-symmetric chiral ligands

The synthesis of three chiral titanocene dichlorides based on a readily-accessible C2-symmetric tetrahydropentalenyl ligand is described. Two of the complexes are unsymmetrical containing also Cp and Cp∗ ligands, and one is the symmetric complex with two chiral tetrahydropentalenyls. The redox properties of the new titanocenes are investigated by cyclic voltammetry and the catalytic performance in asymmetric reductive ketone-nitrile cyclizations and cross-couplings is evaluated. Moderate to good yields and up to 33% ee are observed, which in case of the cross-coupling reactions exceeds the result obtained with (R,R)-ebthi-TiCl2.