A sustainable water-tolerant catalyst with enhanced Lewis acidity: Dual activation of Cp2TiCl2 via ligand and solvent

A new strategy was developed to enhance the activity of titanocene dichloride for the synthesis of 2,4-disubstituted-3H-benzo[b]-[1,4]diazepine derivatives by using Cp2TiCl2 as a pre-catalyst. The titanocene was activated in situ in the catalytic system via the coordination with m-phthalic acid and alcohol solvent accompanied with the secession of a cyclopentadienyl ring, leading to the formation of an activated species, [CpTi(OEt)(2)(eta(1)-C8H5O4)]. In particular, the novel developed half-titanocene catalyst exhibited more superior stability than representative half-titanocene complex, indicated by not only water compatibility for the employment of 30 % aqueous ethanol solution but also the recyclability that the products could be generated without apparent yield decrease after 5 runs. In general, we present a paradigm for sustainable molecular catalysis of titanocene.