Schiff Bases-Titanium (III) & (IV) Complex Compounds: Novel Photocatalysts in Buchwald-Hartwig C–N Cross-Coupling Reaction

Nine novel Schiff bases were derived from salicylic aldehyde and oxalic aldehyde, isolated, and their molecular and spatial structure were explored by a set of experiments (IR, CNMR, HNMR, CHN, SEM, XRD) and theoretical simulation (DFT def2-TZVP). A high potential was predicted in metal cations chelating. The isolated organic species were applied as the ligands in the reaction of complex formation with titanium (III) chloride and (IV) bromide and 12 novel complexes were synthesized and studied experimentally and theoretically. Using the UV–vis spectroscopic titration, the solution stability of the complexes was indicated. Depending on the nature of the Schiff base ligand, their formation constants were calculated in the range of 6.84–17.32. Using the DFT def2-TZVP theoretical method together with the experimental spectroscopic data, the coordination types of the ligands were investigated, and the structure of the complexes was proposed. The photocatalytic ability of the isolated complexes was tested in the C-N cross-coupling reaction under sunlight. Complexes exhibited high visible-light photocatalytic activity for a wide range of aromatic and benzylic amines including electron-withdrawing and electron-donating groups from moderate to good yields ranging in 50–85 %. The use of an inexpensive, clean, and renewable energy source (visible light) is the superiority of the developed photocatalytic systems.