Structural features of titanium complexes of salicylaldiminato derivatives of amino acids

Condensation of salicylaldehyde with amino acid derivatives gave the salicylaldimine derivatives 3 that reacted with TiCl4 with release of HCl to yield the chelate complexes [(SalPhgOMe)TiCl3] (4a), [(SalValOMe)TiCl3] (4b), and the dipeptide derivative [(SalAlaValOMe)TiCl3] (4d). The complex [(Sal*PhgOMe)TiCl3] (4c) was prepared analogously starting from 3,5-di-tert-butyl-2-hydroxybenzaldehyde and phenylglycine methyl ester. Complex rac-4a was characterized by X-ray diffraction and shown to feature a typical structure where the monoanionic ligand is tridentate, coordinating to the central titanium atom through both the phenolate oxygen atom and the ester carbonyl oxygen atom as well as through the imine nitrogen atom. A hydrolyzed carboxylate analogue of 4a exhibits an analogous central structural framework. In this case, however, the overall structure of rac-5a was found to be a metallacyclic tetramer where four titanium atoms bind four such tridentate ligands. (c) Wiley-VCH Verlag GmbH & Co.