Distinctive structural features of hydroxyamino-1,3,5-triazine ligands leading to enhanced hydrolytic stability of their titanium complexes

Three bis(homoleptic) titanium complexes of hydroxyamino-1,3,5-triazine ligands 3a-c were synthesized and characterized, and their kinetic behavior in THF-water solutions was studied at various pH conditions using UV-vis, based on the characteristic Ti-O band at 380 nm. One of these complexes, 3c, was analyzed by X-ray crystallography. Due to the characteristic electronic structure of the triazine rings, high electron density on the nitrogen atoms leads to strong N-Ti bonds, as indicative by the 2.0 coordinative bond lengths in the X-ray structure. Consequently, these complexes exhibit high hydrolytic stability over a wide pH range, where hydrolysis was observed to be promoted by basic conditions. At neutral pH, t_1/2 was estimated to be >200 h, whereas at pH = 5.5, no hydrolysis was observed for a period of at least three days.