Hydrolysis and Condensation Processes of Titanium iso-Propoxide Modified with Catechol: An NMR Study

The hydrolysis and condensation processes of titanium iso-propoxide modified with catechol (C₆H₄(OH)₂; H₂cat) have been investigated by ¹H, ¹³C and ¹⁷O nuclear magnetic resonance spectroscopy. The hydrolysis reactions of the modified titanium iso-propoxide in the system with Ti:tetrahydrofuran (THF):H₂O = 1:20:x (x = 1, 2 and 5 in a molar ratio) are essentially completed in the initial stage (<1 h), and the condensation reactions also proceed significantly during this stage. Upon hydrolysis with H₂O/Ti = 1, the iso-propoxy groups are selectively hydrolyzed and the catecholate groups remain bound to titanium. With H₂O/Ti = 2 and 5, both the iso-propoxy and catecholate groups are hydrolyzed, and the hydrolysis of the iso-propoxy groups is relatively preferential. Approximately half the catecholate groups are stably bound to titanium, even after hydrolysis with H₂O/Ti = 5.