Novel Titanatranes with Different Ring Sizes: Syntheses, Structures, and Lactide Polymerization Catalytic Capabilities

The new titanatranes (Ar = 2,6-di- i -Pr-phenoxy; Ar‘ = 2,4-di-MeC 6 H 2; x = 0, 5; x = 1, 6; x = 2, 7; x = 3, 8 ) featuring three six-membered chelating rings ( 5 ) to three five-membered chelating rings ( 8 ) in a stepwise fashion through 6 and 7 were synthesized from the corresponding trihydroxy chelating ligands 1 − 4, respectively, using an equimolar mixture of Ti(O- i -Pr) 4 and 2,6-di- i -Pr-phenol. The molecular structures of 5 and 6, determined by X-ray means, revealed that in both of these complexes the transannular N−Ti bond lengths [2.305(2) Å, 5; 2.287(4) Å, 6 ] are at the short end of the range for titanatranes possessing three five-membered rings. These compounds show good catalytic activity for the bulk homopolymerization of l - and rac -lactide at 130 °C.