Group 4 catalysts incorporated in 2-(2H-benzotriazol-2-yl)-4-methyl-6-(morpholinomethyl)phenolate ligand ((BTP)-B-C1MO) were synthesized and structurally characterized. The reaction of Ti((OPr)-Pr-t)(4) or M((OPr)-Pr-t)(4)((PrOH)-Pr-t) (M = Zr, Hf) with (BTP)-B-C1MO-H (2.0 M equiv.) in toluene produced the hexa-coordinated bis-adduct metal complex [((BTP)-B-C1MO)(2)M((OPr)-Pr-t)(2)] (M = Ti for 1, Zr for 2 and Hf for 3). Experimental results indicate that hafnium complex 3 displayed the higher catalytic activity than those of (BTP)-B-C1MO-featuring complexes 1 and 2 for the controlled L-LA polymerization. Hafnium alkoxide 3 catalyzes the ring-opening polymerization effectively not only in a "controlled" fashion but also an "immortal" manner, giving the corresponding polymers with the expected molecular weights and narrow molecular weight distributions.
