Zinc and magnesium complexes incorporated by bis(amine) benzotriazole phenoxide ligand: Synthesis, characterization, photoluminescent properties and catalysis for ring-opening polymerization of lactide

A new bis(amine) benzotriazole phenoxide ligand, (BTP)-B-C8NN-H (1) was prepared from the Mannich condensation of 2-(2H-benzotriazol-2-yl)-4-(2,4,4-trimethylpentan-2-yl)phenol with the mixtures of excess paraformaldehyde and N,N,N-trimethylethylenediamine under reflux conditions. Zinc and magnesium complexes bearing the N,N,O-tridentate (BTP)-B-C8NN ligand were synthesized and fully characterized. The reaction of (BTP)-B-C8NN-H with ZnEt2 (1.2 molar equiv.) in toluene gives the monomeric tetra-coordinated zinc complex [((BTP)-B-C8NN) ZnEt] (2). The homoleptic and monomeric complexes [((BTP)-B-C8NN)(2)M] (M = Zn (3) and M = Mg (4)) result from treatment of ZnEt2 or (MgBu2)-Bu-n with (BTP)-B-C8NN-H (two equiv.), in which the metal center is hexa-coordinated by two tridentate (BTP)-B-C8NN ligands. Luminescent properties and catalysis for lactide (LA) polymerizations of complexes 2-4 are studied. Complexes 2-4 produce bright green fluorescence with emission maxima ranging from 510 to 520 nm in the solid state. Experimental results indicate that complex 2 catalyzes the ring-opening polymerization of LA in the presence of 9-anthracenemethanol (9-AnOH) with efficient catalytic activities in a controlled fashion, yielding poly(rac-lactide) with a slight isotactic predominance (P-m = 0.59).