Homoleptic titanium and zirconium complexes exhibiting unusual Oiminol–metal coordination: application in stereoselective ring-opening polymerization of lactide

The synthesis and characterization of novel homoleptic Ti and Zr complexes with tridentate ONO-type Schiff base ligands and their catalytic activities towards the ring-opening polymerization (ROP) of lactide are reported.

Salen complexes of zirconium and hafnium: synthesis, structural characterization and polymerization studies

Salen complexes of zirconium and hafnium were synthesized and used as effective catalysts for the polymerization of lactide and ε-CL and homopolymerization, copolymerization and coupling of epoxides with CO₂.

Palladium complexes containing imino phenoxide ligands: synthesis, luminescence, and their use as catalysts for the ring-opening polymerization of rac-lactide

Abstract

The preparation, structural characterization, luminescence, and catalytic activity of three palladium(II) complexes bearing imino phenoxide ligands are reported. The X-ray studies revealed that the complexes are mononuclear with palladium centres coordinated in a square-planar coordination environment. Two of the complexes are emissive in solution at room temperature. The catalytic activities towards the ring-opening polymerization of rac-lactide (rac-LA) were tested. Polymers with moderate molecular weights and relatively broad dispersity (Ð) were obtained. Kinetic studies revealed that the polymerization followed first-order kinetics.

Graphical abstract

Electronic supplementary material

The online version of this article (10.1007/s00706-017-2119-1) contains supplementary material, which is available to authorized users.

Nb and Ta benzotriazole or benzoxazole phenoxide complexes as catalysts for the ring-opening polymerization of glycidol to synthesize hyperbranched polyglycerols

A series of novel mononuclear (1a-7a and 1b-6b) as well as tetranuclear (8a and 9a) niobium (Nb) and tantalum (Ta) complexes of benzotriazole or benzoxazole phenoxide pro-ligands bearing different substituents at the ortho and para positions of the phenol rings were synthesized and characterized. The reaction of NbCl₅ or TaCl₅ with one equivalent of benzotriazole or benzoxazole phenoxide pro-ligands (L1H-L6H) in dry toluene or chloroform produced the corresponding chloride (1a-6a and 1b-6b) and ethoxy (7a) mononuclear Nb and Ta complexes in high yields. Furthermore, from the mononuclear Nb complexes (1a or 4a), a new structural form of tetrameric niobium complexes (8a and 9a) was synthesized through a controlled hydrolysis reaction. The molecular structures of complexes 1b, 4b, 7a, 8a and 9a were unambiguously confirmed by single crystal X-ray diffraction analyses. Furthermore, all these complexes (1a-9a and 1b-6b) were tested as catalysts for the ring-opening polymerisation (ROP) of glycidol to synthesize hyperbranched polyglycerols (HPG) by using 1,1,1-tris(hydroxymethyl)propane (TMP) as an initiator. The degree of branching (DB) observed was 0.30-0.54, which is an indication of hyperbranched structures. In particular, for the niobium complex with electron-withdrawing substituents on the benzoxazole phenoxide pro-ligand (5a), we achieved superior behavior for the ROP of glycidol in terms of activity, control of molecular weight (M_n) and molecular weight distributions (MWDs) (92% of glycidol to HPG, M_n = 10.52 kg mol^-1, MWDs <1.33, DB = 0.53 and T_g = -57 °C). A highly hydrophilic nature was observed for the synthesized HPG polymer by water contact angle measurement (20° to 35°).