Titanium and Zirconium Complexes of Dianionic and Trianionic Amine−Phenolate-Type Ligands in Catalysis of Lactide Polymerization

Abstract

The synthesis of alkoxotitanium(IV) and -zirconium(IV) complexes of seven chelating tetradentate di- or trianionic amine-phenolate ligands belonging to three families and their application in L-lactide polymerization are described. The isopropoxotitanium complexes were synthesized by a direct reaction between the ligand precursors and titanium tetraisopropoxide, whereas the zirconium complexes were synthesized by various routes. For titanium, complexes of all seven ligands could be synthesized. For zirconium, the hexacoordinate complexes derived from all dianionic ligands were synthesized; however, the only pentacoordinate complex that could be produced was the one derived from the bulky trianionic ligand. X-ray structures of zirconium complexes of the three families indicated a substantial pi donation from the alkoxo ligand to the metal. All complexes were found to be active lactide polymerization catalysts, and their activity was found to depend strongly on the metal, the coordination number around the metal, and the phenolate substituents but not on the ligand backbone.

Factors influencing catalytic behavior of titanium complexes bearing bisphenolate ligands toward ring-opening polymerization of L-lactide and ε-caprolactone

“…It would be reasonable to suppose that the steric effect influences catalytic ability, such that the ligand of the Ti complex would have to occupy the space around the Ti center in order to hinder monomer coordination. This conjecture is in line with previous findings [14]. trisphenol [18] …”

“…For this reason as well as its low cost, titanium complexes [8][9][10][11][12][13][14] were chosen as popular catalysts in ROP. Among these titanium complexes, multi-phenol ligands have proven particularly useful because of its ease of synthesis and diverse structural variation [11][12][13][14]. Two main features of Ti diphenolate complexes that influence their catalytic performance were reported in the literature-chelate effect and steric effect (Figure 1).…”

Synthesis and structure of mono-, bi- and trimetallic amine-bis(phenolate) cobalt(ii) complexes

“…Bond lengths and angles for that version are similar to the methanol adduct and will not be discussed further. Crystallographic data for the mixed aquo and methanol adduct, 1(CH 3 However, the cavity-like nature of these ligands, as has been observed with a range of metals, means that an additional ligand in the apical position can be varied with some degree of control by simply changing the solvent of recrystallization. Also, the bond distance between the Co II center and the apical donor appears to be related to the steric demands of this ligand, with the Co(1)-O(5) bond distance in 1(C 3 H 6 O) being the longest of the three and the shortest being in 1(CH 3 OH).…”

Ring-opening polymerization of ε-caprolactone by lithium piperazinyl-aminephenolate complexes: synthesis, characterization and kinetic studies

“…1 Various ligands of this type have been used in main group and early transition metal chemistry (including lithium, 2-7 magnesium, [8][9][10][11][12][13][14] calcium, 15 rare-earths, 16,17 zinc, [18][19][20][21][22][23][24][25][26][27] aluminum, [28][29][30] zirconium 31,32 and titanium 33 ). Many of these complexes have been reported to be excellent initiators for the ring-opening polymerization (ROP) of cyclic esters such as lactide and ε-caprolactone.…”