Synthesis and Structural Studies of Heterobimetallic Alkoxide Complexes Supported by Bis(phenolate) Ligands: Efficient Catalysts for Ring-Opening Polymerization of l-Lactide

Abstract

A series of heterobimetallic titanium(IV) complexes [LTi(O(i)Pr)(mu-O(i)Pr)(2)Li(THF)(2)], [LTi(O(i)Pr)(mu-O(i)Pr)(2)Na(THF)(2)], [LTi(mu-O(i)Pr)(2)Zn(O(i)Pr)(2)], and [LTi(mu-O(i)Pr)(2)Mg(O(i)Pr)(2)] (where L = bidentate bisphenol ligands) have been synthesized and characterized including a structural determination of [L(1)Ti(mu(2)-O(i)Pr)(2)(O(i)Pr)Li(THF)(2)] (1a). These complexes were investigated for their utility in the ring-opening polymerization (ROP) of l-lactide (LA). Polymerization activities have been shown to correlate with the electronic properties of the substituent within the bisphenol ligand. In contrast to monometallic titanium initiator 1e, all the heterobimetallic titanium initiators (Ti-Li, Ti-Na, Ti-Zn, and Ti-Mg) show enhanced catalytic activity toward ring-opening polymerization (ROP) of l-LA. In addition, the use of electron-donating methoxy or methylphenylsulfonyl functional ligands reveals the highest activity. The bisphenol bimetallic complexes give rise to controlled ring-opening polymerization, as shown by the linear relationship between the percentage conversion and the number-average molecular weight. The polymerization kinetics using 2c as an initiator were also studied, and the experimental results indicate that the reaction rate is first-order with respect to both monomer and catalyst concentration with a polymerization rate constant, k = 81.64 M(-1) min(-1).

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

“…The chromatographic column was JORDI Gel DVB 103 Å, and the calibration curve was made by primary polystyrene standards to calculate Mn(GPC). H-diOH [17] and OTs-diOH [18] were prepared by acid-catalyzed condensation following literature procedures. Me-Ti were prepared following literature procedures [11].…”

Synthesis, characterization and catalytic activity of zinc complex for ring‐opening polymerization of lactide

“…On the basis of the ‘immortal’ property of lactide polymerization demonstrated by several zinc complexes and the evidence of in situ formation of metal alkoxide in the presence of alcohol, the complex Zn‐HMBED was expected to behave as a catalyst towards the ROP of lactide in the presence of benzyl alcohol. The zinc complex Zn‐HMBED in the presence of benzyl alcohol initiates the ROP of l ‐lactide in dichloromethane at 30 o C (Scheme ).…”

“…Thus, use of environmentally benign metals that are part of the mammalian anatomy is essential, so that there will be no damage for living beings . Different metal initiators or catalysts have been used in the formation of PLA, such as compounds of aluminium, lithium, magnesium, iron, tin, titanium and zinc . Recently, initiators or catalysts based on metals such as Ca, Mg, Fe and Zn has received great interest because of their metabolized activity in the body .…”

Use of Titanium Complexes Bearing Diphenolate or Calix[n]arene Ligands in α-Olefin Polymerization and the ROP of Cyclic Esters

“…In fact, 98% conversion was achieved in 1 h while longer reaction times (2.5 h) were required by its dimeric analogue to reach similar values. A series mixed titanium-M (where M = Li, Na, Zn and Mg) heterobimetallic complexes having various substituents on the methylene bridge of the diphenolate ligand were prepared by Lin et al (Figure 13) [27]. All complexes were tested in the ROP of L-lactide, and their activity was compared to that of the monometallic complex 48 (Table 15).…”

“…Catalysts 2020, 10, 210 17 of 29 Figure 13. Diphenolate-supported mixed heterobimetallic Ti complexes [27]. Figure 14) [28].…”