Lead calix[n]arenes (n = 4, 6, 8): structures and ring opening homo-/co-polymerization capability for cyclic esters

Area of Science:

• Coordination Chemistry
• Organometallic Chemistry
• Polymer Chemistry

Background:

• Calixarenes are versatile macrocyclic hosts with tunable cavity sizes and functionalities.
• Lithium and lead compounds are known for their catalytic activities in polymerization reactions.
• Heterometallic complexes offer unique electronic and steric properties for catalysis.

Purpose of the Study:

• To synthesize novel heterometallic lithium-lead complexes using various calixarene ligands.
• To evaluate the catalytic performance of these complexes in the ring-opening polymerization (ROP) of lactones and lactides.
• To investigate the structure-activity relationships of the synthesized complexes in polymerization.

Main Methods:

• Synthesis of heterometallic lithium-lead complexes through reactions of organolithium and organolead precursors with different calixarene derivatives.
• Characterization of the synthesized complexes using spectroscopic and analytical techniques.
• Evaluation of catalytic activity in the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL), and rac-lactide (rac-LA).

Main Results:

• Seven novel heterometallic lithium-lead complexes (1-7) were successfully synthesized and characterized.
• Complexes 1 and 2, containing lithiated calixarene frameworks, exhibited superior catalytic activity in ROP compared to other screened pre-catalysts.
• The synthesized complexes demonstrated moderate to good activity in the ROP of ε-CL and δ-VL, yielding high molecular weight polymers in copolymerization reactions.

Conclusions:

• The synthesized heterometallic lithium-lead calixarene complexes are effective pre-catalysts for ROP of lactones and lactides.
• Lithiated complexes generally show enhanced catalytic performance, highlighting the role of lithium in the catalytic system.
• These complexes represent a promising class of catalysts for producing biodegradable polymers with controlled molecular weights.