Aluminum complexes containing biphenolate phosphine ligands: synthesis and living ring-opening polymerization...

Area of Science:

• Organometallic Chemistry
• Polymer Chemistry

Background:

• Aluminum complexes with novel ligands are explored for catalytic applications.
• Tridentate biphenolate phosphine ligands offer unique coordination environments for metal centers.

Purpose of the Study:

• To synthesize and characterize aluminum complexes featuring tridentate biphenolate phosphine ligands.
• To investigate the catalytic activity of these complexes in ring-opening polymerization (ROP).
• To elucidate the influence of ligand substituents on catalytic performance and stereoselectivity.

Main Methods:

• Synthesis of aluminum methyl complexes via alkane elimination from AlMe3 and H2[2a] or H2[2b].
• Structural characterization using X-ray diffraction studies.
• Catalytic evaluation in the ring-opening polymerization of ε-caprolactone (ε-CL) and lactide isomers (rac-LA, l-lactide).

Main Results:

• Successfully synthesized and structurally characterized aluminum complexes [2a]AlMe(THF) and [2b]AlMe(THF), revealing five-coordinate, trigonal bipyramidal geometries.
• Isolated dimeric benzyloxide complexes {[2a,b]Al(μ2-OCH2Ph)}2 with distorted trigonal bipyramidal aluminum centers.
• Demonstrated catalytic activity of complex 3a in the living ROP of ε-CL and rac-LA, producing well-defined polymers and block copolymers.
• Observed a significant P-substituent effect, with complex 3a showing a 2-fold faster rate for rac-LA polymerization than 3b.
• Reported a 16.5-fold faster polymerization rate for rac-lactide compared to l-lactide catalyzed by complex 3a, indicating stereoselectivity.

Conclusions:

• Aluminum complexes with tridentate biphenolate phosphine ligands are effective pre-catalysts for controlled ROP.
• The ligand's P-substituent plays a crucial role in modulating catalytic activity and stereoselectivity.
• These findings open avenues for designing tailored aluminum catalysts for precise polymer synthesis.