Vanadyl complexes supported by O,O- and N,O-chelate ligation: structures and polymerization catalysis

Area of Science:

• Organometallic Chemistry
• Polymer Chemistry
• Catalysis

Background:

• Vanadium complexes with Schiff base ligands are of interest due to their diverse catalytic applications.
• The synthesis of novel vanadium complexes can lead to new catalytic systems with improved performance.
• Electron-withdrawing substituents on ligands can influence the electronic properties and reactivity of metal complexes.

Purpose of the Study:

• To synthesize and characterize novel vanadium complexes derived from substituted salicylic aldehydes and anilines.
• To evaluate the catalytic activity of these complexes in the ring-opening polymerization (ROP) of lactones.
• To investigate their performance as pre-catalysts for ethylene and propylene polymerization.

Main Methods:

• Multi-step synthesis involving condensation reactions, reduction, and complexation with vanadium precursors.
• Characterization of synthesized ligands and vanadium complexes using spectroscopic techniques and X-ray crystallography.
• Catalytic evaluation in ring-opening polymerization of ε-caprolactone and δ-valerolactone under various conditions.
• Assessment as pre-catalysts for ethylene and ethylene/propylene copolymerization in the presence of co-catalysts.

Main Results:

• Several novel vanadium complexes, including [VO(L)(LH)] and [VO(L')n], were successfully synthesized and characterized.
• Complexes 2, 3, 5, 8, and 10 demonstrated high catalytic activity in the ROP of ε-CL and δ-VL, yielding linear polymers.
• Complex 1, featuring electron-withdrawing bromo substituents, exhibited enhanced activity and higher polymer molecular weight in ethylene (co)polymerization compared to non-substituted analogs.
• Complex 2 showed comparable activity to complex 1 in ethylene polymerization with improved thermal stability.

Conclusions:

• The synthesized vanadium Schiff base complexes are effective catalysts for lactone polymerization.
• The presence of electron-withdrawing groups on the Schiff base ligand significantly enhances catalytic activity in ethylene polymerization.
• These findings highlight the potential of tailored vanadium complexes for olefin and lactone polymerization applications.