Isoprene polymerization mediated by vanadium-[ONNO] complexes.

Area of Science:

• Coordination chemistry
• Polymer science
• Organometallic chemistry

Background:

• Vanadium complexes are explored as catalysts for olefin polymerization.
• Tetradentate amine-bisphenolate ligands ([ONNO]) offer tunable electronic and steric properties.
• Controlling polymer microstructure is crucial for material properties.

Purpose of the Study:

• To synthesize and characterize novel vanadium complexes with [ONNO] ligands.
• To evaluate the catalytic activity of these complexes in isoprene homo-polymerization.
• To analyze the microstructure of the resulting polyisoprene.

Main Methods:

• Synthesis and structural determination of vanadium-[ONNO] complexes.
• Catalytic polymerization of isoprene using dialkylmagnesium or aluminum triisobutyl activators.
• Microstructural analysis of polyisoprene using techniques like NMR spectroscopy.

Main Results:

• Several vanadium complexes with varying [ONNO] ligands were prepared and structurally characterized.
• All complexes showed modest isoprene polymerization activity with dialkylmagnesium activation.
• Quantitative polymerization was achieved with complexes 4 and 6 activated by aluminum triisobutyl, with complex 6 being more active.
• The polyisoprene produced contained approximately 70% 3,4-enchainments and 30% 1,4-enchainments (cis/trans mixture).
• Evidence of β-hydride abstraction during the catalytic cycle was observed.

Conclusions:

• Vanadium-[ONNO] complexes are effective pre-catalysts for isoprene polymerization.
• The choice of ligand substituents and activator significantly impacts catalytic activity and polymer microstructure.
• Complex 6 demonstrates superior performance, suggesting potential for tailored polyisoprene synthesis.