Cationic Group-IV pincer-type complexes for polymerization and hydroamination catalysis.

Area of Science:

• Organometallic Chemistry
• Catalysis
• Polymer Science

Background:

• Pincer ligands offer unique coordination environments for metal centers.
• Zirconium (Zr) and Hafnium (Hf) complexes are known for catalytic applications.
• Unsymmetrical dianionic ligands provide tunable electronic and steric properties.

Purpose of the Study:

• To synthesize and characterize neutral Zr(IV) and Hf(IV) dimethyl complexes supported by {N,C,N'} pincer ligands.
• To investigate the catalytic activity of these complexes in organic transformations and polymerization reactions.

Main Methods:

• Synthesis of Zr(IV) and Hf(IV) bis-amido complexes.
• Treatment with AlMe₃ to form neutral dimethyl complexes.
• In situ conversion to cationic species for catalytic studies.
• Room temperature intramolecular hydroamination/cyclization reactions.
• High temperature ethylene-1-octene copolymerizations.

Main Results:

• Successfully prepared neutral Zr(IV) and Hf(IV) dimethyl complexes stabilized by unsymmetrical dianionic {N,C,N'} pincer ligands.
• Demonstrated the robust M-C bond formation due to the ligand framework.
• Showcased the unique balance between stability and reactivity of these complexes.
• Identified the cationic derivatives as active catalysts for intramolecular hydroamination/cyclization at room temperature.
• Utilized the catalysts for ethylene-1-octene copolymerizations at high temperatures.

Conclusions:

• The {N,C,N'} pincer ligand framework enforces stable M-C bonds, leading to a balance of stability and reactivity in Zr(IV) and Hf(IV) complexes.
• The cationic Zr(IV) and Hf(IV) complexes are effective catalysts for both intramolecular hydroamination/cyclization and olefin copolymerization.