Nonchelated d0 zirconium-alkoxide-alkene complexes.

Area of Science:

• Organometallic Chemistry
• Zirconium Catalysis
• Olefin Coordination Chemistry

Background:

• Zirconocene complexes are vital catalysts in olefin polymerization.
• Understanding ligand binding and electronic effects is crucial for catalyst design.
• Base-free metallocene complexes offer unique reactivity profiles.

Purpose of the Study:

• To synthesize and characterize a novel base-free zirconium complex.
• To investigate the coordination behavior of various alkenes with this complex.
• To elucidate the electronic and steric factors governing alkene binding.

Main Methods:

• Synthesis of a base-free zirconocene complex using Cp'2Zr(O(t)Bu)Me and a trityl borate salt.
• NMR spectroscopy (1H, 13C, 19F) to study complex formation and alkene coordination.
• Variable temperature NMR to analyze dynamic processes and determine equilibrium constants.

Main Results:

• A base-free complex, [Cp'2Zr(O(t)Bu)][B(C6F5)4], was successfully synthesized.
• NMR data revealed unsymmetrical alkene bonding and polarization of the C=C bond.
• Equilibrium constants for alkene coordination showed significant variation based on alkene structure, with vinylferrocene exhibiting the strongest binding.

Conclusions:

• The lack of d-pi* back-bonding in the zirconium complex leads to unique alkene polarization and bonding.
• Steric and electronic factors strongly influence alkene coordination affinity.
• The observed dynamic processes provide insights into the fluxional behavior of these organometallic complexes.