Acid-Base Adducts of Catalytically Active Titanium(IV) Lewis Acids

Area of Science:

• Organometallic Chemistry
• Catalysis
• Coordination Chemistry

Background:

• Titanium(IV) complexes are effective Lewis acids in organic synthesis.
• Diels-Alder reactions are crucial for forming cyclic compounds.
• Tuning catalyst properties through ligand modification is key to improving reaction efficiency.

Purpose of the Study:

• Synthesize novel monomeric Lewis acid-base adducts of Ti(O-2,6-Me(2)C(6)H(3))(2)Cl(2).
• Investigate the coordination chemistry of bidentate diphosphine and diamine ligands with the titanium catalyst.
• Determine the relative binding strengths of various bidentate ligands to the titanium Lewis acid.

Main Methods:

• Synthesis of titanium(IV) complexes with bidentate ligands (diphosphines and diamines).
• X-ray crystallography to determine the solid-state structure of selected adducts.
• Pairwise exchange reactions to establish a relative binding affinity ranking of the ligands.

Main Results:

• Successfully synthesized monomeric Lewis acid-base adducts, Ti(O-2,6-Me(2)C(6)H(3))(2)Cl(2)L(2).
• X-ray structures revealed distorted octahedral coordination with trans-chloride ligands for dmpe and dpeda adducts.
• A qualitative binding strength ranking was established: dmeda >/= dpeda > dmpe >/= depe > tmeda > binam > dppe.

Conclusions:

• The binding affinities of bidentate ligands to the titanium Lewis acid can be rationalized by hard-soft electronic theory.
• Steric factors play a significant role in ligand binding, particularly for ligands like tmeda.
• The synthesized adducts and their binding trends provide valuable information for designing improved Diels-Alder catalysts.