Phosphorus-phosphorus coupling in a diphosphine with a ten bond P...P separation

Area of Science:

• Supramolecular Chemistry
• Organometallic Chemistry
• Coordination Chemistry

Background:

• Calixarenes are versatile macrocyclic hosts with tunable properties.
• Diphosphine ligands are crucial in catalysis and coordination chemistry.
• Achieving specific spatial arrangements of functional groups on calixarenes is synthetically challenging.

Purpose of the Study:

• To synthesize a large, unsymmetrical diphosphine calixarene.
• To investigate the structural and electronic properties of the synthesized diphosphine.
• To explore the coordination behavior of the diphosphine with transition metals.

Main Methods:

• Monobenzoylation and reduction of a precursor calixarene.
• X-ray crystallography for molecular structure determination.
• Nuclear Magnetic Resonance (NMR) spectroscopy for solution-state analysis.
• Complexation studies with palladium.

Main Results:

• Successful synthesis of the unsymmetrical diphosphine calixarene.
• X-ray crystallography confirmed phosphorus atom separation of 5.333(1) Å.
• NMR revealed a significant through-space J(PP") coupling constant of 8.0 Hz.
• Calixarene exhibited conformational mobility in solution.
• Facile formation of a cis-chelate palladium complex.

Conclusions:

• The synthesized diphosphine calixarene possesses a unique structure with proximate phosphorus atoms.
• Through-space coupling and conformational dynamics were observed.
• The ligand readily forms stable complexes, indicating its utility in organometallic chemistry.