Binucleating behaviour of a proximally-diphosphinated calix[4]arene

Area of Science:

• Organometallic Chemistry
• Supramolecular Chemistry
• Coordination Chemistry

Background:

• Calixarenes are versatile macrocyclic platforms with tunable properties.
• Diphosphine ligands are crucial in catalysis and coordination chemistry.
• The synthesis of functionalized calixarenes with pendant phosphine arms presents opportunities for novel metal complexes.

Purpose of the Study:

• To synthesize a novel long diphosphine ligand based on a calix[4]arene scaffold.
• To investigate the coordination behavior of this diphosphine with various metal centers (Au, Ru, Ni, Pd).
• To explore the self-assembly properties of the diphosphine under different conditions.

Main Methods:

• Multi-step synthesis of the functionalized calix[4]arene diphosphine.
• Reaction of the diphosphine with metal precursors including AuCl(SEt(2)), [RuCl(2)(p-cymene)](2), and [PdCl(2)(1,5-cyclooctadiene)(2)].
• Investigation of complex formation under varying concentrations, including high dilution conditions.

Main Results:

• Successful synthesis of the calix[4]arene-based long diphosphine (5).
• Formation of dinuclear metal complexes with gold and ruthenium: [5·(AuCl)(2)] and [5·{RuCl(2)(p-cymene)}(2)].
• Selective formation of dimeric species under high dilution, with a tendency to form oligomers in the presence of AgBF(4) or [Ni(C(5)H(5))(1,5-cyclooctadiene)]BF(4).
• Quantitative synthesis of a rare dinuclear palladium complex where the diphosphine bridges a [PdCl(μ-Cl)(2)PdCl] unit.

Conclusions:

• The synthesized calixarene diphosphine exhibits unique coordination properties.
• The ligand's structure favors bridging or dimeric arrangements over chelation.
• High dilution conditions are effective for controlling the self-assembly of the diphosphine with metal ions.