Trimerization and cyclization of reactive P-functionalities confined within OCO pincers.

Area of Science:

• Organometallic Chemistry
• Phosphorus Chemistry
• Ligand Design

Background:

• Stabilizing low-coordinate phosphorus species is crucial for understanding bonding and reactivity.
• Previous attempts using NCN pincer ligands to achieve a planarized 10-P-3 phosphorus center resulted in aromatic heterocycles.
• The 10-P-3 species with C2v symmetry and two lone pairs on phosphorus presents a significant synthetic challenge.

Purpose of the Study:

• To synthesize and stabilize a 10-P-3 phosphorus species with C2v symmetry.
• To investigate the efficacy of OCO pincer ligands in stabilizing the target phosphorus compound.
• To prevent the formation of aromatic phosphorus heterocycles through ligand design.

Main Methods:

• Synthesis of OCO pincer ligands 1 and 2.
• Metalation, phosphination, and reduction sequences.
• Characterization using NMR spectroscopy (including 19F NMR), elemental analysis, and X-ray crystallography.
• Computational simulation of NMR spectra.

Main Results:

• OCO pincer 1 led to cyclotriphosphane formation via trimerization.
• OCO pincer 2, despite CF3 groups, underwent unexpected cyclization to form monochlorinated phosphole 5.
• Derivative 6 was successfully synthesized from 5 and characterized, confirming the formation of a P-(p-Tol) species.
• Experimental 19F NMR spectra of 5 and 6 were accurately reproduced by simulations.

Conclusions:

• OCO pincer ligands show potential but require further optimization for stabilizing 10-P-3 species.
• The electron-withdrawing nature of oxygen donors and benzylic substituents influences the reactivity of the phosphorus center.
• Unexpected reaction pathways, such as cyclization and trimerization, highlight the complexity of low-coordinate phosphorus chemistry.