P-P Coupling with and without Terminal Metal-Phosphorus Intermediates

Area of Science:

• Organometallic Chemistry
• Inorganic Chemistry
• Photochemistry

Background:

• Terminal metal-phosphorus (M-P) complexes are crucial for P-atom transfer (PAT) chemistry.
• Decarbonylation of metal-phosphaethynolate (M-PCO) complexes is a common route to M-P species.
• Diphosphorus-bridged complexes often imply reactive M-P intermediates, especially without strong M-P stabilization.

Purpose of the Study:

• To investigate the mechanism of P-P coupling in metal-phosphorus systems.
• To determine if terminal M-P complexes are essential intermediates for P-P bond formation.
• To explore alternative pathways for P-P coupling from M-PCO precursors.

Main Methods:

• Photochemical decarbonylation of a pincer-supported Ni(II)-PCO complex at low temperatures (77 K).
• Spectroscopic observation and characterization of the transient terminal Ni-P complex.
• Thermal annealing studies to induce dimerization and P-P coupling.
• Kinetic analysis, isotope-labeling studies, and computational modeling.

Main Results:

• A spectroscopically observed, triplet Ni(II)-metallophosphinidene (terminal Ni-P) complex was generated via photolysis.
• This transient Ni-P complex rapidly dimerized to a P22--bridged dinickel complex upon thermal annealing.
• The same P22--bridged dinickel complex was formed via a distinct thermal pathway, avoiding terminal M-P intermediates.
• Evidence suggests P-P coupling can occur directly from M-PCO species without M-P intermediacy.

Conclusions:

• Terminal M-P complexes are not always required for P-P coupling.
• P-P coupling can proceed directly from M-PCO complexes through noncanonical mechanisms.
• This work provides crucial mechanistic insights into P-atom transfer activation modes.