Interconversion of Phosphinyl Radical and Phosphinidene Complexes by Proton Coupled Electron Transfer

Area of Science:

• Organometallic Chemistry
• Radical Chemistry
• Computational Chemistry

Background:

• Osmium complexes are versatile in catalysis.
• Phosphinyl radicals and phosphinidenes are reactive intermediates.
• Proton-coupled electron transfer (PCET) is a key reaction mechanism.

Purpose of the Study:

• To synthesize and characterize an osmium complex with phosphinyl radical character.
• To investigate the access to phosphinidene complexes via PCET.
• To determine the P-H bond dissociation energy (BDE) and explore the reactivity of the phosphinidene product.

Main Methods:

• Synthesis and isolation of the osmium complex [Os(PHMes*)H(PNP)].
• Isothermal titration calorimetry (ITC) to determine P-H BDE.
• Density Functional Theory (DFT) computations to support experimental findings.
• Investigation of the phosphinidene product's reactivity.

Main Results:

• The isolable complex [Os(PHMes*)H(PNP)] exhibits high phosphinyl radical character.
• Proton-coupled electron transfer (PCET) provides access to the phosphinidene complex [Os(PMes*)H(PNP)].
• The P-H BDE was experimentally determined and computationally supported.
• The resulting phosphinidene complex displays electrophilic reactivity, evidenced by intramolecular C-H activation.

Conclusions:

• Osmium complexes can stabilize phosphinyl radical character.
• PCET is an effective method for generating phosphinidene complexes from P-H containing precursors.
• The synthesized phosphinidene complex is electrophilic and undergoes C-H activation.