Geometrically constrained square pyramidal phosphoranide.

Area of Science:

• Main group chemistry
• Organophosphorus chemistry
• Coordination chemistry

Background:

• Geometrical constriction is a key strategy to tune main group element reactivity.
• Group 15 elements, particularly phosphorus, are a major focus for these methods.
• Trigonal bipyramidal (TBP) phosphoranides are known nucleophiles, but their redox chemistry is largely unexplored.

Purpose of the Study:

• To synthesize and isolate a geometrically constrained, square pyramidal (SP) phosphoranide anion.
• To investigate the reactivity of this novel SP phosphoranide, focusing on its nucleophilic and redox behavior.
• To explore unprecedented reaction pathways for phosphoranyl radicals.

Main Methods:

• Synthesis and isolation of the square pyramidal phosphoranide anion (1^-).
• Preliminary reactivity studies including chemical oxidation and reaction with benzophenone.
• Characterization of reaction products, including a P-P dimer and tetraphenyl epoxide.

Main Results:

• The SP phosphoranide anion (1^-) was successfully synthesized and isolated.
• Unlike TBP phosphoranides, 1^- displays both nucleophilic and reductive properties.
• Chemical oxidation of 1^- yields a P-P dimer (1-1) via dimerization of an unstable SP phosphoranyl radical (1˙).
• Reaction with benzophenone proceeds via single electron transfer (SET), forming 1-OK and tetraphenyl epoxide (4).

Conclusions:

• Geometrically constrained SP phosphoranides offer unique reactivity profiles.
• The observed P-P dimer formation represents an unprecedented decay pathway for phosphoranyl radicals.
• This work expands the known reactivity of phosphorus-based main group compounds.