Reversible Single Electron Redox Steps Convert Polycycles with a C₃ P₃ Core to a Planar Triphosphinine

Area of Science:

• Organophosphorus Chemistry
• Aromaticity Studies
• Redox Chemistry

Background:

• Diphosphete-diides are reactive phosphorus-containing compounds.
• Phosphaalkynes are unsaturated phosphorus compounds.
• The study of cyclic conjugated systems with heteroatoms is crucial for understanding aromaticity.

Purpose of the Study:

• To investigate the reaction products of imidazolium-stabilized diphosphete-diide with trityl phosphaalkyne.
• To characterize the resulting C3P3 dianions and their redox behavior.
• To compare the structural changes upon redox with known hydrocarbon systems.

Main Methods:

• Synthesis of novel C3P3 dianions via reaction of diphosphete-diide with phosphaalkyne.
• Isolation and characterization of dianionic species (1a, 1b) and radical cation (4).
• Electrochemical oxidation and structural analysis of the C3P3 core in different oxidation states.

Main Results:

• Formation of bicyclic [3.1.0] (1a) and tricyclic [2.2.0.0] (1b) C3P3 dianions, existing in dynamic equilibrium.
• Isolation and characterization of a 7π-radical cation intermediate [4]•+.
• Reversible oxidation to a triphosphinine dication [5]2+ with a planar aromatic C3P3 ring.

Conclusions:

• The C3P3 dianions adopt non-planar structures to avoid antiaromaticity.
• A significant reversible structural transformation occurs during the two-electron redox process.
• The observed redox-induced structural change is more pronounced than in benzene/benzene dianion systems.