Isolation of Neutral, Mono-, and Dicationic B₂ P₂ Rings by Diphosphorus Addition to a Boron-Boron Triple Bond

Area of Science:

• Organometallic Chemistry
• Inorganic Chemistry
• Materials Science

Background:

• Diborynes are reactive boron-containing compounds with potential applications in synthesis.
• N-heterocyclic carbenes (NHCs) are effective stabilizers for low-coordinate main group elements.
• Phosphine chemistry offers pathways to novel inorganic ring systems.

Purpose of the Study:

• To investigate the reaction of NHC-stabilised diboryne with tetraethyldiphosphine.
• To explore the oxidation chemistry of the resulting B2P2 heterocycle.
• To elucidate the structural and electronic properties of the neutral and oxidized species.

Main Methods:

• High-yielding P-P bond activation reaction.
• Oxidation reactions using various oxidants and counterions.
• X-ray crystallography for structural determination.
• Density Functional Theory (DFT) and CASSCF/NEVPT2 calculations for electronic structure analysis.

Main Results:

• Formation of a B2P2 heterocycle via 1,2-diphosphination of a diboryne.
• Sequential oxidation to a radical cation and dication with distinct structural changes.
• X-ray and computational studies reveal butterfly-shaped dicationic structures.
• Planar diradicaloid isomers are energetically close to the dicationic species.

Conclusions:

• NHC-stabilised diborynes are versatile precursors for novel B2P2 heterocycles.
• Oxidation provides a route to tune the electronic and structural properties of these systems.
• The study highlights the interplay between electronic structure, charge, and molecular geometry in inorganic rings.