1,4-Phosphagermines: An Anionic 6π-heteroaromatic Biradicaloid and a Persistent π-Delocalized Radical.

Area of Science:

• Main-group chemistry
• Organometallic chemistry
• Aromaticity studies

Background:

• Established diheteroarenes typically feature identical heavy elements.
• Mixed-element analogues remain underexplored, presenting a gap in synthetic chemistry.

Purpose of the Study:

• To synthesize and characterize a novel 1,4-phosphagermine anion and its persistent delocalized radical.
• To explore the adaptability of the synthetic protocol for other mixed-heavy main-group elements.
• To investigate the aromatic and biradicaloid character of the synthesized heterocycle.

Main Methods:

• Synthesis and characterization of the 1,4-phosphagermine anion and radical.
• Computational analyses including 2D-XY NICSπ,zzSOM scans and ELFπ.
• High-level electronic structure calculations (PW6B95-D3BJ/def2-QZVP(CPCMTHF)//TPSS-D3BJ/def2-TZVP(CPCMTHF)) and CASSCF calculations.
• Electrochemical studies and Electron Paramagnetic Resonance (EPR) spectroscopy.

Main Results:

• Successful synthesis and characterization of a persistent 1,4-phosphagermine radical and its aromatic anion.
• Computational studies confirmed aromaticity with significant biradicaloid character.
• Electrochemical stability of the radical was demonstrated, and EPR spectroscopy confirmed its presence in solution.
• A theoretical study on 16 heavy group 14/15 element combinations showed an increasing biradicaloid tendency.

Conclusions:

• The study expands the frontier of main-group chemistry by introducing a novel mixed-heavy-element aromatic system.
• The findings highlight the potential of such systems and the adaptability of the synthetic approach.
• The research underscores the importance of biradicaloid character in understanding the electronic properties of these heterocycles.