A Crystalline Unsupported Phosphagallene and Phosphaindene.

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry
• Inorganic Synthesis

Background:

• The synthesis of low-coordinate main group elements presents significant challenges due to their inherent reactivity.
• Stabilization of unsaturated main group compounds often relies on bulky substituents to prevent aggregation and decomposition.

Purpose of the Study:

• To synthesize and characterize compounds featuring unsupported P═Ga and P═In double bonds.
• To investigate the role of steric bulk in stabilizing reactive low-coordinate main group species.
• To explore the formation of cyclic compounds and the necessity of external bases for stabilization.

Main Methods:

• Synthesis and isolation of novel organometallic compounds.
• Characterization using spectroscopic techniques (NMR, X-ray crystallography).
• Investigating reactivity with varying steric substituents and external bases.

Main Results:

• Successful synthesis of TerP═GaTer and TerP═InTer, featuring unsupported P═Ga and P═In double bonds with two-coordinate triel centers.
• Demonstrated that bulky terphenyl substituents are essential for stabilizing these reactive P═E bonds.
• Isolation of cyclic Mes*P(ETer)₂ compounds with smaller substituents, and stabilization of a phosphagallene (Mes*P═GaTer(PMe₃)) using an external base (PMe₃).

Conclusions:

• Steric protection afforded by large terphenyl groups is key to isolating compounds with unsupported P═E double bonds.
• The steric demands of substituents dictate the outcome, leading to either unsaturated species or cyclic compounds.
• External bases can be employed to stabilize otherwise elusive unsaturated main group compounds.