An Acyclic Arsenium Cation Stabilised by a Single P-As π-Interaction and a Cyclic Diphosphinophosphonium Salt

Area of Science:

• Mainly inorganic chemistry and organometallic chemistry.
• Focuses on the synthesis and characterization of novel main group element compounds.

Background:

• Acyclic arsenium cations (R2As+) are rare compared to phosphenium cations.
• Isoelectronic analogues of germylenes, these compounds present unique bonding challenges.

Purpose of the Study:

• To synthesize and characterize the first stable diphosphaarsenium salt.
• To investigate the electronic structure and bonding in this novel arsenic species.
• To explore the reactivity of related diphosphaphosphenium systems.

Main Methods:

• Synthesis of a novel diphosphaarsenium salt, [{(Dipp)2P}2As][Al{OC(CF3)3}4]·1.5PhMe.
• Characterization using X-ray crystallography and density functional theory (DFT) calculations.
• Attempted synthesis of an analogous diphosphaphosphenium salt.

Main Results:

• The first stable acyclic diphosphaarsenium salt was successfully synthesized and characterized.
• Remarkable stability was observed, attributed to lone pair delocalization from phosphorus to arsenic.
• DFT calculations confirmed the electronic structure and bonding interactions.
• An unexpected cyclization occurred during the synthesis of a related diphosphaphosphenium salt, yielding a cyclic phosphonium salt.

Conclusions:

• The successful synthesis of the diphosphaarsenium salt provides a new class of stable arsenic compounds.
• Electronic delocalization plays a crucial role in stabilizing these unusual arsenic cations.
• The study highlights the complex reactivity pathways in phosphorus-arsenic systems, leading to unexpected cyclic products.