Bis(pyridino-o-carboranyl)phosphenium Cation: A Platform for Dual-Site Reactivity

Area of Science:

• Organometallic Chemistry
• Boron Chemistry
• Phosphorus Chemistry

Background:

• Phosphenium salts are reactive intermediates with diverse applications.
• Carboranyl groups offer unique steric and electronic properties.
• Understanding the reactivity of substituted phosphenium salts is crucial for synthetic chemistry.

Purpose of the Study:

• To synthesize and characterize a novel phosphenium salt bearing pyridino-ortho-carboranyl ligands.
• To investigate the reactivity of this phosphenium salt with small molecules, specifically O-H and N-H containing compounds.
• To explore the potential for dual reactivity at both the phosphorus center and the carboranyl moiety.

Main Methods:

• Synthesis of the phosphenium salt [L2P+][B(C6F5)4].
• Full characterization using spectroscopic and analytical techniques.
• Reactivity studies with various alcohols, amines, and sulfur dioxide.

Main Results:

• The phosphenium salt reacts with O-H bonds (alcohols) at the phosphorus center via hydrolysis or alcoholysis.
• Reaction with N-H bonds (amines) leads to deboronation at the ortho-carboranyl moiety, forming a zwitterionic phosphenium.
• Reaction with SO2 results in dual site reaction at both P and ortho-carboranyl groups, yielding a zwitterionic phosphonium sulfide.

Conclusions:

• The synthesized phosphenium salt exhibits distinct reactivity patterns based on the type of bond encountered (O-H vs. N-H).
• The ortho-carboranyl moiety plays a significant role in modulating the reactivity of the phosphenium center.
• This study highlights the potential for developing new synthetic methodologies utilizing carborane-functionalized phosphorus compounds.