A geminal antimony(iii)/phosphorus(iii) frustrated Lewis pair

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry
• Supramolecular Chemistry

Background:

• The synthesis and reactivity of Lewis pairs are crucial for developing new catalytic systems.
• Understanding the electronic properties of Lewis acidic centers, even with highly electronegative substituents, is key to predicting reactivity.
• Geminal Lewis pairs offer unique structural and electronic properties compared to traditional Lewis acids and bases.

Purpose of the Study:

• To synthesize and characterize a novel geminal Lewis pair, (F5C2)2SbCH2P(tBu)2 (1).
• To investigate the Lewis acidic properties of the antimony center in compound 1, particularly in relation to the HSAB concept.
• To explore the reactivity of compound 1 with small molecules and heterocumulenes, including its potential as a frustrated Lewis pair (FLP).

Main Methods:

• Synthesis of (F5C2)2SbCH2P(tBu)2 (1) via reaction of (F5C2)2SbCl with LiCH2P(tBu)2.
• Characterization using VT-NMR spectroscopy to study reversible CS2 binding.
• Quantum chemical calculations (DFT, QTAIM, IQA) to analyze reaction mechanisms and electronic structures.
• X-ray diffraction, multinuclear NMR, and elemental analyses for structural and compositional verification.

Main Results:

• Compound 1, despite highly electronegative substituents, exhibits a soft Lewis acidic antimony center.
• Reversible binding of CS2 to compound 1 was observed, while CO2 showed no reaction.
• Demonstrated FLP-type reactivity with SO2, PhNCO, PhNCS, and (MePh2P)AuCl, forming various adducts and cyclic products.
• A unique clamp-like adduct with (MePh2P)AuCl was formed, featuring chelation of the chloride anion by two antimony atoms.

Conclusions:

• The geminal Lewis pair (F5C2)2SbCH2P(tBu)2 displays tunable Lewis acidity and versatile reactivity.
• Its soft Lewis acidic nature enables specific interactions with small molecules like CS2.
• The compound serves as a valuable platform for exploring FLP chemistry and designing novel organometallic complexes.