Stable Mesoionic N-Heterocyclic Olefins (mNHOs)

Area of Science:

• Organometallic Chemistry
• Organic Synthesis
• Materials Science

Background:

• Traditional N-heterocyclic olefins (NHOs) are widely used ligands in coordination chemistry.
• Understanding the electronic properties and reactivity of novel olefinic compounds is crucial for advancing catalytic processes.

Purpose of the Study:

• To report a new class of stable mesoionic N-heterocyclic olefins (mNHOs).
• To characterize the unique structural and electronic features of mNHOs.
• To evaluate their potential as strong σ-donor ligands.

Main Methods:

• Deprotonation of methylated N,N'-diaryl-1,2,3-triazolium and N,N'-diaryl-imidazolium salts.
• Synthesis and characterization of coordination complexes with rhodium and boron.
• Computational calculations of proton affinities.
• Experimental determination of basicity and donor abilities (Tolman electronic parameter - TEP).

Main Results:

• A new class of stable mesoionic N-heterocyclic olefins (mNHOs) was synthesized.
• mNHOs possess a highly polarized (strongly ylidic) double bond, distinguishing them from traditional NHOs.
• mNHOs demonstrated strong σ-donor ligand capabilities, exceeding those of reported NHOs.
• Calculated proton affinities and experimentally derived basicities confirmed their enhanced donor properties.

Conclusions:

• Mesoionic N-heterocyclic olefins represent a novel class of ligands with unique electronic properties.
• Their enhanced σ-donor ability and basicity offer significant advantages over traditional NHOs.
• These findings open new possibilities for applications in catalysis and coordination chemistry.