What Is 1,3-Bis[2,6-bis(1-ethylpropyl)phenyl]imidazolium Chloride?

1,3-Bis[2,6-bis(1-ethylpropyl)phenyl]imidazolium chloride is an imidazolium salt bearing two 2,6-bis(1-ethylpropyl)phenyl (3-pentyl-substituted aryl) groups on the nitrogen atoms of the imidazole ring. This compound belongs to the family of bulky, unsymmetrical N-aryl imidazolium salts that serve as bench-stable precursors to N-heterocyclic carbenes (NHCs).

NHC ligands derived from this salt are classified as IPent-type carbenes, named for the 3-pentyl (1-ethylpropyl) substituents appended to the flanking aryl rings. The pronounced steric profile arising from the four 3-pentyl groups creates a highly congested coordination environment that stabilises reactive metal centres and modulates catalyst selectivity in a manner distinct from the more common IMes and IPr NHC families.

The compound is catalogued under Strem catalog number 07-0358 and is available from Aladdin Scientific as SKU B281478.

Structural Features and Steric Properties

The imidazolium core provides a relatively planar, aromatic five-membered ring in which the C2 proton is acidic (pKa approximately 20–24 in DMSO) and can be removed by a suitable base to generate the free carbene. The two flanking 2,6-bis(1-ethylpropyl)phenyl groups are oriented nearly perpendicular to the imidazolium plane, creating a deep buried volume (%Vbur) around the prospective carbene carbon that exceeds that of IPr and IMes analogues.

The 3-pentyl chains (two per aryl ring, four total) are flexible yet bulkier than the isopropyl groups present in the widely used IPr ligand. This flexibility allows the substituents to adapt their conformation to the steric demand of the metal substrate, imparting unique activity and selectivity profiles in catalytic reactions. Computational steric maps and %Vbur analyses are standard tools for quantifying and comparing the steric influence of IPent versus other NHC variants.

Because the molecule is an ionic salt rather than a free carbene, it is air- and moisture-stable under normal laboratory conditions, enabling straightforward storage and handling relative to the free NHC itself.

Applications in Catalysis and Synthesis

NHC–Metal Complex Formation: The primary use of this imidazolium salt is as a precursor for generating NHC–metal complexes. Upon treatment with a metal base (e.g., Pd(OAc)₂ with Cs₂CO₃, or direct transmetalation protocols), the free IPent carbene coordinates to the metal centre, producing well-defined NHC–metal complexes. Palladium, gold, copper, ruthenium, and nickel complexes bearing IPent-type ligands have been reported in the literature.

Cross-Coupling Catalysis: IPent-type NHC–Pd complexes have demonstrated activity in challenging cross-coupling reactions, including Buchwald–Hartwig aminations, Suzuki–Miyaura couplings with sterically hindered substrates, and Negishi couplings. The enhanced steric bulk relative to IPr can accelerate reductive elimination, a key mechanistic step that determines turnover frequency in palladium-catalysed cycles.

Organocatalysis: Free NHCs generated from imidazolium salts can act as Brønsted base catalysts or nucleophilic carbene catalysts. Bulky IPent-type carbenes are particularly suited to asymmetric NHC organocatalysis where steric differentiation of prochiral faces is required.

Gold Catalysis: Bulky NHC–Au complexes are active in π-activation of alkynes and allenes. IPent gold complexes may offer complementary selectivity to IPr gold systems in cyclisation and related reactions.

Handling, Storage, and Safety Considerations

Stability: As an imidazolium chloride salt, this compound is considerably more stable than the corresponding free NHC. It can typically be stored at room temperature in a sealed container away from moisture, though refrigerated storage (2–8 °C) is recommended for long-term preservation of purity. Always consult the supplier's certificate of analysis (CoA) and Safety Data Sheet (SDS) for lot-specific guidance.

Handling: Standard laboratory PPE (lab coat, nitrile gloves, safety glasses) should be worn when handling this material. Although imidazolium salts are generally of low acute toxicity, detailed hazard data specific to this compound should be confirmed in the SDS provided by Aladdin Scientific. Work in a well-ventilated area or fume hood.

Generation of Free NHC: When converting this salt to the free carbene in situ, strong bases such as NaH, KOtBu, NaHMDS, or KHMDS are typically employed. These reagents are themselves hazardous (pyrophoric or strongly basic), and reactions should be conducted under inert atmosphere (nitrogen or argon) using standard Schlenk or glovebox techniques.

Waste Disposal: Dispose of chemical waste in accordance with local and institutional regulations. Do not pour organic or ionic waste into drains.

Ordering Information and Specifications

Aladdin Scientific offers 1,3-Bis[2,6-bis(1-ethylpropyl)phenyl]imidazolium chloride under SKU B281478. This product is cross-referenced to Strem catalog number 07-0358. Researchers requiring this compound for NHC catalyst development, ligand screening libraries, or mechanistic studies should contact Aladdin Scientific for current pricing, available pack sizes, and purity specifications.

When placing an order, providing the SKU (B281478) ensures accurate fulfilment. For bulk quantities or custom specifications, Aladdin Scientific's technical sales team can discuss options including custom synthesis, specific purity grades, and certificate of analysis requirements.

For questions regarding reagent grade, purity confirmation, or compatibility with specific synthetic protocols, please consult the product page or contact Aladdin Scientific customer support directly.