Neopentyllithium CAS No. 7412-67-1

Product Description

Neopentyllithium is a sterically hindered organolithium reagent in which a lithium atom is attached to the terminal methylene carbon of the neopentyl group, (CH₃)₃C–CH₂–Li. Prepared by treating neopentyl chloride with lithium metal in dry pentane or ether, it is normally handled and stored as a colorless to pale-yellow 1.0 M solution in pentane under an inert N₂ or Ar atmosphere because it ignites spontaneously in air and decomposes explosively on contact with water. The bulky tert-butyl substituents shield the C–Li bond, suppressing β-hydride elimination and attenuating nucleophilicity, which makes neopentyllithium a particularly powerful yet selective base for deprotonating weakly acidic substrates such as alcohols or amines while avoiding competing SN2 processes. These properties render it valuable in modern organic synthesis for generating carbanions, preparing other organometallic species, and performing sterically demanding deprotonations at temperatures as low as −78 °C.

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Product Use & Characteristics

1. Identity & Basic Data

• Molecular formula: C₅H₁₁Li • Molar mass: 78.1 g mol⁻¹

• IUPAC name: lithium; 2-methanidyl-2-methylpropane (systematic) or 2,2-dimethylpropyllithium (common)

• Structural motif: Li–CH₂–C(CH₃)₃; neopentyl group provides extreme steric hindrance while the CH₂–Li bond remains primary.

• Typical appearance: colourless to pale-yellow solution (1.0 M in pentane, hexane, ether or THF); solid oligomers (usually tetramers) have been characterised by X-ray diffraction.

2. Physical & Solubility Properties

• Melting point: 130 °C (0.00001 Torr, sublimes)

• Flash point: −30 °C (solution)

• Solubility: freely soluble in non-polar and ethereal solvents—pentane, hexane, diethyl ether, THF; insoluble in water (reacts violently).

3. Chemical Characteristics

• Extremely strong, hindered, non-nucleophilic base (pKₐ of conjugate acid ≈ 50).

• Low nucleophilicity and absence of β-hydrogens suppress elimination and SN2 side reactions.

• Reacts violently with H₂O, O₂, CO₂; pyrophoric; must be handled under rigorously dry N₂ or Ar.

• Forms alkane-soluble Lochmann–Schlosser superbases when combined with KOtBu (Li/K mixed aggregates).

4. Synthesis Methods

• Standard route: neopentyl chloride + 2 Li → neopentyllithium + LiCl in dry pentane or ether at −78 °C to reflux; product purified by filtration and/or sublimation (110 °C, 0.01 mmHg).

• Stabilisation strategies: low-temperature (−78 °C) preparation, addition of TMEDA, crown ethers, or THF/HMPA cosolvents to extend shelf life; DFT-guided ligand choice for aggregate control.

5. Uses

• Deprotonation / metalation: selective removal of hindered or weakly acidic protons (tertiary C–H, alcohols, amines) to generate carbanions for alkylation, cross-coupling or natural-product synthesis.

• Umpolung & polarity-inversion chemistry: delivers quaternary carbon centers via lithium-halide exchange with aromatic ketones.

• Polymer chemistry: living anionic initiator for styrene, dienes and block copolymers (e.g., SIS thermoplastic elastomers) yielding narrow PDI (< 1.1) and controlled stereoregularity.

• Trans-metallation reagent: precursor to neopentyl complexes of Pd(II/IV), Si, B and other main-group elements used in materials and catalysis.

• Catalytic C–C bond formation: catalytic neopentyllithium/Ni or Pd systems reduce stoichiometric waste.

• Superbase component: mixed Li/K neopentyl/tert-butoxy aggregates for highly hindered deprotonations.

6. Safety & Green-Chemistry Notes

• Hazard class: pyrophoric, corrosive, water-reactive; flammable solutions.

• Handling: inert atmosphere, flame-dried glassware, low-temperature storage; avoid halogenated and protic solvents.

• Green advances: exploration of ionic liquids or supercritical CO₂ as safer media; recyclable ligand systems under investigation.

7. Research Frontiers

• Thermal-stability enhancement through ligand design and aggregate engineering.

• Computational (DFT) prediction of reactivity/selectivity relationships.

• Development of water-stable or lithium-free surrogates for pharmaceutical-scale applications.

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