Trimethylboroxine: Properties, Uses & Handling FAQs

Trimethylboroxine is a cyclic trimeric anhydride of methylboronic acid widely employed as a stable, easy-to-handle methyl-transfer reagent in transition-metal-catalyzed cross-coupling reactions.

Chemical Name

Trimethylboroxine (2,4,6-trimethyl-1,3,5,2,4,6-trioxatriborinane)

Molecular Formula

C₃H₉B₃O₃

Molecular Weight

125.55 g/mol

Primary Application

Methyl nucleophile equivalent in Suzuki–Miyaura cross-coupling reactions

Physical Form

Colorless to pale yellow liquid

Storage Conditions

Store under inert atmosphere, sealed, away from moisture

What Is Trimethylboroxine and How Is It Structured?

Trimethylboroxine is the cyclic trimeric anhydride of methylboronic acid. Its core is a six-membered boroxine ring consisting of alternating boron and oxygen atoms (B–O–B–O–B–O), with one methyl group attached to each boron atom. This arrangement confers greater thermal and hydrolytic stability compared with monomeric methylboronic acid, making the reagent easier to weigh, handle, and store on the bench.

Because the boroxine ring can slowly release methylboronic acid equivalents in the presence of water or base, Trimethylboroxine functions as a practical, atom-economical methyl-boron source. Each mole of Trimethylboroxine provides up to three moles of reactive methyl-boronate species under typical catalytic conditions.

Key Applications in Synthetic Chemistry

Suzuki–Miyaura Cross-Coupling: The most prominent use of Trimethylboroxine is as a methyl nucleophile in palladium-catalyzed Suzuki–Miyaura reactions with aryl, heteroaryl, vinyl, and alkyl halides or pseudohalides. It enables efficient introduction of a methyl group onto a carbon framework under mild conditions, a transformation valuable in pharmaceutical, agrochemical, and materials synthesis.

Nickel- and Other Metal-Catalyzed Couplings: Beyond palladium, Trimethylboroxine has been applied in nickel-catalyzed cross-coupling protocols, expanding the scope of base-metal catalysis for C–C bond formation.

Advantages over Methylboronic Acid: Trimethylboroxine offers improved bench stability, lower volatility relative to many organometallic methyl sources, and reduced protodeboronation side reactions in some systems. Its liquid form facilitates accurate volumetric dispensing.

Storage, Stability, and Handling Precautions

Moisture Sensitivity: Trimethylboroxine is sensitive to moisture. Prolonged exposure to atmospheric humidity can lead to hydrolysis of the boroxine ring and gradual formation of methylboronic acid and boric acid degradation products. Always work under an inert atmosphere (nitrogen or argon) when opening and dispensing the reagent.

Storage Recommendations: Store in a tightly sealed container under inert gas at cool temperatures (typically 2–8 °C or as specified on the product label). Keep away from oxidizing agents, strong bases, and ignition sources. Verify storage conditions on the current Aladdin Scientific product page or SDS for SKU T298925.

Flammability: As an organic liquid, Trimethylboroxine is flammable. Avoid open flames and use appropriate ventilation. Consult the Safety Data Sheet (SDS) for full hazard information, first-aid measures, and disposal guidance before use.

Practical Tips for Use in Cross-Coupling Reactions

Equivalents and Loading: Because Trimethylboroxine contains three methyl-boron units per molecule, stoichiometric calculations must account for its trimeric nature. Typically, 0.33–1.0 equivalent of Trimethylboroxine (providing 1.0–3.0 equivalents of methyl-boron) relative to the electrophilic coupling partner is used; exact loading should be optimized for each substrate.

Base and Solvent Selection: Aqueous inorganic bases such as potassium carbonate, cesium carbonate, or potassium phosphate in mixed aqueous-organic solvents (e.g., DMF/water, THF/water, dioxane/water) are commonly employed. The choice of base and water content significantly affects transmetalation efficiency and reaction rate.

Catalyst Systems: Standard Pd(0) or Pd(II) precatalysts (e.g., Pd(PPh₃)₄, Pd(OAc)₂ with phosphine ligands, or commercial Buchwald-type precatalysts) are suitable. Catalyst loading and ligand choice should be tailored to the substrate and desired selectivity.

Frequently asked questions

What is Trimethylboroxine used for in organic synthesis?

Trimethylboroxine is primarily used as a methyl-boron nucleophile in palladium- and nickel-catalyzed Suzuki–Miyaura cross-coupling reactions, enabling methylation of aryl, heteroaryl, and vinyl halides or pseudohalides. It serves as a stable, convenient equivalent of methylboronic acid, offering practical advantages in handling and stoichiometric flexibility due to its trimeric structure.

How should Trimethylboroxine (T298925) be stored to maintain its quality?

Trimethylboroxine should be stored in a tightly sealed container under an inert atmosphere (nitrogen or argon) at cool temperatures, typically 2–8 °C, away from moisture, strong bases, and oxidizing agents. Always consult the current product label and Safety Data Sheet for SKU T298925 on the Aladdin Scientific website for the most up-to-date storage specifications.

How do I calculate the correct amount of Trimethylboroxine to use in a Suzuki coupling reaction?

Because Trimethylboroxine is a trimer, each mole of the reagent delivers three moles of methyl-boron equivalents. To provide one equivalent of methyl-boron relative to your electrophile, use approximately 0.33 molar equivalents of Trimethylboroxine. Many protocols employ a slight excess (1.5–3.0 methyl-boron equivalents, i.e., 0.5–1.0 equiv of Trimethylboroxine) to drive the reaction to completion; optimization is recommended for each substrate system.

Is Trimethylboroxine air- and moisture-sensitive?

Yes, Trimethylboroxine is moisture-sensitive. Exposure to water or atmospheric humidity can hydrolyze the boroxine ring over time, generating methylboronic acid and boric acid byproducts that may diminish reagent purity and reaction performance. Standard Schlenk or glovebox techniques, or at minimum careful use of inert-gas-purged syringes and septa, are recommended when dispensing the reagent.

What are the safety hazards associated with Trimethylboroxine?

Trimethylboroxine is a flammable organic liquid and may be harmful if inhaled, ingested, or in contact with skin. It should be handled in a well-ventilated fume hood away from ignition sources. Always review the full Safety Data Sheet (SDS) for SKU T298925 available on the Aladdin Scientific website before use, and follow your institution's chemical safety protocols for storage, handling, and disposal.

References

1. Hall, D. G. (Ed.) Boronic Acids: Preparation and Applications in Organic Synthesis, Medicine and Materials, 2nd ed.; Wiley-VCH: Weinheim, 2011.
2. Miyaura, N.; Suzuki, A. Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds. Chem. Rev. 1995, 95, 2457–2483. doi:10.1021/cr00039a007
3. Aladdin Scientific. Trimethylboroxine, SKU T298925 — Product Page and Safety Data Sheet. Retrieved from https://www.aladdin-e.com

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