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Introduction
Borane–N-methylmorpholine (abbreviated as BH₃·NMM) is a widely used complex of borane with the tertiary amine N-methylmorpholine.
It is utilized predominantly as a mild and selective reducing agent in synthetic organic chemistry, particularly for the reduction of carbonyl compounds under controlled conditions.
Due to its improved stability compared to borane alone, it offers practical advantages in laboratory and industrial contexts.
Chemical Identification
CAS Number: 37260-57-6
Molecular Formula: C₅H₁₂BNO
Molar Mass: 112.97 g/mol
IUPAC Name: Borane–N-methylmorpholine complex
Synonyms:
N-Methylmorpholine–borane complex
Morpholine, 4-methyl-, borane complex
BH₃·NMM
Borane-morpholine, methylated
Morpholine, 4-methyl-, borane (1:1)
History and Discovery
The use of amine–borane complexes dates back to the mid-20th century, primarily as an effort to stabilize borane (BH₃), which is pyrophoric and unstable in its free form.
The discovery of Borane–N-methylmorpholine came as part of this broader investigation into safer borane delivery systems.
N-methylmorpholine was found to form a stable 1:1 complex with BH₃, producing a crystalline solid that could be stored and used under ambient conditions, unlike free BH₃ gas.
Molecular Structure and Bonding
The molecule consists of a coordinate covalent bond between the nitrogen lone pair of N-methylmorpholine and the electron-deficient boron atom in BH₃.
This dative bond imparts partial ionic character and contributes to the stability of the complex.
Quantum chemical studies show that the nitrogen–boron bond has a bond length of approximately 1.63 Å, and the structure resembles a tetrahedral arrangement around the boron center.
Synthesis and Preparation Methods
Laboratory Synthesis
A common synthesis involves passing borane–THF through a solution of N-methylmorpholine at low temperatures:
BH₃·THF + NMM → BH₃·NMM + THF
Industrial Preparation
For large-scale synthesis, gaseous diborane (B₂H₆) is reacted with N-methylmorpholine under controlled conditions with solvents such as diethyl ether or toluene.
Physical and Chemical Properties
Property Value
Appearance White crystalline solid
Density ~0.93 g/cm³
Melting Point 66–70 °C
Solubility Soluble in ether, THF, acetone
Stability Stable in sealed containers
Odor Amine-like
Borane–NMM is significantly more stable than borane–THF or borane–DMS, especially under ambient air.
Spectroscopic and Analytical Data
NMR:
¹H NMR: Signals appear for BH₃ (broad, ~ -0.6 ppm), N-methyl (~2.3 ppm), and ring protons.
¹³C NMR: Signals for morpholine carbons and methyl groups.
¹¹B NMR: Broad singlet around -18 to -24 ppm.
IR Spectroscopy:
B–H stretching: ~2300–2500 cm⁻¹
N–B stretch: ~650–850 cm⁻¹
Mass Spectrometry:
Molecular ion peak at m/z 113
Fragmentation shows B–N bond cleavage
Reactivity and Mechanism
Borane–NMM acts as a hydride donor in reductions. Mechanistically, it transfers a hydride to electrophilic centers such as carbonyl groups.
It avoids over-reduction and provides regioselectivity under controlled conditions.
Applications in Organic Chemistry
Reductions: Aldehydes, ketones, esters, and acids to alcohols
Amide reductions: To amines without affecting nearby unsaturated systems
Reductive amination: Mild and selective
Chiral synthesis: Paired with chiral auxiliaries
Applications in Industrial and Fine Chemicals
Used in:
Pharmaceutical intermediates
Agrochemical synthesis
Fragrance and flavor compounds
API reduction processes
Catalysis and Coordination Chemistry
Borane–NMM has been investigated as a precursor in:
Transition metal-borane coordination complexes
Hydrogen storage materials
Catalytic hydroboration reactions
SAFETY INFORMATION ABOUT BORANE-N-METHYLMORPHOLINE
First aid measures:
Description of first aid measures:
General advice:
Consult a physician.
Show this safety data sheet to the doctor in attendance.
Move out of dangerous area:
If inhaled:
If breathed in, move person into fresh air.
If not breathing, give artificial respiration.
Consult a physician.
In case of skin contact:
Take off conSAFETYtaminated clothing and shoes immediately.
Wash off with soap and plenty of water.
Consult a physician.
In case of eye contact:
Rinse thoroughly with plenty of water for at least 15 minutes and consult a physician.
Continue rinsing eyes during transport to hospital.
If swallowed:
Do NOT induce vomiting.
Never give anything by mouth to an unconscious person.
Rinse mouth with water.
Consult a physician.
Firefighting measures:
Extinguishing media:
Suitable extinguishing media:
Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide.
Special hazards arising from the substance or mixture
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas
Advice for firefighters:
Wear self-contained breathing apparatus for firefighting if necessary.
Accidental release measures:
Personal precautions, protective equipment and emergency procedures
Use personal protective equipment.
Avoid breathing vapours, mist or gas.
Evacuate personnel to safe areas.
Environmental precautions:
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
Methods and materials for containment and cleaning up:
Soak up with inert absorbent material and dispose of as hazardous waste.
Keep in suitable, closed containers for disposal.
Handling and storage:
Precautions for safe handling:
Avoid inhalation of vapour or mist.
Conditions for safe storage, including any incompatibilities:
Keep container tightly closed in a dry and well-ventilated place.
Containers which are opened must be carefully resealed and kept upright to prevent leakage.
Storage class (TRGS 510): 8A: Combustible, corrosive hazardous materials
Exposure controls/personal protection:
Control parameters:
Components with workplace control parameters
Contains no substances with occupational exposure limit values.
Exposure controls:
Appropriate engineering controls:
Handle in accordance with good industrial hygiene and safety practice.
Wash hands before breaks and at the end of workday.
Personal protective equipment:
Eye/face protection:
Tightly fitting safety goggles.
Faceshield (8-inch minimum).
Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
Skin protection:
Handle with gloves.
Gloves must be inspected prior to use.
Use proper glove
removal technique (without touching glove's outer surface) to avoid skin contact with this product.
Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices.
Wash and dry hands.
Full contact:
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
Splash contact
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
It should not be construed as offering an approval for any specific use scenario.
Body Protection:
Complete suit protecting against chemicals, The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.
Respiratory protection:
Where risk assessment shows air-purifying respirators are appropriate use a fullface respirator with multi-purpose combination (US) or type ABEK (EN 14387) respirator cartridges as a backup to engineering controls.
If the respirator is the sole means of protection, use a full-face supplied air respirator.
Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).
Control of environmental exposure
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
Stability and reactivity:
Chemical stability:
Stable under recommended storage conditions.
Incompatible materials:
Strong oxidizing agents:
Hazardous decomposition products:
Hazardous decomposition products formed under fire conditions.
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas.
Disposal considerations:
Waste treatment methods:
Product:
Offer surplus and non-recyclable solutions to a licensed disposal company.
Contact a licensed professional waste disposal service to dispose of this material.
Contaminated packaging:
Dispose of as unused product
