Dimethyldiborane

1,2-Dimethyldiborane

cis-1,2-Dimethyldiborane
trans-1,2-Dimethyldiborane
Names
IUPAC name 1,2-Dimethyldiborane
Other names Symmetrical dimethyldiborane
Identifiers
CAS Number	17156-88-6 N
3D model (JSmol)	Interactive image
InChI InChI=1S/C2H10B2/c1-3-5-4(2)6-3/h3-4H,1-2H3[1] Key: CMZSWMSJMMTTMF-UHFFFAOYSA-N[2]
SMILES C[BH]1H[BH](C)H1
Properties
Chemical formula	(CH3BH2)2
Molar mass	55.72 g mol−1
Appearance	Colorless gas
Melting point	−124.9 °C (−192.8 °F; 148.2 K)
Boiling point	4 °C (39 °F; 277 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N (what is YN ?)
Infobox references

1,2-Dimethyldiborane is an organoboron compound with the formula [(CH₃)BH₂]₂. Structurally, it is related to diborane, but with methyl groups replacing terminal hydrides on each boron. It is the dimer of methylborane, CH₃BH₂, the simplest alkylborane. 1,2-Dimethyldiborane can exist in a cis- and a trans arrangement. 1,2-Dimethyldiborane is an easily condensed, colorless gas that ignites spontaneously in air.

An isomer of 1,2-dimethyldiborane is 1,1-dimethyldiborane, known as unsymmetrical dimethyldiborane, which has two methyl groups on one boron atom. Other methylated versions of diborane including methyldiborane, trimethyldiborane, tetramethyldiborane. Trimethylborane exists as a monomer.

Methylboranes were first prepared by H. I. Schlesinger and A. O. Walker in the 1930s.

In a more modern synthesis, 1,2-dmethyldiborane is produced by treating lithium methylborohydride with hydrogen chloride:

Instead of hydrogen chloride, methyl iodide or trimethylsilyl chloride can be used.

Lithium methylborohydride can be made by treating methylboronic esters with lithium aluminium hydride.

Methylboranes arise the reaction of diborane and trimethylborane. This reaction produces 1-methyldiborane, 1,1-dimethyldborane, 1,1,2-trimethyldiborane, and 1,1,2,2-tetramethyldiborane. By treating monomethyldiborane with ether, dimethyl ether borane (CH₃)₂O.BH₃ leaving methylborane which rapidly dimerises to 1,2-dimethyldiborane. The reaction is complex.

Tetramethyl lead reacts with diborane to give a range of methyl-substituted diboranes, ending up at trimethylborane, but including 1,1-dimethyldiborane, and trimethyldiborane. Other products are hydrogen gas and lead metal.