Trimethyldiborane
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| Names | |
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IUPAC name
1,1,2-Trimethyldiborane
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| Other names
Trimethyldiborane(6)
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| Identifiers | |
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3D model (JSmol)
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| Properties | |
| (CH 3) 3B 2H 3 |
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| Molar mass | 69.75 g mol−1 |
| Appearance | Colorless pyrophoric liquid |
| Melting point | −122.9 °C (−189.2 °F; 150.2 K) |
| Boiling point | 45.5 °C (113.9 °F; 318.6 K) |
| Thermochemistry | |
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Std enthalpy of
formation (ΔfH |
48 kcal/mol |
| Related compounds | |
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trimethylborane tetramethyldiborane dimethyldiborane methyldiborane |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is   ?) |
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| Infobox references | |
Trimethyldiborane, (CH3)3B2H3 is a molecule containing boron carbon and hydrogen. It is an alkylborane, consisting of three methyl group substituted for a hydrogen in diborane. It can be considered a mixed dimer: (CH3)2BH2BH(CH3) or dimethylborane and methylborane. called 1,2-dimethyldiborane. Other combinations of methylation occur on diborane, including monomethyldiborane, 1,2-dimethyldiborane, tetramethyldiborane, 1,1-dimethylborane and trimethylborane. At room temperature the substance is at equilibrium between these forms, so it is difficult to keep it pure. The methylboranes were first prepared by H. I. Schlesinger and A. O. Walker in the 1930s.
Trimethylborane is formed by the reaction of diborane and trimethylborane. This reaction produces four different substitution of methyl with hydrogen on diborane. Produced is 1-methyldiborane, 1,1-dimethyldborane, 1,1,2-trimethyldiborane and 1,1,2,2-tetramethyldiborane. By reacting monomethyldiborane with ether, dimethylether borine is formed [(CH3)2O].BH3 leaving methylborane which rapidly dimerises to 1,2-dimethyldiborane. The reaction is complex. The yield of trimethyldiborane is maximised with ratio of 1 of diborane to 3 of trimethylborane.
Tetramethyl lead can react with diborane in a 1,2-dimethoxyethane solvent at room temperature to make a range of methyl substituted diboranes, ending up at trimethylborane, but including 1,1-di, tridiborane. The other outputs of the reaction are hydrogen gas and lead metal.
Other methods to form methyldiboranes include reacting hydrogen with trimethylborane between 80 and 200 °C under pressure, or reacting a metal borohydride with trimethylborane in the presence of hydrogen chloride, aluminium chloride or boron trichloride. If the borohydride is sodium borohydride, then methane is a side product. If the metal is lithium then no methane is produced. Dimethylchloroborane and methyldichloroborane are also produced as gaseous products.
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