Tetramethyldiborane

Last updated
Tetramethyldiborane
Tetramethyldiborane.svg
Names
IUPAC name
Tetramethyldiborane(6)
Other names
Dimethylborane dimer
Identifiers
3D model (JSmol)
  • InChI=1S/C4H14B2/c1-5(2)7-6(3,4)8-5/h1-4H3
    Key: DAOILNUAERZCST-UHFFFAOYSA-N
  • InChI=1/C4B2H14/c1-5(2)7-6(3,4)8-5/h1-4H3
  • C[B]1(C)[H][B](C)(C)[H]1
Properties
(CH
3)
2BH
2B(CH
3)
2
Molar mass 83.777
AppearanceColorless liquid
Odor Pungent;
Melting point −72.5 °C (−98.5 °F; 200.7 K)
Boiling point 68.6 °C (155.5 °F; 341.8 K)
Hazards
NFPA 704 (fire diamond)
[1]
2
2
Related compounds
Related alkyl boranes
trimethylborane
dimethyldiborane
diethylborane
Related compounds
 Borane
tetramethyl aluminium hydride
tetramethyl gallium hydride

methylalane

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN (what is  Yes check.svgYX mark.svgN ?)

Dimethylborane, (CH3)2BH is the simplest dialkylborane, consisting of a methyl group substituted for a hydrogen in borane. As for other boranes it normally exists in the form of a dimer called tetramethyldiborane or tetramethylbisborane or TMDB ((CH3)2BH)2. [2] Other combinations of methylation occur on diborane, including monomethyldiborane, trimethyldiborane, 1,2-dimethylborane, 1,1-dimethylborane and trimethylborane. At room temperature the substance is at equilibrium between these forms. [3] The methylboranes were first prepared by H. I. Schlesinger and A. O. Walker in the 1930s. [4] [5]

Contents

Formation

Dimethylborane is formed when lithium dimethylborohydride Li(CH3)2BH2 reacts with an acid. [6] The lithium dimethylborohydride can be made from a dimethylborinic ester and lithium monoethoxy aluminium hydride. [6]

Methylboranes are also formed by the reaction of diborane and trimethylborane. This reaction produces four different substitutions of methyl with hydrogen on diborane. Produced is 1-methyldiborane, 1,1-dimethyldborane, 1,1,2-trimethyldiborane and 1,1,2,2-tetramethyldiborane. [3] The latter is maximised when trimethylborane is six times the concentration of diborane. [7]

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. [4] dimethylchloroborane and methyldichloroborane are also produced as gaseous products. [4]

Atomic hydrogen converts trimethylborane on a graphene monolayer surface to dimethylborane which dimerises to tetramethyldiborane. [8]

Properties

Tetramethyldiborane has two boron atoms linked by a two hydrogen atom bridge, and each boron is linked to two methyl groups. A Tetramethyldiborane molecule belongs to the D2h point group. Its infrared spectrum shows a strong absorption band at 1602 cm−1 due to bridging hydrogen, a weak band at 1968 cm−1 and lines due to methyl between 900 and 1400 cm−1. [9] In the molecule the boron to hydrogen distance is 1.36 Å, the boron to boron distance is 1.84 Å; the boron to carbon distance is 1.590 Å; the angle of boron-boron to carbon is 120.0°; the boron-carbon-hydrogen angle is 112.0°. [10] The NMR J coupling between two boron-11 nuclei in tetramethyldiborane is 55 Hz. [11]

Tetramethyldiborane melts at -72.5 °C and boils at 68.6 °C. [12] Vapour pressure is approximated by Log P = 7.687-(1643/T). [12] Tetramethyldiborane has a vapour pressure of 48 mm Hg at 0 °C. [7] Heat of vapourisation was measured at 7.3 kcal/mol. [13] The predicted heat of formation for the liquid is ΔH0f=-65 kcal/mol, and for the gas -57 kcal/mol. [13]

A gas chromatograph can be used to determine the amounts of the methyl boranes in a mixture. The order they pass through are diborane, monomethyldiborane, trimethylborane, 1,1-dimethyldiborane, 1,2-dimethyldiborane, trimethyldiborane, and lastly tetramethyldiborane. [14]

The nuclear resonance shift for the bridge hydrogen is 8.90 ppm, compared to 10.49 for diborane. [15]

Reactions

Dimethylborane reacts with alkenes with the highest yield in ether to produce a dimethylalkylborane. [6] The dimethylalkylboranes can then be converted to a tertiary alcohol by oxidative carbonylation. This requires heating to 150° with carbon monoxide under 50 bars of pressure, and then oxidation with hydrogen peroxide. [16]

Methylboranes such as tetramethyldiborane disproportionate in the gas phase to trimethylborane and diborane at room temperature. [3] The time period is on the order of a few hours, and disproportionation is faster the higher the temperature. [4] At 0 °C disproportionation takes about a day. [4] At -78.5 °C methyldiborane disproportionates slowly first to diborane and 1,1-dimethyldiborane. [17] In solution methylborane is more stable against disproportionation than dimethylborane. [6]

4(CH3)3B2H3⇌ (CH3)4B2H2 + B2H6 K=0.0067. [18]
3B2H2Me4⇌ 2 B2H3Me3 + 2 BMe3

Dimethylborane is hydrolyzed in water to Dimethylborinic acid (CH3)2BOH. [3]

Dimethyldiborane spontaneously inflames when exposed to air. [17]

Ammonia and tetramethyldiborane combine to form a white solid at -78 °C. The solid decomposes above 10 °C. [19] The structure of the solid is ionic [(CH3)2B(NH3)2]+ [(CH3)2BH2]−. [19] [20] A simple adduct BHMe3.NH3 is formed from tetramethyldiborane and ammonia in ether. This also forms during the thermal decomposition of the diammoniate. [21]

Acetonitrile reacts slowly with tetramethyldiborane at room temperature to form dimeric ethylideneaminodimethylborane (CH3CH=NB(CH3)2)2. This has a cis and a trans isomer, one melting at 76 °C and another at -5 °C. [22]

Tetramethyldiborane reacts with sodium in liquid ammonia to make a salt with formula Na2HB(CH3)2 called sodium dimethylboryl. The salt is white and stable to 90 °C. [21] With potassium K2HB(CH3)2 potassium dimethylboryl is formed. [23] Calcium metal react with tetramethyldiborane to make CaHB(CH3)2.NH3. [21]

Tetramethyldiborane combines with dimethylphosphine to yield an adduct of dimethylborane. [21]

Tetramethyldiborane reacts with organic borates to form methylboronic esters.

2 (CH3)4B2H2 + 4 B(OR)3⇌ 6 CH3(OR)2 + (CH3)2B2H4. [24]

Tetramethyldiborane acts as a catalyst to enable the same results from trimethylborane:

(CH3)3B + 2 B(OR)3 → 3 CH3(OR)2 [24]

The tetramethylborate anion (CH3)4B− only has one boron atom. [25]

Related Research Articles

In chemistry, a hydride is formally the anion of hydrogen (H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride of nitrogen, etc. For inorganic chemists, hydrides refer to compounds and ions in which hydrogen is covalently attached to a less electronegative element. In such cases, the H centre has nucleophilic character, which contrasts with the protic character of acids. The hydride anion is very rarely observed.

<span class="mw-page-title-main">Boranes</span>

Boranes is the name given to compounds with the formula BxHy and related anions. Many such boranes are known. Most common are those with 1 to 12 boron atoms. Although they have few practical applications, the boranes exhibit structures and bonding that differs strongly from the patterns seen in hydrocarbons. Hybrids of boranes and hydrocarbons, the carboranes are also well developed.

Hydroboration–oxidation reaction is a two-step hydration reaction that converts an alkene into an alcohol. The process results in the syn addition of a hydrogen and a hydroxyl group where the double bond had been. Hydroboration–oxidation is an anti-Markovnikov reaction, with the hydroxyl group attaching to the less-substituted carbon. The reaction thus provides a more stereospecific and complementary regiochemical alternative to other hydration reactions such as acid-catalyzed addition and the oxymercuration–reduction process. The reaction was first reported by Herbert C. Brown in the late 1950s and it was recognized in his receiving the Nobel Prize in Chemistry in 1979.

<span class="mw-page-title-main">Diborane</span> Chemical compound

Diborane(6), commonly known as diborane, is the chemical compound with the formula B2H6. It is a toxic, colorless, and pyrophoric gas with a repulsively sweet odor. Diborane is a key boron compound with a variety of applications. It has attracted wide attention for its electronic structure. Several of its derivatives are useful reagents.

<span class="mw-page-title-main">Herbert C. Brown</span> American chemist (1912–2004)

Herbert Charles Brown was an American chemist and recipient of the 1979 Nobel Prize in Chemistry for his work with organoboranes.

<span class="mw-page-title-main">Decaborane</span> Chemical compound

Decaborane, also called decaborane(14), is the borane with the chemical formula B10H14. This white crystalline compound is one of the principal boron hydride clusters, both as a reference structure and as a precursor to other boron hydrides. It is toxic and volatile, giving off a foul odor, like that of burnt rubber or chocolate.

<span class="mw-page-title-main">Organoboron chemistry</span> Study of compounds containing a boron-carbon bond

Organoboron chemistry or organoborane chemistry is the chemistry of organoboron compounds or organoboranes, which are chemical compounds of boron and carbon that are organic derivatives of borane (BH3), for example trialkyl boranes..

<span class="mw-page-title-main">Borazine</span> Boron compound

Borazine, also known as borazole, is an inorganic compound with the chemical formula B3H6N3. In this cyclic compound, the three BH units and three NH units alternate. The compound is isoelectronic and isostructural with benzene. For this reason borazine is sometimes referred to as “inorganic benzene”. Like benzene, borazine is a colourless liquid with an aromatic odor.

In organic chemistry, hydroboration refers to the addition of a hydrogen-boron bond to certain double and triple bonds involving carbon. This chemical reaction is useful in the organic synthesis of organic compounds.

<span class="mw-page-title-main">Ammonia borane</span> Chemical compound

Ammonia borane (also systematically named amminetrihydridoboron), also called borazane, is the chemical compound with the formula H3NBH3. The colourless or white solid is the simplest molecular boron-nitrogen-hydride compound. It has attracted attention as a source of hydrogen fuel, but is otherwise primarily of academic interest.

<span class="mw-page-title-main">Borohydride</span>

Borohydride refers to the anion [BH4]−, which is also called tetrahydroborate, and its salts. Borohydride or hydroborate is also the term used for compounds containing [BH4−nXn]−, where n is an integer from 0 to 3, for example cyanoborohydride or cyanotrihydroborate [BH3(CN)]− and triethylborohydride or triethylhydroborate [BH(CH2CH3)3]−. Borohydrides find wide use as reducing agents in organic synthesis. The most important borohydrides are lithium borohydride and sodium borohydride, but other salts are well known. Tetrahydroborates are also of academic and industrial interest in inorganic chemistry.

<span class="mw-page-title-main">Catecholborane</span> Chemical compound

Catecholborane (abbreviated HBcat) is an organoboron compound that is useful in organic synthesis. This colourless liquid is a derivative of catechol and a borane, having the formula C6H4O2BH.

A frustrated Lewis pair (FLP) is a compound or mixture containing a Lewis acid and a Lewis base that, because of steric hindrance, cannot combine to form a classical adduct. Many kinds of FLPs have been devised, and many simple substrates exhibit activation.

<span class="mw-page-title-main">Diisopinocampheylborane</span> Chemical compound

Diisopinocampheylborane is an organoborane that is useful for asymmetric synthesis. This colourless solid is the precursor to a range of related reagents. The compound was reported in 1961 by Zweifel and Brown in a pioneering demonstration of asymmetric synthesis using boranes. The reagent is mainly used for the synthesis of chiral secondary alcohols.

<span class="mw-page-title-main">Trimethylborane</span> Chemical compound

Trimethylborane (TMB) is a toxic, pyrophoric gas with the formula B(CH3)3 (which can also be written as Me3B, with Me representing methyl).

Borane, also known as borine, is an unstable and highly reactive molecule with the chemical formula BH
3. The preparation of borane carbonyl, BH3(CO), played an important role in exploring the chemistry of boranes, as it indicated the likely existence of the borane molecule. However, the molecular species BH3 is a very strong Lewis acid. Consequently, it is highly reactive and can only be observed directly as a continuously produced, transitory, product in a flow system or from the reaction of laser ablated atomic boron with hydrogen. It normally dimerizes to diborane in the absence of other chemicals.

<span class="mw-page-title-main">1,2-Dimethyldiborane</span> Chemical compound

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.

<span class="mw-page-title-main">Trimethyldiborane</span> Chemical compound

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.

<span class="mw-page-title-main">Methyldiborane</span> Chemical compound

Methyldiborane, CH3B2H5, or monomethyldiborane is the simplest of alkyldiboranes, consisting of a methyl group substituted for a hydrogen in diborane. As with other boranes it exists in the form of a dimer with a twin hydrogen bridge that uses three-center two-electron bonding between the two boron atoms, and can be imagined as methyl borane (CH3BH2) bound to borane (BH3). Other combinations of methylation occur on diborane, including 1,1-dimethylborane, 1,2-dimethyldiborane, trimethyldiborane, tetramethyldiborane, and trimethylborane (which is not a dimer). At room temperature the substance is at equilibrium between these molecules.

<span class="mw-page-title-main">1,1-Dimethyldiborane</span> Chemical compound

1,1-Dimethyldiborane is the organoboron compound with the formula (CH3)2B(μ-H)2BH2. A pair of related 1,2-dimethyldiboranes are also known. It is a colorless gas that ignites in air.

References

  1. ↑ Baker, Charles J. (2001). The Fire Fighter's Handbook of Hazardous Materials. Jones & Bartlett Learning. p. 352. ISBN   9780962705212.
  2. ↑ Srebnik, Morris; Cole, Thomas E.; Brown, Herbert C. (January 1987). "Methylborane - a remarkable unhindered monoalkylborane which achieves the controlled sequential hydroboration of representative alkenes". Tetrahedron Letters. 28 (33): 3771–3774. doi:10.1016/s0040-4039(00)96380-9.
  3. 1 2 3 4 Bell, R. P.; Emeléus, H. J. (1948). "The boron hydrides and related compounds". Quarterly Reviews, Chemical Society. 2 (2): 132. doi:10.1039/QR9480200132.
  4. 1 2 3 4 5 Long, L. H.; Wallbridge, M. G. H. (1965). "646. The chemistry of boron. Part VI. New preparative methods and decomposition studies relating to methyldiboranes". Journal of the Chemical Society (Resumed): 3513–3520. doi:10.1039/JR9650003513.(subscription required)
  5. ↑ Schlesinger, H. I.; Walker, A. O. (April 1935). "Hydrides of Boron. IV. The Methyl Derivatives of Diborane". Journal of the American Chemical Society. 57 (4): 621–625. doi:10.1021/ja01307a009.
  6. 1 2 3 4 Brown, Herbert C.; Cole, Thomas E.; Srebnik, Morris; Kim, Kee Won (December 1986). "Hydroboration. 79. Preparation and properties of methylborane and dimethylborane and their characteristics as hydroborating agents. Synthesis of tertiary alcohols containing methyl groups via hydroboration". The Journal of Organic Chemistry. 51 (25): 4925–4930. doi:10.1021/jo00375a031.
  7. 1 2 Carpenter, J.H.; Jones, W.J.; Jotham, R.W.; Long, L.H. (June 1970). "The Raman spectra of the methyldiboranes—I 1,1 dimethyldiborane and tetramethyldiborane". Spectrochimica Acta Part A: Molecular Spectroscopy. 26 (6): 1199–1214. Bibcode:1970AcSpA..26.1199C. doi:10.1016/0584-8539(70)80027-7.
  8. ↑ Horn, A; Biener, J; Küppers, J (September 1998). "A dimerization reaction induced by hydrogen atoms: from B(CH3)3 adsorbed on C/Pt(100) to B2H2(CH3)4". Surface Science. 414 (1–2): 290–297. Bibcode:1998SurSc.414..290H. doi:10.1016/S0039-6028(98)00534-2.(subscription required)
  9. ↑ Cowan, R. D. (1949). "The Infra-Red Spectra of Borine Carbonyl and Tetramethyldiborane". The Journal of Chemical Physics. 17 (2): 218. Bibcode:1949JChPh..17..218C. doi:10.1063/1.1747225.
  10. ↑ Carroll, Benjamin L.; Bartell, Lawrence S. (February 1968). "Molecular structure and internal rotation in tetramethyldiborane. Electron diffraction study". Inorganic Chemistry. 7 (2): 219–222. doi:10.1021/ic50060a009.
  11. ↑ Perras, Frédéric A.; Ewing, William C.; Dellermann, Theresa; Böhnke, Julian; Ullrich, Stefan; Schäfer, Thomas; Braunschweig, Holger; Bryce, David L. (2015). "Spying on the boron–boron triple bond using spin–spin coupling measured from 11B solid-state NMR spectroscopy". Chem. Sci. 6 (6): 3378–3382. doi:10.1039/C5SC00644A. PMC   5657093 . PMID   29142694.
  12. 1 2 Onak, Thomas (1 January 1966). Stone, F. G. A.; West, Robert (eds.). Advances in Organometallic Chemistry. New York, London: Academic Press. p. 284. ISBN   9780080580043 . Retrieved 14 August 2015.
  13. 1 2 Altschuller, Aubrey P. (4 October 1955). "Calculated Heats of Formation and Combustion of Boron Compounds (Boron, Hydrogen, Carbon, Silicon)" (PDF). NACA Research Memorandum. Cleveland, Ohio: National Advisory Committee for Aeronautics. p. 22. Retrieved 14 August 2015.
  14. ↑ Seely, G. R.; Oliver, J. P.; Ritter, D. M. (December 1959). "Gas-Liquid Chromatographic Analysis of Mixtures Containing Methyldiboranes". Analytical Chemistry. 31 (12): 1993–1995. doi:10.1021/ac60156a032.
  15. ↑ Leach, John B.; Ungermann, Charles B.; Onak, Thomas P. (January 1972). "Proton magnetic resonance studies on methyl and chloro substituted diboranes". Journal of Magnetic Resonance. 6 (1): 74–83. Bibcode:1972JMagR...6...74L. doi:10.1016/0022-2364(72)90088-1.
  16. ↑ Srebnik, Morris; Cole, Thomas E.; Brown, Herbert C. (August 1990). "Hydroboration. 87. Controlled and sequential hydroboration of simple representative alkenes with methylborane in tetrahydrofuran. An examination of the directive effects in the first and second stages of hydroboration". The Journal of Organic Chemistry. 55 (17): 5051–5058. doi:10.1021/jo00304a017.
  17. 1 2 Bunting, Roger K. (22 Sep 2009). "55 1-Methyldiborane". In Duward F. Shriver (ed.). Inorganic Syntheses, Volume 19. John Wiley and Sons. pp. 237–238. ISBN   978-0471045427.
  18. ↑ Onak, Thomas (1 January 1966). "Carboranes and Organo-Substituted Boron Hydrides". In Stone, F. G. A.; West, Robert (eds.). Advances in Organometallic Chemistry. New York, London: Academic Press. p. 284. ISBN   9780080580043 . Retrieved 19 August 2015.
  19. 1 2 Moews, P. C.; Parry, R. W. (September 1966). "The Reactions between Tetramethyldiborane and Ammonia. The Dimethyldiammineboron(III) Cation, the Dihydridodimethylborate Anion, and Ammonia Dimethylborane". Inorganic Chemistry. 5 (9): 1552–1556. doi:10.1021/ic50043a018.
  20. ↑ Zhao, Qianyi; Li, Jiaxuan; Hamilton, Ewan J.M.; Chen, Xuenian (May 2015). "The continuing story of the diammoniate of diborane". Journal of Organometallic Chemistry. 798: 24–29. doi:10.1016/j.jorganchem.2015.05.027.
  21. 1 2 3 4 Onak, Thomas (2 December 2012). Organoborane Chemistry. Elsevier. pp. 183–184. ISBN   9780323153614 . Retrieved 12 August 2015.
  22. ↑ Lloyd, J. E.; Wade, K. (1964). "325. Reactions between dialkylboranes and methyl cyanide. Ethylideneaminodimethylborane and diethylethylideneaminoborane". Journal of the Chemical Society (Resumed): 1649–1654. doi:10.1039/JR9640001649 . Retrieved 24 July 2015.
  23. ↑ Adams, Roy M. (September 1959). "Organoboron Compounds" (PDF). Metal-Organic Compounds. Advances in Chemistry. Vol. 23. p. 92. doi:10.1021/ba-1959-0023.ch010. ISBN   0-8412-0024-6 . Retrieved 17 August 2015.
  24. 1 2 Mikhailov, B. M. (April 1962). "The Chemistry Of Diborane". Russian Chemical Reviews. 31 (4): 219. Bibcode:1962RuCRv..31..207M. doi:10.1070/RC1962v031n04ABEH001281. S2CID   250909492.
  25. ↑ "tetramethylborate". ChemSpider. Retrieved 19 August 2015.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.