Methyldiborane

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Methyldiborane
Methyldiborane.svg
Names
IUPAC name
Methyldiborane
Other names
monomethyldiborane
methylated diborane
boraethane
Identifiers
3D model (JSmol)
  • InChI=1S/CH8B2/c1-3-4-2-5-3/h3H,2H2,1H3 [2]
    Key: ALTSFFGCORZGRQ-UHFFFAOYSA-N [3]
  • C[BH]1[H][BH2][H]1
Properties
CH
3BH
3BH
2
Molar mass 41.70 g mol−1
AppearanceColorless gas
Density 0.546 at -126°
Boiling point −43 °C (−45 °F; 230 K)
Related compounds
Related alkyl boranes
dimethyldiborane
trimethyldiborane
tetramethyldiborane
trimethylborane
ethyldiborane
Related compounds
 Diborane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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). [4] 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. [5]

Contents

The methylboranes were first prepared by H. I. Schlesinger and A. O. Walker in the 1930s. [6] [7]

Formation

Methylboranes are 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. [5] The reaction is complex. At 0 °C when diborane is in excess, monomethyldiborane is initially produced, coming to a steady but low level, and 1,1-dimethyldiborane level increases over a long time, until all trimethylborane is consumed. Monomethyldiborane ends up at equilibrium with a mixture of diborane and dimethyldiborane. At 0° the equilibrium constant for 2B2H5Me ←→ B2H6 + (BH2Me)2 is around 0.07, so monomethyldiborane will typically be the majority of the mixture, but there will still be a significant amount of diborane and dimethyldiborane present. [8] Monomethyldiborane yield is best with a ratio of 4 of diborane to 1 of trimethylborane. [9] The yield of trimethyldiborane is maximised with ratio of 1 of diborane to 3 of trimethylborane. [9]

When methyllithium reacts with diborane, monomethyldiborane is produced in about a 20% yield. [10]

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. [11]

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. [6] dimethylchloroborane and methyldichloroborane are also produced as gaseous products. [6]

When Cp2Zr(CH3)2 reacts with borane dissolved in tetrahydrofuran, a borohydro group inserts into the zirconium carbon bond, and methyl diboranes are produced. [12]

When trimethylgallium reacts with diborane at -45°, methyldiborane is produced along with dimethylgallium borohydride.

2(CH3)3Ga + B2H6 → (CH3)2GaBH4 + CH3B2H5. [13]

At room temperature trimethylgallium reacts with diborane to make a volatile substance that decomposes to gallium metal along with methyldiborane.

(CH3)3Ga + 3B2H6 → Ga + 3CH3B2H5 +1.5H2. [13]

Properties

The compound boils at −43 °C. [14] Methyldiborane liquid has a density of 0.546 g/ml at −126° [15] At −78.5 the vapour pressure is 55 torr. [15]

Methyldiborane HCH3BH2BH2 has one methyl group and a hydrogen on a boron atom. The other boron atom is only bound to hydrogen atoms. A bridge of two hydrogen atoms links the boron atoms together. The methyldiborane molecule has the following measurements: B1 is the boron atom not attached to the methyl group and B2 is the boron atom that has methyl group attached, and Hμ is one of the bridge hydrogen atoms between the boron atoms. The distance between boron atoms is 1.82 Å, Distance between boron atoms and bridging hydrogen atoms is 1.34 Å. Distances to non bridging hydrogens from B1 are 1.195 and 1.187 Å. B2 distance to non bridging hydrogen is 1.2 Å. Distance between two bridging hydrogen atoms is 1.96 Å. The carbon to boron bond is 1.49 Å long. The angle subtended from the bridging hydrogens to the boron to boron axis is 47°. The angle of carbon to the boron-boron axis is 120°. The dipole moment of methyldiborane is 0.56 D. [16] It has a vapour pressure of 61 mm Hg at −77.2 °C. [9] The predicted heat of formation for the liquid is ΔH0f=−14 kcal/mol, and for the gas −9 kcal/mol. [17]

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 last tetramethyldiborane. [18]

The nuclear resonance shift for the bridge hydrogen is 10.09 ppm, compared to 10.49 for diborane. [19]

Reactions

At -78.5 °C methyldiborane disproportionates slowly first to diborane and 1,1-dimethyldiborane. [15] In solution methylborane is more stable against disproportionation than dimethylborane. [20]

2MeB2H5⇌ 1,1-Me2B2H4 + B2H6 K=2.8 Me=CH3. [21]

By reacting methyldiborane with ether, dimethylether borine is formed (CH3)2O.BH3 leaving methylborane which rapidly dimerises to 1,2-dimethyldiborane. [5] [22]

Methyldiborane is hydrolyzed in water to methylboronic acid CH3B(OH)2. [5] Methyldiborane reacts with trimethylamine to yield solid derivatives trimethylamine-methylborane (CH3)3N—BHCH3 and trimethylamine-borane (CH3)3N—BH3. [5]

Methyldiborane is pyrophoric, spontaneously inflaming when exposed to air. [15]

When methyldiborane is oxidised around 150 °C a substance 2-methyl-1,3,4-trioxadiboralane is produced. This is a ring of three oxygen atoms and two boron atoms, with methyl attached to one boron atom. At the same time dimethyltrioxadiboralane and trimethylboroxine are also formed, and also hydrocarbons, diborane, hydrogen, and dimethoxyborane (dimethyl methylboronic ester). [23]

When methyldiborane, or dimethyldiborane is combined with ammonia, aminodimethylborine (NH2BMe2) is formed and on heating around 180 °C B-methyl borazoles are produced. These borazoles can have zero, one, two or three methyl groups substituted on the boron atoms (B3N3H6, MeB3N3H5, Me2B3N3H4 or Me3B3N3H3). [24] [25]

A specific way to make 1,2-dimethyldiborane is to react methyldiborane with a sufficient amount of a Lewis base. This will strip off borane to combine with the Lewis base, and let two methyl borane molecules dimerise. [26]

Methyldiborane can methylate tetraborane.

CH3B2H5 + B4H10 → 2-CH3B4H9 + B2H6 [27]

Bis(trimethylphosphine) methyldiborane is an adduct of methyldiborane formed when methylpentaborane (1-CH3B5H8 or 2-CH3B5H8) is reacted with trimethylphosphine. [28]

Related Research Articles

<span class="mw-page-title-main">Hydride</span> Molecule with a hydrogen bound to a more electropositive element or group

In chemistry, a hydride is formally the anion of hydrogen (H−), a hydrogen atom with two electrons. 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>

A borane is a compound with the formula BxHy or a related anion. 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. Given its simple formula, borane is a fundamental boron compound. 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">Carborane</span> Class of chemical compounds

Carboranes are electron-delocalized clusters composed of boron, carbon and hydrogen atoms. Like many of the related boron hydrides, these clusters are polyhedra or fragments of polyhedra. Carboranes are one class of heteroboranes.

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

Organoboron chemistry or organoborane chemistry studies organoboron compounds, also called organoboranes. These chemical compounds combine boron and carbon; typically, they are organic derivatives of borane (BH3), as in the 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

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

Boron compounds are compounds containing the element boron. In the most familiar compounds, boron has the formal oxidation state +3. These include oxides, sulfides, nitrides, and halides.

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

Borohydride refers to the anion [BH4]−, which is also called tetrahydridoborate, 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">Boroxine</span> 6-sided cyclic compound of oxygen and boron

Boroxine is a 6-membered heterocyclic compound composed of alternating oxygen and singly-hydrogenated boron atoms. Boroxine derivatives such as trimethylboroxine and triphenylboroxine also make up a broader class of compounds called boroxines. These compounds are solids that are usually in equilibrium with their respective boronic acids at room temperature. Beside being used in theoretical studies, boroxine is primarily used in the production of optics.

<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">Tetramethyldiborane</span> Chemical compound

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

<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">Borane carbonyl</span> Chemical compound

Borane carbonyl is the inorganic compound with the formula H3BCO. This colorless gas is the adduct of borane and carbon monoxide. It is usually prepared by combining borane-ether complexes and CO. The compound is mainly of theoretical and pedagogical interest.

<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. ↑ Jane E. Macintyre, ed. (1994-11-10). Dictionary of Organometallic Compounds. CRC Press. p. 463. ISBN   978-0-412-43060-2.
  2. ↑ http://cactus.nci.nih.gov/chemical/structure/C%5BBH%5D1H%5BBH2%5DH1/stdinchi [ bare URL plain text file ]
  3. ↑ http://cactus.nci.nih.gov/chemical/structure/C%5BBH%5D1H%5BBH2%5DH1/stdinchikey [ bare URL plain text file ]
  4. ↑ 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.
  5. 1 2 3 4 5 Bell, R. P.; Emeléus, H. J. (1948). "The boron hydrides and related compounds". Quarterly Reviews, Chemical Society. 2 (2): 132. doi:10.1039/QR9480200132.(subscription required)
  6. 1 2 3 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: 3513–3520. doi:10.1039/JR9650003513.(subscription required)
  7. ↑ 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.
  8. ↑ van Aalten, Lloyd; Seely, G. R.; Oliver, Juhn; Ritter, D. M. (1 June 1961). Kinetics and Equilibria in the Alkylation of Diborane Preliminary Report (PDF). Advances in Chemistry. Vol. 32. American Chemical Society. pp. 107–114. doi:10.1021/ba-1961-0032.ch012. ISBN   978-0-8412-0033-3.
  9. 1 2 3 Carpenter, J.H.; Jones, W.J.; Jotham, R.W.; Long, L.H. (September 1971). "The Raman spectra of the methyldiboranes—II Monomethyldiborane and trimethyldiborane, and characteristic frequencies of the methyldiboranes". Spectrochimica Acta Part A: Molecular Spectroscopy. 27 (9): 1721–1734. Bibcode:1971AcSpA..27.1721C. doi: 10.1016/0584-8539(71)80227-1 .
  10. ↑ Massey, A. G. (1979). "Chapter 2. The typical elements. Part II: Group III". Annual Reports on the Progress of Chemistry, Section A. 76: 13–15. doi:10.1039/IC9797600013.(subscription required)
  11. ↑ Holliday, A.K.; N. Jessop, G. (November 1967). "The reaction of tetramethyllead with diborane". Journal of Organometallic Chemistry. 10 (2): 291–293. doi:10.1016/s0022-328x(00)93089-4.
  12. ↑ Marsella, John A.; Caulton, Kenneth G. (May 1982). "Dealkylation of zirconium(IV) by borane: the intimate mechanism of an alkyl transfer reaction". Journal of the American Chemical Society. 104 (9): 2361–2365. doi:10.1021/ja00373a005.
  13. 1 2 Schlesinger, H. I.; Brown, Herbert C (September 1943). "The Borohydrides of Gallium". Journal of the American Chemical Society. 65 (9): 1787. doi:10.1021/ja01249a512 . Retrieved 17 August 2015.
  14. ↑ Lamneck, John H Jr; Kaye, Samuel (4 September 1958). "Thermal reaction of diborane with trimethylborane". National Advisory Committee for Aeronautics.
  15. 1 2 3 4 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   978-0-471-04542-7.
  16. ↑ Chiu, C. W.; Burg, A. B.; Beaudet, R. A. (March 1982). "Molecular structure determination of methyldiborane". Inorganic Chemistry. 21 (3): 1204–1208. doi:10.1021/ic00133a064.
  17. ↑ 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.
  18. ↑ 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.
  19. ↑ 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.
  20. ↑ 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.
  21. ↑ 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   978-0-08-058004-3 . Retrieved 19 August 2015.
  22. ↑ 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   978-0-8412-0024-1 . Retrieved 17 August 2015.
  23. ↑ Barton, Lawrence; Crump, John M.; Wheatley, Jeffrey B. (June 1974). "Trioxadiborolanes from the oxidation of methyldiborane". Journal of Organometallic Chemistry. 72 (1): C1–C3. doi:10.1016/s0022-328x(00)82027-6.
  24. ↑ Sheldon, J. C.; Smith, B. C. (1960). "The borazoles". Quarterly Reviews, Chemical Society. 14 (2): 202. doi:10.1039/QR9601400200.
  25. ↑ Schlesinger, H. I.; Horvitz, Leo; Burg, A. B. (March 1936). "Hydrides of Boron. VI. The Action of Ammonia on the Methyl Diboranes". Journal of the American Chemical Society. 58 (3): 409–414. doi:10.1021/ja01294a008.
  26. ↑ Wade, Kenneth (1971). "The General Chemistry of the Boron Hydrides". Electron Deficient Compounds. Thomas Nelson. pp. 91–92. ISBN   978-1-4684-6056-8 . Retrieved 17 August 2015.
  27. ↑ Onak, Thomas (1975). Organoborane chemistry. New York: Academic Press. pp. 193–194. ISBN   978-0-12-526550-8 . Retrieved 17 August 2015.
  28. ↑ Kameda, Mitsuaki; Driscoll, Jerry A.; Kodama, Goji (September 1990). "Formation and reactions of bis(trimethylphosphine)-methyldiborane(4)". Inorganic Chemistry. 29 (19): 3791–3795. doi:10.1021/ic00344a028.

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