1,2-Dimethyldiborane

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1,2-Dimethyldiborane
Cis-1,2-dimethyldiborane.svg
cis-1,2-Dimethyldiborane
Trans-1,2-dimethyldiborane.svg
trans-1,2-Dimethyldiborane
Names
Preferred IUPAC name
1,2-Dimethyldiborane(6)
Other names
Symmetrical dimethyldiborane
Identifiers
3D model (JSmol)
  • C[BH]1[H][BH](C)[H]1
Properties
(CH3BH2)2
Molar mass 55.72 g mol−1
AppearanceColorless 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).
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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] 1,2-Dimethyldiborane can exist in a cis- and a trans arrangement. [2] 1,2-Dimethyldiborane is an easily condensed, colorless gas that ignites spontaneously in air.

Contents

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.

Preparation

Methylboranes were first prepared by H. I. Schlesinger and A. O. Walker in the 1930s. [3] [4]

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

2 LiCH3BH3 + 2 HCl → (CH3BH2)2 + 2 H2 + 2 LiCl

Instead of hydrogen chloride, methyl iodide or trimethylsilyl chloride can be used. [5]

Lithium methylborohydride can be made by treating methylboronic esters with lithium aluminium hydride. [5]

Miscellaneous routes

Methylboranes arise the reaction of diborane and trimethylborane. This reaction produces 1-methyldiborane, 1,1-dimethyldiborane, 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. [6] 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. [7]

Other methods to form methyldiboranes include treating hydrogen with trimethylborane between 80 and 200 °C under pressure, or treating 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. [3] dimethylchloroborane and methyldichloroborane are also produced as gaseous products. [3]

When Cp2Zr(CH3)2 reacts with diborane, a borohydro group inserts into the zirconium-carbon bond, and methyl diboranes are produced. [8]

In ether dimethylcalcium reacts with diborane to produce dimethyldiborane and calcium borohydride: [9]

Ca(CH3)2 + 2 B2H6 → Ca(BH4)2 + B2H4(CH3)2

1,2-Dimethyldiborane is produced by the room temperature disproportionation of trimethyldiborane. [10]

Physical and spectroscopic properties

cis-1,2-Dimethyldiborane melts at −132.5 °C; trans-1,2-dimethyldiborane melts at −102 °C. [11] The cis-1,2-dimethyldiborane molecule has point group Cs. A trans-1,2-dimethyldiborane molecule has point group C2. Unsymmetrical dimethyldiborane melts at −150.2 °C. [12] Vapour pressure is approximated by Log P = 7.363−(1212/T). [12] The vapour pressure for the symmetrical isomer is given by Log P = 7.523−(1290/T). [12]

Gas chromatography can be used to determine the amounts of the methyl boranes in a mixture. The order of elution are: diborane, monomethyldiborane, trimethylborane, 1,1-dimethyldiborane, 1,2-dimethyldiborane, trimethyldiborane, and last tetramethyldiborane. [13]

The nuclear resonance shift for the bridge hydrogen is 9.55 ppm for the unsymmetrical isomer and 9.73 ppm for the symmetrical isomers, compared to 10.49 for diborane. [14]

Reactions

Methylborane shows little tendency to disproportionate (redistribute) at room temperature. It reacts stepwise with alkenes to produce mono and dialkylmethylboranes. More methylated boranes are less stable. [5]

1,2-Dimethyldiborane slowly converts to 1,1-dimethyldiborane. [15]

Methylborane hydrolyzes to methylboronic acid: [6]

(MeBH2)2 + 4 H2O → CH3B(OH)2 + 4 H2

Symmetrical dimethyldiborane reacts with trimethylamine to yield a solid adduct trimethylamine-methylborane (CH3)3N·BH2CH3. [6]

When dimethyldiborane is combined with ammonia and heated, B-methyl borazoles are produced. These borazoles can have one, two or three methyl groups substituted on the boron atoms. [16] [17]

Under normal conditions dimethyldiborane does not react with hydrogen. [18]

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 ion with two electrons. In modern usage, this is typically only used for ionic bonds, but it is sometimes (and more frequently in the past) been applied to all compounds containing covalently bound H atoms. In this broad and potentially archaic sense, water (H2O) is a hydride of oxygen, ammonia is a hydride of nitrogen, etc. In covalent compounds, it implies hydrogen is 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">Diborane</span> Chemical compound

Diborane(6), commonly known as diborane, is the chemical compound with the formula B2H6. It is a highly 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, inorganic benzene, 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 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 for hydrogen fuel, but is otherwise primarily of academic interest.

<span class="mw-page-title-main">Borohydride</span> Any chemical compound having a borohydride anion

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">Carbonyl reduction</span> Organic reduction of any carbonyl group by a reducing agent

In organic chemistry, carbonyl reduction is the conversion of any carbonyl group, usually to an alcohol. It is a common transformation that is practiced in many ways. Ketones, aldehydes, carboxylic acids, esters, amides, and acid halides - some of the most pervasive functional groups, -comprise carbonyl compounds. Carboxylic acids, esters, and acid halides can be reduced to either aldehydes or a step further to primary alcohols, depending on the strength of the reducing agent. Aldehydes and ketones can be reduced respectively to primary and secondary alcohols. In deoxygenation, the alcohol group can be further reduced and removed altogether by replacement with H.

<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 is an inorganic compound with the chemical formula BH
3. Because it tends to dimerize or form adducts, borane is very rarely observed. It normally dimerizes to diborane in the absence of other chemicals. It can be observed directly as a continuously produced, transitory, product in a flow system or from the reaction of laser ablated atomic boron with hydrogen.

<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">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.

Germanium(II) hydrides, also called germylene hydrides, are a class of Group 14 compounds consisting of low-valent germanium and a terminal hydride. They are also typically stabilized by an electron donor-acceptor interaction between the germanium atom and a large, bulky ligand.

<i>ortho</i>-Carborane Chemical compound

ortho-Carborane is the organoboron compound with the formula C2B10H12. The prefix ortho is derived from ortho. It is the most prominent carborane. This derivative has been considered for a wide range of applications from heat-resistant polymers to medical applications. It is a colorless solid that melts, without decomposition, at 320 °C

<span class="mw-page-title-main">Boranes</span> Class of chemical compounds

A borane is a compound with the formula BRxHy although examples include multi-boron derivatives. A large family of boron hydride clusters is also known. In addition to some applications in organic chemistry, the boranes have attracted much attention as they exhibit structures and bonding that differs strongly from the patterns seen in hydrocarbons. Hybrids of boranes and hydrocarbons, the carboranes, are also a well developed class of compounds.

References

  1. 1 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.
  2. ↑ Low, M. J. D. (1968). "Characteristic Infrared Frequencies of Methyldiboranes". The Journal of Chemical Physics. 48 (5): 2386–2387. Bibcode:1968JChPh..48.2386L. doi:10.1063/1.1669454.
  3. 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 (Resumed): 3513–3520. doi:10.1039/JR9650003513.(subscription required)
  4. ↑ 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.
  5. 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 Sgents. Synthesis of Tertiary Alcohols Containing Methyl Groups via Hydroboration". The Journal of Organic Chemistry. 51 (25): 4925–4930. doi:10.1021/jo00375a031.
  6. 1 2 3 Bell, R. P.; Emeléus, H. J. (1948). "The Boron Hydrides and Related Compounds". Quarterly Reviews, Chemical Society. 2 (2): 132. doi:10.1039/QR9480200132.
  7. ↑ 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.
  8. ↑ 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.
  9. ↑ James, B. D.; Wallbridge, M. G. H. (1970). "Metal Tetrahydroborates". In Lippard, Stephen J. (ed.). Progress in Inorganic Chemistry, Volume 11. Wiley. p. 185. ISBN   0471-54081-1.
  10. ↑ Lehmann, Walter J.; Wilson, Charles O.; Shapiro, I. (1961). "Infrared Spectra of Alkyldiboranes. V. Tri- and Tetramethyl- and Ethyldiboranes". The Journal of Chemical Physics. 34 (3): 783. Bibcode:1961JChPh..34..783L. doi:10.1063/1.1731675.
  11. ↑ Hedberg, Lise; Hedberg, Kenneth; Kohler, David A.; Ritter, David M.; Schomaker, Verner (May 1980). "Electron-diffraction investigations of the molecular structures of cis- and trans-1,2-dimethyldiborane". Journal of the American Chemical Society. 102 (10): 3430–3434. doi:10.1021/ja00530a021.
  12. 1 2 3 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. ↑ 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.
  14. ↑ 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.
  15. ↑ Lehmann, Walter J.; Wilson, Charles O.; Shapiro, I. (1960). "Infrared Spectra of Alkyldiboranes. III. 1,2-Dimethyl- and 1,2-Diethyldiboranes". The Journal of Chemical Physics. 33 (2): 590. Bibcode:1960JChPh..33..590L. doi:10.1063/1.1731190.
  16. ↑ Sheldon, J. C.; Smith, B. C. (1960). "The borazoles". Quarterly Reviews, Chemical Society. 14 (2): 202. doi:10.1039/QR9601400200.
  17. ↑ 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.
  18. ↑ 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.
  19. ↑ Mikhailov, B. M. (April 1962). "The Chemistry Of Diborane". Russian Chemical Reviews. 31 (4): 209. Bibcode:1962RuCRv..31..207M. doi:10.1070/RC1962v031n04ABEH001281. S2CID   250909492.
  20. ↑ Deever, William R.; Ritter, David M. (November 1969). "Methyltetraboranes. I. 2-Methyl and 1,2-, 2,2-, and 2,4-dimethyl derivatives". Inorganic Chemistry. 8 (11): 2461–2467. doi:10.1021/ic50081a043.
  21. ↑ Addison, C. C.; Davidson, G. (1973). "Elements of Group III". Inorganic Chemistry of the Main-Group Elements. Vol. 1. p. 68. doi:10.1039/9781847556370-00053. ISBN   978-0-85186-752-6.(subscription required)
  22. ↑ Onak, Thomas; Friedman, Lawrence B.; Hartsuck, Jean A.; Lipscomb, William N. (July 1966). "Rearrangement of 1,2- to 2,3-Dimethylpentaborane(9)". Journal of the American Chemical Society. 88 (14): 3439–3440. doi:10.1021/ja00966a051.
  23. ↑ Shore, S. G. (1975). "Nido and Arachno Boron Hydrides". In Muetterties, Earl L (ed.). Boron Hydride Chemistry. Academic Press. p. 150. ISBN   0-12-509650-X.
  24. ↑ Dunstan, I.; Williams, R. L.; Blay, N. J. (1960). "970. Boron hydride derivatives. Part V. Nucleophilic substitution in decaborane". Journal of the Chemical Society (IV): 5012–5015. doi:10.1039/JR9600005012 . Retrieved 19 August 2015.

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