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
  • 17156-88-6 X mark.svgN
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).
X mark.svgN (what is  Yes check.svgYX mark.svgN ?)
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] 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

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.

Boranes

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.

Diborane Chemical compound

Diborane(6), generally known as diborane, is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless, pyrophoric gas with a repulsively sweet odor. Synonyms include boroethane, boron hydride, and diboron hexahydride. Diborane is a key boron compound with a variety of applications. It has attracted wide attention for its electronic structure. Its derivatives are useful reagents.

Herbert C. Brown

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

Carborane

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.

Sodium borohydride Chemical compound

Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as a powder, is a reducing agent that finds application in chemistry, both in the laboratory and on an industrial scale. It has been tested as pretreatment for pulping of wood, but is too costly to be commercialized. The compound is soluble in alcohols, certain ethers, and water, although it slowly hydrolyzes.

Organoboron chemistry

Organoborane or organoboron compounds are chemical compounds of boron and carbon that are organic derivatives of BH3, for example trialkyl boranes. Organoboron chemistry or organoborane chemistry is the chemistry of these compounds.

In chemistry, hydroboration refers to the addition of a hydrogen-boron bond to C-C, C-N, and C-O double bonds, as well as C-C triple bonds. This chemical reaction is useful in the organic synthesis of organic compounds. The development of this technology and the underlying concepts were recognized by the Nobel Prize in Chemistry to Herbert C. Brown. He shared the Nobel prize in chemistry with Georg Wittig in 1979 for his pioneering research on organoboranes as important synthetic intermediates.

Ammonia borane 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.

Tris(pentafluorophenyl)borane Chemical compound

Tris(pentafluorophenyl)borane, sometimes referred to as "BCF", is the chemical compound (C6F5)3B. It is a white, volatile solid. The molecule consists of three pentafluorophenyl groups attached in a "paddle-wheel" manner to a central boron atom; the BC3 core is planar. It has been described as the “ideal Lewis acid” because of its high thermal stability and the relative inertness of the B-C bonds. Related fluoro-substituted boron compounds, such as those containing B−CF3 groups, decompose with formation of B-F bonds. Tris(pentafluorophenyl)borane is thermally stable at temperatures wide over 200 °C, resistant to oxygen and water-tolerant.

Borohydride

Borohydride refers to the anion BH−4 and its salts. Borohydride is also the term used for compounds containing BH
4−nX−
n, for example cyanoborohydride (B(CN)H−
3) and triethylborohydride (B(C2H5)3H−). 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 (see Table). Tetrahydroborates are also of academic and industrial interest in inorganic chemistry.

Lithium borohydride Chemical compound

Lithium borohydride (LiBH4) is a borohydride and known in organic synthesis as a reducing agent for esters. Although less common than the related sodium borohydride, the lithium salt offers some advantages, being a stronger reducing agent and highly soluble in ethers, whilst remaining safer to handle than lithium aluminium hydride.

Carbonyl reduction

In organic chemistry, carbonyl reduction is the organic reduction of any carbonyl group by a reducing agent.

Trimethylborane 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).

Binary compounds of hydrogen are binary chemical compounds containing just hydrogen and one other chemical element. By convention all binary hydrogen compounds are called hydrides even when the hydrogen atom in it is not an anion. These hydrogen compounds can be grouped into several types.

Trihydridoboron, also known as borane or 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.

Tetramethyldiborane 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.

Trimethyldiborane 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.

Methyldiborane 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.

1,1-Dimethyldiborane 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. 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. 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.
  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. 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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