Copper hydride

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Copper hydride
Names
IUPAC name
Copper hydride
Other names
Copper(I) hydride
Cuprous hydride
Cuprane
Identifiers
13517-00-5
PubChem 3335333
  • InChI=1S/Cu.H YesY
    Key: JJFLDSOAQUJVBF-UHFFFAOYSA-N YesY
Properties
CuH
Molar mass 64.55 g·mol−1
Vapor pressure {{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Copper hydride is a pyrophoric, inorganic compound with the chemical formula (CuH)
n (also written as ([CuH])
n or CuH). It is an odourless, metastable, red solid, rarely isolated as a pure composition, that decomposes to the elements.[1] Copper hydride is mainly produced as a reducing agent in organic synthesis and as a precursor to extremely reactive catalysts.[2]

Nomenclature

The systematic name copper hydride is the most commonly used name. It is a valid IUPAC name, and is constructed according to the compositional nomenclature.

Copper hydride is also used generically to refer to the alloyed mixture of copper and atomic hydrogen, known as the copper-hydrogen system, of which there exists various phases. It is also used to refer to any compound containing a Cu-H bond. The oxidation state of copper in copper hydride is +1.

History

In 1844, the French chemist Adolphe Wurtz synthesised copper hydride for the first time. This reaction consisted of the reduction of copper sulfate with hypophosphorous acid. In 2011, Panitat Hasin and Yiying Wu were the first to synthesise a metal hydride (copper hydride) using the technique of sonication.[3] Copper hydride has the distinction of being the first metal hydride discovered. In 2013, it was established by Donnerer et al. that, at least up to fifty gigapascals, copper hydride cannot be synthesised by pressure alone. However, they were successful in synthesising several copper-hydrogen alloys under pressure.[2]

Chemical properties

Acidity

Copper hydride can assimilate a hydroxyl centre into the molecule by ionisation:

CuH + OH−
 → CuO−
 + H
2

Because of this capture of the hydroxide (OH−
), copper hydride has an acidic character. Its hydroxylation product is oxocuprate(1−). Copper hydride does not form aqueous solutions, due to it being a covalent network solid; however, it does form colloidal suspensions. It is also oxidised by water, albeit slowly.

Structure

Wurtzite structure

In copper hydride, elements adopt the Wurtzite crystal structure[4][5] (polymeric), being connected by covalent bonds.[6] Other lower metal hydrides polymerise in a similar fashion (c.f. aluminium hydride). Under certain conditions, a metastable amorphous solid forms. This solid decomposes above 60 °C (140 °F).

Chemical reactions

Upon treatment with a standard base, copper hydride converts to metal oxocuprate(1−) and hydrogen gas. Reduction of copper hydride gives copper metal. The H segment is the main site of reaction, as is evident from the conversion of copper hydride to copper chloride. When heated above −5 °C (23 °F), copper hydride decomposes to produce a copper hydride alloy and hydrogen gas:

CuH → Cu + x H + ½(1 − x) H
2

Solid copper hydride is the irreversible autopolymerisation product of the molecular form, and the molecular form cannot be isolated in concentration.

Production

Copper does not react with hydrogen even on heating,[7] thus copper hydrides are made indirectly from copper(I) and copper(II) precursors. Examples include the reduction of copper(II) sulfate with sodium hypophosphite in the presence of sulfuric acid,[6] or more simply with just hypophosphorous acid.[8] Other reducing agents, including classical aluminium hydrides can be used.[9]

4 Cu2+ + 6 H3PO2 + 6 H2O → 4 CuH + 6 H3PO3 + 8 H+

The reactions produce a red-colored precipitate of CuH, which is generally impure and slowly decomposes to liberate hydrogen, even at 0 °C.[8]

2 CuH → 2 Cu + H2

This slow decomposition also takes place underwater,[10] however there are reports of the material becoming pyrophoric if dried.[11]

Reductive sonication

Copper hydride is also produced by reductive sonication. In this process, hexaaquacopper(II) and hydrogen(•) react to produce copper hydride and oxonium according to the equation:

[Cu(H2O)6]2+ + 3 H• → 1/n (CuH)n + 2 [H3O]+ + 4 H2O

Hydrogen(•) is obtained in situ from the homolytic sonication of water. Reductive sonication produces molecular copper hydride as an intermediate.[3]

Molecular form

Molecular copper hydride (systematically named hydridocopper) is a related inorganic compound with the chemical formula CuH. It is a metastable, colourless gas. It is classified as a strong reductant.

History

Molecular copper hydride was discovered in the vibration-rotation emission of a hollow-cathode lamp in 2000 by Bernath, who detected it at the University of Waterloo. It was first detected as a contaminant while attempting to generate NeH+ using the hollow-cathode lamp.[12][13] Molecular copper hydride has the distinction of being the first metal hydride to be detected in this way. (1,0) (2,0) and (2,1) vibrational bands were observed along with line splitting due to the presence of two copper isotopes, 63Cu and 65Cu.[14][15]

The A1Σ+-X1Σ+ absorption lines from CuH have been claimed to have been observed in sunspots and in the star 19 Piscium.[16][17]

Chemical properties

Molecular copper hydride has acidic behavior for the same reason as normal copper hydride. However, it does not form stable aqueous solutions, due in part to its autopolymerisation, and its tendency to be oxidised by water. Copper hydride reversibly precipitates from pyridine solution, as an amorphous solid. However, repeated dissolution affords the regular crystalline form, which is insoluble. Under standard conditions, molecular copper hydride autopolymerises to form the crystalline form, including under aqueous conditions, hence the aqueous production method devised by Wurtz.

Production

Molecular copper hydride can be formed by reducing copper iodide with lithium aluminium hydride in ether and pyridine.[18] CuI + LiAlH4 → CuH + LiI + AlI3 This was discovered by E Wiberg and W Henle in 1952.[19] The solution of this CuH in the pyridine is typically dark red to dark orange.[18] A precipitate is formed if ether is added to this solution.[18] This will redissolve in pyridine. Impurities of the reaction products remain in the product.[18] In this study, it was found that the solidified diatomic substance is distinct from the Wurtzite structure. The Wurtzite substance was insoluble and was decomposed by lithium iodide, but not the solidified diatomic species. Moreover, while the Wurtzite substance's decomposition is strongly base catalysed, whereas the solidified diatomic species is not strongly affected at all. Dilts distinguishes between the two copper hydrides as the 'insoluble-' and 'soluble copper hydrides'. The soluble hydride is susceptible to pyrolysis under vacuum and proceeds to completion under 100 °C.

Ligated diatomic copper hydride is useful in the hydrodefluorination of fluoroarenes.[20]

The largest use of diatomic copper hydride is as a reducing agent in the form of a variety of activated complexes, the most well-known being Stryker's reagent.[21]

A variety of phosphine adducts are known, e.g. the bright red cluster Stryker's reagent Cu6H6(PPh3)6, which is a reagent in organic chemistry. Such complexes, however, are prepared by hydride reduction of copper(I) precursors[22]

Anhydrous reduction

Amorphous copper hydride is also produced by anhydrous reduction. In this process copper(I) and tetrahydroaluminate react to produce molecular copper hydride and triiodoaluminium adducts. The molecular copper hydride is precipitated into amorphous copper hydride with the addition of diethyl ether. Amorphous copper hydride is converted into the Wurtz phase by annealing, accompanied by some decomposition.[18]

Direct synthesis

It can be directly synthesised when copper and hydrogen is exposed to 310 nanometre radiation.[1]

Cu + H2 ↔ CuH + H•

This route is difficult to control, since there is little or no activation barrier for the reverse reaction, which occurs readily even at 20 Kelvin.

Other copper hydrides

  • Although there are no conventional alloys of copper that intentionally incorporate hydrogen, it is known to cause embrittlement of copper.[23]
  • A binary dihydride (CuH
    2    ) also exists, in the form of an unstable reactive intermediate in the reduction of copper hydride by atomic hydrogen.

References

  1. ↑ 1.0 1.1 Hydrides of the Main-Group Metals: New Variations on an Old Theme Simon Aldridge , Anthony J. Downs Chem. Rev., 2001, vol. 101, pp 3305–3366 doi:10.1021/cr960151d
  2. ↑ 2.0 2.1 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ 3.0 3.1 Lua error in package.lua at line 80: module 'strict' not found.
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  6. ↑ 6.0 6.1 Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ 8.0 8.1 Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ The crystal structure of copper hydride J. A. Goedkoop and A. F. Andresen Acta Crystallogr. (1955). 8, 118-119 doi:10.1107/S0365110X55000480
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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  18. ↑ 18.0 18.1 18.2 18.3 18.4 Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  20. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ Riant, Olivier "Copper(I) hydride reagents and catalysts" in Chemistry of Organocopper Compounds, Edited by Zvi Rappoport, Ilan Marek. 2009, Wiley, (Pt. 2), 731-773.
  23. ↑ S. Nakahara "On the effect of hydrogen on properties of copper" Scripta Metallurgica Volume 19, Issue 4, April 1985, Pages 517–519 {{doi:10.1016/0036-9748(85)90125-5}}
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