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Other names
Hydrogen pentacarbonylmanganate(-I) (7CI); Manganese, pentacarbonylhydro- (8CI); Hydridomanganese pentacarbonyl; Hydridopentacarbonylmanganese; Manganese pentacarbonyl hydride; Pentacarbonylhydromanganese; Pentacarbonylmanganese hydride
Molar mass 195.99799 g/mol
Appearance At room temperature, it is liquid and colorless. Below its melting point, it may be sublimed in vacuum.[1]
Acidity (pKa) 7.1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Pentacarbonylhydridomanganese is an organometallic compound with formula HMn(CO)5. This compound is one of the most stable "first-row" transition metal hydrides.


It was first reported in 1931.[2] Of the several ways to produce this compound,[3] is the protonation of the pentacarbonyl manganate anion. The latter is formed from reduction of dimanganese decacarbonyl (Mn(CO)5)2. The reaction is shown below.

LiHB(C2H5)3 (Superhydride) + ½Mn2(CO)10 → Li[Mn(CO)5] + ½H2 + (C2H5)3B
Li[Mn(CO)5] + CF3SO3H → HMn(CO)5 + Li+

Salts of [Mn(CO)5]
can be isolated as crystalline PPN+
(μ-nitrido—bis-(triphenylphosphorus)) salt, which is smoothly protonated by CF3SO3H.[3]

PPN[Mn(CO)5] + CF3SO3H → HMn(CO)5 + PPN+

This compound can also be formed by the reaction of a solution of pentacarbonyl(trimethylsilyl)manganese with water.[4] The reaction is shown below.

2(CO)5MnSiMe3 + H2O → HMn(CO)5 + Me3SiOSiMe3

Structure and Properties[edit]

The compound has octahedral symmetry [5] and its molecular point group is C4v.[6] The H-Mn bond length is 1.44 ± 0.03 Å.[6] A gas phase electron diffraction study confirms this data.

The structure of HMn(CO)5 has been studied by many methods including X-Ray diffraction, neutron diffraction, and electron diffraction.[6] HMn(CO)5 can be related to the structure of a hexacarbonyl complex such as Mn(CO)+
, and therefore has the following similar properties.[7] The occupied molecular orbitals on the top are the 2 t2g orbitals. They are characterized as metal 3dπ orbitals. Since the antibonding 2π orbitals interact with the carbonyl groups, (or in this case, H
) the t2g orbital is stabilized compared to the 3dπ orbital, which in turn will cause changes in the sigma and pi interactions.

Main Reactions[edit]

The pKa of HMn(CO)5 in water is 7.1.[8] It is thus comparable to hydrogen sulfide, a common inorganic acid, in its acidity.

A common reaction involving the HMn(CO)5 species is substitution of the CO ligands by organophosphines, as occurs both thermally and photochemically.[9] In this way the following derivatives form MnH(CO)3P2, MnH(CO)2P3, and MnH(CO)P4, (where P = P(OEt)3, PPh(OEt)2, PPh2OEt, PPh(OiPr)2.

The compound HMn(CO)5 can be used to reduce olefins and other organic compounds, as well as metal halides.[3]

Carbonyl ligands are substituted in this complex with the appropriate phosphite, resulting in the complexes shown above.

This compound can be methylated with diazomethane.[1]

HMn(CO)5 + CH2N2 → Mn(CO)5CH3 + N2


  1. ^ a b Eley, D.D.; Pines, Herman; Weisz, P.B. Advances In Catalysis. 32. 385. ISBN 978-0-12-007832-5
  2. ^ Hieber, W. Leutert, F. Naturwissenschaften. 1931. 360.
  3. ^ a b c Hunter, Alan D; Bianconi, Larry J; DiMuzio, Steven J; Braho, Dianne L. Synthesis and Structure- Property Relationships in η6-Arene) Cr(CO)3 Chemistry: From Guided Experiments to Discovery Research. J. Chem. Educ. 75. 1998. 891. doi:10.1021/ed075p891
  4. ^ Finn, M.G. Pentacarbonyl(trimethylsilyl)manganese. Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rp022s
  5. ^ Liu, Xian-mei; Wang, Chao-yang; Qian-shu; Xie; Yaoming; King, R. Bruce; Schaefer, Henry F., III. Mononuclear and binuclear manganese carbonyl hydrides. Dalton Trans., 2009, 3774-3785, doi:10.1039/b822913a
  6. ^ a b c Kukolich, S.G. Microwave Spectrum and Molecular Structure for Manganese Pentacarbonyl Hydride. 33. 1994. 1217-1219
  7. ^ Fenske, Richard. Electronic Structure and Bonding in Manganese Pentacarbonyl Halides and Hydride. Inorganic Chemistry. 9. 1970. 1053-1060.
  8. ^ Morris, Robert H. (2016-08-10). "Brønsted–Lowry Acid Strength of Metal Hydride and Dihydrogen Complexes". Chemical Reviews. 116 (15): 8588–8654. ISSN 0009-2665. doi:10.1021/acs.chemrev.5b00695. 
  9. ^ Albertin, Gabriele. Cationic Molecular Hydrogen Complexes of Mn (I). Organometallics. 16. 1997. 4959-4969.