Pentacarbonylhydridomanganese is an

organometallic compound Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and s ...

with formula HMn(CO)₅. This compound is one of the most stable "first-row"

transition metal hydride Transition metal hydrides are chemical compounds containing a transition metal bonded to hydrogen. Most transition metals form hydride complexes and some are significant in various catalytic and synthetic reactions. The term "hydride" is used loo ...

Preparation

It was first reported in 1931. Of the several ways to produce this compound, is the protonation of the pentacarbonyl manganate anion. The latter is formed from reduction of

dimanganese decacarbonyl Dimanganese decacarbonyl is the chemical compound with the formula Mn2(CO)10. This metal carbonyl is an important reagent in the organometallic chemistry of manganese. Synthesis The compound was first prepared in low yield by the reduction of ...

, (Mn(CO)₅)₂. The reaction is shown below. :LiHB(C₂H₅)₃ (

Superhydride Lithium triethylborohydride is the organoboron compound with the formula Li Et3 BH. Commonly referred to as LiTEBH or Superhydride, it is a powerful reducing agent used in organometallic and organic chemistry. It is a colorless or white liquid bu ...

) + ½ Mn₂(CO)₁₀ → Li n(CO)₅+ ½ H₂ + (C₂H₅)₃B :Li n(CO)₅+ CF₃SO₃H → HMn(CO)₅ + Salts of can be isolated as crystalline (μ-nitrido—bis-(triphenylphosphorus)) salt, which is smoothly protonated by CF₃SO₃H. :PPN n(CO)₅+ CF₃SO₃H → HMn(CO)₅ + This compound can also be formed by the reaction of a solution of pentacarbonyl(trimethylsilyl)manganese with water. The reaction is shown below. :2 (CO)₅MnSiMe₃ + H₂O → HMn(CO)₅ + Me₃SiOSiMe₃

Structure and properties

The compound has octahedral symmetry and its

molecular point group Molecular symmetry in chemistry describes the symmetry present in molecules and the classification of these molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can be used to predict or explain m ...

is C_4v. The H-Mn

bond length In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of ...

is 1.44 ± 0.03 Å. 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 Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material. A sample to be examined is placed in a beam of thermal or cold neutrons to o ...

, and electron diffraction. HMn(CO)₅ can be related to the structure of a hexacarbonyl complex such as , and therefore has the following similar properties. The occupied

molecular orbitals In chemistry, a molecular orbital is a mathematical function describing the location and wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of findin ...

on the top are the 2 t_2g orbitals. They are characterized as metal 3d_π orbitals. Since the antibonding 2π orbitals interact with the carbonyl groups, (or in this case, ) the t_2g orbital is stabilized compared to the 3d_π orbital, which in turn will cause changes in the sigma and pi interactions.

Main reactions

The pK_a of HMn(CO)₅ in water is 7.1. 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

organophosphine Organophosphines are organophosphorus compounds with the formula PR''n''H3−''n'', where R is an organic substituent. These compounds can be classified according to the value of ''n'': primary phosphines (''n'' = 1), secondary phosphine ...

s, as occurs both thermally and photochemically. In this way the following derivatives form: MnH(CO)₃ sub>2, MnH(CO)₂ sub>3, and MnH(CO) sub>4, (where = 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. This compound can be methylated with

diazomethane Diazomethane is the chemical compound CH2N2, discovered by German chemist Hans von Pechmann in 1894. It is the simplest diazo compound. In the pure form at room temperature, it is an extremely sensitive explosive yellow gas; thus, it is almost ...

. :HMn(CO)₅ + CH₂N₂ → Mn(CO)₅CH₃ + N₂

Notes

{{manganese compounds Carbonyl complexes Organomanganese compounds Metal hydrides Substances discovered in the 1930s