Pentacarbonylhydridomanganese

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

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, e.g., with superhydride:


 * 2 LiHB(C2H5)3 + Mn2(CO)10 → 2 LiMn(CO)5 + H2 +  2 B(C2H5)3
 * Li[Mn(CO)5] + CF3SO3H → HMn(CO)5 + CF3SO3Li

Salts of can be isolated as crystalline  (μ-nitrido—bis-(triphenylphosphorus)) salt, which is smoothly protonated by Triflic acid.
 * → HMn(CO)5 +

This compound can also be formed by the hydrolysis of pentacarbonyl(trimethylsilyl)manganese:
 * (CO)5MnSiMe3 + H2O → HMn(CO)5 + Me3SiOH (Me = CH3)

Structure and properties
The structure of HMn(CO)$5$ has been studied by many methods including X-ray diffraction, neutron diffraction, and electron diffraction. HMn(CO)$5$ can be related to the structure of a hexacarbonyl complex such as, and therefore has similar properties. The compound has octahedral symmetry and its molecular point group is C$5$. The H-Mn bond length is 1.44 ± 0.03 Å. Gas phase electron diffraction analysis confirms these conclusions.

Main reactions
The pK$4v$ of HMn(CO)$a$ in water is 7.1. It is thus comparable to hydrogen sulfide, a common inorganic acid, in its acidity.

A common reaction involving HMn(CO)$5$ is substitution of the CO ligands by organophosphines, as occurs both thermally and photochemically. In this way the many derivatives form of the type HMn(CO)$5$(PR$5-x$)$3$. (R here need not be a purely hydrocarbon component; it may, for instance, be OEt, where Et = ethyl group.)

HMn(CO)$x$ can be used to reduce olefins and other organic compounds, as well as metal halides.

It can be methylated with diazomethane.
 * HMn(CO)$5$ + CH$5$N$2$ → Mn(CO)$2$CH$5$ + N$3$