Metal carbonyl hydride

Metallcarbonylhydride are complex compounds of transition metals with carbon monoxide and hydrogen as a ligand. The compounds are used in organic synthesis, and as catalysts in homogeneous catalysis, for example in the hydroformylation.

Representation

The first representation of a Metallcarbonylhydrids succeeded Walter Hieber in 1931 in the study of so-called Hieber 's base reaction of the metal carbonyls. Here, a hydroxide ion with a metal carbonyl such as iron pentacarbonyl with a nucleophilic attack on the carbonyl reacts with release of carbon dioxide and formation of Metallcarbonylaten. In a further step can be Eisencarbonylhydrid, synthesize a highly temperature - and air-sensitive complex hydride. Displaying Cobaltcarbonylhydrid ( HCo (CO ) 4) is achieved in the same manner.

A further synthesis is the reaction of metal carbonyls with hydrogen. Protonation of Metallcarbonylaten also leads to Metallcarbonylhydrid.

Properties

The hydrogen atom is bound in Metallcarbonylhydriden directly to the metal. For Cobaltcarbonylhydrid example is the metal-hydrogen distance 114 pm, the metal-carbon distance for the axial CO ligands 176 pm and for the equatorial CO ligands 182 pm. The neutral Metallcarbonylhydride are often volatile and are acidic in aqueous solution.

Use

Metallcarbonylhydride be used as catalysts for the hydroformylation. The reaction begins with the generation of a coordinatively unsaturated Metallcarbonylhydrid complex as HCo (CO) 3 or HRh (CO) ( PPh3) 2 by cleavage of a Kohlenstoffmonoxidliganden. Such species bind alkenes initially by π - bond. By insertion into the metal - hydrogen bond is formed a alkyl complex. In the metal -carbon bond of the alkyl radical may inserting carbon monoxide. Oxidative addition of hydrogen and the subsequent elimination of the aldehyde from the complex arises again the Ausgangsmetallcarbonylhydridkomplex.

Analytical characterization

It has long been uncertain whether the Metallcarbonylhydride had a direct metal- hydrogen bond, although this was already suspected of Hieber. By X-ray diffraction the exact structure could not be identified, especially the length of a possible metal -hydrogen bond remained unclear. The exact structure of Metallcarbonylhydride has been determined mainly by neutron diffraction and nuclear magnetic resonance spectroscopy.