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Organometallic Compounds in Catalysis
Introduction
Hydrogenation of Alkenes
Hydroformylation of Alkenes
Introduction
The International Union of Pure and Applied Chemistry defines catalysis as the phenomenon in which a relatively small amount of a foreign material, called a catalyst, augments the rate of a chemical reaction without itself being consumed. In practice this means that a catalyst reduces the activation energy of a reaction, which must itself be energetically favoured.
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Organometallic compounds are important in many catalytic reactions involving organic molecules. Catalytic activity occures widely among the transition metals, but there are also a few instances where main group compounds act as catalysts. In many cases a series of steps can be drawn up in which transition metal complexes undergo a sequence of oxidative addition, insertion and reductive-elimination reactions. During the sequence the organic reactants are converted into the product and the transition metal complex is regenerated so that the sequence forms a closed loop called a "catalytic cycle". Catalytical cycles can be studied by: Spectroscopy (NMR, IR), Isotopic labelling, Optical activity (reflects stereochemical changes during a reaction).
Note:
Catalysts can be heterogeneous (in different phase eg: gases passing
over a metal surface) or homogeneous.
Homogeneous catalysis:
that means the catalysis is in the same phase as the reactants and the
products, for organometallic compounds, this is usually means in solution.
Advantages
- all atoms present are potential catalytic centres.
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a homogeneous catalyst gives reproducible results because it has a definite
stichiometry and structure.
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specificity of the catalyst can be modified.
Disadvantages - can be difficult
to seperate catalyst from products.
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increasing the rate through heating may couse problems with the stability
of the organometallic catalyst.
What makes a good catalyst?
