text: The dominant application of metal carbenes involves none of the above classes of compounds, but rather heterogeneous catalysts used for alkene metathesis for the synthesis of higher alkenes. A variety of related reactions are used to interconvert light alkenes, e.g. butenes, propylene, and ethylene. Carbene complexes are invoked as intermediates in the Fischer–Tropsch route to hydrocarbons.
  A variety of homogeneous carbene catalysts, especially the Grubbs' ruthenium and Schrock molybdenum-imido catalysts have been used for olefin metathesis in laboratory-scale synthesis of natural products and materials science.