Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 2001, 40 (7), 1211-1215
Solvents In Retreat
A new catalyst
for selective solvent-free
hydrogenation at low temperatures
A number of cyclic hydrocarbons with multiple double bonds are readily accessible intermediates in chemical industry. In the course of further processing it is often necessary to saturate some of the double bonds with hydrogen to form single bonds. This type of reaction, known as selective hydrogenation, is a tricky undertaking. Not all of the double bonds are meant to react at random; a certain number of the double bonds must be retained. How is the hydrogen to "know" which and how many of the bonds it should attack, and which it should avoid? As is so often the case, it is a catalyst that guides the reaction along the desired path.
British researchers were not willing to accept the disadvantages of the catalysts that are currently used for this type of reaction: temperatures sometimes higher than 300 °C and the use of organic solvents. For environmental reasons it is best to avoid the use of solvents whenever possible. Also, their recovery or disposal are expenses for industry.
In the British laboratory, Sir John Meurig Thomas, Brian F.G. Johnson, Robert Raja and Sophie Hermans set their sights on three different cyclic hydrocarbons with two or three double bonds each. In all three cases, the versions with only one double bond are important intermediates for chemical industry - in the manufacture of man-made fibres, plastics, and coatings, for example. The researchers developed a new catalyst that can selectively convert the three compounds at relatively low temeratures, without the presence of a solvent.
Tiny particles of the metals ruthenium and tin, finely and evenly distributed in the pores of a silicon dioxide support form the core of the new catalyst. This is formed by charging the silicon dioxide with a coordination complex and heating it. The outer shells of the complexes are burned off, leaving the cores, tiny atomic clusters containing six ruthenium, one tin, and one carbon atom. The tin tighly anchors the clusters to the inner surface of the silicon dioxide.
It is interesting that such bimetallic catalysts work significantly better and more selectively than analogs with only one metallic component. "Building on this principle, we would like to develop more catalysts to selectively convert other organic compounds without using solvents," Sir John M. Thomas says optimistically.