Alkenes are not spontaneously reduced to alkanes when treated with hydrogen. However in the presence of a transition metal catalyst the reaction proceeds efficiently - and usually with cis- stereospecificity - at room temperature and with either 1 At or elevated pressures of hydrogen.
Catalysts can either be soluble in the reaction mixture (homogeneous) or insoluble (heterogeneous).
One of the most important of the homogeneous catalysts is (PPh3)3RhCl, tris(triphenylphosphine)rhodium(I) chloride ('Wilkinson's catalyst').
Typical heterogeneous catalysts are palladium on charcoal (Pd/C) or platinum oxide (PtO2, 'Adam's catalyst').
Reduction of alkenes with the aid of homogeneous catalysts such as Wilkinson's Catalyst will be studied in depth as part of the Module CM4104.