Platinum Metals Review - Volume 9, Issue 2, 1965

Although in many cases it will not be necessary, the assembly of molecular models can prove extremely valuable in studying certain types of catalytic hydrogenations. They may, for example, help in understanding problems of selectivity when more than one reducible group is present, and they can also show whether poisoning by certain atoms will occur, offering a possibility of overcoming this by the use of more vigorous conditions or of more catalyst.

Complexes made by reacting the platinum group metals with alkyl or aryl phosphines are of considerable potential interest. Many of them are soluble in aromatic or polar aliphatic solvents and are already finding applications as homogenous catalysts. In this paper the methods available for producing the phosphine complexes are reviewed, and details are given of a range of phosphine stabilised hydrido and phosphine stabilised carbonyl hydrido complexes of the metals, all of which have been produced under controlled conditions and are now available in research quantities.

In the second part of this survey of the oxidation of the platinum metals attention is given to the formation of solid oxide films on the more reactive metals ruthenium, rhodium, iridium and osmium. The films formed in air on these metals are thick enough to give tarnish colours at temperatures of 400 to 500°C, and they may be in equilibrium with an appreciable partial pressure of gaseous oxides at temperatures below that at which they decompose. Diagrams showing the solid (oxide and metal) phases and the vapour pressures of the gaseous oxide phases in equilibrium with one atmosphere of oxygen at temperatures up to about 1800°C are given for four of the platinum metals. A third part of this paper will deal with the oxidation of palladium.