# Precious Metal Catalysts for Homogeneous Catalysis

## Hydrosilylation

Hydrosilylation is a catalytic method for the production of silicon-organic compounds, e.g. silicones.

Fig.1
Schematic representation of hydrosilylation

Platinum is used in particular as the catalyst metal. The catalysts employed are various platinum compounds, such as hexachloroplatinic acid (H2[PtCl6]), cisplatin ([PtCl2(NH3)2]) and Karstedt’s catalyst, which is named for its discoverer. The platinum requirement for hydrosilylation worldwide is in the range of several tonnes Pt per year, putting it in the leading group of homogeneous catalytic processes with precious metals. Karstedt’s catalyst plays the most important role in this field of application. The catalyst is a platinum complex with vinylsiloxane ligands.

Fig.2
Fig.3

Binuclear platinum(0) complex

Examples of applications

A very important application is to be found in the field of dentistry where the catalyst is employed in the manufacture of impression materials.

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A further field of application of Karstedt’s catalyst is found in the area of paper coating. In this application, a thin silicone layer is coated onto the paper so that self-adhesive labels can be applied to the paper and then removed from it again without difficulty. This process is used on an industrial scale and the corresponding labels are to be found on many everyday products, e.g. packaging and bottles.

As Karstedt’s catalyst is very active in the hydrosilylation reaction, the precious metal is only present in the $ppm$ range in the silicone film on the paper and in the dental impression materials. For this reason, it is not possible to recycle the platinum economically.

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