Chloroplatinic Acid as a Homogeneous Catalyst

Commonly, when chloroplatinic acid is the source of the catalyst for hydrosilation and sometimes when salts of other metals are used, no effect is observed for some time after it has been added to a mixture of reagents. Then, rather suddenly a rapid reaction can ensue. This induction period can in some cases last for a relatively long time, even hours. An unpredictable induction period, followed by a very fast exothermic reaction, leads to difficult, sometimes dangerous situations when large amounts of reagents are employed. 

Nothing has been found in the published literature about what takes place during the induction period. We believe that an active catalytic species is formed during this period, and that its formation requires reduction of chloroplatinic acid, or of whatever transition metal salt or complex one uses. 

Our experiences with chlorosilanes (12) indicate some of the processes that take place during an induction period. The experiences are synop-sized as though they were obtained in one experiment. The results are in general accord with those described by Benkeseref al. (13), who studied the hydrosilation of styrene in ethylbenzene. 

A very strong solution of chloroplatinic acid (about 50% in isopropanol) was stirred with an olefin to make a mixture containing the extremely high concentration of about 0.01 g-atom of Pt/mole of olefin. This is more than 100 times the amount one would use for hydrosilation. At room 

If one were able to carry the reactions to completion with a large excess of olefin, chloroplatinic acid, and the chlorosilane, the reactions might be described by Eq. (2). 

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