The hydrosilylation reaction refers to the addition reaction that occurs under certain conditions between organosilicon compounds containing Si-H bonds and compounds with unsaturated bonds. It is the main form of forming Si-C bonds and one of the most fundamental and important reaction types in organosilicon chemistry. Unsaturated bonds can include carbon-carbon double bonds, carbon-carbon triple bonds, carbon-oxygen double bonds, carbon-nitrogen double bonds, etc. Among them, the addition reaction between Si-H bonds and carbon-carbon double bonds is the most common hydrosilylation reaction in the organosilicon industry and is the core reaction of many addition-type organosilicon products.

For the hydrosilylation reaction, in addition to the silicon-hydrogen compounds and unsaturated compounds, a catalyst is an indispensable component, which serves to accelerate the reaction rate, shorten the reaction time, and lower the reaction temperature. The catalysts for the hydrosilylation reaction are mainly compounds and complexes of transition metal elements in Group VIII B of the periodic table, such as platinum, palladium, nickel, and rhodium, etc. Among them, the platinum catalyst has the highest catalytic activity and is the most widely used.

The platinum catalysts used for catalyzing the hydrosilylation reaction are mainly divided into homogeneous catalysts and heterogeneous catalysts. Among them, the homogeneous catalyst and the reactant are in the same phase, and there is no phase interface. In the hydrosilylation reaction, the homogeneous catalyst generally refers to the liquid catalyst.

The homogeneous platinum catalysts mainly have three types: The first type is dissolving chloroplatinic acid (H2PtCl6▪6H2O) in organic solvents such as ethanol, isopropanol, and tetrahydrofuran, allowing them to interact and form a complex, known as the "Speier catalyst". This catalyst is straightforward to prepare and convenient to use. The second type of platinum catalyst is the complex of platinum and vinyl end-capped groups, known as the Karstedt's catalyst. It has high reaction activity, can be stored stably, and has good compatibility with various types of polysiloxanes. It is the most widely used catalyst in addition-type organosilicon release agents. The third type of platinum catalyst is formed when chloroplatinic acid forms complexes not only with some other unsaturated compounds but also with ketones, cyclopentadiene, esters, alcohols, crown ethers, heteroatom-containing crown ethers, and polysiloxanes, and is used as a catalyst.

Homogeneous platinum catalysts have high activity and reaction selectivity. However, since they are in the same phase as the reactants, they are difficult to separate after the reaction and cannot be reused, resulting in higher costs and the possibility of heavy metal ion pollution. Therefore, researchers have immobilized homogeneous catalysts to prepare heterogeneous catalysts. The immobilization of homogeneous catalysts refers to combining homogeneous catalysts with solid supports through physical or chemical methods to form a special catalyst. Heterogeneous platinum catalysts are in different phases from the reactants, and the common form is that solid catalysts catalyze the hydrosilylation reaction of liquid mixed reactants.

The heterogeneous catalysts for the hydrosilylation reaction are mainly divided into two types: traditional heterogeneous platinum catalysts and polymer-metal complex catalysts. Among them, traditional heterogeneous catalysts are formed by adsorbing transition metals on inorganic particles such as carbon black and alumina. Such catalysts have high stability, can be recycled and reused, but have lower catalytic activity and selectivity, and the reaction process requires higher temperatures and pressures. The polymer-metal complex catalyst consists of three parts: the polymer support, the coordination groups bonded to the support, and the transition metal. Overall, although heterogeneous catalysts have the advantages of high stability and recyclability, their applications are limited due to their lower activity and selectivity, as well as the complex preparation process and the reduced catalytic activity during reuse.

Many substances can "poison" platinum catalysts, resulting in reduced catalytic activity or even loss of activity. For example, organic compounds containing elements such as nitrogen, phosphorus, and sulfur, and ionic compounds containing heavy metals such as tin, lead, mercury, bismuth, and arsenic. Therefore, special attention must be paid during the use of platinum catalysts to avoid contact with these substances that can poison them. There are many types and forms of platinum catalysts. Therefore, in the application process, it is necessary to select the appropriate platinum catalyst based on the characteristics of the reaction system to achieve the best catalytic effect. 

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