Hydrosilylation Of Hydrosilanes And The Synthesis Of Pt Catalyst Supported On HNTs

Organosilicon compounds and organosilicon material are widely used in petroleum, construction, electrical, textile, automotive and other traditional industrial sectors. In addition, applications in electronics, new materials, life science and other high-tech fields are being developed. Hydrosilylation is one of the most important Si-C bond formation reactions in organosilicon chemistry. Many silicon monomers containing functional groups have been synthesized via this reaction.As is known, hydrosilylation is one of the reactions which attract public attention in organosilicon chemistry. Currently, Speier catalyst is a kind of homogeneous catalyst widely used in industrial hydrosilylation, but it also has its own limitations. In the first part of this paper, our research focused on the preparation of vinylsilane coupling agents via hydrosilylation reactions between gaseous acetylene and hydrosilanes such as triethoxysilane, diethoxymethylsilane, trichlorosilane and dichloromethylsilane. Speier's catalyst is not a good choice because a large amount of diadduct and other byproducts are produced. Based on this consideration, another homogeneous catalyst Pt-PMVS was synthesized and compared with Speier's catalyst, Pt-PPh₃ complexes. The results shows that Pt-PMVS complex is the best one, and besides, the selectivity and yield of the target products are improved by mixing acetylene and hydrosilanes before entering the reactor. Under the optimum reaction conditions, the selectivity and yield of vinylsilanes reach 97.7%, 94.0%, 99.4%, 98.8% and 95.5%, 85.3%, 61.3%, 97.6%, respectively.The second part is about the preparation of a novel long-chain silane coupling agents. Using Pt-PMVS complexes as the catalyst for hydrosilylation reactions of dihydromyrcenol and hydrosilanes (triethoxysilane, trimethoxysilane), apart from aimed products (α-adduct andβ-adduct), a small amount of tetraalkoxysilane, alcohol and other byproducts were found. Under reaction conditions such as toluene solvent, 80℃, molar ratio of Pt and trimethoxysilane (2.4×10^-5), the conversion of trimethoxysilane is 95.8% and the overall yield of the target products is 90.9%; Similarly, the conversion of triethoxysilane is 93.2% and the overall yield is 90.8%. The third part of this paper is about the synthesis of supported catalyst Pt-CS/HNTs and evaluation of its catalytic performance. Although homogeneous catalyst Pt-PMVS is an effective catalyst for above-mentioned reactions, it is not suitable for large-scale industrial production because Pt is a kind of precious metal and it's hard to separate and recycle. One of the solutions for this problem is using supported catalyst instead of homogeneous catalyst. In this paper, supported catalyst Pt-CS/HNTs was prepared with halloysite nanotubes (HNTs), chitosan and Pt used as support, ligand and active component respectively. There is no significant loss in catalytic activity after been reused five times in the hydrosilylation of dihydromyrcenol and triethoxysilane. When it's used in the hydrosilylation of acetylene and hydrosilane for several times, the results showed that the product was mostly diadduct each time.