Synthesis And Catalytic Properties Of Silicone Dendrimers-transition Metal Complexes

Catalyst is a kind of substance that can improve the reaction rate, but not be consumed in the course of the chemistry reaction. Catalyst can be classified as two kinds according to the action conformation: homogeneous catalyst and heterogeneous catalyst. Making the homogeneous catalyst heterogeneous can overcome the inherent defects of homogeneous catalytic reaction with the character of heterogeneous catalytic reaction on the basis of retaining the inherent merit of homogeneous catalyst. Making the homogeneous catalyst heterogeneous comprises physical technique and chemical technique. Physical technique is to combine the transition metal complex and carrier with physical method, and chemical technique is to hold the active component on the surface of the carrier with chemical bonds or lock the transition metal complex in the cage-like cavity of molecular sieve through chemical method. Macromolecular metal catalyst is a catalyst that hold the transition metal complex on the polymer, and this catalyst is very stable, having little causticity, being recycled and reused easily. Moreover, due to special macromolecular effect, its catalysis activity will be higher than that of low molecular catalyst, and it has good selectivity.Dendrimers are new tree-like branched synthesized macromolecules that appeared in the area of macromolecule chemistry during the last decades. They are perfect monodisperse macromolecules with a regular and highly branched three-dimensional architecture. Catalyst is a research area in which promising application for dendrimer may be developed. Dendrimers have nanoscopic dimensions and can be molecularly dissolved. This features make dendrimers suited to combine the advantages of homo-and heterogeneous catalysts as the carrier of transition metal complex: on one hand they can control the number and structure of active sites exactly, on the other hand they can be removed from the solution of reaction mixture conveniently." In this dissertation, we choosed carbosilane dendrimers with peripheralaminopropyl groups as carrier of low molecular homogeneous catalyst, and synthesized platinated and palladious organosilicon decdritic catalyst through complexing bond between the transition metals and exterior linked ligands having unshared electron pair. The catalytic activity of palladious catalyst in catalytic hydrogenation of olefin, aldehyde and ketone and catalytic activity of platinated catalyst in the catalytic hydrosilation of unsaturated compounds were investigated. A new effectively catalyst in organic synthesis was explored and the research field of organosilicon dendrimers was extended.The zero generation of carbosilane dendrimers were synthesized using Grignard reaction from methyltrichlorosilane and allyl chloride first of all. Then the first and second generations of carbosilane dendrimers with six and twelve peripheral allyl groups were synthesized through repeating sequence of alternating hydrosilylation with dichlorosilane and alkenylation with allyl magnesium chloride. The compounds obtained were characterized by *H NMR, 13C NMR, GC-MS(EI)and elemental analysis. As a result, the structure of the synthesized carbosilane dendrimers with peripheral allyl groups was consistent with the theoretic designation. The key of successfully preparation is to ensure the reaction atmosphere be free of water and oxygen and keep at low temperature in the Grignard reaction.Carbosilane dendrimers with peripheral aminopropyl groups were synthesized firstly. The hydrosilylation reaction of acrylic amine and HMe2SiOSiMe2H with 1:1 ratio was finished, then the hydrosilylation reaction of remainder silicon hydrogen and the peripheral allyl groups of the synthesized carbosilane dendrimer was carried out. The amino groups were linked to the periphery of the first and second generation of dendrimers successfully, and the functionalization of carbosilane dendrimer was realized. In the course of the reaction, the amino groups of acrylic amine were protected with trimethylsilyl groups, the intermediate products were characterized with FT~IR. The key of successfully reaction was to control the relative quantity of the reactants. The products were characterized with FT—IR, 'H NMR, 13C NMR and elementalanalysis, the results indicated that there were still little unreacted allyl groups on the periphery of the synthesized carbosilane dendrimers with amino groups, but this groups didn't influence the next reaction. The content of amino groups was determined by nonaqueous titration, and the value was: Gl-NH2:0.2269; G2-NH2:0.2658.The organosilicon dendritic catalysts were prepared with the reaction of the peripheral amino groups of functionalized carbosilane dendrimers and low molecular transition metal compounds ° The platinum complex of carbosilane dendrimer can be prepared from hydrous chloroplatinic acid (H2PtCl6*6H2O) and the carbosilane dendrimer with peripheral amino groups in refluxing ethanol, the synthesized dendritic metal catalysts were characterized with FT—IR, *H NMR and so on. The results indicated that the allyl groups of the dendrimers with amino groups disappeared after the complexing reaction, which is due to the addition reaction of terminal amino groups and the allyl groups of different dendrimer under the catalysis of Pt during the preparation of the complex.The platinum complex of the first dendrimer was analyzed with Inductively Coupled Plasma Atomic Emission Spectrometric (ICP-AES), the platinum content was 8.38%, and the silicon content was 7-19%. The X-ray Photoelectron Spectroscopic (XPS) analysis indicated that the bonding energies of the transition metal in dendritic catalyst" was lower than that in the transition metal compound, the unshared electron pair of the N atoms in carrier transferred to Pt atoms forming the complex between N and Pt atoms.The palladious complex of the carbosilane dendrimer can be prepared from hydrous palladium chloride(PdCl2*2H2O) and carbosilane dendrimer with peripheral amino groups in refluxing ethanol. The XPS spectral analysis indicated that the unshared electron pairs of the N atoms in carrier transferred to Pd atoms forming the complex between N and Pd atoms.Scaning electron microscope analysis of platinum complex of the second carbosilane dendrimer indicated that the diameters of the platinum complex grain were about 80nm, and the bigger grains also existed at the same time, whose magnitude was about150-200nm. The big grains were Which verified the addition reaction of terminal amino groups and the allyl groups of different dendrimer under the catalysis of Pt during the preparation of the complex This nanoscopic dimension has very important significance to improve its catalytic activity.The catalytic activity of palladious carbosilane dendritic catalyst in the catalyzed hydrogenation of olefins, aldehyde and ketones was investigated. The results indicated that in the condition of 30°C\ latm, and when the base substances quantity was 2000 times of catalyst, this catalyst can catalyze the hydrogenation of styrene, acrylonitrile, acrylic acid, hexamethylene, benzaldehyde etc. in ethanol, and this catalyst had upper catalytic activity. The activity peak appeared when the ratio of N to Pd was 2 and ethanol used as solvent. The change of boding energy of palladium fore and aft of the catalyzed reaction was investigated, indicating that part of Pd( II) was deoxidized to Pd(0).The performance of recycling and reusing of the catalyst was investigated showing this catalyst could be recycled after simple filtration and the activity decreased slightly.The catalytic activity of platinated carbosilane dendritic catalyst in the hydrosilylation of unsaturated compounds was investigated. The results indicated that along with the increase of ratio of N to Pt the activity decreased gradually. But for the different generations of dendrimers, the trends were different: For the first carbosilane dendritic platinum complex Gl-N-Pt, the catalytic activity descended rapidly with the increase of the ratio of N to Pt; For the G2-N-Pt, the catalytic activity was still very high when the ratio of N to Pt was 4, so the ratio of N to Pt of activity peak was between 2 and 4. When the first dendritic platinum catalyst was used to catalyze the hydrosilylation of 1-hexene and triethoxysilane, and when the ratio of N to Pt was 2, the turnover rate could reach 98% at 65 °C for 2hrs. At 25 °C, the turnover rate could reach 97.6% after lOHr. The performance of recycling of the catalyst was investigated, showing the catalyst could be used four times and the activity didn't descend obviously.