J. Chem. Sci. (2018) 130:58 © Indian Academy of Sciences https://doi.org/10.1007/s12039-018-1457-9 REGULAR ARTICLE Disproportionation mechanism of methylchlorosilanes catalyzed by different clusters AlCl3/ZSM-5 WENYUAN XUa,∗ , MEI YANGa, YONGXIN LIUa, ZANRU GUOa,LINHUa, SHAOMING YANGa and SANGUO HONGb aSchool of Material Science and Engineering, East China Jiaotong University, Nanchang 330013, China bCollege of Chemistry, Nanchang University, Nanchang 330031, China E-mail: [email protected] MS received 22 October 2017; revised 18 March 2018; accepted 23 March 2018; published online 23 May 2018 Abstract. Organosilicon material is widely used because of its dual structure. Dimethyldichlorosilane is the largest and most versatile of organic silicon monomer. In this article, MP2/6-311 ++G (3df, 2pd) basis set has been used to calculate the reaction mechanism of disproportionation for producing dimethyldichlorosilane by catalysts AlCl3/ZSM-5 (3T, 4T, 6T). The results show that the activation energies (3T, 4T, 6T) of the rate- determining step of the main reaction are: 100.3, 110.6 and 113.1kJmol−1, respectively. The structure analysis, activation energy analysis and LOL analysis for different catalysts all show that the catalytic effect of 4T cluster AlCl3/ZSM-5 is the best. Keywords. AlCl3/ZSM-5; disproportionation; dimethyldichlorosilane; organosilicon. 1. Introduction that the yield of dimethyldichlorosilane was 70.3%. B. Pachaly et al., 11 used organic amine as catalyst, and Organosilicon material 1,2 has many excellent properties found that the yield of dimethyldichlorosilane was 27%. such as high and low-temperature resistance, corrosion W. Kalchauer et al., 12 used transition metals (more resistance and physiological inertia. It is widely used expensive) as catalysts and found that the yield of in electronics, building materials, transportation, and dimethyldichlorosilane was 67%. When AlCl3 is used other fields. 3–5 The level of industrial silicon is deter- as a catalyst, the yield of dimethyldichlorosilane is the mined by the production of its monomer, in which highest. But it requires the reaction environments of (( ) , ) dichlorodimethylsilane CH3 2SiCl2 M2 is the largest high temperature and high pressure. Because its sub- and most versatile organic silicon monomer. 6,7 At limation temperature (178 ◦C) is low, 13 it is easy to present, the dichlorodimethylsilane is prepared from cause a loss when reacting at atmospheric pressure. 8 direct synthesis method. But this method will accu- Therefore, AlCl3 is loaded on the carrier to improve mulate a lot of waste, such as methyltrichlorosilane its sublimation temperature. 14,15 As a solid acid catalyst, ( , ) (( ) , 16 CH3SiCl3 M1 and trimethylchlorosilane CH3 3SiCl AlCl3 has demonstrated the good catalytic effect in the ) 9 M3 . Some experts use disproportionation method to scission reaction between high-boiling and low-boiling 17 prepare the M2, this method not only solves the prob- components of silicone. The reaction mechanism was lem of waste accumulation but it can also improve studied for disproportionation of dimethyldichlorosi- 18 the economic efficiency. In the disproportionation reac- lane catalyzed by 5T cluster AlCl3/ZSM-5, 24T and tion for producing dimethyldichlorosilane, the choice 7T clusters ZSM-5 in our laboratory. The preliminary 10 of catalyst is very important. Bin Ku et al., studied work showed that the 5T cluster AlCl3/ZSM-5 cata- the disproportionation for producing dichlorodimethyl- lyst not only improved the stability, but also increased silane by using AlCl3 as catalysts under the conditions the yield of dimethyldichlorosilane. The macroporous of high temperature and high pressure. They found 24T cluster ZSM-5 has weaker activity in its interior, and the small pore 7T cluster ZSM-5 has no catalytic 19 / *For correspondence activity. Experiment indicates that AlCl3 ZSM-5 has Electronic supplementary material: The online version of this article (https:// doi.org/ 10.1007/ s12039-018-1457-9) contains supplementary material, which is available to authorized users. 1 58 Page 2 of 7 J. Chem. Sci. (2018) 130:58 Figure 1. The formation process of 3T, 4T, and 6T clusters AlCl3/ZSM-5 catalysts and the numbers of key atoms. a good catalytic effect. Therefore, the catalytic activity is Energy (ZPE) 29 correction is considered. Finally, we perform mainly provided by its surface. At present, the 5T cluster LOL (localized-orbital locator) 30,31 and bond order analysis 20 AlCl3/ZSM-5 catalyst is a relatively popular research on the three catalysts to compare their catalytic activity. The area in the preparation of dimethyldichlorosilane. In localized-orbital locator can not only analyze the problems order to determine the active clusters on the surface of of localization and delocalization but also characterize the ZSM-5, it is necessary to discuss other small clusters chemical bonds. In the paper, all the calculations are com- pleted through Gaussian 09 program. (3T, 4T and 6T) in depth. Finally, the catalytic proper- ties of small clusters model catalysts are explained from a microscopic perspective. 3. Results and Discussion 2. Computational The formation process of 3T (Cat.3T), 4T (Cat.4T) and In this paper, Density Functional Theory (DFT) method 21–23 6T (Cat.6T) clusters AlCl3/ZSM-5 catalysts is shown of quantum chemistry is used to calculate the structures of the / reactants, transition states, intermediates, and products at the in Figure 1. The stable structure of AlCl3 ZSM-5 cata- B3LYP/6-31G level. For structural optimization calculations, lyst (taking Cat.3T as an example) is mainly composed the structures are constructed and adjusted by using the Gaus- of Al-O-Al-O four-membered ring and four O atoms sian view. 24 Then the input files are written and the structures are bonded to two Al atoms, respectively. During the 25,26 are optimized for calculation with Gaussian 09 (Gaus- formation of AlCl3/ZSM-5 catalyst, AlCl3 and ZSM- sian Inc., Wallingford CT). The transition states are searched 5 are close to each other, one of Cl atom in AlCl3 is by utilizing TS 27 method in this paper. We perform vibration removed, and it combines with the active site H atom in analysis and frequency calculations for all structures (reac- ZSM-5 to form HCl. The important geometric param- tants, intermediates, transition states, products). The results eters of the stable structures are shown in Table 1. of calculations show that the frequencies of all the reactants, From Table 1, the order of the bond angle is: Cat.4T > intermediates, and products are positive and all the transi- Cat.3T > Cat.6T. The bond angle ( O1-Al1-O2) of the tion states have only one negative frequency, indicating that active site of Cat.4T is increased. It shows that the pore the transition states are the saddle points on the potential energy surface. Therefore the transition state structures are of the catalyst is enlarged, which is conducive for large credible. In order to further confirm the authenticity of the trimethylchlorosilane to participate in reaction into the transition states and the reaction paths, we have carried out channel. It is found that the order of bond length is: IRC/Path calculation. The second-order Moller-Plesset per- Cat.4T > Cat.3T > Cat.6T by comparing the bond turbation theory 28 (at MP2/6-311 ++G (3df, 2pd) level) is length of Al1-Cl1 of the active site. The longer bond used to calculate the energy of each step and the Zero Point length indicates that the Al1-Cl1 bond is more easily J. Chem. Sci. (2018) 130:58 Page 3 of 7 58 Table 1. Optimized geometric parameters of 3T, 4T, and 6T clusters of AlCl3/ZSM-5 catalysts. Cat.3T Cat.4T Cat.6T Bond length/nm Al1-Cl1 0.2192 0.2195 0.2189 Al1-Cl2 0.2118 0.2189 0.2190 Al1-O1 0.1814 0.1809 0.1811 Al1-O2 0.1809 0.1810 0.1812 Al2-O1 0.1839 0.1843 0.1843 Al2-O2 0.1856 0.1838 0.1849 O1-Si1 0.1731 0.1731 0.1734 O2-H1 0.0979 - - O2-Si2 - 0.1340 0.1728 Bond angle/◦ O1-Al1-O2 84.4982 84.7504 82.5858 O1-Al2-O2 82.7476 82.7869 80.9239 Si2-C1 bond and Al1-Cll bond are broken gradually. C1 atom and Al1 atom gradually approach and bond. These processes produce the product P1. C1 atom gradually moves to the Si2 atom, and bonds with it. Meanwhile, the Al1-C1 bond and the Si2-Cl1 bond stay away from each other and break. Cl1 atom and Al1 atom gradually approach and bond. These processes produce the reac- tant R1. Finally, the reactant and the product are found, which confirms the reliability of the transition state. The transition states are tracked during calculation in Figure 2. The reaction equations of the catalytic process. Forward and Reverse using the IRC method. The spac- ing trend of key atoms along the IRC of 3T, 4T, and 6T / broken and Cl is more likely to be involved in the reac- clusters AlCl3 ZSM-5 catalysts are shown in Figure 5. tion. All in all, they show that the catalytic activity of The spacing of critical atoms has gradually stretched or 4T cluster AlCl3/ZSM-5 is the best. shortened from the reactants to the products via transi- The reaction equations of disproportionation for tion states. Thus, the authenticity of the transition state CH3SiCl3 and (CH3)3SiCl catalyzed by Cat.3T (Cat.4T structures is further proved, and the mechanism men- and Cat.6T are same as Cat.3T) are shown in Fig- tioned above is believable. ure 2. The reaction is divided into two channels. In The reaction heat and activation energy of each reac- channel 1, the Cat.3T reacts with (CH3)3SiCl to pro- tion step are calculated by using second-order Moller- ++ duce (CH3)2SiCl2 and intermediate (I) via the transition Plesset perturbation theory (at MP2/6-311 G (3df, state TS1.