A DFT Computational Study of the Bis-Silylation Reaction of Acetylene Catalyzed by Palladium Complexes

• Published in: Journal of the American Chemical Society Vol. 124; no. 19; pp. 5506 - 5513
• Main Authors: Bottoni, Andrea, Higueruelo, Alicia Perez, Miscione, Gian Pietro
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.05.2002
• Subjects: Chemistry; Exact sciences and technology; Kinetics and mechanisms; Organic chemistry; Reactivity and mechanisms; Catalytic reaction; Tertiary phosphine; Regioselectivity; Palladium Complexes; Silicon Organic compounds; Silylation; Theoretical study; Organic silane; Transition metal Complexes; Cis trans isomerization; Complex catalyst; Energy barrier; Acetylene; Pseudopotential method; Transition state; Reaction mechanism; Density functional method; Potential energy surfaces; Platinoid Complexes; Ab initio calculations
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0118892

In this paper we have investigated at the DFT(B3LYP) level the catalytic cycle for the bis-silylation reaction of alkynes promoted by palladium complexes. A model-system formed by an acetylene molecule, a disilane molecule, and the Pd(PH3)2 complex has been used. The most relevant features of this catalytic cycle can be summarized as follows:  (i) The first step of the cycle is an oxidative addition involving H3Si−SiH3 and Pd(PH3)2. It occurs easily and leads to the cis (SiH3)2Pd(PH3)2 complex that is 5.39 kcal mol-1 lower in energy than reactants. (ii) The transfer of the two silyl groups to the C−C triple bond does not occur in a concerted way, but involves many steps. (iii) The cis (SiH3)2Pd(PH3)2 complex, obtained from the oxidative addition, is involved in the formation of the first C−Si bond (activation barrier of 18.34 kcal mol-1). The two intermediates that form in this step cannot lead directly to the formation of the final bis(silyl)ethene product. However, they can isomerize rather easily (the two possible isomerizations have a barrier of 16.79 and 7.17 kcal mol-1) to new more stable species. In both these new intermediates the second silyl group is adjacent to the acetylene moiety and the formation of the second C−Si bond can occur rapidly leading to the (Z)-bis(silyl)ethene, as experimentally observed. (iv) The whole catalytic process is exothermic by 41.54 kcal mol-1, in quite good agreement with the experimental estimate of this quantity (about 40 kcal mol-1).