Palladium-Catalyzed Desymmetrization of Silacyclobutanes with Alkynes to Silicon-Stereogenic Silanes: A Density Functional Theory Study.
The palladium-catalyzed desymmetrization of silacyclobutanes using electron-deficient alkynes proceeds with high enantioselectivity in the presence of a chiral P ligand; this provides a facile approach for the synthesis of novel silicon-stereogenic silanes. In this work, we used hybrid density functional theory (DFT) to elucidate the mechanism of the palladium-catalyzed desymmetrization of silacyclobutanes with dimethyl acetylenedicarboxylate. Full catalytic cycle including two different initiation modes that were proposed to be a possible initial step to the formation of the 1-pallada-2-silacyclopentane/alkyne intermediate-the oxidative addition of the palladium complex to the silacyclobutane Si-C bond (cycle MA) or coordination of the Pd0complex with the alkyne C≡C bond (cycle MB)-have been studied. It was found that the ring-expansion reaction began with cycle MB is energetically more favorable. The formation of a seven-membered metallocyclic PdIIintermediate was found to be the rate-determining step, whereas the enantioselectivity-determining step, oxidative addition of silacyclobutane to the three-membered metallocyclic PdIIintermediate, was found to be quite sensitive to the steric repulsion between the chiral ligand and silacyclobutane.
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, No. 1378, Wenyi West Road, Science Park of HZNU, Hangzhou, 311121, China.
Jin
J
Zhang
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, No. 1378, Wenyi West Road, Science Park of HZNU, Hangzhou, 311121, China.
Jin-Zhou
JZ
Xu
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, No. 1378, Wenyi West Road, Science Park of HZNU, Hangzhou, 311121, China.
Zhan-Jiang
ZJ
Zheng
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, No. 1378, Wenyi West Road, Science Park of HZNU, Hangzhou, 311121, China. zhengxu@hznu.edu.cn.
Zheng
Z
Xu
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, No. 1378, Wenyi West Road, Science Park of HZNU, Hangzhou, 311121, China.
Yu-Ming
YM
Cui
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, No. 1378, Wenyi West Road, Science Park of HZNU, Hangzhou, 311121, China.
Jian
J
Cao
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, No. 1378, Wenyi West Road, Science Park of HZNU, Hangzhou, 311121, China. liwenxu@hznu.edu.cn.|State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, P.R. China. liwenxu@hznu.edu.cn.
Li-Wen
LW
Xu
density functional calculations; desymmetrization; reaction mechanisms; ring expansion; silylation