Quantum-chemical study of organic reaction mechanisms. Part 2. Addition of selenium dichloride to acetylene

The mechanism of the addition of selenium dichloride to acetylene has been studied theoretically at the DFT-B3LYP/6-311+G(d,p) level. The reaction proceeds as anti-anti-addition via the formation of the intermediate selenirenium compounds with the four-coordinated selenium atom. Both thermodynamically and kinetically, a favorable E-2-chloroselenenyl chloride is formed on the first stage of the reaction. The experimentally observed E,E-bis(2-chlorovinyl) selenide is kinetically more favorable as compared to E,Z-isomer. Possible alternative reaction mechanisms require much higher energy barriers. Stereoselectivity of the process is achieved through the kinetic control of the reaction. In the reaction profile of a preferable route leading to a kinetically favorable E,E-bis(2-chlorovinyl) selenide the entropy factor doesnʹt play a major role in the energetics of both stages.