Density functional theory study on the mechanism and thermochemistry of olefins addition to nickel dithiolenes

Abstract

We investigated the reaction mechanism and thermochemical property of conjugated dienes or mono-olefins with nickel dithiolenes (Ni(S2C2R2)(2)) using density functional theory. The reactions between conjugated dienes and nickel dithiolenes are concerted reactions. The thermochemical property study shows that the introduction of electron-withdrawing groups (-CF3 or -CN) to nickel dithiolene (Ni(S2C2H2)(2)) not only significantly lowers the activation energy barrier but also strongly stabilises the products. The introduction of electron-donating group (-CH3) to butadiene has the same effect. So, we conclude that the reactions between nickel dithiolenes and conjugated dienes are electrophilic cycloaddition. Mono-olefins can add to nickel dithiolenes through interligand pathway, which is a two-step process or through intraligand pathway, which is a one-step process. The thermochemical property study shows that the activation enthalpy for the reaction of butadiene with Ni(S2C2(CF3)(2))(2) is much lower than those of C4 mono-olefins with Ni(S2C2(CF3)(2))(2) for both interligand addition and intraligand addition. The Gibbs free energy for the reaction of butadiene with Ni(S2C2(CF3)(2))(2) is also more favourable than those of C4 mono-olefins with Ni(S2C2(CF3)(2))(2). It is the very preferential pathway for Ni(S2C2(CF3)(2))(2) to bind butadiene than C4 mono-olefins