Theoretical study on the halogen-zinc exchange reaction by using organozincate compounds

Density functional theory (DFT) calculations have been performed to examine the mechanism of the halogen-zinc exchange reaction of organozincate reagents (Me(2)RZnLi x OMe(2); R = Me, Et, iPr, and tBu) with organohalides (RX; R = Me, vinyl, ethynyl, -CH(Cl)CH(3), -CH(CH(3))CHCH(2); X = Cl, Br, I). We focused on three areas: 1) the effect of the halogen species, 2) the effect of the alkyl ligand on zinc, 3) the effect of the substrate nature. Fragment-energy analysis of each reaction was conducted to elucidate the factors determining the activation energy. The nature of the halogen atom affects the interaction (INT) energy but does not affect the deformation (DEF) energy. On the other hand, the type of alkyl ligand influences DEF rather than INT and bulky ligands (including tert-butyl and iso-propyl groups) decrease the activation energy compared with smaller ligands, such as ethyl and methyl groups. In the reaction with vinyl iodide, a decrease in DEF promoted the reaction, whereas INT was almost unchanged. However, in the case of iodoacetylene, a decrease in INT lowered the activation energy. For allyl iodide derivatives DEF appears to be the determining factor, whereas for gem-dihaloalkane derivatives INT is the main determinant of reactivity.