Computational study of the Grignard reaction with alkynes

The complexation of MgX 2 , MeMgX, and Me 2 Mg (X=Cl, Br) with propyne have been studied both in the gas phase and in the presence of dimethyl ether (Me 2 O) by means of the density functional theory B3LYP/6-31+G* method. Solvation was modeled using the supermolecule approach. The complex formation between disolvated magnesium compound and alkyne is connected with replacement of a coordinated solvent molecule by the alkyne, being necessary for the reaction to proceed to the end. The reaction towards end products, an acetylenic Grignard reagent and an alkane, is exothermic. The transition state has a cyclic structure, which is almost triangular with practically linear proton transfer. The transition state resembles more the reagents than the products.