AN AB-INITIO MOLECULAR-ORBITAL STUDY OF THE GRIGNARD-REAGENTS CH3MGCLAND [CH3MGCL]2 - THE SCHLENK EQUILIBRIUM

Ab initio molecular orbital calculations are used to study the modifie d Schlenk equilibrium: 2RMgCl <-> (RMgCl)2 <-> MgR2 + MgCl2 <-> Mg(Cl2 )MgR2 With R = H and CH3. In the absence of any solvents, calculations indicate that the formation of the various possible bridged dimers (R MgCl)2 is substantially exothermic. However, using dimethylether as a model solvent, we show that the formation of the dimer (Me2O)(CH3)Mg(m uCl2)Mg(CH3)(OMe2) is exothermic only when entropic effects are includ ed.