Intermolecular Methyl-to-Magnesium Bonds in Organomagnesium Aggregates

Abstract

Using MgMe2 as a model system, quantum calculations probe the propensity of the methyl C of one molecule to form a noncovalent bond with the Mg of another. Also tested is the effect of halogenation of each molecule, and how its prior dimerization to [MeMgX]2, which contains a square (Mg2X2), core affects its participation in a C···Mg bond with another molecule. These intermolecular bonds can be fairly strong, some exceeding 80 kJ mol–1. The strongest interaction arises when dimeric [MgMe2]2 serves as the electron donor and is paired with an organomagnesium halide electron acceptor. This strength is magnified as the halogen of the latter grows in size: F < Cl < Br < I. The electrostatic interaction furnishes the largest component, followed by polarization and dispersion in that order. Intermolecular methyl-to-magnesium donation represents a genuine magnesium bond important to the organization of Schlenk-type aggregates.