Methylthiomethyl Compounds of Aluminum, Gallium, and Indium

Abstract

The dimethyl(methylthiomethyl)metal compounds (Me2MCH2SMe)(2) (M=Al, Ga, In) have been prepared from LiCH2SMe and the respective dimethylmetal chlorides. Unlike the corresponding lithium compounds, the thiomethyl compounds with AlMe2 and GaMe2 groups are sublimable and well soluble in nonpolar solvents. The compounds (Me2MCH2SMe)(2) have been characterized by elemental analyses, multinuclear NMR spectroscopy, and, in the cases M = Al and Ga, by single-crystal X-ray crystallography. The Al and Ga compounds' are dimeric in the solid and in nondonor solvents, but are cleaved by stronger donors such as ethers and amines. They adopt conformations in which the S-bound methyl groups are placed in equatorial-positions of the chair-like six-membered ring systems. Ab initio calculations up to the MP2/6-31G(d) and B3LYP/6-31G(d) levels-of theory confirmed these conformations to be the ground states, the one with both S-Me groups in axial position being higher in energy by ca. 25 kJ mol(-1). The barriers to inversion of the heterocyclohexane rings in toluene solution (NMR) are 39 kJ mol(-1) for the Al compound and 36 kJ mol(-1) for the Ga compound.