Group 13 Decamethylmetallocenium Cations

Salts containing the decamethylmetallocenium cations, ( C5Me5) M-2 ( or CpM-2(+)) of the group 13 "metals" B, Al and Ga have been prepared using a variety of synthetic routes. Precursor molecules of the type Cp2MX ( X = Cl, Br, Me) exhibit structural features that vary significantly depending on the size and electronegativity of the central atom. While salt metathesis, halide abstraction and methanide abstraction methods represent viable routes for the preparation of salts of CpB-2(+) and CpAl-2(+), acidolysis of a Cp* group from CpGa-3 is the most reliable method for the synthesis of the analogous gallium cation. Gallocenium cations are less stable than either of the lighter congeneric cations since they prove to be susceptible to decomposition reactions involving the "back-transfer" of ligands from the counter anion. Density functional theory (DFT) calculations revealed that, whereas CpGa-2(+) is predicted to adopt a molecular structure more similar to that of CpB-2(+), the electronic structure of the gallium cation bears a greater resemblance to that of CpAl-2(+).