Chemistry of C-Trimethylsilyl-Substituted Heterocarboranes. 28. Selective Alkylation and Reactivity of \dqCarbons Adjacent\dq and \dqCarbons Apart\dq Tetracarba-nido-dodecaborane(12) Derivatives toward Group 1 and Group 2 Metals. Synthetic, Spectroscopic, and Structural Investigations on Lithium-, Sodium-, Potassium-, Cesium-, and Magnesium-Complexed C4B8 Carboranes. Organometallics, (19)4:497--508, 2000. [PUMA: DFT Group IA alkylation;magnesacarborane calcn calcn;mol crystal geometry magnesacarborane;heterocarborane magnesium metal metalation metallacarborane optimized prepn structure substituted substituted;DFT trimethylsilyl]