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: Group calcn;mol crystal magnesium metallacarborane optimized metal metalation structure trimethylsilyl DFT magnesacarborane;heterocarborane substituted IA calcn substituted;DFT geometry alkylation;magnesacarborane prepn]