Reaction of a 14-Vertex Carborane with Nucleophiles: Formation of <i>nido</i>-C₂B₁₂, <i>nido</i>-C₂B_11, and <i>closo</i>-CB₁₁ Carborane Anions

Nucleophilic reactions of a 14-vertex closo-carborane are reported. 2,3-(CH2)3-2,3-C2B12H12 (1) reacts with MeOH at 70 °C to give closo-CB11 anions [1,2-(CH2)3CH(OMe)-1-CB11H10]− ([2a]−), [1,2-(CH2)2CH(OMe)CH2-1-CB11H10]− ([2b]−), and [1,2-(CH2)2CHCH-1-CB11H10]− ([2c]−). It is suggested that [2c]− is an intermediate for the isomerization from [2a]− to [2b]−. Treatment of 1 with MeOH/Me3N, tBuOK or LiNMe2 affords nido-C2B12 species [8,9-(CH2)3-μ-11,12-(Nu)BH-8,9-C2B11H11]− (Nu = MeO ([3a]−), tBuO ([3b]−), and Me2N ([3c]−)). In the presence of acid such as HCl, anions [3]− are converted to 1. However, [3]− undergo deboration reaction, in the presence of bases, to generate a nido-C2B11 anion [8,9-(CH2)3-8,9-C2B11H12]− ([4]−) that can also be formed directly from the reaction of 1 with excess CsF or piperidine. Mechanistic studies show that [3a]− is the first intermediate in the reaction of 1 with MeOH and [4]− is unlikely an intermediate.