ic901335w_si_002.cif (48.95 kB)

Reaction of a 14-Vertex Carborane with Nucleophiles: Formation of nido-C2B12, nido-C2B11, and closo-CB11 Carborane Anions

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posted on 19.10.2009, 00:00 by Jian Zhang, Fangrui Zheng, Hoi-Shan Chan, Zuowei Xie
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.