Unusual Cage Rearrangements in 10-Vertex nido-5,6-Dicarbaborane Derivatives: An Interplay between Theory and Experiment

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• 作者：Bohumil Štíbr ; Josef Holub ; Mario Bakardjiev ; Paul D. Lane ; Michael L. McKee ; Derek A. Wann ; Drahomír Hnyk
• 刊名：Inorganic Chemistry
• 出版年：2017
• 出版时间：January 17, 2017
• 年：2017
• 卷：56
• 期：2
• 页码：852-860
• 全文大小：518K
• ISSN：1520-510X

文摘

The reaction between selected X-nido-5,6-C₂B₈H₁₁ compounds (where X = Cl, Br, I) and “Proton Sponge” [PS; 1,8-bis(dimethylamino)naphthalene], followed by acidification, results in extensive rearrangement of all cage vertices. Specifically, deprotonation of 7-X-5,6-C₂B₈H₁₁ compounds with one equivalent of PS in hexane or CH₂Cl₂ at ambient temperature led to a 7 → 10 halogen rearrangement, forming a series of PSH⁺[10-X-5,6-C₂B₈H₁₀]⁻ salts. Reprotonation using concentrated H₂SO₄ in CH₂Cl₂ generates a series of neutral carbaboranes 10-X-5,6-C₂B₈H₁₁, with the overall 7 → 10 conversion being 75%, 95%, and 100% for X = Cl, Br, and I, respectively. Under similar conditions, 4-Cl-5,6-C₂B₈H₁₁ gave ∼66% conversion to 3-Cl-5,6-C₂B₈H₁₁. Since these rearrangements could not be rationalized using the B-vertex swing mechanism, new cage rearrangement mechanisms, which are substantiated using DFT calculations, have been proposed. Experimental ¹¹B NMR chemical shifts are well reproduced by the computations; as expected δ(¹¹B) for B(10) atoms in derivatives with X = Br and I are heavily affected by spin–orbit coupling.