Syntheses, Crystallographic/Computational Characterizations, and Reactions of the First 10-Vertex arachno- and nido-Phosphamonocarbaboranes

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• 作者：Alexandra M. Shedlow ; Daniel E. Kadlecek ; Jude C. Clapper ; Scott E. Rathmill ; Patrick J. Carroll ; and Larry G. Sneddon
• 刊名：Journal of the American Chemical Society
• 出版年：2003
• 出版时间：January 8, 2003
• 年：2003
• 卷：125
• 期：1
• 页码：200 - 211
• 全文大小：638K
• 年卷期：v.125,no.1(January 8, 2003)
• ISSN：1520-5126

文摘

A synthetic sequence involving the initial reaction of a substituted phosphorus dihalide (RPCl₂,R = CH₃, C₆H₅) with the arachno-CB₈H₁₃^- (1^-) monoanion followed by an in situ dehydrohalogenationreaction initiated by Proton Sponge, resulted in phosphorus cage insertion to yield the first 10-vertex arachno-and nido-phosphamonocarbaboranes, exo-6-R-arachno-6,7-PCB₈H₁₂ (2a, 2b) and PSH⁺6-R-nido-6,9-PCB₈H₉^- (PSH⁺3a^-, PSH⁺3b^-) (R = C₆H₅ (a), CH₃ (b)). Alternatively, 2a and 2b were synthesized in highyield as the sole product of the reaction of the arachno-4-CB₈H₁₂^2- (1^2-) dianion with RPCl₂. Crystallographicdeterminations of PSH⁺3a^- and PSH⁺3b^- in conjunction with DFT/GIAO computational studies of the anionshave confirmed the expected nido cage framework based on an octadecahedron missing the six-coordinatevertex. DFT/GIAO computational studies have also shown that while the gross cage geometries of theexo-6-R-arachno-6,7-PCB₈H₁₂ compounds 2a and 2b resemble the known isoelectronic arachno-6,9-SCB₈H₁₂, the phosphorus and carbon atoms are in thermodynamically unfavorable adjacent positions onthe six-membered puckered face. They also each have an endo-hydrogen at the P6-position arising fromproton transfer to the basic phosphorus during the cage-insertion reaction. Possible stepwise reactionpathways that can account for the formation of both the arachno and nido products are discussed.Deprotonation of 2a and 2b resulted in the formation of their corresponding conjugate monoanions, 6-R-arachno-6,7-PCB₈H₁₁^- (2a^-, 2b^-), in which the proton that had been attached to the P6 atom was removed.Reactions of 2a^- with O₂, S₈, BH₃·THF, or Br₂ further demonstrated the basicity of the P6-phosphorusyielding the new arachno-substituted compounds, endo-6-O-exo-6-(C₆H₅)-arachno-6,7-PCB₈H₁₁^- (4a^-),endo-6-S-exo-6-(C₆H₅)-arachno-6,7-PCB₈H₁₁^- (5a^-), endo-6-BH₃-exo-6-(C₆H₅)-arachno-6,7-PCB₈H₁₁^- (6a^-),and endo-6-Br-exo-6-(C₆H₅)-arachno-6,7-PCB₈H₁₁ (7a), respectively, in which the O, S, BH₃, and Brsubstituents are bound to the phosphorus at the endo position.