Chemistry of C-Trimethylsilyl-Substituted Heterocarboranes. 28. Selective Alkylation and Reactivity of "Carbons Adjacent" and "Carbons Apart" Tetracarba-nido-dodecaborane(12) Derivatives
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- 作者：Narayan S. Hosmane ; Hongming Zhang ; John A. Maguire ; Ying Wang ; Temesgen Demissie ; Thomas J. Colacot ; Maria B. Ezhova ; Kai-Juan Lu ; Dunming Zhu ; Thomas G. Gray ; Sarah C. Helfert ; Suneil N. Hosmane ; Je
- 刊名：Organometallics
- 出版年：2000
- 出版时间：February 21, 2000
- 年：2000
- 卷：19
- 期：4
- 页码：497 - 508
- 全文大小：183K
- 年卷期：v.19,no.4(February 21, 2000)
- ISSN：1520-6041
文摘
The "carbons apart" tetracarbon carborane nido-2,6-(R)2-4,12-(SiMe3)2-2,4,6,12-C4B8H8 (R = SiMe3(I), n-butyl (II)) and several of its B-alkylated derivatives react with Mg metal in THF solvent toproduce magnesacarboranes (IV-VI and XI) in yields ranging from 57% to 74%. The magnesacarboranes were characterized by chemical analysis and infrared and 1H, 11B, and 13C NMRspectroscopy and by single-crystal X-ray diffraction. Two types of cages were found, one in (THF)2Mg(SiMe3)4(B-Me)C4B7H7 (IV) and the other in (L)2Mg(SiMe3)2(R)2(B-Y)C4B7H7 (L = THF, R = SiMe3,Y = t-Bu (V); L = THF, R = SiMe3, Y = H (VI); (L)2 = TMEDA, R = n-Bu, Y = H (XI)). Both cagesshowed the presence of electron-precise C and B atoms, as well as electron-deficient fragments.Approximate density functional ab initio molecular orbital calculations showed that the dianionicC4B8 cage can exist in a number of energy-equivalent isomeric forms that can be trapped by a metalion such as Mg. The reactions of I with the group 1 metals followed a different course in which twodistinct steps occurred. The first step formed the paramagnetic intermediates which, in a slowerstep, reacted with a second equivalent of the metal to give the diamagnetic [(SiMe3)4C4B8H8]2-. Forthe lighter metals, this dianion picked up a proton to give the products [(THF)4M][(SiMe3)4C4B8H9](M = Li (VIII), Na (IX), K (X)) in 35-54% yield. In the case of Cs, no protonation occurred and thefinal product was a polymeric dicesiacarborane, [exo-Cs(TMEDA)-1-Cs-(SiMe3)4C4B8H8]n (VII),isolated in 41% yield. All were characterized by chemical analysis and infrared and 1H, 11B, and13C NMR spectroscopy; VII and VIII were additionally characterized by single-crystal X-raydiffraction studies. In VIII-X the group 1 metal was solvated by four THF molecules and was notinvolved in the cage, while in VII one Cs occupied an apical position above a C3B3 open face of onecarborane and bonded to a B3 face of a neighboring carborane. The second Cs, solvated by a TMEDAmolecule, occupies an exo-polyhedral position and was not part of the polymeric chain. One "carbonsadjacent" magnesacarborane, exo-(
-H)3Mg(THF)3(SiMe3)2(Me)2C4B8H8 (XII), was also synthesized,in 81% yield, by the reaction of the metal with the (SiMe3)2(Me)2C4B8H8 precursor. Single-crystalX-ray diffraction studies showed the compound to be composed of an exo-polyhedral [Mg(THF)3]2+that is loosely bound to a [(SiMe3)2(Me)2C4B8H8]2- cage. The carborane is best described as an 10-vertex arachno-(SiMe3)2C2B8H8 cage that subtends an electron-precise MeC=CMe fragment.
-H)3Mg(THF)3(SiMe3)2(Me)2C4B8H8 (XII), was also synthesized,in 81% yield, by the reaction of the metal with the (SiMe3)2(Me)2C4B8H8 precursor. Single-crystalX-ray diffraction studies showed the compound to be composed of an exo-polyhedral [Mg(THF)3]2+that is loosely bound to a [(SiMe3)2(Me)2C4B8H8]2- cage. The carborane is best described as an 10-vertex arachno-(SiMe3)2C2B8H8 cage that subtends an electron-precise MeC=CMe fragment.