in-Cyclophanes containing second-row elements poised above aromatic rings
摘要:
The silicon- and phosphorus-containing cyclophanes 2 and 3 were prepared by base-promoted condensation of tris(2-mercaptophenyl)silane and tris(2-mercaptophenyl)phosphine, respectively, with 1,3,5-tris(bromomethyl)benzene. The structures of both cyclophanes were determined by X-ray crystallography. In compound 2, the distance from the apical silicon to the center of the basal aromatic ring was 3.34 angstrom, and in 3 the corresponding phosphorus to ring distance was 2.90 angstrom. The H-1 NMR spectrum of 2 was characterized by a high-field Si-H resonance (delta-1.04, 5 ppm upfield from the corresponding resonance in an acyclic model), and the IR spectrum showed a high-frequency Si-H stretching band (2457 cm-1, 280 cm-1 above the acyclic model); both features result from the proximity of the in-hydrosilane to the aromatic ring. For cyclophane 3, the C-13 NMR spectrum exhibited ''through-space'' spin-spin coupling of the phosphorus atom with the carbons of the basal aromatic ring (J(PC)(methine) = 7.5 Hz and J(PC)(quaternary) = 3.5 Hz) and in the P-31 NMR spectrum the phosphorus resonance was 32 ppm downfield from that of an acyclic model, both features suggesting an unusual electronic interaction of the phosphine with the base. Due to a strong preference for an in geometry (pyramidalization of the phosphine toward the basal ring) and the consequent steric shielding, the phosphine of 3 was quite unreactive: It was not protonated by anhydrous HBr, and even when 3 was heated in refluxing hydrogen peroxide and acetic acid, the corresponding trisulfone was obtained without formation of the phosphine oxide.
in-Cyclophanes containing second-row elements poised above aromatic rings
摘要:
The silicon- and phosphorus-containing cyclophanes 2 and 3 were prepared by base-promoted condensation of tris(2-mercaptophenyl)silane and tris(2-mercaptophenyl)phosphine, respectively, with 1,3,5-tris(bromomethyl)benzene. The structures of both cyclophanes were determined by X-ray crystallography. In compound 2, the distance from the apical silicon to the center of the basal aromatic ring was 3.34 angstrom, and in 3 the corresponding phosphorus to ring distance was 2.90 angstrom. The H-1 NMR spectrum of 2 was characterized by a high-field Si-H resonance (delta-1.04, 5 ppm upfield from the corresponding resonance in an acyclic model), and the IR spectrum showed a high-frequency Si-H stretching band (2457 cm-1, 280 cm-1 above the acyclic model); both features result from the proximity of the in-hydrosilane to the aromatic ring. For cyclophane 3, the C-13 NMR spectrum exhibited ''through-space'' spin-spin coupling of the phosphorus atom with the carbons of the basal aromatic ring (J(PC)(methine) = 7.5 Hz and J(PC)(quaternary) = 3.5 Hz) and in the P-31 NMR spectrum the phosphorus resonance was 32 ppm downfield from that of an acyclic model, both features suggesting an unusual electronic interaction of the phosphine with the base. Due to a strong preference for an in geometry (pyramidalization of the phosphine toward the basal ring) and the consequent steric shielding, the phosphine of 3 was quite unreactive: It was not protonated by anhydrous HBr, and even when 3 was heated in refluxing hydrogen peroxide and acetic acid, the corresponding trisulfone was obtained without formation of the phosphine oxide.
Sterically congested macrobicycles with heteroatomic bridgehead functionality
作者:Jie Zong、Joel T. Mague、E. Celeste Welch、Isaac M.K. Eckert、Robert A. Pascal
DOI:10.1016/j.tet.2013.10.018
日期:2013.12
two-atom bridges has been synthesized. The bridgeheadfunctional groups include phosphines in combination with amines, hydrosilanes, methylsilanes, and ethoxysilanes. Computational studies accurately predicted that when the bridgehead substituents are small (lone pairs or protons), an in,in bridgehead stereochemistry is strongly favored, but larger bridgehead substituents favor the formations of in,out
合成了一系列由两个三原子桥连接的三芳基帽组成的环环烷。桥头官能团包括与胺,氢硅烷,甲基硅烷和乙氧基硅烷结合的膦。计算研究准确地预测,当桥头取代基较小时(孤对或质子),强烈建议在桥头立体化学中使用in ,in,但较大的桥头取代基则有利于in in ,out立体异构体的形成。讨论了这些化合物的X射线结构,光谱和反应性,以及其中一种环烷拆分为纯对映体的方法。
Experimental and computational studies of molecules with close, non-bonded hydrogen–hydrogen contacts: common computational methods grossly overestimate some ‘through-space’ NMR scalar coupling constants
作者:Robert A. Pascal、Jie Zong、Kelly J. Dougherty、Xin Geng、Joel T. Mague
DOI:10.1016/j.tet.2014.08.010
日期:2014.10
The NMR spin spin scalar coupling constants (J(HH)'s) of closely contacting, but non-bonded hydrogen atoms in a series of highly strained molecules (including a new in,in-cyclophane made specifically for this study) have been examined both experimentally and computationally. The experimental J(HH)'s are invariably quite small (0.1-0.6 Hz), but common DFT methods with modest basis sets nearly always overestimate these values, by factors of 10-30, and even with quite large basis sets (up to cc-pVQZ) the J(HH)'s of two of the molecules are overestimated by a factor of 10 or more. Possible reasons for these discrepancies are discussed. (C) 2014 Elsevier Ltd. All rights reserved.
Exceptional Steric Congestion in an <i>in</i>,<i>in</i>-Bis(hydrosilane)
作者:Jie Zong、Joel T. Mague、Robert A. Pascal
DOI:10.1021/ja407398w
日期:2013.9.11
The synthesis and characterization of a macrobicyclic in,in-bis(hydrosilane) is described. A combination of crystallographic and computational data indicate that the central hydrogen-hydrogen nonbonded contact distance is the shortest for any crystallographically characterized compound.
LESPERANCE, ROBERT P.;WEST, ANTHONY P. (JR);VAN, ENGEN DONNA;PASCAL, ROBE+, J. AMER. CHEM. SOC., 113,(1991) N, C. 2672-2676
作者:LESPERANCE, ROBERT P.、WEST, ANTHONY P. (JR)、VAN, ENGEN DONNA、PASCAL, ROBE+
DOI:——
日期:——
in-Cyclophanes containing second-row elements poised above aromatic rings
作者:Robert P. L'Esperance、Anthony P. West、Donna Van Engen、Robert A. Pascal
DOI:10.1021/ja00007a047
日期:1991.3
The silicon- and phosphorus-containing cyclophanes 2 and 3 were prepared by base-promoted condensation of tris(2-mercaptophenyl)silane and tris(2-mercaptophenyl)phosphine, respectively, with 1,3,5-tris(bromomethyl)benzene. The structures of both cyclophanes were determined by X-ray crystallography. In compound 2, the distance from the apical silicon to the center of the basal aromatic ring was 3.34 angstrom, and in 3 the corresponding phosphorus to ring distance was 2.90 angstrom. The H-1 NMR spectrum of 2 was characterized by a high-field Si-H resonance (delta-1.04, 5 ppm upfield from the corresponding resonance in an acyclic model), and the IR spectrum showed a high-frequency Si-H stretching band (2457 cm-1, 280 cm-1 above the acyclic model); both features result from the proximity of the in-hydrosilane to the aromatic ring. For cyclophane 3, the C-13 NMR spectrum exhibited ''through-space'' spin-spin coupling of the phosphorus atom with the carbons of the basal aromatic ring (J(PC)(methine) = 7.5 Hz and J(PC)(quaternary) = 3.5 Hz) and in the P-31 NMR spectrum the phosphorus resonance was 32 ppm downfield from that of an acyclic model, both features suggesting an unusual electronic interaction of the phosphine with the base. Due to a strong preference for an in geometry (pyramidalization of the phosphine toward the basal ring) and the consequent steric shielding, the phosphine of 3 was quite unreactive: It was not protonated by anhydrous HBr, and even when 3 was heated in refluxing hydrogen peroxide and acetic acid, the corresponding trisulfone was obtained without formation of the phosphine oxide.