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ABSTRACT: Two perfluoroaryl-substituted cyclobutadiene derivatives, 6 and 7, were prepared as air- and moisture-sensitive red solids by the photochemical isomerization of the corresponding tetrahedranes (4 and 5, respectively). Remarkably, the 9,10-dicyanoanthracene-sensitized photochemical reaction of 4 also proceeded, giving 6, and the mechanism of this reaction is also discussed. The first aryl-substituted cyclobutadienes were characterized by spectroscopic data as well as by X-ray crystallography for 6, showing a distorted rectangular structure with extremely long C-C single bonds.
Journal of the American Chemical Society 09/2011; 133(41):16436-9. · 9.91 Impact Factor
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ABSTRACT: The stable sulfur-substituted tetrahedrane derivatives 2-4 were synthesized by the reaction of tris(trimethylsilyl)tetrahedranyllithium 1 with diphenyl disulfide, bis(4-nitrophenyl) disulfide, and bis(2,4-dinitrophenyl) disulfide, respectively, and characterized by both NMR spectroscopy and X-ray crystallography. Phenylsulfonyltetrahedrane 5 was prepared by the reaction of 2 and m-chloroperbenzoic acid. The UV-vis absorption spectra of 2-4 suggested an interaction of the σ orbital of the tetrahedrane core and the lone-pair electrons on the sulfur atom, whereas no interaction for 5 was found. Thermal reactions of 2 and 5 are also reported; 2 underwent fragmentation into two acetylene molecules, whereas 5 gave the corresponding cyclobutadiene.
Journal of the American Chemical Society 08/2011; 133(30):11504-7. · 9.91 Impact Factor
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ABSTRACT: A new procedure for synthesizing tetrakis(trimethylsilyl)tetrahedrane from tetrakis(trimethylsilyl)cyclobutadiene is reported. Valence isomerization of cyclobutadiene to tetrahedrane induced by one-electron oxidation has been developed by the addition of tris(pentafluorophenyl)borane as an oxidant. This new method has great synthetic advantages for easy, quick, and high-yielding reaction to achieve gram-order-scale synthesis of tetrakis(trimethylsilyl)tetrahedrane. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:412–416, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20699
Heteroatom Chemistry 04/2011; 22(3‐4):412 - 416. · 1.24 Impact Factor
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ABSTRACT: A series of stable radicals centered on persilyl-substituted heavy Group 14 elements, (tBu(2)MeSi)(3)E(*) (E = Si, Ge, Sn), was studied by cyclic voltammetry in different solvents to determine their first oxidation and reduction potentials and to compare their ease of oxidation and reduction with known experimental and computed ionization energies (E(i)) and electron affinities (E(ea)), respectively. It has been observed that all of the first oxidation and reduction potentials for the three radicals studied are irreversible in o-dichlorobenzene (o-DCB), whereas the reduction waves are quasi-reversible in THF. A good correlation has been found between measured oxidation potentials and ionization energy values, but no correlation between reduction potentials and electron affinity values was found, probably due to kinetic and surface effects.
Chemistry 08/2009; 15(34):8480-4. · 5.93 Impact Factor
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ABSTRACT: The first stable aryl-substituted tetrahedrane derivatives 4-6 were synthesized by the reaction of tris(trimethylsilyl)tetrahedranyllithium with hexafluorobenzene or [(pentafluorophenyl)ethynyl]benzene in THF. Tetrahedranes having the fluoroaryl groups as electron-withdrawing substituents were found to be thermally stable up to 170 degrees C. X-ray analyses of 4 and 6 and UV-vis absorption spectra of 4-6 suggest sigma-pi conjugation between the strained tetrahedrane core and the benzene ring, which causes a considerable bathochromic shift.
Journal of the American Chemical Society 03/2009; 131(9):3172-3. · 9.91 Impact Factor
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ABSTRACT: A series of stable persilyl-substituted heavy group 14 element-centered radicals (tBu2MeSi)3E• (E = Si, Ge, Sn) was studied by UV-photoelectron spectroscopy in order to determine the values of the first ionization energies of the title species and to make a systematic comparison of their ease of oxidation.
06/2008;
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Berichte der deutschen chemischen Gesellschaft 03/2008; 2008(11):1752 - 1755. · 2.94 Impact Factor
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Annalen der Chemie und Pharmacie 02/2008; 2008(10):1715 - 1722. · 3.10 Impact Factor
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ABSTRACT: ((t)Bu(2)MeSi)(2)Sn=Sn(SiMe(t)Bu(2))(2) 1, prepared by the reaction of (t)Bu(2)MeSiNa with SnCl(2)-diox in THF and isolated as dark-green crystals, represents the first example of acyclic distannene with a Sn=Sn double bond that is stable both in the crystalline form and in solution. This was proved by the crystal and NMR spectral data of 1. Distannene 1 has these peculiar structural features: a shortest among all acyclic distannenes Sn=Sn double bond of 2.6683(10) A, a nearly planar geometry around both Sn atoms, and a highly twisted Sn=Sn double bond. The reactions of 1 toward carbon tetrachloride and phenylacetylene also correspond to the reactivity anticipated for the Sn=Sn double bond. The one-electron reduction of 1 with potassium produced the distannene anion radical, the heavy analogue of alkene ion radicals, for which the particular crystal structure and low-temperature EPR behavior are also discussed.
Journal of the American Chemical Society 10/2006; 128(35):11643-51. · 9.91 Impact Factor
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ABSTRACT: The reaction of a chlorophosphorane (9-Cl) with primary amines produced anti-apicophilic spirophosphoranes (5, O-equatorial phosphoranes), which violate the apicophilicity concept, having an apical carbon-equatorial oxygen configuration, along with the ordinarily expected O-apical stereoisomers (6) with the apical oxygen-equatorial carbon configuration. Although the amino group is electronegative in nature, the O-equatorial phosphoranes were found to be stable at room temperature and could still be converted to their more stable O-apical pseudorotamers (6) when they were heated in solution. X-ray analysis implied that this remarkable stability of the O-equatorial isomers could be attributed to the orbital interaction between the lone-pair electrons of the nitrogen atom (n(N)) and the antibonding sigma(P-O) orbital in the equatorial plane. A kinetic study of the isomerization of 5 to 6 and that between diastereomeric O-apical phosphoranes 13b-exo and 13b-endo revealed that 5b bearing an n-propylamino substituent at the central phosphorus atom was found to be less stable than the corresponding isomeric 6b by ca. 7.5 kcal mol(-1). This value was smaller than the difference in energy (11.9 kcal mol(-1)) between the O-equatorial (1b) and the O-apical n-butylphosphorane (2b) by 4.4 kcal mol(-1). This value of 4.4 kcal mol(-1) can be regarded as the stabilization energy induced by the n(N) --> sigma(P-O) interaction. The experimentally determined value was in excellent agreement with that derived from density functional theory (DFT) calculations at the B3PW91 level (4.0 kcal mol(-1)) between the nonsubstituted aminophosphoranes (5g is less stable than 6g by 10.1 kcal mol(-1)) and their P-methyl-substituted counterparts (1a is less stable than 2a by 14.1 kcal mol(-1)).
Inorganic Chemistry 10/2006; 45(18):7269-77. · 4.60 Impact Factor
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ABSTRACT: (tBu2MeSi)2SnSn(SiMetBu2)2 1, prepared by the reaction of tBu2MeSiNa with SnCl2-diox in THF and isolated as dark-green crystals, represents the first example of acyclic distannene with a SnSn double bond that is stable both in the crystalline form and in solution. This was proved by the crystal and NMR spectral data of 1. Distannene 1 has these peculiar structural features: a shortest among all acyclic distannenes SnSn double bond of 2.6683(10) Å, a nearly planar geometry around both Sn atoms, and a highly twisted SnSn double bond. The reactions of 1 toward carbon tetrachloride and phenylacetylene also correspond to the reactivity anticipated for the SnSn double bond. The one-electron reduction of 1 with potassium produced the distannene anion radical, the heavy analogue of alkene ion radicals, for which the particular crystal structure and low-temperature EPR behavior are also discussed.
08/2006;
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Annalen der Chemie und Pharmacie 11/2005; 2006(1):218 - 234. · 3.10 Impact Factor
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ABSTRACT: The one-electron reduction of tris(di-tert-butylmethylsilyl)aluminum and -gallium with alkali metals (Li, Na, K) results in the formation of the corresponding radical anions [(tBu2MeSi)3Al*-] (3) and [(tBu2MeSi)3Ga]*- (4), which were isolated in the form of the potassium salt as extremely air- and moisture-sensitive deep red crystals, representing the first isolable mononuclear radical anions of heavier group 13 elements. The molecular structures of both 3.[K+(2.2.2-cryptand)] and 4.[K+(2.2.2-cryptand)] were established by X-ray crystallography, which showed a nearly planar geometry around the radical centers. The EPR spectra of 3 and 4 showed strong characteristic signals with g-values of 2.005 for 3 and 2.015 for 4 with hyperfine coupling constants of a(27Al) = 6.2 mT for 3, a(69Ga) = 12.3 mT, and a(71Ga) = 15.7 mT for 4, corresponding to a planar geometry of the radical center.
Journal of the American Chemical Society 06/2005; 127(19):6954-5. · 9.91 Impact Factor
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ABSTRACT: Tetrakis(di-tert-butylmethylsilyl)distannene 1 was synthesized by the coupling reaction of tBu2MeSiNa with SnCl2-diox in THF and isolated as dark-green crystals. X-ray analysis of 1 showed the shortest Sn=Sn double bond (2.6683(10) A) among all acyclic distannenes, an almost planar geometry around the Sn atoms, and a highly twisted Sn=Sn double bond. The reaction of distannene 1 with CCl4 produced 1,2-dichlorodistannane 2, implying that 1 does not dissociate into stannylenes, both in the solid state and in solution. The one-electron reduction of 1 with potassium furnished the corresponding distannene anion radical 3, the stable ion radical of the heavy alkene analogues, which has been fully characterized by X-ray crystallography and ESR spectroscopy.
Journal of the American Chemical Society 10/2004; 126(38):11758-9. · 9.91 Impact Factor
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ABSTRACT: The one-electron reduction of the tris(di-tert-butylmethylsilyl)stannyl radical (tBu2MeSi)3Sn• was studied in a variety of solvents: polar, nonpolar, and aromatic. The structure of the resulting tris(di-tert-butylmethylsilyl)stannyl anion depends on the reaction conditions. Thus, the reduction of 3 with potassium in the presence of [2.2.2]cryptand resulted in the formation of the free anion 5, whose structure is very similar to that of the THF-solvated stannyllithium species 4. The reduction of 3 with lithium in heptane produced the dimeric structure 6, whereas the reduction in benzene gave 7 as an anion complexed with Li(η6-benzene). The 119Sn NMR spectrum of 7 at room temperature showed a quartet at −819.8 ppm due to the 119Sn−7Li coupling. This gives evidence for the existence of a covalent Sn−Li bond in solution, even at room temperature.
04/2004;
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ABSTRACT: The first stable stannyl radical (tBu2MeSi)3Sn* (1) has been synthesized by the reaction of tBu2MeSiNa with SnCl2-dioxane in diethyl ether. The X-ray crystal structure and electron paramagnetic resonance (EPR) data of this radical show that 1 has a planar geometry, being a pi-radical in both the solid and the liquid states. One-electron oxidation of 1 with Ph3C+.B(C6F5)4- in benzene quantitatively produced the corresponding cation (tBu2MeSi)3Sn+.B(C6F5)4- (2), representing the stable free stannylium ion that has been fully characterized by X-ray analysis and NMR data. Being free, 2 features a record downfield shifted resonance for stannylium ions: +2653 ppm.
Journal of the American Chemical Society 09/2003; 125(31):9250-1. · 9.91 Impact Factor
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Angewandte Chemie International Edition 04/2003; 42(10):1143-5. · 13.45 Impact Factor
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ABSTRACT: Pale-yellow crystals of the nonsolvated monomeric silyl- and germyllithiums, tris[di-tert-butyl(methyl)silyl]silyllithium 2a and tris[di-tert-butyl(methyl)silyl]germyllithium 2b, were obtained by one-electron reduction of the corresponding silyl and germyl radicals with lithium in hexane. The crystal structure analysis of both 2a and 2b showed almost planar geometry around the anionic centers, due to both intramolecular CH-Li agostic interactions and steric reasons. However, the free anions [(tBu2MeSi)3Si-][Li+(THF)4] 3a and [(tBu2MeSi)3Ge-][Li+(THF)n] (n = 3, 4) 3b no longer showed a planar geometry, because of the absence of the intramolecular CH-Li agostic interaction. A temperature-dependent 1H NMR study of 2a showed that the CH-Li interaction is weak.
Journal of the American Chemical Society 01/2003; 124(51):15160-1. · 9.91 Impact Factor
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ABSTRACT: The one-electron oxidation reaction of tris[di-tert-butyl(methyl)silyl]silyl and -germyl anions with dichlorogermylene-dioxane complex results in the formation of stable tris[di-tert-butyl(methyl)silyl]silyl and -germyl radicals 1 and 2, representing the first isolable radical species of heavier Group 14 elements lacking stabilization by conjugation with pi-bonds. The crystal structures of both silyl and germyl radicals 1 and 2 showed a completely planar geometry around the radical centers. The ESR spectra of 1 and 2 showed strong signals with characteristic satellites due to the coupling with the 29Si and 73Ge nuclei. The small values of the hyperfine coupling constants a(29Si) and a(73Ge) clearly indicate the pi-character of both radicals, corresponding to a planar geometry and sp2 hybridization of the radical centers. Both 1 and 2 easily undergo halogenation reactions with carbon tetrachloride, 1,2-dibromoethane, and benzyl bromide to form the corresponding halosilanes and halogermanes.
Journal of the American Chemical Society 09/2002; 124(33):9865-9. · 9.91 Impact Factor
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ABSTRACT: An anti-apicophilic phosphorane bearing an oxaphosphetane ring, in which the ring carbon is apical and the ring oxygen is equatorial (C-apical), has been prepared as a thermally less stable stereoisomer of a phosphorane with an ordinary equatorial carbon-apical oxygen array in the oxaphosphetane ring (O-apical). This novel C-apical phosphorane, which could be considered to be a model compound of the reactive intermediate in the Wittig reaction, was fully characterized by NMR and X-ray structural analysis. The compound was found to easily isomerize to its more stable O-apical isomer, especially in the presence of proton sources, and the latter O-apical compound was found to furnish olefin at elevated temperatures.
Journal of the American Chemical Society 08/2002; 124(26):7674-5. · 9.91 Impact Factor
