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Akira Sekiguchi

Bio: Akira Sekiguchi is an academic researcher from University of Tsukuba. The author has contributed to research in topics: Trimethylsilyl & Silylation. The author has an hindex of 52, co-authored 401 publications receiving 9929 citations. Previous affiliations of Akira Sekiguchi include Technion – Israel Institute of Technology & University of Wisconsin-Madison.


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Journal ArticleDOI
17 Sep 2004-Science
TL;DR: The reaction of 2,2,3,3-tetrabromo-1,1,4, 4,4-tetrakis[bis(trimethylsilyl)methyl]-1, 4-diisopropyltetrasilane with four equivalents of potassium graphite (KC8) in tetrahydrofuran produces 1,1-4,4-, which shows half the magnitude of the bond shortening of alkynes compared with that
Abstract: The reaction of 2,2,3,3-tetrabromo-1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasilane with four equivalents of potassium graphite (KC 8 ) in tetrahydrofuran produces 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyl-2-tetrasilyne, a stable compound with a silicon-silicon triple bond, which can be isolated as emerald green crystals stable up to 100°C in the absence of air. The SiSi triple-bond length (and its estimated standard deviation) is 2.0622(9) angstroms, which shows half the magnitude of the bond shortening of alkynes compared with that of alkenes. Unlike alkynes, the substituents at the SiSi group are not arranged in a linear fashion, but are trans-bent with a bond angle of 137.44(4)°.

467 citations

Book
30 Aug 2010
TL;DR: Theoretical studies of RR'R'E+Cations: Free or Coordinated? 1.1 Introduction. 2.2 Synthesis. 3.3 Structure. 4.4 Reactions and Synthetic Applications as discussed by the authors.
Abstract: Preface. Abbreviations. 1. Heavy Analogs of Carbenium Ions: Si-, Ge-, Sn- and Pb-Centered Cations. 1.1 Introduction. 1.2 Synthesis of RR'R"E+Cations (E = Si-Pb). 1.3 Reactions and Synthetic Applications of RRRE+ Cations16. 1.4 Theoretical Studies. 1.5 Early Studies of RR'R"E+ Cations: Free or Coordinated? 1.6 Stable RR'R"E+ Cations. 1.7 Summary and Outlook. 1.8 References. 2. Heavy Analogs of Organic Free Radicals: Si-, Ge-, Sn- and Pb-Centered Radicals. 2.1 Introduction. 2.2 Early Studies: Transient Species RR'R"E. 2.3 Persistent Radicals (Generation and Identification). 2.4 Stable Radicals. 2.5 Summary and Outlook. 2.6 References. 3. Heavy Analogs of Carbanions: Si-, Ge-, Sn- and Pb-Centered Anions. 3.1 Introduction. 3.2 Synthesis. 3.3 Structure. 3.4 Reactions and Synthetic Applications. 3.5 Recent Developments. 3.6 Summary and Outlook. 3.7 References. 4. Heavy Analogs of Carbenes: Silylenes, Germylenes, Stannylenes and Plumbylenes. 4.1 Introduction. 4.2 Generation. 4.3 Spectroscopic Identification. 4.4 Structure. 4.5 Reactions of Transient Species. 4.6 Stable/Persistent Silylenes, Germylenes, Stannylenes and Plumbylenes. 4.7 Summary and Outlook. 4.8 References. 5. Heavy Analogs of Alkenes, 1,3-Dienes, Allenes and Alkynes: Multiply Bonded Derivatives of Si, Ge, Sn and Pb. 5.1 Introduction. 5.2 Early Studies: Generation and Identification. 5.3 Stable Derivatives (Synthesis and Structure). 5.4 Summary and Outlook. 5.5 References. 6. Heavy Analogs of Aromatic Compounds. 6.1 Introduction. 6.2 Early Studies. 6.3 Stable Compounds (Synthesis and Structure). 6.4 Summary and Outlook. 6.5 References. Index.

207 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that the reaction proceeds via the interaction between the LUMO (πin*) of 1 and the HOMO of 2-butene, resulting in a formal [1 + 2] cycloaddition to give the silacyclopropyl−silylene intermediate, followed by its ring expansion to produce the final product.
Abstract: The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with cis- and trans-butenes produced cis- and trans-3,4-dimethyl-1,2-disilacyclobutenes 2a and 2b, respectively. The reactions proceeded in a stereospecific manner. Theoretical calculations on the reaction between 1 and 2-butenes show that the reaction proceeds via the interaction between the LUMO (πin*) of 1 and the HOMO of 2-butene, resulting in a formal [1 + 2] cycloaddition to give the silacyclopropyl−silylene intermediate, followed by its ring expansion to produce the final product. The reaction of 1 with phenylacetylene produced 1,2-disilabenzene derivative as a mixture of the two regioisomers, one of them being characterized by X-ray crystallography. The six-membered ring of 1,2-disilabenzene of 3a is almost planar with an Si−Si bond length of 2.2018(18) A and Si−C bond lengths of 1.804(4) and 1.799(5) A.

170 citations

Journal ArticleDOI
TL;DR: The current state of affairs in the chemistry of aromatic compounds of the heavier Group 14 elements, the latest experimental achievements, as well as future prospects in the field are discussed.
Abstract: The long story of aromatic compounds has extended over almost two centuries, since the discovery by Faraday of "bicarburet of hydrogen", or C 6 H 6 , now called benzene. Since then, the chemistry of aromatic compounds has been developed extensively; this is reflected in the synthesis of novel classes of aromatic derivatives including charged species, nonclassical (Mobius, three-dimensional, homo-, metalla-) aromatics, and fullerenes. The theory of aromaticity has also undergone a spectacular evolution since the first definition of aromaticity by Huckel; the classification of aromaticity now requires the consideration of versatile criteria: energetic, structural, magnetic, among others. In this Review, we discuss the current state of affairs in the chemistry of aromatic compounds of the heavier Group 14 elements, the latest experimental achievements, as well as future prospects in the field.

151 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

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Journal ArticleDOI

2,151 citations

Journal ArticleDOI
TL;DR: In this article, a couple-monomer methodology (CMM) is proposed for hyperbranched polymers, which is based on the in situ formation of ABn intermediates from specific monomer pairs.

1,896 citations

01 Feb 1995
TL;DR: In this paper, the unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio using DFT, MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set.
Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

1,652 citations

Journal ArticleDOI
TL;DR: The ETS-NOCV scheme offers a compact, qualitative, and quantitative picture of the chemical bond formation within one common theoretical framework and can be widely used for the description of different types of chemical bonds.
Abstract: In the present study we have introduced a new scheme for chemical bond analysis by combining the Extended Transition State (ETS) method [Theor. Chim. Acta 1977, 46, 1] with the Natural Orbitals for Chemical Valence (NOCV) theory [J. Phys. Chem. A 2008, 112, 1933; J. Mol. Model. 2007, 13, 347]. The ETS-NOCV charge and energy decomposition scheme based on the Kohn−Sham approach makes it not only possible to decompose the deformation density, Δρ, into the different components (such as σ, π, δ, etc.) of the chemical bond, but it also provides the corresponding energy contributions to the total bond energy. Thus, the ETS-NOCV scheme offers a compact, qualitative, and quantitative picture of the chemical bond formation within one common theoretical framework. Although, the ETS-NOCV approach contains a certain arbitrariness in the definition of the molecular subsystems that constitute the whole molecule, it can be widely used for the description of different types of chemical bonds. The applicability of the ETS-...

1,193 citations