Akira Sekiguchi

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Name: Akira Sekiguchi

Organization: University of Tsukuba , Japan

Department: Department of Chemistry

Title: Professor(PhD)

TOPICS

Organic Chemistry

Diels Alder Reaction allene

Chemicals
References

Bis(stibahousene)

Co-reporter:Vladimir Ya. Lee, Kei Ota, Yuki Ito, Olga A. Gapurenko, Akira Sekiguchi, Ruslan M. Minyaev, Vladimir I. Minkin, and Heinz Gornitzka

Journal of the American Chemical Society October 4, 2017 Volume 139(Issue 39) pp:13897-13897

Publication Date(Web):September 11, 2017

DOI:10.1021/jacs.7b07712

Strained hydrocarbons constitute one of the most prominent classes of organic compounds. Among them, bicyclo[2.1.0]pentene (“housene”) derivatives represent a highly challenging and very attractive class. Although organic housenes have been known for more than five decades, there are still very few of them containing heavier main group elements. In this paper, we report on the two housene-type structures, novel monomeric stibahousene and dimeric bis(stibahousene). The bonding natures of both compounds were approached from both experimental and computational directions to reveal their peculiar structural features.

Hybrid group 15(E15)–group 14(E14) element cationic pyramidal structures E15[E144(SiR3)4]+: A DFT study

Co-reporter:Olga A. Gapurenko, Vladimir Ya. Lee, Ruslan M. Minyaev, Vladimir I. Minkin, Akira Sekiguchi

Tetrahedron Letters 2017 Volume 58, Issue 21(Issue 21) pp:

Publication Date(Web):24 May 2017

DOI:10.1016/j.tetlet.2017.04.040

•Cationic pyramidanes of the group 14/15 elements were computationally studied.•Our computational studies predicted stability for these hybrid pyramidanes.•The promising synthetic candidates for pyramidal systems were suggested.Hybrid cationic pyramidanes {E15[E144R4]}+ (E15 = P–Bi; E14 = C–Ge, R = H, SiMe3) have been studied by the DFT calculations, and their structures, electronic properties and bonding nature are discussed. Square-pyramidal geometry in the real neutral compounds {E15[E144(SiMe3)4]}+[AlCl4]− is preserved.Download high-res image (86KB)Download full-size image

Pyramidanes: The Covalent Form of the Ionic Compounds

Co-reporter:Vladimir Ya. Lee, Olga A. Gapurenko, Yuki Ito, Takahiko Meguro, Haruka Sugasawa, Akira Sekiguchi, Ruslan M. Minyaev, Vladimir I. Minkin, Rolfe H. Herber, and Heinz Gornitzka

Organometallics 2016 Volume 35(Issue 3) pp:346-356

Publication Date(Web):January 20, 2016

DOI:10.1021/acs.organomet.5b00924

Pyramidane and its derivatives are among the most desirable synthetic chemistry targets, whose appealing square-pyramidal design, fascinating nonclassical structure, and unusual bonding features have attracted the permanently growing interest of organic chemists for decades. Although they have been comprehensively approached on theoretical grounds, no member of the pyramidane family was experimentally realized until very recently, thus remaining one of the biggest synthetic challenges for experimental pursuits. In this paper, we report on a series of stable hybrid pyramidanes of group 14 elements, featuring germanium, tin, or lead at the apex of the square pyramid, capping the four-membered-ring base made of carbon, silicon, or germanium atoms. On the basis of the experimental results (X-ray diffraction and NMR and Mössbauer spectroscopy) and computational studies at the B3LYP/Def2TZVP level of theory (MO, NBO, NRT, and AIM), an extraordinarily high degree of ionicity of the pyramidal apex-to-base bonds was attributed to the overall structure of these nonclassical covalent compounds.

Observation of a Thermally Accessible Triplet State Resulting from Rotation around a Main-Group Bond

Co-reporter:Arseni Kostenko;Dr. Boris Tumanskii;Dr. Miriam Karni; Shigeyoshi Inoue; Masaaki Ichinohe; Akira Sekiguchi; Yitzhak Apeloig

Angewandte Chemie International Edition 2015 Volume 54( Issue 41) pp:12144-12148

Publication Date(Web):

DOI:10.1002/anie.201506291

Abstract

We report the first direct spectroscopic observation by electron paramagnetic resonance (EPR) spectroscopy of a triplet diradical that is formed in a thermally induced rotation around a main-group π bond, that is, the SiSi double bond of tetrakis(di-tert-butylmethylsilyl)disilene (1). The highly twisted ground-state geometry of singlet 1 allows access to the perpendicular triplet diradical 2 at moderate temperatures of 350–410 K. DFT-calculated zero-field splitting (ZFS) parameters of 2 accurately reproduce the experimentally observed half-field transition. Experiment and theory suggest a thermal equilibrium between 1 and 2 with a very low singlet–triplet energy gap of only 7.3 kcal mol⁻¹.

Observation of a Thermally Accessible Triplet State Resulting from Rotation around a Main-Group Bond

Co-reporter:Arseni Kostenko;Dr. Boris Tumanskii;Dr. Miriam Karni; Shigeyoshi Inoue; Masaaki Ichinohe; Akira Sekiguchi; Yitzhak Apeloig

Angewandte Chemie 2015 Volume 127( Issue 41) pp:12312-12316

Publication Date(Web):

DOI:10.1002/ange.201506291

Abstract

Stibasilene Sb═Si and Its Lighter Homologues: A Comparative Study

Co-reporter:Vladimir Ya. Lee ; Shinji Aoki ; Manami Kawai ; Takahiko Meguro

Journal of the American Chemical Society 2014 Volume 136(Issue 17) pp:6243-6246

Publication Date(Web):April 17, 2014

DOI:10.1021/ja5026084

The multiply bonded derivatives of the heavier main group elements are among the most challenging targets for synthetic pursuits. Those of them featuring a double bond between the silicon and group 15 element are represented mostly by the silaimines —N═Si< and phosphasilenes —P═Si< with a very few examples of arsasilenes —As═Si<. In this contribution, we report on the synthesis and structural elucidation of the first stable stibasilene and novel phosphasilene and arsasilene derivatives, featuring an identical substitution pattern. A systematic comparison within the series phosphasilene–arsasilene–stibasilene is made on the basis of their experimental and computational studies.

Tetrakis(di-tert-butylmethylsilyl)digermene: Synthesis, Structure, Electrochemical Properties, and Reactivity

Co-reporter:Vladimir Ya Lee;Kiera McNiece;Yuki Ito;Natalie Geinik;James Y. Becker

Heteroatom Chemistry 2014 Volume 25( Issue 5) pp:313-319

Publication Date(Web):

DOI:10.1002/hc.21165

ABSTRACT

The tetrasilyl-substituted digermene (^tBu₂MeSi)₂GeGe(SiMe^tBu₂)₂ 1 was prepared by the reduction of the readily available 1,1-dichlorogermane (^tBu₂MeSi)₂GeCl₂ with potassium graphite. Compound 1 is a rather unusual example of a digermene featuring planar geometry at the doubly bonded germanium atoms, on the one hand, and an extraordinarily twisted GeGe bond, on the other hand, caused by the electronic and steric factors of the bulky σ-donating silyl substituents. Although it maintains the structural integrity of its double bond in solution, 1 revealed reactivity that is not characteristic of the >GeGe< bond but is typical for germylenes >Ge: upon reaction with nucleophilic reagents (isocyanide, orthoquinone). Unlike common alkenes, 1 affords stable cation and anion radicals generated by cyclic voltammetry.

Isolable Aryl-Substituted Silyl Radicals: Synthesis, Characterization, and Reactivity

Co-reporter:Kanako Taira;Dr. Masaaki Ichinohe ; Akira Sekiguchi

Chemistry - A European Journal 2014 Volume 20( Issue 30) pp:9342-9348

Publication Date(Web):

DOI:10.1002/chem.201402482

Abstract

Isolable aryl-substituted silyl radicals (tBu₂MeSi)₂(Ar)Si^. (Ar=C₆H₅, 4-tBuC₆H₄, 4-PhC₆H₄, 3,5-tBu₂C₆H₃) were synthesized by the reaction of the corresponding iodosilane with an equimolar amount of potassium graphite (KC₈) in tetrahydrofuran (THF). The crystal structure of 3,5-tBu₂C₆H₃ derivative, which was determined by X-ray crystallography, showed a planar geometry around the Si atom for the radical center. EPR studies of all four radicals revealed the lack of the delocalization of the unpaired electron over the aromatic ring. Reactivity and spectroscopic studies of the less-hindered phenyl-substituted silyl radical showed that it exists as an equilibrium mixture of the radical and its silene-type dimer in solution.

Toward a Silicon Version of Metathesis: From Schrock-Type Titanium Silylidenes to Silatitanacyclobutenes

Co-reporter:Vladimir Ya. Lee ; Shinji Aoki ; Taka Yokoyama ; Satoru Horiguchi ; Akira Sekiguchi ; Heinz Gornitzka ; Jing-Dong Guo ;Shigeru Nagase

Journal of the American Chemical Society 2013 Volume 135(Issue 8) pp:2987-2990

Publication Date(Web):February 13, 2013

DOI:10.1021/ja401072j

Olefin metathesis is one of the most important industrial processes for the production of alkenes. In contrast, silicon versions of metathesis are unknown given the lack of available silylene transition-metal complexes suitable for [2 + 2] cycloaddition with unsaturated substrates. Here, we report the synthesis of 18-electron titanium silylene complexes featuring different Lewis base ligands and classified on the basis of structural, computational, and reactivity studies as Schrock-type silylene complexes. Because of the presence of loosely bound Lewis base ligands, such silylene complexes readily undergo reaction with simple unsaturated hydrocarbons, such as alkynes, forming the corresponding [2 + 2] cycloaddition products.

Spirobis(pentagerma[1.1.1]propellane): A Stable Tetraradicaloid

Co-reporter:Yuki Ito ; Vladimir Ya. Lee ; Heinz Gornitzka ; Catharina Goedecke ; Gernot Frenking

Journal of the American Chemical Society 2013 Volume 135(Issue 18) pp:6770-6773

Publication Date(Web):April 17, 2013

DOI:10.1021/ja401650q

In this contribution, we report a spirobis(pentagerma[1.1.1]propellane) derivative as a novel type of molecular architecture in cluster chemistry that features two spiro-fused [1.1.1]propellane units and represents a stable tetraradicaloid species. The crucial issue of the nature of the interaction between the germanium bridgeheads was probed computationally, revealing weak bonding interactions between the formally unpaired electrons.

Pyramidanes

Co-reporter:Vladimir Ya. Lee ; Yuki Ito ; Akira Sekiguchi ; Heinz Gornitzka ; Olga A. Gapurenko ; Vladimir I. Minkin ;Ruslan M. Minyaev

Journal of the American Chemical Society 2013 Volume 135(Issue 24) pp:8794-8797

Publication Date(Web):May 29, 2013

DOI:10.1021/ja403173e

Pyramidane is an elusive but highly desirable target for synthetic chemists that has attracted a great deal of attention because of its nonclassical structure and unusual bonding features. Although well studied on theoretical grounds, neither the parent all-carbon pyramidane nor its derivatives containing heavier group 14 elements have ever been isolated and characterized. In this Communication, we report on the synthesis and structural elucidation of the first stable representatives of this class of highly strained polyhedral compounds: germa- and stannapyramidanes Ge[C4(SiMe3)4] and Sn[C4(SiMe3)4]. The peculiar structural and bonding features of these compounds are verified by combined experimental and computational analyses, showing these derivatives to be nonclassical neutral compounds with a very large contribution of ionic character.

UV-Photoelectron Spectroscopy of a Tetrakis(trimethylsilyl)tetrahedrane and Its Pentafluorophenyl Derivative

Co-reporter:Dr. Anna Chrostowska; Alain Dargelos;Patrick Baylère; Alain Graciaa;Yusuke Inagaki;Dr. Masaaki Nakamoto;Dr. Vladimir Ya. Lee;Dr. Akira Sekiguchi

ChemPlusChem 2013 Volume 78( Issue 5) pp:398-401

Publication Date(Web):

DOI:10.1002/cplu.201300044

Carbonylation of Cyclotrisilenes

Co-reporter:Dr. Michael J. Cowley;Yu Ohmori;Dr. Volker Huch;Dr. Masaaki Ichinohe;Dr. Akira Sekiguchi;Dr. David Scheschkewitz

Angewandte Chemie International Edition 2013 Volume 52( Issue 50) pp:13247-13250

Publication Date(Web):

DOI:10.1002/anie.201307450

Carbonylierung von Cyclotrisilenen

Co-reporter:Dr. Michael J. Cowley;Yu Ohmori;Dr. Volker Huch;Dr. Masaaki Ichinohe;Dr. Akira Sekiguchi;Dr. David Scheschkewitz

Angewandte Chemie 2013 Volume 125( Issue 50) pp:13489-13492

Publication Date(Web):

DOI:10.1002/ange.201307450

Functionalized Cyclic Disilenes via Ring Expansion of Cyclotrisilenes with Isocyanides

Co-reporter:Yu Ohmori, Masaaki Ichinohe, Akira Sekiguchi, Michael J. Cowley, Volker Huch, and David Scheschkewitz

Organometallics 2013 Volume 32(Issue 6) pp:1591-1594

Publication Date(Web):February 22, 2013

DOI:10.1021/om400054u

The reaction of cyclotrisilenes 1 with 1 equiv of alkyl and aryl isocyanides at 25 °C affords the four-membered trisilacyclobutenes 2 with an exocyclic imine functionality as the major products of formal insertion into one of the Si–Si single bonds of 1. Minor quantities of the iminotrisilabicyclo[1.1.0]butanes 3 are obtained as side products, formally resulting from [1 + 2] cycloaddition of the isocyanides to the Si–Si double bond of 1. The bicyclo[1.1.0]butanes 3 become dominant at lower temperatures and may react with an additional 1 equiv of isonitriles to give the diiminotrisilabicyclo[1.1.1]pentanes 4.

A New Disilene with π-Accepting Groups from the Reaction of Disilyne RSi≡SiR (R = SiiPr[CH(SiMe3)2]) with Isocyanides

Co-reporter:Katsuhiko Takeuchi ; Masaaki Ichinohe

Journal of the American Chemical Society 2012 Volume 134(Issue 6) pp:2954-2957

Publication Date(Web):January 26, 2012

DOI:10.1021/ja212065a

The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne (1) with tert-butylisocyanide or tert-octylisocyanide produced the corresponding disilyne–isocyanide adducts [RSiSiR(CNR′)2] (R = SiiPr[CH(SiMe3)2]2, R′ = tBu (2a) or CMe2CH2tBu (2b)), which are stable below −30 °C and were characterized by spectroscopic data and, in the case of 2a, X-ray crystallography. Upon warming to room temperature, 2 underwent thermal decomposition to produce 1,2-dicyanodisilene R(NC)Si═Si(CN)R (3) and 1,2-dicyanodisilane R(NC)HSiSiH(CN)R (4) via C–N bond cleavage and elimination of an alkane and an alkene. The 1,2-dicyanodisilene derivative 3 was characterized by X-ray crystallography.

An Isolable NHC-Stabilized Silylene Radical Cation: Synthesis and Structural Characterization

Co-reporter:Hiroaki Tanaka ; Masaaki Ichinohe

Journal of the American Chemical Society 2012 Volume 134(Issue 12) pp:5540-5543

Publication Date(Web):March 15, 2012

DOI:10.1021/ja301180v

The silyl-substituted silylene–NHC complex bis(tri-tert-butylsilyl)silylene–(1,3,4,5-tetramethylimidazol-2-ylidene) [(tBu3Si)2Si:←NHCMe, 2] was synthesized and isolated as air- and moisture-sensitive orange crystals by reductive debromination of the dibromosilane (tBu3Si)2SiBr2 (1) with 2.0 equiv of KC8 in the presence of NHCMe. In addition, the silylene–NHC complex 2 cleanly underwent one-electron oxidation with 1.0 equiv of Ph3C+·Ar4B– (Ar4B– = tetrakis[4-(tert-butyldimethylsilyl)-2,3,5,6-tetrafluorophenyl]borate) in benzene to afford the NHC-stabilized silylene radical cation [(tBu3Si)2Si←NHCMe]•+·Ar4B– (3). The radical cation 3 was isolated as air- and moisture-sensitive yellow crystals and structurally characterized by X-ray crystallography and electron paramagnetic resonance spectroscopy, which showed that 3 has a planar structure with a π-radical nature.

Sulfur-Substituted Tetrahedranes

Co-reporter:Tatsumi Ochiai ; Masaaki Nakamoto ; Yusuke Inagaki

Journal of the American Chemical Society 2011 Volume 133(Issue 30) pp:11504-11507

Publication Date(Web):July 5, 2011

DOI:10.1021/ja205361a

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.

Photoisomerization of Perfluoroaryltetrahedranes to Perfluoroarylcyclobutadienes

Co-reporter:Yusuke Inagaki ; Masaaki Nakamoto

Journal of the American Chemical Society 2011 Volume 133(Issue 41) pp:16436-16439

Publication Date(Web):September 16, 2011

DOI:10.1021/ja208354x

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.

[[(Me3Si)2CH]2iPrSi(NHC)Si═Si(Me)SiiPr[CH(SiMe3)2]2]+: A Molecule with Disilenyl Cation Character

Co-reporter:Torahiko Yamaguchi ; Matthew Asay

Journal of the American Chemical Society 2011 Volume 134(Issue 2) pp:886-889

Publication Date(Web):December 21, 2011

DOI:10.1021/ja210669n

Reaction of the disilyne–NHC complex 1 [RLSi═SiR: (R = SiiPr[CH(SiMe3)2]2, L = NHC)] with MeOTf gave the cation 2 [RLSi═SiRMe]+, which is the first example of a base-stabilized heavy group 14 element analogue with vinyl cation character. Cation 2 has been fully characterized by multinuclear NMR spectroscopy and X-ray diffraction analysis. The molecular structure indicates that there are significant contributions from the NHC-stabilized cationic resonance structure 2A, the disilene-like structure 2B, and even some contribution from the silylene-like structure 2C.

Access to a Stable Si2N2 Four-Membered Ring with Non-Kekulé Singlet Biradical Character from a Disilyne

Co-reporter:Katsuhiko Takeuchi ; Masaaki Ichinohe

Journal of the American Chemical Society 2011 Volume 133(Issue 32) pp:12478-12481

Publication Date(Web):July 21, 2011

DOI:10.1021/ja2059846

The reactions of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with an equivalent amount of trans- and cis-3,3′,5,5′-tetramethylazobenzenes produced a Si2N2 four-membered ring biradicaloid [RSi(μ-NAr)2SiR] 2 (R = SiiPr[CH(SiMe3)2]2, Ar = 3,5-Me2C6H3), which was isolated as air- and moisture-sensitive dark purple crystals. Compound 2 displays no EPR signal, and the molecular structure of 2 was characterized by NMR spectroscopy and X-ray crystallography, revealing that 2 has a planar centrosymmetric Si2N2 four-membered ring. The Si1–Si1′ distance is 2.63380(9) Å, and there is no bond interaction between the Si1 and Si1′ atoms of 2. The reactions of 2 with methanol and carbon tetrachloride show that 2 has both closed-shell and radical-type reactivity.

Unusual Reactivity of a Disilyne with 4-Dimethylaminopyridine: Formation of an Intramolecularly N-Coordinated Silylene and Its Isomerization to a Zwitterionic Silyl Anion

Co-reporter:Torahiko Yamaguchi

Journal of the American Chemical Society 2011 Volume 133(Issue 19) pp:7352-7354

Publication Date(Web):April 26, 2011

DOI:10.1021/ja202605x

Reaction of isolable 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne (1) with an equiv amount of 4-dimethylaminopyridine unexpectedly produced the intramolecularly N-coordinated silylene 2 as the primary product. However, 2 was not thermally stable at room temperature in solution and slowly isomerized to silyl anion 3 with a zwitterionic structure via 1,2-hydrogen migration followed by Si–N bond formation.

From Tetragermacyclobutene to Tetragermacyclobutadiene Dianion to Tetragermacyclobutadiene Transition Metal Complexes

Co-reporter:Vladimir Ya. Lee ; Yuki Ito ; Hiroyuki Yasuda ; Kazunori Takanashi

Journal of the American Chemical Society 2011 Volume 133(Issue 13) pp:5103-5108

Publication Date(Web):March 11, 2011

DOI:10.1021/ja111596g

The reaction of 3,4-dichlorotetragermetene derivative 2 with Na2[Fe(CO)4] in THF produced a (tetragermacyclobutadiene)tricarbonyliron complex, [{η4-(tBu2MeSi)4Ge4}]Fe(CO)34, which has a slightly folded Ge4 ring perhaptocoordinated to the Fe center. Structural and spectral characteristics of 4 show a remarkable π-donating ability of the tetragermacyclobutadiene ligand toward the transition metal, surpassing that of tetrasilacyclobutadiene and cyclobutadiene ligands. Reduction of 2 with KC8 resulted in exclusive formation of the dipotassium salt of the tetragermacyclobutadiene dianion derivative 32−·[K+(thf)2]2, representing a rare example of a 6π-electron compound that, on the basis of its structural and magnetic properties, was recognized as a nonaromatic species. Reaction of 32−·[K+(thf)2]2 with CpCoI2(PPh3) produced a (cyclopentadienyl)(tetragermacyclobutadiene)cobalt complex, [{η4-(tBu2MeSi)4Ge4}]CoCp 7, as the first example of a sandwich compound featuring an all-germanium-containing cyclic polyene ligand.

A blue digermene (t-Bu2MeSi)2GeGe(SiMet-Bu2)2

Co-reporter:Vladimir Ya. Lee, Kiera McNeice, Yuki Ito and Akira Sekiguchi

Chemical Communications 2011 vol. 47(Issue 11) pp:3272-3274

Publication Date(Web):01 Feb 2011

DOI:10.1039/C0CC05415A

A novel tetrakis(trialkylsilyl)digermene, featuring rather unusual structural and chemical properties, was synthesized by a straightforward synthetic protocol: reduction of the corresponding dichlorobis(trialkylsilyl)germane precursor with potassium graphite.

Novel Organometallic Reagents: Geminal Dianionic Derivatives of the Heavy Group 14 Elements

Co-reporter:Vladimir Ya. Lee and Akira Sekiguchi

Inorganic Chemistry 2011 Volume 50(Issue 24) pp:12303-12314

Publication Date(Web):June 1, 2011

DOI:10.1021/ic2006106

This Forum review describes the most recent achievements in the novel prospective field of highly reactive main-group organometallics, namely, geminal dianionic derivatives of the heavy group 14 elements (Si, Ge, Sn). A brief historical introduction to the topic is followed by discussion of the current state of affairs in the field of stable derivatives and prospects for future efforts, highlighting our own synthetic approach and recent results. The most important experimental contributions, including synthesis of 1,1-dilithiosilane, -germane, and -stannane derivatives; dilithio(halo)silanes (lithiosilylenoids); metallole 1,1-dianions; and heavy analogues of the cyclobutadiene dianion derivatives, are presented, along with a discussion of the synthetic applications of the above-mentioned organometallic compounds.

Cyclobutadiene to tetrahedrane: Valence isomerization induced by one-electron oxidation

Co-reporter:Masaaki Nakamoto;Yusuke Inagaki;Tatsumi Ochiai;Masanobu Tanaka

Heteroatom Chemistry 2011 Volume 22( Issue 3-4) pp:412-416

Publication Date(Web):

DOI:10.1002/hc.20699

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

Silicon version of enamines: Amino-substituted disilenes by the reactions of the disilyne RSiSiR (R = SiiPr[CH(SiMe3)2]2) with amines

Co-reporter:Katsuhiko Takeuchi, Masao Ikoshi, Masaaki Ichinohe, Akira Sekiguchi

Journal of Organometallic Chemistry 2011 696(6) pp: 1156-1162

Publication Date(Web):

DOI:10.1016/j.jorganchem.2010.07.008

Hydroboration of Disilyne RSi≡SiR (R = SiiPr[CH(SiMe3)2]2), Giving Boryl-Substituted Disilenes

Co-reporter:Katsuhiko Takeuchi, Masaaki Ichinohe, and Akira Sekiguchi

Organometallics 2011 Volume 30(Issue 7) pp:2044-2050

Publication Date(Web):March 15, 2011

DOI:10.1021/om200106h

The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne (1) with hydroboranes afforded boryl-substituted disilenes R(R′2B)Si═SiHR 3a and 3b (R = SiiPr[CH(SiMe3)2]2, R′2B = 9-borabicyclo[3.3.1]nonan-9-yl (3a), catecholboryl (3b)). Spectroscopic and X-ray crystallographic analyses of 3a and 3b showed that 3a has a nearly coplanar arrangement of the Si═Si double bond and the boryl group, allowing π-conjugation between them, whereas 3b, with a markedly twisted arrangement, exhibits no such conjugation. Theoretical calculations suggest that π-conjugation between the π-orbital of the Si═Si double bond and the vacant 2p-orbital on the boron atom is markedly influenced by the dihedral angle between the Si═Si double-bond plane and boryl group plane.

Synthesis and Striking Reactivity of an Isolable Tetrasilyl-Substituted Trisilaallene

Co-reporter:Hiroaki Tanaka, Shigeyoshi Inoue, Masaaki Ichinohe, Matthias Driess, and Akira Sekiguchi

Organometallics 2011 Volume 30(Issue 13) pp:3475-3478

Publication Date(Web):June 14, 2011

DOI:10.1021/om200405e

The first silyl-substituted Si3-allene, namely 1,1,3,3-tetrakis(di-tert-butylmethylsilyl)trisilaallene (4), was prepared as an air- and moisture-sensitive red solid by the reaction of the dilithiosilane (tBu2MeSi)2SiLi2 with the dichlorosilylene–NHC complex :SiCl2←NHC (NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) in benzene at room temperature. Remarkably, the reaction of 4 with methanol proceeds regioselectively to form only the 3,3-dimethoxypentasilane derivative 5, in contrast to the case for a previously reported trisilaallene. In addition, 4 undergoes unprecedented thermal isomerization to tetrakis(di-tert-butylmethylsilyl)cyclotrisilene (7).

Making a Cyclotrigermene from a Digermene

Co-reporter:Kiera McNeice, Vladimir Ya. Lee, and Akira Sekiguchi

Organometallics 2011 Volume 30(Issue 17) pp:4796-4797

Publication Date(Web):August 8, 2011

DOI:10.1021/om200619v

A straightforward method for the preparation of the cyclotrigermene cyclo-[(R3Si)4Ge3] 2 (R = SiMetBu2), based on the thermolysis of the digermene (R3Si)2Ge═Ge(SiR3)21, is presented.

An N-Heterocyclic Carbene−Disilyne Complex and Its Reactivity toward ZnCl2

Co-reporter:Torahiko Yamaguchi ; Akira Sekiguchi ;Matthias Driess

Journal of the American Chemical Society 2010 Volume 132(Issue 40) pp:14061-14063

Publication Date(Web):September 15, 2010

DOI:10.1021/ja107160g

The reaction of disilyne 1 with 1,3,4,5-tetramethylimidazol-2-ylidene (an N-heterocyclic carbene, NHC) produced the disilyne−NHC complex 2, RLSi═SiR: (R = SiiPr[CH(SiMe3)2]2, L = NHC), with a trans geometry of the Si═Si moiety and lone-pair electrons residing on one of the double-bonded Si atoms. Upon complexation of 2 with ZnCl2, the disilyne−NHC−ZnCl2 complex 3 was produced, in which the Si═Si bond adopted the cis geometry.

A two-and-a-half-layer sandwich: potassium salt of anionic (η4-tetrasilacyclobutadiene)(η5-cyclopentadienyl)ruthenium

Co-reporter:Vladimir Ya. Lee, Kazunori Takanashi and Akira Sekiguchi

Dalton Transactions 2010 vol. 39(Issue 39) pp:9229-9231

Publication Date(Web):21 Apr 2010

DOI:10.1039/C0DT00009D

An anionic ruthenium sandwich complex featuring the tetrasilacyclobutadiene ligand, [η4-tetrakis(di-tert-butylmethylsilyl)tetrasilacyclobutadiene](η5-pentamethylcyclopentadienyl)ruthenium was synthesized and isolated as its potassium salt [(η4-R4Si4)RuCp*]−·[K+(thf)2] (R = SiMet-Bu2, Cp* = η5-Me5C5), 1−·[K+(thf)2], by the reaction of the tetrasilacyclobutadiene dianion dipotassium salt [R4Si4]2−·[K+(thf)2]2 with 0.25 equiv. of [Cp*RuCl]4 in THF. In its crystalline form, 1−·[K+(thf)2] features a nearly square-planar tetrasilacyclobutadiene ligand.

The hexasiladigermacubane dianion

Co-reporter:Vladimir Ya. Lee;Kazunori Takanashi;Tadahiro Matsuno;Masaaki Ichinohe

Applied Organometallic Chemistry 2010 Volume 24( Issue 12) pp:834-836

Publication Date(Web):

DOI:10.1002/aoc.1688

Abstract

Interaction of the heavy analog of the cyclobutadiene dianion derivative [(t-Bu₂MeSi)₄Si₃Ge]²⁻·2K⁺ with the complexing reagent, [2.2.2]cryptand, results in the formation of the first heteronuclear cubane dianion derivative [(t-Bu₂MeSi)₆Si₆Ge₂]²⁻·2K⁺, in which both negative charges are exclusively localized at the diagonal Ge atoms. The structure of the title compound was determined by X-ray crystallography. Copyright © 2010 John Wiley & Sons, Ltd.

Reactivity of the disilyne RSiSiR (R=SiiPr[CH(SiMe3)2]2) toward bis(silylcyanide) forming a 1,4-diaza-2,3-disilabenzene analog

Co-reporter:Katsuhiko Takeuchi;Masaaki Ichinohe;Jing-Dong Guo;Shigeru Nagase

Journal of Physical Organic Chemistry 2010 Volume 23( Issue 4) pp:390-394

Publication Date(Web):

DOI:10.1002/poc.1617

Abstract

The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyl-2-tetrasilyne 1 with 1,3-bis(cyanodimethylsilyl)propane 4 produced the 1:1 adduct, 1,4-diaza-2,3-disilabenzene analog 5 as deep red crystals, which was characterized by spectroscopic data and X-ray crystallography. Theoretical calculations on the reaction between the disilyne and silylcyanide show that the reaction proceeds via σ-coordination of silylcyanide, in which two molecules of silylcyanide coordinate with the sp-silicon atoms of disilyne, enabling CC bond formation. Copyright © 2009 John Wiley & Sons, Ltd.

Si3C2-Rings: From a Nonconjugated Trisilacyclopentadiene to an Aromatic Trisilacyclopentadienide and Cyclic Disilenide

Co-reporter:Hiroyuki Yasuda ; Vladimir Ya. Lee

Journal of the American Chemical Society 2009 Volume 131(Issue 18) pp:6352-6353

Publication Date(Web):April 20, 2009

DOI:10.1021/ja901881z

1,2,3-Trisilacyclopenta-1,4-diene 2, featuring three skeletal Si atoms in the five-membered ring, was synthesized by the thermolysis of the 1,2,3-trisilabicyclo[1.1.0]butane derivative 1 at 130 °C in the presence of hex-3-yne. Possessing the properties of nonconjugated cyclopentadiene, 2 readily underwent reduction with KC8, which was followed by treatment with LiBr to form the lithium salt of 1,2,3-trisilacyclopentadienide 3−•[Li+(thf)], from which the ketone-coordinated derivative 3−•[Li+(O═CtBu2)] was prepared. Both 3−•[Li+(L)] (L = thf, O═CtBu2) are classified as novel 6π-electron aromatic systems based on their characteristic X-ray crystal and NMR spectral data. Addition of 12-crown-4 to 3−•[Li+(thf)] resulted in the unexpected formation of 4−•[Li+(12-crown-4)2], featuring the unprecedented cyclic disilenide ion 4−.

η5-1,2,3-Trisilacyclopentadienyl - A Ligand for Transition Metal Complexes: Rhodium Half-Sandwich and Ruthenium Sandwich

Co-reporter:Hiroyuki Yasuda ; Vladimir Ya. Lee

Journal of the American Chemical Society 2009 Volume 131(Issue 29) pp:9902-9903

Publication Date(Web):July 1, 2009

DOI:10.1021/ja9038664

The lithium salt of 1,2,3-trisilacyclopentadienide [η5-(tBu2MeSi)3Si3C2Et2]− 1−•[Li+(thf)] reacted with an equivalent amount of Rh(CO)2(acac) in toluene to form the half-sandwich (trisilacyclopentadienyl)dicarbonylrhodium complex [η5-(tBu2MeSi)3Si3C2Et2]Rh(CO)2 2. π-Electron delocalization in the trisilacyclopentadienyl ring in 2 was manifested in the shielding of the ring atoms upon complexation, as well as by the observation of 1JRh−C and 1JRh−Si coupling constants. In the solid state, cyclic delocalization in 2 was seen in the diagnostic η5-coordination of the heavy cyclopentadienyl ring to the Rh center and the remarkable flattening of the Si3C2 five-membered ring. Reaction of 1−•[Li+(thf)] with 0.25 equiv of [Cp*RuCl]4 (Cp* = η5-C5Me5) resulted in the formation of the sandwich complex Cp*Ru[η5-(tBu2MeSi)3Si3C2Et2] 3 as the heavy analogue of ruthenocene

Interaction of π-bonds of the silicon–silicon triple bond with alkali metals: An isolable anion radical upon reduction of a disilyne

Co-reporter:Akira Sekiguchi, Rei Kinjo, Masaaki Ichinohe

Synthetic Metals 2009 Volume 159(9–10) pp:773-775

Publication Date(Web):May 2009

DOI:10.1016/j.synthmet.2009.01.007

The reduction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with an equivalent amount of alkali metal (Li, Na, K, KC8) in THF produced the corresponding disilyne anion radicals 2a–c. Their EPR spectra are independent of the metals used in THF, indicating that the disilyne anion radical species exists as solvent-separated ion pairs in polar solvents. The one-electron reduction also occurred with potassium in toluene to produce the potassium salt of the anion radical 3, which was isolated as extremely air- and moisture-sensitive dark brown crystals. The molecular structure of 3 was established by X-ray crystallography, which showed that the potassium ion is solvated by one toluene molecule. The EPR spectrum of 3 in toluene showed the interaction of the anionic silicon atom with the K+ ion.

Electrochemical Properties and Computations of Stable Radicals of the Heavy Group14 Elements (Si, Ge, and Sn)

Co-reporter:JamesY. Becker ;VladimirYa. Lee Dr.;Masaaki Nakamoto Dr. ;Anna Chrostowska ;Alain Dargelos

Chemistry - A European Journal 2009 Volume 15( Issue 34) pp:8480-8484

Publication Date(Web):

DOI:10.1002/chem.200900935

Abstract

A series of stable radicals centered on persilyl-substituted heavy Group 14 elements, (tBu₂MeSi)₃E^. (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.

Pentasilatricyclo[2.1.0.02,5]pentane and Its Anion

Co-reporter:VladimirYa. Lee Dr.;Taka Yokoyama Dipl.-Chem.;Kazunori Takanashi Dr.

Chemistry - A European Journal 2009 Volume 15( Issue 34) pp:8401-8404

Publication Date(Web):

DOI:10.1002/chem.200900567

Tetrasilacyclobutadiene and Cyclobutadiene Tricarbonylruthenium Complexes: [η4-(tBu2MeSi)4Si4]Ru(CO)3 and [η4-(Me3Si)4C4]Ru(CO)3

Co-reporter:Kazunori Takanashi, Vladimir Ya. Lee and Akira Sekiguchi

Organometallics 2009 Volume 28(Issue 4) pp:1248-1251

Publication Date(Web):January 30, 2009

DOI:10.1021/om801128h

The novel ruthenium tricarbonyl complexes (η4-tetrasilacyclobutadiene)tricarbonylruthenium [η4-(tBu2MeSi)4Si4]Ru(CO)3 2 and (η4-cyclobutadiene)tricarbonylruthenium [η4-(Me3Si)4C4]Ru(CO)3 4 were synthesized by the reaction of either the dipotassium salt of a tetrasilacyclobutadiene dianion derivative [(tBu2MeSi)4Si4]2−•2K+ 1 or the dilithium salt of a cyclobutadiene dianion derivative [(Me3Si)4C4]2−•2Li+ 3 with [Ru(CO)3Cl2]2. The spectral and structural characteristics of both 2 and 4 were compared with each other to reveal the general tendencies of the influence of the nature of skeletal atoms and transition metal on the geometry of the four-membered ring ligand and its electronic properties.

Reactivity of the Disilyne RSi≡SiR (R = SiiPr[CH(SiMe3)2]2) toward Nitriles: Unexpected Formation of Triaza-1,4-disilabicyclo[2.2.2]octa-2,5,7-triene Derivatives

Co-reporter:Katsuhiko Takeuchi, Masaaki Ichinohe, Akira Sekiguchi, Jing-Dong Guo and Shigeru Nagase

Organometallics 2009 Volume 28(Issue 9) pp:2658-2660

Publication Date(Web):April 15, 2009

DOI:10.1021/om900164h

The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyl-2-tetrasilyne (1) with acetonitrile or benzonitrile produced the tris adduct triaza-1,4-disilabicyclo[2.2.2]octa-2,5,7-triene derivatives RSi(N═CR′)3SiR (R = SiiPr[CH(SiMe3)2]2, R′ = Me (2a), Ph (2b)), which were characterized by spectroscopic data as well as X-ray crystallography (for 2b). Theoretical calculations on the reaction between the disilyne and nitriles show that the reaction starts with the interaction between the LUMO (πin*) of 1 and the HOMO (lone pair) of the nitriles, followed by several consecutive steps to produce the diazadisila-Dewar benzene intermediate, which reacts with the third nitrile molecule to produce the final products.

A “Push−Pull” Phosphasilene and Phosphagermene and Their Anion-Radicals

Co-reporter:Vladimir Ya. Lee, Manami Kawai, Akira Sekiguchi, Henri Ranaivonjatovo and Jean Escudié

Organometallics 2009 Volume 28(Issue 15) pp:4262-4265

Publication Date(Web):July 7, 2009

DOI:10.1021/om900310u

Phosphasilene 1a and phosphagermene 1b, featuring unprecedented substitution patterns (donors on Si or Ge and acceptor on P), were synthesized utilizing a one-step synthetic approach: direct coupling of dilithiosilane/dilithiogermane and dichlorophosphine. The structural features of both 1a and 1b based on their NMR and X-ray crystal data are discussed, as well as their one-electron reduction forming persistent phosphasilene and phosphagermene anion-radicals.

An (η3-Disilaallyl)lithium Derivative: Interconversion of π-Allyl-Type Bonding and η1 Coordination to a Silyllithium Fragment

Co-reporter:Hiroaki Tanaka, Shigeyoshi Inoue, Masaaki Ichinohe and Akira Sekiguchi

Organometallics 2009 Volume 28(Issue 23) pp:6625-6628

Publication Date(Web):November 3, 2009

DOI:10.1021/om900861z

The (η3-disilaallyl)lithium derivative 5 was synthesized by the reaction of the disilenyllithium species (tBu2MeSi)2Si═Si(SiMetBu2)Li (1) with tris(3,5-di-tert-butylphenyl)acetaldehyde. All data, including X-ray analysis and NMR spectra, show that 5 has a π-allyl-type structure, with an interaction between the Li+ ion and the Si═C π-electrons of the silene moiety in both the crystal structure and in toluene solution but no such interaction in polar THF solvent.

Cyclic polyenes of heavy group 14 elements: new generation ligands for transition-metal complexes

Co-reporter:Vladimir Ya. Lee and Akira Sekiguchi

Chemical Society Reviews 2008 vol. 37(Issue 8) pp:1652-1665

Publication Date(Web):24 Jun 2008

DOI:10.1039/B800580J

Cyclic polyenes, such as benzene, cyclopentadienyl and cyclobutadiene, are widely used as key ligands for a variety of transition-metal complexes. The heavy versions of these compounds, in which the skeletal carbon atoms are fully (or partially) replaced with heavy group 14 elements (Si, Ge, Sn and Pb) were not synthetically accessible until quite recently. However, they are now readily available following the pioneering discoveries of derivatives of sila- and germabenzenes, sila- and germacyclopentadienide ions and tetrasila- and disiladigermacyclobutadiene dianions. Apart from their undoubted structural and synthetic interest, such organometallic compounds are particularly important as the precursors of novel ligands for new-generation transition-metal complexes, and this is covered in this critical review (124 references).

Tetrakis(trimethylsilyl)cyclobutadiene Dianion Alkaline Earth Metal Salts: New Members of the 6-Electron Aromatics Family

Co-reporter:Kazunori Takanashi;Akira Inatomi;Vladimir Ya. Lee;Masaaki Nakamoto;Masaaki Ichinohe

European Journal of Inorganic Chemistry 2008 Volume 2008( Issue 11) pp:1752-1755

Publication Date(Web):

DOI:10.1002/ejic.200800066

Abstract

The magnesium and calcium salts of the tetrakis(trimethylsilyl)cyclobutadiene dianion, [Mg(thf)₃]²⁺[(Me₃Si)₄C₄]^2– (2a) and [Ca(thf)_n]²⁺[(Me₃Si)₄C₄]^2– (2b), were synthesized by the reduction of tetrakis(trimethylsilyl)cyclobutadiene [(Me₃Si)₄C₄, 1] with metallic magnesium or calcium, respectively. X-ray analysis of 2a showed a planar four-membered ring, featuring a diagnostic η⁴-coordination to the magnesium atom and skeletal C–C bond lengths intermediate between those of typical C–C single and C=C double bonds. The structural and spectral features of the cyclobutadiene dianion magnesium salt 2a give evidence for its appreciable aromaticity.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

A stable silagermene (tBu3Si)2Si=Ge(mes)2 (mes = 2,4,6-trimethylphenyl): Synthesis, X-ray crystal structure, and thermal isomerization

Co-reporter:Masayasu Igarashi;Masaaki &x131;chinohe

Heteroatom Chemistry 2008 Volume 19( Issue 7) pp:649-653

Publication Date(Web):

DOI:10.1002/hc.20503

Abstract

A stable silagermene, 1,1-bis(tri-tert-butylsilyl)-2,2-bis(2,4,6-trimethylphenyl)silagermene, was synthesized by the reaction of dilithiosilane (^tBu₃Si)₂SiLi₂ with dichlorodimesitylgermane. Its structure was determined by spectroscopic data and X-ray crystallography, which showed the SiGe length to be 2.2769(8) Å. The silagermene underwent isomerization at 100ˆC to form the corresponding symmetrically substituted isomer (E)-1,2-bis(tri-tert-butylsilyl)-1,2-bis(2,4,6-trimethylphenyl)silagermene. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:649–653, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20503

Photochemical reaction of silyl-substituted 1,4-disila(dewar-benzene) with isocyanide and phenylacetylene

Co-reporter:Toru Oikawa;Norio Nakata;Takeshi Matsumoto;Yoshio Kabe

Heteroatom Chemistry 2008 Volume 19( Issue 1) pp:87-92

Publication Date(Web):

DOI:10.1002/hc.20411

Abstract

The irradiation of silyl-substituted 1,4-disila(Dewar-benzene) 1 with light of wavelength λ > 320 nm in the presence of 2,6-dimethylphenyl-isocyanide or phenylacetylene produced 1,4-bis(di-tert-butylmethylsilyl)-2,3,5,6-tetraethyl-7-(2,6-dime-thylphenylimino)-1,4-disilabicyclo[2.2.1]hepta-2,5-diene 5 or 1,4-bis(di-tert-butylmethylsilyl)-2,3,5,6-tetraethyl-1-(2-phenylethynyl)-1,4-disilacyclohexa-2,5-diene 6, respectively. The molecular structures of 5 and 6 were determined by spectroscopic data and X-ray crystallography. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:87–92, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20411

1,2-Disilacyclobut-2-enes: Donor-Free Four-Membered Cyclic Silenes from Reaction of Disilenides with Vinylbromides

Co-reporter:Iulia Bejan Dipl.-Chem.;Shigeyoshi Inoue Dr.;Masaaki Ichinohe Dr. ;David Scheschkewitz Dr.

Chemistry - A European Journal 2008 Volume 14( Issue 24) pp:7119-7122

Publication Date(Web):

DOI:10.1002/chem.200800919

Isolable Alkali-Metal-Substituted Silyl Radicals (tBu2MeSi)2SiM (M = Li, Na, K): Electronically and Sterically Accessible Planar Silyl Radicals

Co-reporter:Shigeyoshi Inoue, Masaaki Ichinohe and Akira Sekiguchi

Organometallics 2008 Volume 27(Issue 7) pp:1358-1360

Publication Date(Web):March 4, 2008

DOI:10.1021/om8000185

Tetrakis(di-tert-butylmethylsilyl)disilene (1) was treated with 2.2 equiv of MNp (metal naphthalenide, M = Na, K) in THF followed by addition of 2 equiv of a crown ether (2b, 15-crown-5; 2c, 18-crown-6), resulting in the formation of the first isolable alkali-metal-substituted silyl radicals 2, which were characterized by both EPR spectra and X-ray crystallography. The lithium-substituted silyl radical 2a was also synthesized as an isolable compound by the reaction of free silylene anion radical with LiBr, and it has a monomeric structure in solution but a dimeric structure in the solid state.

Electronic Structure of Stable Radicals of the Heavy Group 14 Elements: UV-Photoelectron Spectroscopy Characterization

Co-reporter:Anna Chrostowska ; Alain Dargelos ; Alain Graciaa ; Patrick Baylère ; Vladimir Ya. Lee ; Masaaki Nakamoto

Organometallics 2008 Volume 27(Issue 13) pp:2915-2917

Publication Date(Web):June 5, 2008

DOI:10.1021/om7012925

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.

A Free Silylium Ion: A Cyclotetrasilenylium Ion with Allylic Character

Co-reporter:Shigeyoshi Inoue, Masaaki Ichinohe, Torahiko Yamaguchi and Akira Sekiguchi

Organometallics 2008 Volume 27(Issue 23) pp:6056-6058

Publication Date(Web):October 29, 2008

DOI:10.1021/om800912v

1,3,4,4-Tetra-tert-butyl-2-(di-tert-butylmethylsilyl)cyclotetrasilenylium (3+), a silylium ion with an allylic cation character, was synthesized by the reaction of tetrakis(di-tert-butylmethylsilyl)disilene with [Et3Si(benzene)]+·TPFPB− in toluene. The NMR spectral data and X-ray structure of 3+·TPFPB− show that it is a free silylium ion with an allylic cation structure.

Stable Silyl, Germyl, and Stannyl Cations, Radicals, and Anions: Heavy Versions of Carbocations, Carbon Radicals, and Carbanions

Co-reporter:Vladimir Ya. Lee and Akira Sekiguchi

Accounts of Chemical Research 2007 Volume 40(Issue 6) pp:410

Publication Date(Web):May 8, 2007

DOI:10.1021/ar6000473

The rapidly growing chemistry of the cations, radicals, and anions based on the group 14 elements heavier than carbon (Si, Ge, Sn, and Pb) is one of the most important organometallic fields. Recent developments in this research area moved such species from the class of short-lived reactive intermediates to the class of easily accessible, isolable, and fully characterizable compounds. In this Account, we deal with the major accomplishments in the field of the stable representatives of “heavy” cations, radicals, and anions.

(η5-Cyclopentadienyl)(η4-tetrasila- and η4-trisilagermacyclobutadiene)cobalt: Sandwich Complexes Featuring Heavy Cyclobutadiene Ligands

Co-reporter:Kazunori Takanashi;Vladimir Ya. Lee;Masaaki Ichinohe

European Journal of Inorganic Chemistry 2007 Volume 2007(Issue 35) pp:

Publication Date(Web):8 NOV 2007

DOI:10.1002/ejic.200701046

(η⁵-Cyclopentadienyl)(η⁴-tetrasilacyclobutadiene)cobalt{[(η⁴-R₄Si₄)CoCp], 2} and (η⁵-cyclopentadienyl)(η⁴-trisilagermacyclobutadiene)cobalt {[(η⁴-R₄Si₃Ge)CoCp], 4} (R = SiMetBu₂) were synthesized by reaction of the dipotassium salts of tetrasilacyclobutadiene dianion K⁺₂·[R₄Si₄]^2– (1) and trisilagermacyclobutadiene dianion K⁺₂·[R₄Si₃Ge]^2– (3) with [CpCoI₂(PPh₃)]. Alternatively, 4 was prepared by the reaction of 3 with [Cp₂Co]⁺·[PF₆]^–. X-ray crystallographic analysis of 2 confirmed its sandwich-type structure, manifesting a nearly square-planar Si₄ ring and diagnostic perhaptocoordination of both ligands, η⁴-tetrasilacyclobutadiene and η⁵-cyclopentadienyl, to the Co atom. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

(η5-Cyclopentadienyl)(η4-tetrasila- and η4-trisilagermacyclobutadiene)cobalt: Sandwich Complexes Featuring Heavy Cyclobutadiene Ligands (Eur. J. Inorg. Chem. 35/2007)

Co-reporter:Kazunori Takanashi;Vladimir Ya. Lee;Masaaki Ichinohe

European Journal of Inorganic Chemistry 2007 Volume 2007(Issue 35) pp:

Publication Date(Web):28 NOV 2007

DOI:10.1002/ejic.200790092

The cover picture shows two spotlights illuminating the structure of the first sandwich complex featuring an all-heavy group 14 element-consisting Si₄-cyclic ligand, namely, a derivative of (?⁵-cyclopentadienyl)(η⁴-tetrasilacyclobutadiene)cobalt [(η⁴-R₄Si₄)CoCp] (R = SiMetBu₂). The Me and tBu groups on the Si substituents, as well as the H atoms on the Cp ring, are removed for simplicity. The title compound was smoothly prepared by a ligand exchange reaction between the tetrasilacyclobutadiene dianion salt K⁺₂·[R₄Si₄]₂ and [CpCoI₂(PPh₃)]. Systematic comparison of the complex [(η⁴-R₄Si₄)CoCp] and its carbon analogue [η⁴-(Me₃Si)₄C₄]CoCp revealed important structural distinctions between the two complexes that result from the different ring sizes of the cyclobutadiene ligands η⁴-R₄E₄ (R = SiMetBu₂, E = Si vs. R = SiMe₃, E = C). Details of the synthesis of the novel Co complex, as well as of its structural and electronic peculiarities, are discussed in the Short Communication by A. Sekiguchi et al. on p. 5471 ff.

Conversion of a Disilenide into a Silene: Silyl-Anion-Substituted Silene by a Sila-Peterson-Type Reaction from an sp2-Type Silyl Anion

Co-reporter:Shigeyoshi Inoue Dipl.-Chem.;Masaaki Ichinohe Dr. Dr.

Angewandte Chemie International Edition 2007 Volume 46(Issue 18) pp:

Publication Date(Web):16 FEB 2007

DOI:10.1002/anie.200605140

From SiSi to SiC: Silyl-anion-substituted silene 2 was synthesized as air- and moisture-sensitive yellow crystals by the reaction of the disilenyl lithium derivative 1 with adamantanone (see scheme). The physical properties of 2 suggest a silene-type structure containing a silicon–carbon double bond, with no contribution from 1,2-disilaallyl-anion-type and disilene-type structures.

Conversion of a Disilenide into a Silene: Silyl-Anion-Substituted Silene by a Sila-Peterson-Type Reaction from an sp2-Type Silyl Anion

Co-reporter:Shigeyoshi Inoue Dipl.-Chem.;Masaaki Ichinohe Dr. Dr.

Angewandte Chemie 2007 Volume 119(Issue 18) pp:

Publication Date(Web):16 FEB 2007

DOI:10.1002/ange.200605140

Von SiSi zu SiC: Das Silylanion-substituierte Silen 2 entstand bei der Reaktion des Disilenyllithium-Derivats 1 mit Adamantanon in Form luft- und feuchtigkeitsempfindlicher gelber Kristalle (siehe Schema). Die physikalischen Eigenschaften von 2 sprechen für eine silenartige Struktur mit einer Silicium-Kohlenstoff-Doppelbindung ohne Beiträge von Strukturen vom 1,2-Disilaallylanion- und Disilentyp.

Aromatizität von metallorganischen Verbindungen mit Gruppe-14-Elementen: experimentelle Aspekte

Co-reporter:Vladimir Ya. Lee Dr. Dr.

Angewandte Chemie 2007 Volume 119(Issue 35) pp:

Publication Date(Web):2 AUG 2007

DOI:10.1002/ange.200604869

Die Aromatizität ist eines der wegweisenden Konzepte in der Chemie, dessen Geschichte sich über fast zwei Jahrhunderte erstreckt, beginnend mit der Entdeckung des “Doppelt-Kohlenwasserstoffs” (bicarburet of hydrogen), heute Benzol genannt, durch Faraday. Die seitherigen Fortschritte auf dem Gebiet der aromatischen Verbindungen sind erheblich, was sich in der Synthese neuartiger Klassen aromatischer Verbindungen widerspiegelt, darunter geladene Spezies, nichtklassische (Möbius-, dreidimensionale, Homo-, Metalla-)Arene und Fullerene. Zugleich wurde die Theorie der Aromatizität stetig weiterentwickelt; die Abgrenzung der Aromatizität erfordert heute eine Abwägung vielfältiger Kriterien: energetischer, struktureller, magnetischer Kriterien usw. Im vorliegenden Aufsatz diskutieren wir den derzeitigen Forschungsstand auf dem Gebiet der aromatischen Verbindungen von schwereren Gruppe-14-Elementen und geben einen Ausblick auf die Zukunft dieses Gebiets.

Aromaticity of Group 14 Organometallics: Experimental Aspects

Co-reporter:Vladimir Ya. Lee Dr. Dr.

Angewandte Chemie International Edition 2007 Volume 46(Issue 35) pp:

Publication Date(Web):2 AUG 2007

DOI:10.1002/anie.200604869

The long story of aromatic compounds has extended over almost two centuries, since the discovery by Faraday of “bicarburet of hydrogen”, or C₆H₆, 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 (Möbius, three-dimensional, homo-, metalla-) aromatics, and fullerenes. The theory of aromaticity has also undergone a spectacular evolution since the first definition of aromaticity by Hückel; 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.

A blue digermene (t-Bu2MeSi)2GeGe(SiMet-Bu2)2

Co-reporter:Vladimir Ya. Lee, Kiera McNeice, Yuki Ito and Akira Sekiguchi

Chemical Communications 2011 - vol. 47(Issue 11) pp:NaN3274-3274

Publication Date(Web):2011/02/01

DOI:10.1039/C0CC05415A

Cyclic polyenes of heavy group 14 elements: new generation ligands for transition-metal complexes

Co-reporter:Vladimir Ya. Lee and Akira Sekiguchi

Chemical Society Reviews 2008 - vol. 37(Issue 8) pp:NaN1665-1665

Publication Date(Web):2008/06/24

DOI:10.1039/B800580J

A two-and-a-half-layer sandwich: potassium salt of anionic (η4-tetrasilacyclobutadiene)(η5-cyclopentadienyl)ruthenium

Co-reporter:Vladimir Ya. Lee, Kazunori Takanashi and Akira Sekiguchi