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Journal ArticleDOI

A stable compound containing a silicon-silicon triple bond.

17 Sep 2004-Science (American Association for the Advancement of Science)-Vol. 305, Iss: 5691, pp 1755-1757
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)°.

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Citations
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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

Journal ArticleDOI
14 Jan 2010-Nature
TL;DR: The last quarter of the twentieth century and the beginning decade of the twenty-first witnessed spectacular discoveries in the chemistry of the heavier main-group elements, which led to new structural and bonding insights as well as a gradually increasing realization that the science more resembles that of transition-metal complexes than that of their lighter main- group congeners.
Abstract: The chemistry of heavier main-group elements such as aluminium, silicon and phosphorus is very different from that of the lighter ones such as boron, carbon and nitrogen, yet discussions of this topic have been dominated by comparisons with the light elements. Philip Power's review focuses on advances in chemistry of the heavier main-group elements that reveal them as having more in common with the transition metals than the lighter members of the main groups. The concept of heavier main-group elements as 'transition metals' is supported by recent work showing that many of the new compounds react with small molecules such as H2, NH3, C2H4 and CO under mild conditions and display potential as catalysts. The last quarter of the twentieth century and the beginning decade of the twenty-first witnessed spectacular discoveries in the chemistry of the heavier main-group elements. The new compounds that were synthesized highlighted the fundamental differences between their electronic properties and those of the lighter elements to a degree that was not previously apparent. This has led to new structural and bonding insights as well as a gradually increasing realization that the chemistry of the heavier main-group elements more resembles that of transition-metal complexes than that of their lighter main-group congeners. The similarity is underlined by recent work, which has shown that many of the new compounds react with small molecules such as H2, NH3, C2H4 or CO under mild conditions and display potential for applications in catalysis.

1,077 citations

Journal ArticleDOI
TL;DR: The past decade has witnessed renewed interest and numerous unexpected discoveries in the area of main group organometallic chemistry, and unusual bonding modes have been uncovered and new materials have been developed and new applications are being pursued.
Abstract: The past decade has witnessed renewed interest and numerous unexpected discoveries in the area of main group organometallic chemistry. Unusual bonding modes have been uncovered,1-4 new materials have been developed,5,6 and new applications are being pursued.7-12 With respect to new materials with unusual properties, an exciting field is the development of hybrid polymers that combine main group elements with typical organic structures in one framework.13,14 Among main group organic-inorganic hybrid polymers, those involving Group 14 and Group 15 elements have received tremendous attention over the past several decades, with silicones, polysilanes, and polyphosphazenes among the most thoroughly studied materials.15-17 A variety of other classes of new polymers containing not only silicon and phosphorus,18-22 but also the heavier homologues, such as germanium, tin, arsenic, and antimony have been introduced more recently.23-26

879 citations

Journal ArticleDOI
TL;DR: The key unifying feature of almost all molecules discussed in this review is that they are generally stabilized by the use of bulky substituents which block associative or various decomposition pathways.
Abstract: This review is essentially an update of one entitled “πBonding and The Lone Pair Effect in Multiple Bonds Between Heavier Main Group Elements” which was published more than 10 years ago in this journal.1 The coverage of that survey was focused on the synthesis, structure, and bonding of stable compounds2 of heavier main group elements that correspond to the skeletal drawings reproduced in Tables 1 and 2. A row of numbers is listed at the bottom of each column in these tables. This refers to the number of stable complexes from each class that are currently known. The numbers in parentheses refer to the number of stable species that were known at the time of the previous review. Clearly, many of the compound classes listed have undergone considerable expansion although some remain stubbornly rare. The most significant developments for each class will be discussed in detail under the respective sections. As will be seen, there are also a limited number of multiple bonded heavier main group species that do not fit neatly in the classifications in Tables 1 and 2. However, to keep the review to a manageable length, the limits and exclusions, which parallel those used earlier, are summarized as follows: (i) discussion is mainly confined to compounds where experimental data on stable, isolated species have been obtained, (ii) stable compounds having multiple bonding between heavier main group elements and transition metals are not generally discussed, (iii) compounds in which a multiple bonded heavier main group element is incorporated within a ring are generally not covered, and (iv) hypervalent main group compounds that may incorporate faux multiple bonding are generally excluded. Such compounds are distinguished from those in Tables 1 and 2 in that they apparently require the use of more than four valence bonding orbitals at one or more of the bonded atoms. The remainder of this review is organized in a similar manner to that of the previous one wherein the compounds to be discussed are classified according to those summarized in Tables 1 and 2. The key unifying feature of almost all molecules discussed in this review is that they are generally stabilized by the use of bulky substituents which block associative or various decomposition pathways.3 Since the previous review was published in 1999, several review articles that cover parts of the subject matter have appeared.4

865 citations

Journal ArticleDOI
TL;DR: The early silylene research was concerned largely with comparing the chemistry of the dihalosilylenes with that of carbenes, so it might be difficult to isolate metallylenes as stable compounds under ambient conditions.
Abstract: In recent decades, it has generally been recognized that carbenes play an important role as transient intermediates. As a result of a number of stable carbenes having been isolated and investigated in detail, it is not an exaggeration to say that the chemistry of carbenes has been thoroughly investigated and is now well-understood.1 In addition, much attention has also been paid to the heavier analogues of carbenes, i.e., silylenes (R2Si:), germylenes (R2Ge:), stannylenes (R2Sn:), and plumbylenes (R2Pb:). These so-called metallylenes are monomeric species of the polymetallanes. This is especially true of the silylenes, which are believed to be monomers of polysilane. The metallylenes could be expected to be of great importance in fundamental and applied chemistry as a result of their many differences and similarities to carbenes. The valency of the central atom of the heavier carbene analogues (R2M:, M ) Si, Ge, Sn, Pb) is two. That is, its oxidation state is MII and its stability increases as the principal quantum number (n) increases. In fact, dichloroplumbylene and dichlorostannylene, PbCl2 and SnCl2, respectively, are very stable ionic compounds. However, these dihalides exist as polymers or ion pairs both in solution and in the solid state. The dichlorogermylene complex GeCl2 · (dioxane)3 is also known to be stable and isolable, whereas the dihalosilylenes are barely isolable compounds.2 The early silylene research was concerned largely with comparing the chemistry of the dihalosilylenes with that of carbenes. Hence, the chemistry of the metallylenes has been considered mainly from the molecular chemistry point of view.4 In contrast to the carbon atom, the heavier group 14 atoms have a low ability to form hybrid orbitals. They therefore prefer the (ns)2(np)2 valence electron configurations in their divalent species.5 Since two electrons remain as a singlet pair in the ns orbital, the ground state of H2M: (M ) Si, Ge, Sn, Pb) is a singlet, unlike the case of H2C:, where the ground state is a triplet (Figure 1).1a On the basis of theoretical calculations, the singlet-triplet energy differences ∆EST for H2M, [∆EST ) E(triplet) E(singlet)], are found to be 16.7 (M ) Si), 21.8 (M ) Ge), 24.8 (M ) Sn), and 34.8 (M ) Pb) kcal/mol, respectively. That of H2C: is estimated as -14.0 kcal/mol.6 Furthermore, the relative stabilities of the singlet species of R2M: (M ) C, Si, Ge, Sn, Pb; R ) alkyl or aryl) compared to the corresponding dimer, R2MdMR2, are estimated to increase as the element row descends, C < Si < Ge < Sn < Pb. It follows, therefore, that one can expect that a divalent organolead compound such as plumbylene should be isolable as a stable compound. However, some plumbylenes, without any electronic or steric stabilization effects, are known to be thermally unstable and undergo facile disproportionation reactions, giving rise to elemental lead and the corresponding tetravalent organolead compounds.7 On this basis, it could be concluded that it might be difficult to isolate metallylenes as stable compounds under ambient conditions, since they generally exhibit extremely high reactivity toward other molecules as well as themselves. Metallylenes have a singlet ground state with a vacant p-orbital and a lone pair of valence orbitals. This extremely high reactivity must be due to their vacant p-orbitals, since 6 valence electrons is less than the 8 electrons of the “octet rule”. Their lone pair is expected to be inert due to its high s-character. In order to stabilize metallylenes enough to be isolated, either some thermodynamic and/or kinetic stabilization of the reactive vacant p-orbital is required (Figure 2). A range of “isolable” metallylenes have been synthesized through the thermodynamic stabilization of coordinating Cp* ligands, the inclusion of heteroatoms such as N, O, and P, * To whom correspondence should be addressed. Phone: +81-774-38-3200. Fax: +81-774-38-3209. E-mail: tokitoh@boc.kuicr.kyoto-u.ac.jp. Chem. Rev. 2009, 109, 3479–3511 3479

727 citations

References
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BookDOI
25 Jan 1989
TL;DR: A.R.Bassindale and P.G.Taylor as mentioned in this paper discussed the photochemistry of organosilicon compounds, A.R., B.B.Birkofer and O.Ojima.
Abstract: Historical overview and comparison of silicon with carbon, J.Y.Corey theoretical aspects of organosilicon compounds, Y.Apeloig structural chemistry of organic silicon compounds, W.S.Sheldrick dynamic stereochemistry at silicon, R.J.P.Corriu et al thermochemistry, R.Walsh analysis of organosilicon compounds, T.R.C.Crompton positive and negative ion chemistry of silicon-containing molecules in the gas phase, H.Schwarz NMR spectroscopy of organosilicon compounds, E.A.Williams photoelectron spectra of silicon compounds, H.Bock and B.Solouki general synthetic pathways to organosilicon compounds, L.Birkofer and O.Stuhl recent synthetic application of organosilanes, G.L.Larson acidity, basicity and complex formation of organosilicon compounds, A.R.Bassindale and P.G.Taylor reaction mechanisms of nucleophilic attacks at silicon, A.R.Bassindale and P.G.Taylor activating and directive effects of silicon, A.R.Bassindale and P.G.Taylor the photochemistry of organosilicon compounds, A.G.Brook trivalent silyl ions, J.B.Lambert and W.J.Schulz Jr multiple bonds to silicon, G.Raabe and J.Michl bio-organic chemistry, R.Tacke and J.Linoh polysilanes, R.West hypervalent silicon compounds, R.J.P.Corriu and J.C.Young siloxane polymers and copolymers, T.C.Kendrick organosilicon derivatives of phosphorus arsenic, antimony and bismuth, D.A.Armitage chemistry of compounds with silicon-sulphur, silicon-selenium and silicon-tellurium bonds, D.A.Armitage transition-metal silyl derivatives, T.D.Tilley the hydrosilylation reaction, I.Ojima.

2,254 citations

Journal ArticleDOI
18 Dec 1981-Science
TL;DR: Irradiation of 2,2-bis(2,4,6-trimethylphenyl)hexamethyltrisilane in hydrocarbon solution produces tetramesityldisilene, which can be isolated as a yellow-orange solid stable to room temperature and above in the absence of air.
Abstract: Irradiation of 2,2-bis(2,4,6-trimethylphenyl)hexamethyltrisilane in hydrocarbon solution produces tetramesityldisilene, which can be isolated as a yellow-orange solid stable to room temperature and above in the absence of air Like the olefins of carbon chemistry, tetramesityldisilene undergoes addition reactions across the silicon-silicon double bond

756 citations

Journal ArticleDOI
TL;DR: The Stable Heavier Group 14 Element Analogue of an Alkyne (SHE 14) as discussed by the authors is a stable heavier group 14 analogue of an alkyne.
Abstract: Synthesis and Characterization of 2,6-Trip2H3C6PbPbC6H3-2,6-Trip2 (Trip = C6H2-2,4,6-i-Pr3): A Stable Heavier Group 14 Element Analogue of an Alkyne

301 citations