- Silylene R*XSi (R=SitBu3; X=H, Me, Ph, Hal, R*): Bildung und Reaktionen
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Thermolyses of disupersilylsilanes R*2SiX2 (R=supersilyl=SitBu3; X=H, Hal or H together with Me, Ph, Br) at about 160°C lead - besides R*X (R*H preferred to R*Br) - to silylenes R*XSi (X=H, Me, Ph, Br), the inte
- Wiberg, Nils,Niedermayer, Wolfgang
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- 29Si NMR Spectroscopy as a Probe of s- And f-Block Metal(II)-Silanide Bond Covalency
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We report the use of 29Si NMR spectroscopy and DFT calculations combined to benchmark the covalency in the chemical bonding of s- and f-block metal-silicon bonds. The complexes [M(SitBu3)2(THF)2(THF)x] (1-M: M = Mg, Ca, Yb, x = 0; M = Sm, Eu, x = 1) and [M(SitBu2Me)2(THF)2(THF)x] (2-M: M = Mg, x = 0; M = Ca, Sm, Eu, Yb, x = 1) have been synthesized and characterized. DFT calculations and 29Si NMR spectroscopic analyses of 1-M and 2-M (M = Mg, Ca, Yb, No, the last in silico due to experimental unavailability) together with known {Si(SiMe3)3}-, {Si(SiMe2H)3}-, and {SiPh3}-substituted analogues provide 20 representative examples spanning five silanide ligands and four divalent metals, revealing that the metal-bound 29Si NMR isotropic chemical shifts, ?Si, span a wide (?225 ppm) range when the metal is kept constant, and direct, linear correlations are found between ?Si and computed delocalization indices and quantum chemical topology interatomic exchange-correlation energies that are measures of bond covalency. The calculations reveal dominant s- and d-orbital character in the bonding of these silanide complexes, with no significant f-orbital contributions. The ?Si is determined, relatively, by paramagnetic shielding for a given metal when the silanide is varied but by the spin-orbit shielding term when the metal is varied for a given ligand. The calculations suggest a covalency ordering of No(II) > Yb(II) > Ca(II) ≈ Mg(II), challenging the traditional view of late actinide chemical bonding being equivalent to that of the late lanthanides.
- Basford, Annabel R.,Berryman, Victoria E. J.,Kaltsoyannis, Nikolas,Liddle, Stephen T.,Mills, David P.,Nodaraki, Lydia E.,Réant, Benjamin L. L.,Tuna, Floriana,Wooles, Ashley J.
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supporting information
p. 9813 - 9824
(2021/07/21)
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- Isoelectronic caesium compounds: The triphosphenide Cs[tBu 3SiPPPSitBu3] and the enolate Cs[OCH=CH2]
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The caesium triphosphenide Cs[tBu3SiPPPSitBu3] was accessible from the reaction of CsF with the sodium triphosphenide Na[tBu 3SiPPPSitBu3] in tetrahydrofuran at room temperature. In contrast to the preparation of tetrahydrofuran-solvated silanides M[SitBu 3] (M = Li, Na, K), our efforts to synthesize the caesium silanide Cs[SitBu3] as a tetrahydrofuran complex failed. When tBu 3SiBr was treated with an excess of caesium metal in tetrahydrofuran at room temperature, the caesium enolate Cs[OCH=CH2] and the supersilane tBu3SiH formed rather than the silanide Cs[SitBu 3]. X-Ray quality crystals of the enolate Cs[OCH=CH2] (orthorhombic, Pnma) were obtained from tetrahydrofuran at ambient temperature. In contrast to the structures of its homologues M[tBu3SiPPPSitBu 3] (M = Na, K), the caesium triphosphenide Cs[tBu 3SiPPPSitBu3] features a polymer in the solid state (orthorhombic, Cmcm). The Royal Society of Chemistry.
- Lerner, Hans-Wolfram,Saenger, Inge,Schoedel, Frauke,Lorbach, Andreas,Bolte, Michael,Wagner, Matthias
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p. 787 - 792
(2008/09/20)
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- Octagallane (tBu3Si)6Ga8 and its reduction to (tBu3Si)6Ga82- - On the existence of isomeric gallium clusters
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Thermolysis of the trigallanyl radical R*4Ga3 in heptane at 60 °C leads to the dark blue octagallane R*6Ga8 (R* = supersilyl SitBu3), as well as the digallanyl radical R*3Ga2 and the tetrahedro-tetragallane R*4Ga4. In addition, supersilyl radicals R* are formed which stabilize themselves either by dimerization or by addition of hydrogen atoms. R*6Ga8 can be reduced in THF with NaC10H8 to the dark-red octagallanediide Na2Ga8R*6·2THF. According to an X-ray structure analysis of R*6Ga8 and R*6Ga82- one finds that the Ga atoms of four R*Ga moieties, together with two naked Ga atoms, occupy the corners of a distorted octahedron; the naked Ga atoms themselves are located, along with Ga atoms of two further R*Ga moieties, at the corners of a distorted square. The reduction of R*6Ga8 leads only to a negligible shortening of the Ga-Ga distances from 2.64 to 2.61 A (mean values) in R*6Ga82-. Both the octagallanes possess Ga8 frameworks previously unknown for group 13 clusters. They are isomeric to the recently described Ga8 framework of the octagallane Tsi6Ga8 [Tsi = trisyl C(SiMe3)3]. Hence, not only boron but also the heavier group 13 atoms form isomeric clusters.
- Wiberg, Nils,Blank, Thomas,Noeth, Heinrich,Suter, Max,Warchhold, Markus
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p. 929 - 934
(2007/10/03)
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- Supersilylsilanes R*SiX3: Syntheses, characterization and structures; steric and van-der-Waals effects of substituents X [1]
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Supersilylsilanes R*SiX3 (R* = supersilyl = SitBu3; X = H, Me, tBu, Ph, SiMe3, F, Cl, Br, I, OMe, OSO2CF3) are prepared (i) by reactions of supersilylhalosilanes with supersilyl sodium NaR* (Hal/R* ex
- Wiberg, Nils,Niedermayer, Wolfgang,No?th, Heinrich,Knizek, Jo?rg,Ponikwar, Werner,Polborn, Kurt
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p. 389 - 405
(2007/10/03)
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Supersilyl alkaline metals (alkali supersilanides) tBu3SiM without or with donors Do like ethers, amines, aromatic hydrocarbons are easily obtained by the action of alkaline metals M on supersilyl halides tBu3Si
- Wiberg,Amelunxen,Lerner,Schuster,Noeth,Krossing,Schmidt-Amelunxen,Seifert
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- Donoraddukte des Silanimins Me2Si=NSitBu3: Darstellung, Stabilitaet, Reaktivitaet
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Silaneimine Me2Si=NSitBu3 (1), which is unstable under normal conditions with regard to dimerization, forms metastable adducts D.Me2Si=NSitBu3 (1.D = 3 with D = Et2O, THF, NEt3, NMe2Et), which can be decomposed thermally to give 1 and D and, can thus serve as sources of 1.Adducts 1.D result from Me2SiXNLi(SitBu3) (X = halogen, amides formed by reaction of Me2SiXNH(SitBu3) with RLi) under LiX elimination in the presence of D and CF3SO3SiMe3.Lewis basicity of D, relative to 1, increases in the order Et2O - -.Similarly resistance of 1.D to decompose into the dimer of 1 and D also increases.Adducts 1.D also decompose by action of excess donor, (viz. 1.OEt2 decomposes in Et2O into ethylene and Me2SiOEt-NHSitBu3, 1.NMe2Et decomposes in NMe2Et under Stevens migration into EtMeNCH2SiMe2NHSitBu3).Reaction of adducts 1.D with water, alcohols and amines, or with organic enes (propene, isobutene, dimethylbutadiene, cyclopentadiene), or with silyl azides (MentBu3-nSiN3), or with benzophenone, respectively, gives the OH and NH bond insertion products, or ene reaction products, or cycloadducts, or a cycloadduct of 1, respectively.
- Wiberg, Nils,Schurz, Klaus
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p. 145 - 164
(2007/10/02)
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- SILICIUM-VERBINDUNGEN MIT STARKEN INTRAMOLEKULAREN STERISCHEN WECHSELWIRKUNGEN X. NEUE WEGE ZU 1,3,2,4-DITHIADISILETANEN
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2,2,4,4-Tetraorganyl-1,3,2,4-dithiadisiletanes containing bulky organyl groups are obtained by copyrolysis of the disilanes R3Si-SiR3 with sulfur or sulfur hexafluoride, or better by reaction of the disilanes R2HSi-SiHR2 (R=CH3, i-C3H7, cyclo-C6H11, t-C4H9) with sulfur.In the case of R=t-C4H9 a considerable amount of the t-butyl groups is isomerized to the less crowded isobutyl groups.Monomeric silathiones R2Si=S are not available by this route.The sulfur insertion reaction into 1,1-di-t-butyl-1-silacyclobutane yields 2,4-di-t-butyl-2,4-dipropyl-1,3,2,4-dithiadisiletane instead of the expected 1,1-di-t-butyl-1-sila-2-thiacyclopentane.The latter compound, however, results from the crown ether catalyzed cyclisation reaction of 3-bromopropyltrichlorosilane with Na2S followed by transalkylation with t-butyllithium.The iodosilanes R3SiI (R=i-C3H7, cyclo-C6H11) react with Na2S to give the corresponding hexaorganyldisilathianes in high yields.
- Weidenbruch, M.,Schaefer, A.,Rankers, R.
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p. 171 - 184
(2007/10/02)
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