Uwe Klingebiel

Bicyclische lithium-t-butylaminofluorsilane, moleküle mit zwei- und vierfachkoordinierten lithium

Abstract Dimeric lithium-t-butylamino-di-t-butylfluorosilane, [(CMe 3 ) 2 SiFLiNCMe 3 ] 2 , adds one molecule of THF per dimer when crystallized from THF. A bicyclic compound is obtained with fourfold [F 2 Li(THF)N] and twofold [NLiN] coordinated lithium. The Si(1)N(1) bond lenght in the six-membered ring has the lenght expected for a bond and is 5.4 pm shorter than the Si(2)N(2) bond of the four-membered ring. The 7 Li and the solid state 13 C NMR spectra confirm the asymmetry of the molecule. NMR spectra in solution show an equilibration of the H, C, F and Si atoms, a feature which is consistent with fluctuation of Li(1)N(1) and Li(1)N(2) bonds. The THF adduct of lithiated t-butylamino-bis(methyltrimethylsilylamino)-fluorosilane exhibits similar NMR effects.

A facile synthesis of iminosilanes. Crystal structure of (Me3C)2(THF)Si=N-SiMe(CMe3)2

Abstract The aminofluorosilane 1 (Me 3 C) 2 SiFNHSiMe(CMe 3 ) 2 is formed by treatment of (Me 3 C) 2 SiF 2 with (Me 3 C) 2 MeSiNHLi. The lithium derivative of 1 , (Me 3 C) 2 SiFLi(THF) 2 NSiMe(CMe 3 ) 2 , 3 , is formed by treatment with n-C 4 H 9 Li. Treatment of 3 with Me 3 SiCl gives Me 3 SiF, LiCl and the iminosilane (Me 3 C) 2 (THF)Si=N-SiMe(CMe 3 ) 2 , 4 . Compound 4 can be distilled and recrystallized from benzene. Its crystal structure has been determined.

From aminosilane to iminosilane

Abstract Lithium derivatives of aminofluorosilanes are stable at room temperature and thus can be fully characterized by NMR spectroscopy, crystal structure analysis, etc. Crystal structure determinations prove that lithiated aminosilanes can, depending on the solvent and the substituent, be regarded as LiF adducts of iminosilanes. LiF elimination leads to dimerizations and interconversions of the iminosilanes formed. Lithiated aminosilanes react like silylamides as well as like iminosilanes. They are suitable precursors to iminosilanes after fluorine-chlorine exchange.

Stabilisation of silicenium ylids by adduct formation with aluminium trihalides: the crystal structure of [(Me3C)2SiNCMe3]2AlClF2

Abstract Lithium salts of t-butylamino-diorganylfluorosilanes [RR′SiFN(CMe3)Li] react with aluminium trichloride in petroleum ether, eliminating LiF, to give AlCl3 adducts of silicenium ylids, (RR′SiNCMe3)AlCl3. Hydrolysis of these adducts leads to Me3CNH2·AlCl3 and (RR′SiO)3). The compound [(Me3C)2SiNCMe3]2AlClF2 has been obtained as the major product of the reaction of (Me3C)2SiFN(CMe3)Li with Al2Cl6 in tetrahydrofuran. It forms orthorhombic crystals, space group Pnna, with a 16.063(2), b 21.896(2), c 17.987(2) A, Z = 8. The crystal structure has been determined from 3389 unique diffractometer-measured intensities, and refined to R=0.070. The molecular structure and NMR spectra support the formulation of this compound as a 2:1 adduct of a silicenium ylid with AlClF2. The hydrolysis product Me3CNH2·AlCl3 forms monoclinic crystals, space group P21/n, with a 8.348(5), b 10.908(4), c 11.322(9) A, β 103.63(10°, Z = 4, R = 0.052 for 1067 reflections. Molecules are monomeric in the solid state.

Characterization of AlN powder produced by the reaction of AlCl3 with hexamethyldisilazane

Preparation des poudres et caracterisation par diffraction des RX et microscopie electronique a balayage

Cyclosilazanes and borazines : polymer precursors to silicon- and boron-containing ceramics

The chemistry of cyclosilazanes and borazines is a topic of current interest in view of preceramic polymers which yield on pyrolysis various useful ceramic materials, e.g. silicon and boron carbide, silicon and boron nitride, and ternary or quaternary mixtures of these materials. These materials are hard and have high oxidative and thermal stability. Other useful properties are resistance to corrosion, thermal shock and creep, low electrical conductivity and low coefficient of thermal expansion. One of the best application prospects is the use of the preceramic polymers as protective coating material for carbon fibres.

Lithiumsalze eines Imino- und eines Aminosilans; Kristallstrukturen

Zusammenfassung The lithium salt of the iminosilane (THF)3 LiF(i-Pr)2Si=NC6H2(CMe3)3 (II) was obtained by the reaction of the aminofluorosilane (I) with methyllithium. The iminosilane character of the lithium salt II was confirmed by crystal structure analysis. The SiN doublebond length is 161.9(5) pm and an SiNC angle of 172.1(4)° is an imine angle. II is converted into the lithiated aminochlorosilane (III) by treating it with Me3SiCl. The crystal structure analysis of III affirmed the aminosilane character of this compound. The SiN bond length is 164.9 pm and the SiNC angle is 138.3°, which is a typical amine angle.

Synthesis and hydrolysis of a fluorosilyl-t-butylaminodichloroalane. Crystal structures of the cyclic compounds [(Me3SiNMe)2SiNCMe3]2 and (Me3CNHAlCl2)2

Abstract The lithium salt of t-butylaminofluorobis(methyltrimethylsilylamino)silane, (Me 3 SiNMe) 2 SiFNLiCMe 3 , reacts with aluminium trichloride to form a dimeric silylaminodichloroalane, [(Me 2 SiNMe) 2 SiFNCMe 3 AlCl 2 ] 2 (I); the cyclodisilazane [(Me 3 SiNMe) 2 SiNCMe 3 ] 2 (II) is formed as a by-product. Hydrolysis of I cleaves the SiN bonds to produce the four-membered ring compound (Me 3 CNHAlCl 2 ) 2 (III). II forms monoclinic crystals, space group P 2 1 / n , with a 10.721(2), b 10.099(2), c 17.166(3) A, β 93.46(2)°, Z = 2. III also crystallises in P 2 1 / n , with a 6.500(2), b 11.957(2), c 10.802(2) A, β 96.31(2)°, Z = 2. The structures were determined from 2655 and 1382 diffractometer-measured intensities, and refined to R = 0.046 and 0.032, respectively. Molecules of both compounds have crystallographic inversion centres, requiring planar four-membered rings (Si 2 N 2 and Al 2 N 2 , respectively), and additionally a trans arrangement of the nitrogen substituents in III.

Interconversions in Cyclosilazanes and their Application to Sin - Ceramics

Abstract Rearrangements occur very frequently in reactions of cyclosilazanes. We have found an equilibrium between the eight-, six-, and four-membered ring anions, which is strongly dependent on thermal and kinetic effects, the choice of substituents and the properties of the attacking group. Knowledge of the interconversion mechanisms has enabled us to prepare silyl-bridged and coupled cyclosilazanes of high molecular weight. These coumpounds are useful precursors of SiN-ceramics.

Synthesis of (SiNSiO) four-membered rings; crystal structure of (Me3C)2SiOSi(CMe3)2NSiMe3

Abstract Siloxanes (1–3), of the type are formed in the reaction of halogenosilanes with a lithiated aminosilanol. Lithium salts of 1–3 (4–6) react with halogenosilanes to yield 7–9 ; 8 and 9 are structural isomers. The silyl group introduced normally becomes bonded to the oxygen atom. The silyl group migration can be kinetically controlled, as shown by the formation of 7. Compounds 7 and 8 form the thermally stable lithium compounds 10, 11 , which are direct precursors of four-membered 1-oxa-3-aza-2,4-disiletanes (12, 13). The intramolecular cyclization is catalyzed by fluorosilanes present. The crystal structure of the four-membered (SiNSiO) ring species 12, has been determined, and its features are compared with those of ring species.