Uwe Böhme

Octahedral HSiCl3 and HSiCl2Me adducts with pyridines.

Stable solid adducts of substituted pyridines (Rpy) with HSiCl(3) and HSiCl(2)Me were prepared in high yields under aprotic and anaerobic conditions at room temperature. The octahedral complexes of HSiCl(3) underwent dismutation reactions in polar solvents. In contrast, the HSiCl(2)Me(Rpy)(2) adducts were not susceptible to dismutation under comparable conditions, but they tended to dissociate more easily because of the reduced Lewis acidity of HSiCl(2)Me relative to HSiCl(3). The bonding between silicon and its surrounding ligands is highly ionic, as can be seen from QTAIM and charge distribution analyses. (29)Si CP/MAS spectra in combination with quantum-chemical calculations show that the lowest shielding is along the Cl-Si-Cl axis. The other two components of the shielding tensor are oriented along the N-Si-N and H-Si-Cl/Me axes. It is known that many reactions of (hydrido)chlorosilanes are catalyzed by pyridine bases. Therefore, the results presented here provide a basis for better control of these reactions, especially chlorine substitution and hydrosilylation.

Octahedral Adducts of Dichlorosilane with Substituted Pyridines: Synthesis, Reactivity and a Comparison of Their Structures and 29Si NMR Chemical Shifts

H(2)SiCl(2) and substituted pyridines (Rpy) form adducts of the type all-trans-SiH(2*)Cl(2)2 Rpy. Pyridines with substituents in the 4- (CH(3), C(2)H(5), H(2)C=CH, (CH(3))(3)C, (CH(3))(2)N) and 3-positions (Br) give the colourless solids 1 a-f. The reaction with pyrazine results in the first 1:2 adduct (2) of H(2)SiCl(2) with an electron-deficient heteroaromatic compound. Treatment of 1 d and 1 e with CHCl(3) yields the ionic complexes [SiH(2)(Rpy)(4)]Cl(2*)6 CHCl(3) (Rpy=4-methylpyridine (3 d) and 4-ethylpyridine (3 e)). All products are investigated by single-crystal X-ray diffraction and (29)Si CP/MAS NMR spectroscopy. The Si atoms are found to be situated on centres of symmetry (inversion, rotation), and the Si-N distances vary between 193.3 pm for 1 c (4-(dimethylamino)pyridine complex) and 197.3 pm for 2. Interestingly, the pyridine moieties are coplanar and nearly in an eclipsed position with respect to the SiH(2) units, except for the ethyl-substituted derivative 1 e, which shows a more staggered conformation in the solid state. Calculation of the energy profile for the rotation of one pyridine ring indicates two minima that are separated by only 1.2 kJ mol(-1) and a maximum barrier of 12.5 kJ mol(-1). The (29)Si NMR chemical shifts (delta(iso)) range from -145.2 to -152.2 ppm and correlate with the electron density at the Si atoms, in other words with the +I and +M effects of the substituents. Again, compound 1 e is an exception and shows the highest shielding. The bonding situation at the Si atoms and the (29)Si NMR tensor components are analysed by quantum chemical methods at the density functional theory level. The natural bond orbital analysis indicates polar covalent Si-H bonds and very polar Si-Cl bonds, with the highest bond polarisation being observed for the Si-N interaction, which must be considered a donor-acceptor interaction. An analysis of the topological properties of the electron distribution (AIM) suggests a Lewis structure, thereby supporting this bonding situation.

Preparation, characterization and properties of dipolar 1,2-N,N-dimethylaminomethylferrocenylsilanes

Abstract A series of substituted 1,2-N,N-dimethylaminomethylferrocenyl compounds were synthesized and characterized by 1H-NMR, 13C-NMR, 29Si-NMR, ES–MS, IR, UV–vis and 57Fe-Mossbauer spectroscopy. The new (R,S)-2-(N,N-dimethylaminomethyl)ferrocenyl-(aryl)silanes (R,S)-FcNSiMen(C6H4X)m (n=2–0, m=1, X=p-F (5); m=2, X=p-F (6); m=3, X=p-F (7) and m=1, X=p-Br (14) were formed by the reaction of 2-dimethylaminomethylferrocenyllithium FcNLi (1) with chloroarylsilanes ClSi(Me)n(C6H4X)m (n=2–0, m=1, X=p-F (2); m=2, X=p-F (3); m=3, X=p-F (4) and m=1, X=p-Br (13)). The treatment of 5, 6 and 14 with gaseous hydrogen chloride or picric acid resulted in the formation of the hydrochloride complexes 9, 10, 15 and the picrates 11, 12 and 16. The treatment of 14 with LiR or Mg and DMF resulted in the formation of (R,S)-2-(N,N-dimethylaminomethyl)ferrocenyl(4-formylphenyl)dimethylsilane (18). The crystal structures of 7, 12 and 15 were determined by single crystal X-ray analyses. 57Fe-Mossbauer spectroscopy gives evidence of a significant electronic coupling between the ferrocenyl unit and the organic acceptor moiety of the molecules in the ground state.

Formation and characterization of cyclic and polycyclic silthianes containing Si Si bonds

Abstract The reactions of several organochlorosilanes and -oligosilanes with H2S and NEt3 have been investigated. Different bicyclic silthianes with bis-cyclopentyl, bicyclo-[3,3,0]-octane, bicyclo-[2,2,1]-heptane (norbornane), bicyclo-[3,2,1]-octane, bicyclo-[2,2,2]-octane and bicyclo-[3,2,1]-nonane skeletons were formed and have been characterized by MS and 1H-, 13C- and 29Si-NMR. The reaction of 1,1,2,2-tetrachlorodimethyldisilane with H2S and NEt3 yields 1,3,5,7,9,11-hexamethyl-1,3,5,7,9,11-hexasila-2,4,6,8,10,12-hexathiatetracyclo-[5,5,03,11,05,9]-dodecane (4c) containing three disilane units. Density functional theory calculations proved the general observation that compounds with Si3S2 five-membered rings are preferred. The crystal structures of 4c, 1,3,3,5,7,7-hexamethyl-1,3,5,7-tetrasila-2,4,6,8-tetrathiabicyclo-[3,3,0]-octane (6) and 1,2,2,4,4,5,6,6,8,8-decamethyl-1,2,4,5,6,8-hexasila-3,7-dithiabicyclo-[3,3,0]-octane (9) have been determined.

Hexacoordinate Silicon-Azomethine Complexes: Synthesis, Characterization, and Properties

N,N′-Ethylene-bis(2-hydroxyacetophenoneimine) = salen*H2 and N,N′-ethylene-bis(3,5-di-tert-butyl-salicylideneimine) = salen′H2 react both with SiCl4 under formation of hexacoordinate silicon compounds ((salen′)SiCl2′ salen′ = salen* or salen‡). The analogous fluoro derivatives (salen′)SiF2 have been prepared by reaction of (salen′)SiCl2 with ZnF2. X-ray structure analysis of (salen*)SiF2 clearly demonstrates the octahedral coordination of silicon. Salen* acts as a tetradentate chelating ligand, two halogen atoms remaining at the silicon atom. The reduction of (salen*)SiCl2 by alkaline metal affords polysilanes containing main chain hexacoordinate silicon. Coupling with acetylides results in polycarbosilanes with a Si-C≡C-Si backbone.

Synthesis of silicophosphates containing SiO6-octahedra under ambient conditions – reactions of anhydrous H3PO4 with alkoxysilanes

Anhydrous H(3)PO(4) reacts in diethylether solution at room temperature with ethoxysilanes to form silicophosphates which contain SiO(6)-units. A single crystal X-ray structure provides evidence for silicophosphate structures comprised of alternating SiO(4)- and PO(4)-tetrahedra as well as SiO(6)-octahedra.

Melem- and melamine-derived iminophosphoranes

Iminophosphorane derivatives of s-triazine and tri-s-triazine, C3N3(NPCl3)3 (1), [H2C3N3NH2(NPPh3)2]Br2 (2), [HC3N3NH2(NPPh3)2]Br (3), C6N7(NPCl3)3 (5), [HC6N7(NPCl3)3]Cl (6) were obtained by the Kirsanov reaction of melamine (1–3) and melem (5 and 6) with halogenated phosphorus compounds. The products were characterized by FTIR and solution NMR spectroscopy as well as by single-crystal X-ray diffraction. Additionally, in order to investigate the electron density distribution in the s-triazine or s-heptazine systems combined with the phosphinimine group, and to understand the influence of protonation on the triazine and heptazine moieties, quantum chemical analyses of compounds 2, 3, 5 and 6 were performed. Furthermore, by reaction of 5 with phenol the compound C6N7(NP(OPh)3)3 (7) was obtained. Its potential application as a flame retardant was examined by the UL 94 flammability test.

Use of melem as a nucleophilic reagent to form the triphthalimide C6N7(phthal)3--new targets and prospects.

Melem (1), as one of the most important representatives of the tri-s-triazine compounds, can be used as a nucleophilic reagent in reactions with phthalic acid derivatives. The synthesis of 2,5,8-triphthalimido-tri-s-triazine (C(6)N(7)(phthal)(3), 2) was investigated starting from phthalic anhydride or phthalic dichloride in various solvents, at different temperatures as well as in the solid state. NMR measurements (solution and solid state), IR spectroscopy and elemental analysis indicated the formation of a cyclic imide. Single-crystal structure analysis of a 1:1 adduct of 2 with nitromethane proved the molecular structure expected for a phthalimido-s-heptazine. DFT calculations were performed to obtain a better insight into the structural features of compound 2, especially the interaction of the carbonyl groups with the tri-s-triazine nitrogen atoms. The title compound 2 shows promising properties: it is thermally stable up to 500 °C in air and shows strong photoluminescence with a maximum emission at around 500 nm. The potential of the nucleophilic reaction of melem with other strong electrophiles provides new targets and prospects.

Group 14 chalcogenides featuring a bicyclo[3.3.0]octane skeleton

Abstract Reactions of mixtures of Cl2MeSiSiMeCl2 (1) and Me2MCl2 (M=Si, Ge, Sn) with either H2S/NEt3 or Li2E (E=Se, Te) yielded the bicyclo[3.3.0]octanes Me2M(E)2Si2Me2(E)2MMe2. A carbon containing analog, (CH2)5C(S)2Si2Me2(S)2C(CH2)5, was prepared from 1 and (CH2)5C(SH)2. Crystal structures of three of these compounds were determined and the observed conformations of the bicyclo[3.3.0]octane skeletons compared with results of density functional theory calculations. Another class of silchalcogenides featuring a bicyclo[3.3.0]octane skeleton, E(Me2Si)2Si2Me2(SiMe2)2E, was formed from the doubly branched hexasilane (ClMe2Si)2Si2Me2(SiMe2Cl)2 and H2S/NEt3 or Li2E. All products were characterized by multinuclear NMR (1H, 13C, 29Si, 77Se, 119Sn, and 125Te).

Crystalline packings of diketoarylhydrazones controlled by a methyl for trifluoromethyl structural change

Three new hydrazone compounds having a p-iodoaryl and diketohydrazone molecular skeleton in common but feature a gradual replacement of the two methyl groups for trifluoromethyl terminal ones were prepared and comparatively studied with regard to their crystal structures. A quantum chemical calculation of the single trifluoromethyl modified compound was undertaken to decide on the hydrogen bonded ring site. While the molecular structures of the compounds remain rather unimpaired by the fluorine substitution, their crystalline packings are markedly affected, showing a distinct supramolecular control in the crystal lattices.