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Matthias Driess

Publications and source records attributed to Matthias Driess.

16 recordsLinked to original sources
PubMed2006

A new type of N-heterocyclic silylene with ambivalent reactivity.

The synthesis of a novel divalent silicon compound by debromination of the corresponding dibromosilyl precursor is reported. The silylene possesses a unique reactivity toward electrophiles of the type R-X (R = H, silyl; X = halogen, triflate) in comparison with the germanium congener. DFT calculations suggest that this is due to a much higher basicity of the silylene versus that of germylene lone-pair electrons. Thus, addition of Me3SiX to the silylene (X = OSO2CF3, triflate) furnishes the corresponding (kinetically favored) 1,4-adduct which subsequently rearranges to the thermodynamically favored 1,1-adduct.

Journal Article↗
PubMed2005

Chemical vapor synthesis of size-selected zinc oxide nanoparticles.

ZnO can be regarded as one of the most important metal oxide semiconductors for future applications. Similar to silicon in microelectronics, it is not only important to obtain nanoscale building blocks of ZnO, but also extraordinary purity has to be ensured. A new gas-phase approach to obtain size-selected, nanocrystalline ZnO particles is presented. The tetrameric alkyl-alkoxy zinc compound [CH(3)ZnOCH(CH(3))(2)](4) is chemically transformed into ZnO, and the mechanism of gas-phase transformation is studied in detail. Furthermore, the morphological genesis of particles via gas-phase sintering is investigated, and for the first time a detailed model of the gas-phase sintering processes of ZnO is presented. Various analytical techniques (powder XRD, TEM/energy-dispersive X-ray spectroscopy, magic-angle spinning NMR spectroscopy, FTIR spectroscopy, etc.) are used to investigate the structure and purity of the samples. In particular, the defect structure of the ZnO was studied by photoluminescence spectroscopy.

Gases↗
PubMed2004

Novel hypervalent complexes of main-group metals by intramolecular ligand-->metal electron transfer.

New fascinating electronic features of the simple diketoamine chelate ligand HN[CH2C(tBu)=O]2 (1) are described. Unexpectedly, the corresponding trianionic amido-dienolate form of 1 is capable of reducing main-group metal atoms M after initial coordination and intramolecular L-->M two-electron transfer and of stabilizing main-group elements in unusual low oxidation states. This is impressively shown by the synthesis and structural characterization of the novel Ge and Sn complexes 4-6 by redox reactions of lithiated 1 with the corresponding metal halides GeCl4 and MCl2 (M=Ge, Sn). Surprisingly, conversion of tris-lithiated 1 with GeCl4 readily consumes two molar equivalents of GeCl4 and results in the formation of the neutral GeCl3 complex 4 and GeCl2. The former represents the second example of a structurally characterized neutral octahedrally coordinated germanium compound. Reaction of dilithiated 1 with GeCl2 does not lead to the expected ClGe(+2) complex but affords the novel dimeric germylene 5, whereas similar reaction using SnCl2 furnishes the monomeric stannylene (ClSn(+2) complex) 2 and elemental tin due to the higher oxidation potential of Sn(+2). Unexpectedly, a similar redox reaction of dilithiated 1 with PbCl2 furnishes the first air- and water-stable lithium 1,2-diketoimine-enolate 7 and elemental lead. Compound 7 is tetrameric in the solid state and consists of a strongly distorted Li4O4 cubic core with trigonal-bipyramidal coordinated Li+ ions.

Journal Article↗
PubMed2004

First preparation of nanocrystalline zinc silicate by chemical vapor synthesis using an organometallic single-source precursor.

A method is presented to prepare nanocrystalline alpha-Zn(2)SiO(4) with the smallest crystal size reported so far for this system. Our approach combines the advantages of organometallic single-source precursor routes with aerosol processing techniques. The chemical design of the precursor enables the preferential formation of pure zinc silicates. Since gas-phase synthesis reduces intermolecular processes, and keeps the particles small, zinc silicate was synthesized from the volatile organometallic precursor [[MeZnOSiMe(3)](4)], possessing a Zn-methyl- and O-silyl-substituted Zn(4)O(4)-heterocubane framework (cubane), under oxidizing conditions, using the chemical vapor synthesis (CVS) method. The products obtained under different process conditions and their structural evolution after sintering were investigated by using various analytical techniques (powder X-ray diffraction, transmission electron microscopy, EDX analysis, solid-state NMR, IR, Raman, and UV/Vis spectroscopy). The deposited aerosol obtained first (processing temperature 750 degrees C) was amorphous, and contained agglomerates with primary particles of 12 nm in size. These primary particles can be described by a [Zn-O-Si] phase without long-range order. The deposit obtained at 900 degrees C contained particles with embedded nanocrystallites (3-5 nm) of beta-Zn(2)SiO(4), Zn(1.7)SiO(4), and ZnO in an amorphous matrix. On further ageing, the as-deposited particles obtained at 900 degrees C form alpha-Zn(2)SiO(4) imbedded in amorphous SiO(2). The crystallite sizes and primary particle sizes in the formed alpha-Zn(2)SiO(4) were found to be below approximately 50 nm and mainly spherical in morphology. A gas-phase mechanism for the particle formation is proposed. In addition, the solid-state reactions of the same precursor were studied in detail to investigate the fundamental differences between a gas-phase and a solid-state synthesis route.

Organometallic Compounds↗
PubMed2003

Synthesis of the first fluoro(phosphanyl)- and diphosphanyl-stannanes and surprising formation of [P(SnMe3)4]+ SiF5-.

Monophosphanylation of the difluorostannane Is2SnF2 (Is = 2,4,6-triisopropylphenyl) with Si(PH2)4 furnishes the first isolable fluoro(phosphanyl)stannane Is2Sn(F)PH2 1, which readily undergoes unique SiO2-assisted decompostion to [Is2Sn(PH)]2 2 and HF, while further phosphanylation of 1 leads to the remarkably stable diphosphanylstannane Is2Sn(PH2)2 3; the latter reacts with Me3SnF at the glass-wall to give the first perstannylphosphonium pentafluorosilicate [P(SnMe3)4]+ SiF5- 4.

Journal Article↗
PubMed2002

Germanium(IV) chloride at 193 K.

Single crystals of germanium(IV) tetrachloride, GeCl(4), were grown at 193 K. In the crystal structure, the isolated molecules have very well realised tetrahedral geometry.

Journal Article↗