Challenges in the Synthesis and Processing of Hydrosilanes as Precursors for Silicon Deposition.

Hydrosilanes are highly attractive compounds, which can be processed as liquids with printing technology to amorphous silicon films on nearly any solid substrate. The silicon layers can be processed for electronic devices like transistors or thin-film solar cells. The endothermic character of hydrosilanes with their positive enthalpies of formation results in favorable properties for processing. The larger the molecules, the lower their decomposition temperature and the higher their photoactivity. Cyclic hydrosilanes such as cyclopentasilane and cyclohexasilane can be easily deposited. The branched neopentasilane is more difficult to deposit but yields better-quality films after processing. The key challenge is the complex synthesis of the precursors and the hydrosilanes. The available preparative methods are presented in this review and their advantages and disadvantages are evaluated. The following synthesis methods are presented and discussed in this article: Wurtz coupling and other reductive coupling processes, dehydrogenative coupling of silanes, plasma synthesis of chlorinated polysilanes, amine- or chloride-induced disproportionations, and transformation of monosilane to higher silanes. Plasma synthesis is already carried out today as a continuous industrial process. The most effective synthesis methods in the laboratory are currently amine- and chloride-induced disproportionations. There is a great need to further optimize the syntheses of hydrosilanes and to develop new simple synthesis variants.

{N-[1-(2-Oxidophen-yl)ethyl-idene]-dl-alaninato}(pentane-1,5-di-yl)silicon(IV).

The title SiIV complex, C16H21NO3Si, is built up by a tridentate dinegative Schiff base ligand bound to a sila-cyclo-hexane unit. The coordination geometry of the penta-coordinated SiIV atom is a distorted trigonal bipyramid. The presence of the sila-cyclo-hexane ring in the complex leads to an unusual coordination geometry of the SiIV atom with the N atom from the Schiff base ligand and an alkyl-C atom in apical positions of the trigonal bipyramid. There is a disorder of the methyl group at the imine bond with two orientations resolved for the H atoms [major orientation = 0.55 (3)]. In the crystal, C-H⋯O inter-actions are found within corrugated layers of mol-ecules parallel to the ab plane.

New Complexes of Antimony(III) with Tridentate O,E,O-Ligands (E = O, S, Se, Te, NH, NMe) Derived from N-Methyldiethanolamine.

We synthesized a series of new antimony(III) compounds by reaction of Sb(OEt)3 with organic ligands of the type E(CH2-CH2-OH)2, with E = NH, NMe, O, S, Se, and Te. The synthesized compounds have the general composition [E(CH2-CH2-O)2]Sb(OEt). For comparison, the compound (O-CH2-CH2-S)Sb(OEt) was prepared. All compounds are characterized using NMR, IR, and Raman spectroscopy. The molecular structures of the products reveal the formation of chelate complexes, wherein the ligand molecules coordinate as tridentate O,E,O-ligands to the antimony atom. Dimer formation in the solid state allows the antimony atoms to reach pentacoordination. Quantum chemical calculations including topological analysis of electron density reveal that there are polar shared bonds between antimony and the oxygen atoms bound to antimony. The interactions between the donor atom E and the Sb atom and the interactions in the dimers can be characterized as Van der Waals interactions. The reactivity of [MeN(CH2-CH2-O)2]Sb(OEt) was investigated as an example. For this purpose, the compound reacted with a range of organic compounds such as carboxylic acids and carboxylic anhydrides and small molecules like CO2 and NH3. This study establishes a new and easy accessible class of antimony(III) compounds, provides new insights into the chemistry of antimony compounds and opens up new opportunities for further research in this field.

9-(Pyrrolidinium-1-yl)-9-boranuidabi-cyclo-[3.3.1]nona-ne.

The title compound, C12H24BN, is an adduct formed from 9-borabi-cyclo-[3.3.1]nonane (9-BBN) and pyrrolidine. It crystallizes in the triclinic space group P with three mol-ecules in the asymmetric unit, one of which has disorder of the pyrrolidine ring. The B-N bond lengths are between 1.631 (2) and 1.641 (2) Å. The boron and nitro-gen atoms are bound to one hydrogen atom each. These hydrogen atoms are in anti-periplanar orientation. Both six-membered rings of the 9-BBN unit are in a chair conformation in all three mol-ecules. Differences between the three crystallographic independent mol-ecules are found in the five-membered rings of the pyrrolidine unit. These adopt different twisted and envelope conformations.

{N-[(4-Meth-oxy-2-oxidophen-yl)(phen-yl)methyl-idene]glycinato}di-phenyl-silicon(IV).

The title compound, C28H23NO4Si, crystallizes in the monoclinic space group P21/c. The silicon complex consists of a tridentate dinegative Schiff base ligand bound to a di-phenyl-silyl unit. The coordination geometry of the penta-coordinate silicon atom is a distorted trigonal bipyramid.

Two polymorphs of N,N'-diphenyl-2-[1-(propyl-amino)-ethyl-idene]propanedi-amide.

Two polymorphs of the title compound, C20H23N3O2, have been isolated. Polymorph (I) crystallizes in the monoclinic space group P2 1/n and polymorph (II) in the tetra-gonal space group I4 1/a. The main difference between the two polymorphs on the mol-ecular level is the orientation of the n-propyl group. This group is anti-periplanar in (I) and synclinal in (II). The core of the mol-ecule consists of two carbamoyl units bound to an enamine unit. The most prominent features are intra-molecular N-H⋯O hydrogen bonds in both polymorphs. Both polymorphs form dimers with graph set R 2 2(12) via inter-molecular N-H⋯O hydrogen bonds. Adjacent dimers of (I) are connected via a weak C-H⋯O inter-action, resulting in a chain parallel to the crystallographic a-axis. The dimers of (II) are connected by weak C-H⋯π inter-actions, forming inter-molecular chains along the c-axis direction.

(E)-N-Phenyl-N-(phenyl-carbamo-yl)-3-[prop-yl(tri-methyl-sil-yl)amino]-acryl-amide chloro-form hemisolvate.

The title compound, C22H29N3O2Si·0.5CHCl3, crystallizes in the the triclinic space group P with two host mol-ecules and one chloro-form mol-ecule in the asymmetric unit. The core of the mol-ecule consists of a urea unit bound to a 3-amino-acryloyl group. These units are almost planar in both mol-ecules [average deviation from plane of 0.05 (6) Šin mol-ecule A and 0.04 (5) Šin mol-ecule B]. The main difference between mol-ecules A and B involves the dihedral angles of the phenyl groups. One phenyl ring makes dihedral angles of 71.14 (6)° (mol-ecule A) and 82.81 (7)° (mol-ecule B) with respect to the core (C4N3O2) of the mol-ecule [14.56 (9)° (mol-ecule A) and 5.7 (1)° (mol-ecule B) for the other phenyl ring]. Another prominent feature is the intra-molecular N-H⋯O hydrogen bond present in both crystallographically independent mol-ecules.

Synthesis and temperature-dependent NMR studies of monomeric and dimeric tris(dialkylamido)alanes.

After an introductory overview of all currently known tris(dialkylamido)alanes with the formula [Al(NR2)3]n (n = 1, 2), a simplified synthetic method based on the usage of is presented. The simplification results from the fact that the ether adduct can already be obtained during the necessary synthesis of the alane moiety and that the use of trimethylamine is no longer required. Current conflicts regarding the experimental data of tris(diethylamido)alane and their interpretation have been resolved by means of single crystal structure analysis. The N-methylpiperazine derivative was described for the first time and characterised by various analytical methods. In temperature-dependent NMR measurements ranging from -35 °C to 90 °C coalescence phenomena of 13C and 1H NMR signals of tris(N-methylpiperazino)alane as well as thermal migration of 1H NMR signals of tris(diethylamido)alane were observed.

Formation of a macrocycle from di-chloro-dimethyl-silane and a pyridoxalimine Schiff base ligand.

The reaction of di-chloro-dimethyl-silane with a polydentate Schiff base ligand derived from pyridoxal and 2-ethano-lamine yielded the macrocyclic silicon compound (8E,22E)-4,4,12,18,18,26-hexa-methyl-3,5,17,19-tetra-oxa-8,13,22,27-tetra-aza-4,18-disilatri-cyclo-[22.4.0.010,15]octa-cosa-1(24),8,10,12,14,22,25,27-octa-ene-11,25-diol, C24H36N4O6Si2. The asymmetric unit contains the half macrocycle with an intra-molecular O-H⋯N hydrogen bond between the imine nitro-gen atom and a neighbouring oxygen atom. The crystal structure is dominated by C-H⋯O and C-H⋯π inter-actions, which form a high ordered mol-ecular network.

Syntheses and Molecular Structures of Liquid Pyrophoric Hydridosilanes.

Trisilane, isotetrasilane, neopentasilane, and cyclohexasilane have been prepared in gram scale. In-situ cryo crystallization of these pyrophoric liquids in sealed capillaries on the diffractometer allows access to the single crystal structures of these compounds. Structural parameters are discussed and compared to gas-phase electron diffraction structures from literature and with the results from quantum chemical calculations. Significantly higher packing indices are found for the silanes compared to the corresponding alkanes. Radiation with ultraviolet light (365 nm) and parallel ESR (EPR) measurement shows that cyclohexasilane is easily split into radicals, which subsequently leads to the formation of branched and chain-like oligomers. The other compounds form no radicals under these conditions. NMR spectra of all four compounds have been recorded.

6-[(2-Hy-droxy-5-methyl-anilino)methyl-idene]-4-nitro-cyclo-hexa-2,4-dien-1-one.

The title compound, C14H12N2O4, is nearly planar with a dihedral angle between the aromatic rings of 1.41 (8)°. The phenolic O atom is deprotonated and the N atom of the azomethine unit carries the proton, thereby forming an intra-molecular N-H⋯O hydrogen bond. In the crystal, the mol-ecules form inversion dimers via pairwise O-H⋯O hydrogen bonds.

(3,5-Dimethyl-1H-pyrazol-1-yl)tri-methyl-silane.

The title compound, C8H16N2Si, crystallizes in the the ortho-rhom-bic space group P212121 with one mol-ecule in the asymmetric unit. The Si-N bond is 1.782 (2) Å, which is substanti-ally longer than is found in comparable (3,5-di-methyl-pyrazol-yl)silanes. The tri-methyl-silyl group adopts a staggered conformation with respect to the planar 3,5-di-methyl-pyrazolyl unit. C-H⋯N hydrogen bonds between neighboring mol-ecules form a strand of mol-ecules along the b-axis direction.

Synthesis of Thiocyameluric Acid C6 N7 S3 H3 , Its Reaction to Alkali Metal Thiocyamelurates and Organic Tris(dithio)cyamelurates.

Thiocyameluric acid C6 N7 S3 H3 , the tri-thio analogue of cyameluric acid, is a key compound for the synthesis of new s-heptazine (tri-s-triazine) derivatives. Here, two different routes for the synthesis of thiocyameluric acid and its reaction to tris(aryldithio)- and tris(alkyldithio)cyamelurates C6 N7 (SSR)3 are reported as well as transformation to alkali metal thiocyamelurates M3 [C6 N7 S3 ], M=Na, K. These compounds were characterised by FTIR, Raman, solution 13 C and 1 H NMR spectroscopies, thermal gravimetric analysis (TGA) and elemental analysis. The three (de)protonation steps of thiocyameluric acid were investigated by acid-base titration followed via UV/Vis absorption spectroscopy. While it was not possible to determine the three pKa values, it could be postulated that the acid strength probably increases in the following order: cyanuric acid (C3 N3 O3 H3 ) < thiocyanuric acid (C3 N3 S3 H3 ) < cyameluric acid (C6 N7 O3 H3 ) < thiocyameluric acid (C6 N7 S3 H3 ). Single crystals of Na3 [C6 N7 S3 ]⋅10 H2 O and K3 [C6 N7 S3 ]⋅6 H2 O were obtained and the structures analyzed by single crystal X-ray diffraction. Additionally, quantum chemical calculations were performed to get insights into the electronic structure of thiocyameluric acid and to clarify the thiol-thione tautomerism. Based on a comparison of calculated and measured vibrational spectra it can be concluded that thiocyameluric acid and the di- and mono-protonated anions exist in the thione form.

The heteroscorpionate ligand 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethanol and an easy preparation of its tungsten complex.

The heteroscorpionate ligand 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethanol, C24H26N4O, features in the solid state an intramolecular O-H...N hydrogen bond. A heteroscorpionate tungsten complex, cis-[2,2-bis(3,5-dimethylpyrazolyl)-1,1-diphenylethanolato]chloridodioxidotungsten(VI) tetrahydrofuran monosolvate, [W(C24H25N4O)ClO2]·C4H8O, was prepared by the simple mixing of solutions of the ligand and WOCl4 in tetrahydrofuran. The tungsten complex was isolated after standing for several weeks. The complex exhibits a κ3N,N',O-coordination of the ligand. This simple synthetic procedure allows access to the cis isomer in high yield without additional purification steps. The Hirshfeld surface analysis shows a change of the intermolecular contacts due to the coordination of the WO2Cl unit with the ligand molecule.

Sulfides and Disulfides of s-Triazine: Potential Thermal Thiyl Radical Generators.

A series of aliphatic and aromatic thioethers and dithioethers of s-triazine were synthesised to study their thermal properties, in particular the thermally induced thiyl radical generation ability. Four symmetric s-triazine sulfides of the type (RS)3 C3 N3 , namely 2,4,6-tris(phenylthio)- (1), 2,4,6-tris(para-tolylthio)- (3), 2,4,6-tris(ethylthio)- (5) and 2,4,6-tris(tert-butylthio)-1,3,5-triazine (7), as well as four symmetric s-triazine disulfides of the type (RSS)3 C3 N3 , namely 2,4,6-tris(phenyldithio)- (2), 2,4,6-tris(para-tolyldithio)- (4), 2,4,6-tris(ethyldithio)- (6) and 2,4,6-tris(tert-butyldithio)-1,3,5-triazine (8) were synthesised. All compounds were comprehensively characterised by 1 H and 13 C NMR, infrared and Raman spectroscopy as well as elemental analyses. Single-crystal X-ray diffraction analyses of 1, 2 and 5 are discussed. The thermal behaviour was studied by thermogravimetric analyses coupled with mass spectrometry (TGA-MS) and quantum chemical calculations. Limiting oxygen index (LOI) flammability tests showed that the disulfides are the most promising radical generators, and are most likely suitable flame retardants for selected polymers.

Arylthio- and Arylseleno-Substituted s-Heptazines.

In contrast to numerous thio- and selenocyanuric acid derivatives, sulfur- or selenium-containing s-heptazines have not been reported so far. Thio- and selenocyameluric acid esters were obtained by substitution reactions of s-heptazine chloride C6 N7 Cl3 with aromatic thiols and selenophenol; the resultant white or yellow solids were stable in air. They were comprehensively characterized by elemental analysis, 1 H, 13 C NMR, and IR spectroscopy. The thiocyameluric acid phenyl ester (1, C6 N7 (S(C6 H5 ))3 ) and the corresponding selenium compound (7) formed co-crystals with mesitylene, which were analyzed by single-crystal X-ray diffraction. Both structures showed unusually large channels of ≈12 Šdiameter. The thermal stability was measured by TGA (thermogravimetric analysis), and the flame retardancy of compound 1 was tested in PP by carrying out limiting oxygen index (LOI) measurements, which gave promising results. Quantum chemical calculations of the title compounds were performed to explain the observed properties and structural characteristics.

Two reversible enantiotropic phase transitions in a pentacoordinate silicon complex with an O,N,O'-tridentate valinate ligand.

Dimethyl[N-(4-oxidopent-3-en-2-ylidene)valinato-κ(3)O,N,O']silicon(IV), C12H21NO3Si, (II), crystallizes in the orthorhombic space group P212121. The chiral compound undergoes two sharp enantiotropic phase transitions upon cooling. The first transformation occurs at 163 K to yield a unit cell with one axis having double length. This intermediate-temperature form has the monoclinic space group P21. The second transition takes place at 142 K and converts the single crystal into the low-temperature form in the orthorhombic space group P212121. This transition proceeds under tripling of the a axis of the high-temperature form. Both phase transitions are fully reversible and correspond to order-disorder transitions of the isopropyl group of the valine unit in the ligand backbone. The phase transitions presented here raise questions, since they do not fit into the rules of group-subgroup relationships.

Enantiotropic phase transition in a binuclear tin complex with an O,N,O'-tridentate ligand.

The crystal structure of chlorido{µ-2-[(2-oxidobenzylidene)amino]ethanolato-κ(4)O,N,O':O'}{2-[(2-oxidobenzylidene)amino]ethanolato-κ(3)O,N,O'}trivinylditin(IV), [Sn2(C2H3)3(C9H9NO2)2Cl], is disordered above 178 K. A doubling of the unit-cell volume is observed on cooling. The asymmetric unit at 93 K contains two ordered molecules. The phase transition corresponds to an order-disorder transition of one vinyl group bound to the Sn(IV) atom.

Enantiomerically pure and racemic dimethyl{N-[(2-oxidonaphthalen-1-yl-κO)methylidene]valinato-κ2N,O}tin(IV).

The title compound, [Sn(CH(3))(2)(C(16)H(15)NO(3))], crystallized from one reaction batch with high enantiomeric excess as both a pure enantiomer and a racemate. The S enantiomer crystallizes in the chiral space group P3(2). The racemate crystallizes in the space group P1 with R and S enantiomers in the crystal lattice; these form dimers about a crystallographic inversion centre.

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.