Browsing by Author "Stern, Daniel"

Pyrido[2',1':2,3] imidazo[4,5-c]isoquinolin-5(6H)-ones such as the title compound, C(24)H(21)N(3)O(3), can be obtained in a few minutes in a microwave-assisted three-component reaction from 2-aminopyridines, isocyanides and 2-carboxybenzaldehydes. In the title compound, the pyrido[2',1':2,3]imidazo[4,5-c] isoquinolin-5(6H)-one ring system is almost planar (mean deviation 0.068 angstrom). The dihedral angle between the benzyl ring and the pyrido[2',1':2,3] imidazo[4,5-c] isoquinolin-5(6H)-one ring system is 78.2 degrees. The crystal structure is stabilized by intermolecular C-H center dot center dot center dot O and C-H center dot center dot center dot N hydrogen bonds.

Experiments are described in which a direct comparison was made between a conventional 2 kW water-cooled sealed-tube X-ray source and a 30 W air-cooled microfocus source with focusing multilayer optics, using the same goniometer, detector, radiation (Mo K alpha), crystals and software. The beam characteristics of the two sources were analyzed and the quality of the resulting data sets compared. The Incoatec Microfocus Source (I mu S) gave a narrow approximately Gaussian-shaped primary beam profile, whereas the Bruker AXS sealed-tube source, equipped with a graphite monochromator and a monocapillary collimator, had a broader beam with an approximate intensity plateau. Both sources were mounted on the same Bruker D8 goniometer with a SMART APEX II CCD detector and Bruker Kryoflex low-temperature device. Switching between sources simply required changing the software zero setting of the 2 theta circle and could be performed in a few minutes, so it was possible to use the same crystal for both sources without changing its temperature or orientation. A representative cross section of compounds (organic, organometallic and salt) with and without heavy atoms was investigated. For each compound, two data sets, one from a small and one from a large crystal, were collected using each source. In another experiment, the data quality was compared for crystals of the same compound that had been chosen so that they had dimensions similar to the width of the beam. The data were processed and the structures refined using standard Bruker and SHELX software. The experiments show that the I mu S gives superior data for small crystals whereas the diffracted intensities were comparable for the large crystals. Appropriate scaling is particularly important for the I mu S data.

Various 2-thienyllithium derivatives were investigated in the solid state by X-ray diffraction and in solution by 2D NMR experiments. The determined structures of [(Et2O)Li(C4H3S)](4) (1), [(THF)(2),Li(C4H3S)](2) (2), [(DME)Li(C4H3S)](2), (3), [(TMEDA)Li(C4H3S)](2) (4), and [(PMDETA)Li(C4H3S)] (5) (DME = 1,2-dimethoxyethane, TMEDA = N,N,N',N'-tetramethylethylene-1,2-diamine, and PMDETA = N,N,N',N",N"-pentamethyldiethylenetriamine) were solved in nondonating toluene and provide firm ground for diffusion-ordered NMR spectroscopy as well as heteronuclear Overhauser enhancement NMR spectroscopy. The distance relation of nuclear Overhauser effects with a factor of r(-6) is employed to gain further insight into the aggregation degree of 1-5 in solution. Comparison of the slope provided by the linear region of the buildup curves and of the Sigma r(-6) calculated distances from the crystal structures offers a handle to judge the structure retention versus conversion in solution. The structures of 3-5 are maintained in toluene solution. The data of 2, however, indicate a partial dissociation or a rapid exchange between the vertices of a tetrameric core and free THF molecules. Auxiliary exchange spectroscopy investigations showed that the signals of the nitrogen donor base containing compounds 4 and 5 exchange with the signals of nonlithiated thiophene. This is explained by exchange of the deuterium by a hydrogen atom via lithiation of toluene molecules.

In the charge density study of 9-diphenylthiophosphinoylanthracene the thermal motion of several atoms needed an anharmonic description via Gram-Charlier coefficients even for data collected at 15 K. As several data sets at different temperatures were measured, this anharmonic model could be proved to be superior to a disorder model. Refinements against theoretical data showed the resemblance of an anharmonic model and a disorder model with two positions very close to each other (similar to 0.2 angstrom), whereas these two models could be clearly distinguished if the second position is 0.5 angstrom apart. The refined multipole parameters were distorted when the anharmonic motion was not properly refined. Therefore, this study reveals the importance of detecting and properly handling anharmonic motion. Unrefined anharmonic motion leads to typical shashlik-like residual density patterns. Therefore, careful analysis of the residual density and the derived probability density function after the refinement of the Gram-Charlier coefficients proved to be the most useful tools to indicate the presence of anharmonic motion.

Based on lithium anthracenes RLi, the formation of mixed complexes from organolithiums and lithium salts RLi.LiX is illustrated. The [RLi(L)](2) dimers formed in presence of different donating solvents L as well as the corresponding mixed lithium bromide complexes [RLi(L).LiX] were isolated and structurally characterized.

In this communication we present the experimental charge density distribution in [Mg{(pz )(3)C}(2)] (1), (pz = 3,5-dimethylpyrazolyl), containing two non-coordinating sp(3) carbanionic lone-pairs.

The lithium salt (HC-NCMe3)(2)SiFNLiR (1) R = C6H3(2,6-CHMe2)(2) reacts with trichlorogallium under displacement of the lithium ion by GaCl3 to give the adduct [(HC-NCMe3)(2)SiFN](-) [(GaCl3)R.Li(thf)(4)](+) (1). Compound 1 thermally loses LiCl and forms the bicyclic ring intermediates V and VI. Compound VI adds the aniline H2NC6H3(2,6-CHMe2)(2) and the unsaturated, seven-membered ring compound -NCMe3-CH2-CH=NCMe3GaCl2-NR-SiFNKR- (2) is obtained. The addition is accompanied by an enamine-imine-tautomerism and proves the Lewis acid character of the silicon atom in an unknown 3-center-2-electron interaction of one nitrogen atom with the silicon and gallium atoms. Quantum chemical calculations of the thermal isomerisation process and crystal structures of 1 and 2 are reported.

Two new approaches for synthesizing RSiCl, (R = PhC(NtBu)(2)) are reported by the reaction of RSiHCl2 with bis-trimethyl silyl lithium amide and N-heterocyclic carbene respectively. In the former method silylene is produced in 90% yield. The silylene was treated with biphenyl alkyne to afford the disilacyclobutene system. This is a rare example of two five-coordinate silicon centers arranged adjacent to each other in a four-membered ring. Furthermore, we fluorinated the four-membered ring by trimethyltin fluoride to obtain the fluoro substituted disilacyclobutene.

The organobismuth(III) and dibismuthine complexes bearing N,N'-disubstituted 1,8-diaminonaphthalene ligand were prepared. The reaction of LBiNMe2 (1) [L = 1,8-(NSiMe3)(2)C10H6] with ClSiMe3 results in the elimination of Me3SiNMe2, while PhCCH, Cp H, and PhOH proceed via HNMe2 elimination and provide the complexes of LBiCl (2), LBiCCPh (3), LBiCp (4), and LBiOPh (5), respectively. Reaction of 1 with AlMe3 in n-hexane yields LBiMe (6). Compound 1 reacts with diisopropylcarbodiimide and phenyl isocyanate under insertion at the Bi-NMe2 bond to give the addition products LBi(NiPr)(2)CNMe2 (7) and LBiN(Ph)C(O)NMe2 (8). The reactions of 1 with sulfur and PhSiH3 result in the formation of LBi-S-BiL (9) and LBi-BiL (10), respectively. Compounds 2-10 were characterized by elemental analysis, H-1, C-13, and Si-29 NMR spectroscopy, and X-ray crystallographic studies.

The title compound, [MgBr(2)(C(4)H(8)O)(4)] (1a), forms twinned four-component monoclinic crystals as a new polymorph, space group P2(l)/n with Z' = 2, in addition to the already known tetragonal polymorph (1b). Although the molecular parameters in the two polymorphs match very well, the packing patterns are significantly different. Furthermore, the correct constitution of the mixed halide bromo-chloro-tetrakis(tetrahydrofuran-kappa O)magnesium(II) (2) could be determined.

This Communication describes two strikingly different reactivities of a digermylene [{PhC(NtBu)(2)}(2)Ge-2] (1) featuring a Ge-1-Ge-1 single bond. In the reaction with azobenzene, 1 affords the oxidative addition product LGeN(Ph)N(Ph)GeL [2; L = PhC(NtBu)(2)], with simultaneous cleavage of the Ge-Ge bond, whereas treatment of 1 with Fe-2(CO)(9) yields the Lewis acid-base adduct LGe[Fe(CO)(4)]Ge[(Fe(CO)(4)]L (3). Both compounds were characterized by single-crystal X-ray diffraction, NMR spectroscopy, electrospray ionization mass spectrometry, and elemental analysis.

The diisopropylphosphanyl-substituted anthracenes i-Pr(2)P(C(14)H(9)) (1a), i-Pr(2)P(C(14)H(8))Br (2a), and (i-Pr(2)P)(2)(C(14)H(8)) (3a) and some of their oxidation products were prepared from 9-bromoanthracene and 9,10-dibromoanthracene, respectively. Low-temperature (1)H NMR spectra of the 9-monophosphanyl-substituted anthracenes la and 2a are in accordance with a staggered conformer, while above room temperature dynamic processes occur. The low-temperature NMR spectrum of the 9,10-diphosphanylanthracene 3a indicates the presence of two different rotational isomers. The rotational barrier for la was determined from variable-temperature (1)H NMR spectra to be 56 kJ mol(-1) (Delta G(298K)). The crystal structure determinations show the solid-state conformers to be consistent with the prevailing conformer at low temperature.

Treatment of 9,10-dibromoanthracene with one mole equivalent of n-butyllithium and chlorodiphenylphosphane yields 9-bromo-10-diphenylphosphanylanthracene (1). Oxidation of 1 with chalcogens leads to {Br(C14H8)(Ph2P=E)} with E = O (2), S (3) and Se (4). The syntheses and structure determinations of the parent compound 1 and the oxidized species 2 - 4 are reported.

Monoanionic iminophosphonamide ligands have a N-P-N linkage and undergo four-membered ring N,N-ligand formation when treated with aluminum compounds. The reaction of LLi (L = [Ph(2)P(NSiMe(3))(2)]) with equivalent amounts of AlCl(3) and AlMeCl(2) in toluene afforded LAlCl(2) (3) and LAlClMe (4), respectively, L(2)AlH (5), LAlEt(2) (6), and LAl(NMe(2))(2) (7) respectively were prepared by the reaction of LH with AlH(3)center dot NMe(3), AlEt(3), and Al(NMe(2))(3) in n-hexane. Subsequently compounds 3-7 were characterized by elemental analysis, (1)H, (13)C, and (31)P NMR spectroscopy and X-ray crystallographic studies (for 3, 4, 5, and 7).

The heterobimetallic bismuth-oxo-bridged complexes containing the Bi-O-M (M = Al, Ga, Ge, Zr, Hf) core were prepared. The reaction of L(1)BiNMe(2) (1) [L(1) = 1,8-C(10)H(6)(NSiMe(3))(2)] with LM-(Me)(OH) and LGe(OH) (M = Al, Ga, L = CH((CMe)NAr)(2), Ar 2,6-iPr(2)C(6)H(3)) proceeds via HNMe(2) elimination and provides the complexes L(1)Bi(mu-O)MMeL(M = Al2; Ga, 3) and L(1)Bi(mu-O)-GeL (4). The transition metal hydroxides Cp (2)ZrMe(OH) and Cp (2)HfCl(OH) react with 1 in n-hexane and toluene, respectively, under elimination of 1 equiv of HNMe(2) to generate the corresponding complexes L(1)Bi(mu-O)ZrMeCp (2) (5) and L(1)Bi(mu-O)HfClCP (2) (6). Compounds 3, 4, and 6 represent the first examples of structurally characterized heterobimetallic complexes featuring the Bi-O-Ga, Bi-O-Ge, and Bi-O-Hf moiety, respectively. The crystal structural data show that the complexes 3 and 4 crystallize in the monoclinic space group P2(1)/c and P2(1)/n, while the complexes 5 and 6 are present in the monoclinic space group Pn. Moreover all compounds have been characterized by element analysis, electron impact mass spectrometry, and NMR spectroscopy.

LGeCl (L = PhC(NtBu)(2)) was treated with elemental sulfur in THF to afford [{PhC(NtBu)(2)}(2)Ge-2(mu-S)(2)Cl-2] (2) in 44% yield instead of yielding a compound containing a Ge=S double bond. It was revealed by the X-ray single-crystal structure that there is no Ge=S unit in 2. Instead, 2 features a four-membered ring containing two germanium and two sulfur atoms. The four-membered Ge2S2 ring is planar and is formed by a weak [2 + 2] cycloaddition interaction. Within the ring skeleton the two germanium atoms are arranged opposite to each other. Furthermore, 2 was reduced with 2 equiv of potassium graphite in THF to yield a potassium salt of a germathiocarboxylate analogue of composition [{PhC(NtBu)(2)}Ge(S)SK(THF)](2) (3). Compounds 2 and 3 were characterized by single-crystal X-ray diffraction studies, NMR spectroscopy, EI-MS spectrometry, and elemental analysis.