Arno Pfitzner

Visible‐Light‐Promoted Stereoselective Alkylation by Combining Heterogeneous Photocatalysis with Organocatalysis

Dream team: Heterogeneous inorganic semiconductors and chiral organocatalysts team up for the stereoselective photocatalytic formation of carbon–carbon bonds. However, the connection between the organic and inorganic catalysts should not be too tight: Covalent immobilization inactivates the system.

The extended stability range of phosphorus allotropes.

Phosphorus displays fascinating structural diversity and the discovery of new modifications continues to attract attention. In this work, a complete stability range of known and novel crystalline allotropes of phosphorus is described for the first time. This includes recently discovered tubular modifications and the prediction of not-yet-known crystal structures of [P12] nanorods and not-yet-isolated [P14] nanorods. Despite significant structural differences, all P allotropes consist of covalent substructures, which are held together by van der Waals interactions. Their correct reproduction by ab initio calculations is a core issue of current research. While some predictions with the established DFT functionals GGA and LDA differ significantly from experimental data in the description of the P allotropes, consistently excellent agreement with the GGA-D2 approach is used to predict the solid structures of the P nanorods.

A new modification of MnSb2S4 crystallizing in the HgBi2S4 structure type

A new modification of MnSb2S4 was synthesized by solid state reaction of MnS, and Sb2S3 at 500 °C. The monoclinic, purple-red compound crystallizes in the HgBi2S4 structure type. Single crystal measurements provided the space group C2/m (no. 12) with a = 12.747(3) Å, b = 3.799(1) Å, c = 15.106(3) Å, β = 113.91(3)°, V = 668.7(3) Å3, and Z = 4. The refinement converged to R = 0.0403, and wR = 0.1001 for 913 unique reflections and 46 parameters. The crystal structure of MnSb2S4 (mC28) consists of strands of edge-sharing octahedra [MnS6] which are interlinked to layers by distorted square pyramids [SbS5] (d(Sb-S) < 3.1 Å). MnSb2S4(mC28) shows a greater distortion of the [Sb-S] polyhedra as compared to the [Bi-S] polyhedra in analogous MnBi2S4. This is due to an enhanced stereochemical influence of the lone electron pair of Sb3+. Raman spectra of MnSb2S4 (mC28) are dominated by ν Sb-S stretching modes at 300 cm-1, and at 283 cm-1, respectively.

Selective photocatalytic reductions of nitrobenzene derivatives using PbBiO2X and blue light

Blue light irradiation of heterogeneous photocatalysts PbBiO2X (X = Cl, Br) in the presence of triethanolamine as an electron donor leads to hydrogen evolution, and the selective, clean and complete reduction of nitrobenzene derivatives to their corresponding anilines.

The use of copper(I) halides as a preparative tool

The use of copper(I) halides as a preparative tool is discussed with respect to the synthesis of adduct compounds with new polymeric and oligomeric main group molecules. By using this approach new polymers of main group elements--some of which have been predicted by theoretical investigations--can be obtained in a crystalline state and are therefore accessible for a basic structural characterization. Thus, it becomes possible to compare the structural data, experimental data, and theoretical results. Mixed copper halide chalcogenides are accessible when complex copper thiometalates and copper halides are combined. These solid-state compounds are of special interest since they provide experimental access to new main group molecules. In addition, they exhibit a high copper ion conductivity when certain structural features are present in the compounds. A survey is given of basic synthetic and general structural aspects.

Refinement of the crystal structures of Cu₃PS₄ and Cu₃SbS₄ and a comment on normal tetrahedral structures

Abstract The crystal structures of yellow Cu3PS4 and of black Cu3SbS4 were refined from single crystal X-ray diffraction data. Cu3PS4 crystallizes orthorhombic in an ordered wurtzite superstructure type with the space group Pmn21 (no. 31), a = 7.282(1) Å, b = 6.339(1) Å, c = 6.075(1) Å, V = 280.38(8) Å3, and Z = 2. The refinement converged to R = 0.0276, and wR2 = 0.0710 for 737 unique reflections and 44 parameters. Cu3SbS4 crystallizes tetragonal in an ordered sphalerite superstructure type with the space group I4̅2m (no. 121), a = 5.391(1) Å, c = 10.764(1) Å, V = 312.83(9) Å3, and Z = 2. The refinement converged to R = 0.0213, and wR2 = 0.0532 for 492 unique reflections and 14 parameters. The crystal structures of the title compounds and related normal tetrahedral structures are discussed with respect to the preference of either hexagonal or cubic packing of the anions.

A structural differentiation of quaternary copper argyrodites: Structure – Property relations of high temperature ion conductors

Abstract The crystal structures of 12 argyrodite type copper compounds with the general formula Cu(12–)B+nQ2–6–yX–y (B = P, As, Si, Ge; Q = S, Se; X = Cl, Br, I) were refined. The positions of the copper atoms were refined by using a non-harmonic approach. All polymorphic argyrodites were investigated in their cubic high temperature modification crystallizing in spacegroup F-43m (No. 216). A comprehensible way to describe the complex structures was developed based on a topological description of the rigid anion- and B-cation substructure as an arrangement of Frank-Kasper polyhedra. An analysis of the joint probability density function and of the one particle potentials for the copper atoms was performed to get a detailed insight in the copper distribution in these argyrodites. They can be divided into four types based on their different distribution of copper. This classification corresponds to the physical properties of the argyrodites, especially to their ionic conductivities, which show a significant dependence on the composition.

Zinc‐ and Tin‐Mediated C−C Coupling Reactions of Metalated (2‐Pyridylmethyl)(trialkylsilyl)amines − Mechanistic, NMR Spectroscopic, and Structural Studies

The zincation of (2-pyridylmethyl)(triisopropylsilyl)amine (1) gives dimeric methylzinc (2-pyridylmethyl)(triisopropylsilyl)amide (2). Further addition of dimethylzinc to a toluene solution of 2 at raised temperatures yields the C−C coupling product [1,2-dipyridyl-1,2-bis(triisopropylsilylamido)ethane]bis(methylzinc) (3). Heating of molten 2, or UV irradiation of 2, results in the formation of 3 and zinc bis[(2-pyridylmethyl)(triisopropylsilyl)amide] (4). The reaction between the zinc dihalide complexes of 1 [5a (X = Cl) and 5b (X = Br)] and methyllithium yields the C−C coupling product 3 and the heteroleptic complex 2, observed by NMR spectroscopy. During this reaction, zinc metal precipitates. The magnesiation of 1 with dibutylmagnesium gives magnesium bis[(2-pyridylmethyl)(triisopropylsilyl)amide] (6) in a quantitative yield. Subsequent addition of dimethylmagnesium results in a dismutation reaction and the formation of heteroleptic methylmagnesium (2-pyridylmethyl)(triisopropylsilyl)amide (7). Treatment of 1 with dimethylmagnesium also gives 7. This complex slowly undergoes an intramolecular metalation during which dark red single crystals of (tetrahydrofuran)magnesium 2-(triisopropylsilylamidomethylidene)-1-azacyclohexa-3,5-dien-1-ide (8) precipitate. In this compound the aromaticity of the pyridyl fragment is abolished. The magnesiation of (tert-butyldimethylsilyl)(2-pyridylmethyl)amine (I) proceeds quantitatively to give methylmagnesium (tert-butyldimethylsilyl)(2-pyridylmethyl)amide (9). This compound also undergoes an intramolecular metalation reaction, which results in the loss of the aromaticity of the pyridyl substituent and the formation of (tetrahydrofuran)magnesium 2-(tertbutyldimethylsilylamidomethylidene)-1-azacyclohexa-3,5dien-1-ide (10). The metalation of 1 with tin(II) bis[bis(trimethylsilyl)amide] yields [bis(trimethylsilyl)amido]tin(II) (2-pyridylmethyl)(triisopropylsilyl)amide (11). The elimination of tin metal occurs even at room temperature, and the C−C coupling product [1,2-dipyridyl-1,2-bis(triisopropylsilylamido)ethane]tin(II) (12) is formed. The metalation of (tert-butyldimethylsilyl)(2-pyridylmethyl)amine with Sn[N(SiMe3)2]2 gives [bis(trimethylsilyl)amido]tin(II) (tert-butyldimethylsilyl)(2-pyridylmethyl)amide (13). Within a few minutes, precipitation of tin metal takes place and the C−C coupled product [1,2-bis(tert-butyldimethylsilylamido)-1,2-dipyridylethane]tin(II) (14) is produced. In order to examine the importance of the pyridyl ligand for the C−C coupling reactions, zinc bis[N-(tert-butyldimethylsilyl)benzylamide] (15) was prepared by means of the metathesis reaction between lithium N-(tert-butyldimethylsilyl)benzylamide and zinc(II) halide. Treatment of 15 with dimethylzinc yields heteroleptic methylzinc N-(tert-butyldimethylsilyl)benzylamide (16). Refluxing of 16 with an excess of dimethylzinc in toluene does not give any C−C coupling reactions.

(CuI)3P4S4: Preparation, Structural, and NMR Spectroscopic Characterization of a Copper(I) Halide Adduct with β-P4S4

(CuI)(3)P(4)S(4) is obtained by reaction of stoichiometric amounts of CuI, P, and S in evacuated silica ampoules. The yellow compound consists of monomeric beta-P(4)S(4) cage molecules that are separated by hexagonal columns of CuI. (CuI)(3)P(4)S(4) crystallizes isotypic to (CuI)(3)P(4)Se(4) in the hexagonal system, space group P6(3)cm (no. 185) with a=19.082(3), c=6.691(1) A, V=2109.9(6) A(3), and Z=6. Three of the four phosphorus atoms are bonded to copper, whereas no bonds between copper and sulfur are observed. The two crystallographically distinct copper sites are clearly differentiated by (65)Cu magic-angle spinning (MAS) NMR spectroscopy. Furthermore, an unequivocal assignment of the (31)P MAS-NMR spectra is possible on the basis of homo- and heteronuclear dipole-dipole and scalar interactions. Dipolar coupling to the adjacent quadrupolar spins (63, 65)Cu generates a clear multiplet structure of the peaks attributable to P1 and P2, respectively. Furthermore, the utility of a newly developed two-dimensional NMR technique is illustrated to reveal direct connectivity between P atoms based on ((31)P-(31)P) scalar interactions.

NMR studies of phosphorus chalcogenide–copper iodide coordination compounds

The local structures of the new phosphorus chalcogenide – copper iodide coordination compounds (CuI)P4Se4, (CuI)2P8Se3, (CuI)3P4Se4, and (CuI)3P4S4 are investigated using comprehensive 63Cu, 65Cu, and 31P magic angle spinning NMR techniques. Peak assignments are proposed on the basis of homo- and heteronuclear indirect spin–spin interactions, available from lineshape analysis and/or two-dimensional correlation spectroscopy. In particular, the 31P-63,65Cu scalar coupling constants have been extracted from detailed lineshape simulations of the 31P resonances associated with the Cu-bonded P atoms. In addition, the RNνn pulse symmetry concept of Levitt and coworkers has been utilized for total through-bond correlation spectroscopy (TOBSY) of directly-bonded phosphorus species. The resonance assignments obtained facilitate a discussion of the 31P and 63,65Cu NMR Hamiltonian parameters in terms of the detailed local atomic environments. Analysis of the limited data set available for this group of closely related compounds offers the following conclusions: (1) bonding of a special phosphorus site in a given P4Xn (X = S, Se) molecule to Cu+ ions shifts the corresponding 31P NMR signal upfield by about 50 ppm relative to the uncomplexed molecule, (2) the magnitude of the corresponding scalar 31P-63,65Cu spin–spin coupling constant tends to decrease with increasing Cu–P distance, and (3) the 63,65Cu nuclear electric quadrupolar coupling constants appear to be weakly correlated with the shear strain parameter specifying the degree of local distortion present in the four-coordinated [CuI2P2] and [CuI3P] environments. Overall, the results illustrate the power and potential of advanced solid state NMR methodology to provide useful structural information in this class of materials.