Heinrich Marsmann

Tetrakis(2,4,6-triisopropylphenyl)diplumbene: A Molecule with a Lead–Lead Double Bond

There is good agreement between the length of the lead–lead double bond calculated for H2Pb=PbH2 and that present in the tetraaryldiplumbene 1 (R=2,4,6-iPr3C6H2), which has now been synthesized and structurally characterized. Furthermore, the calculated and experimentally observed trans bent angles Θ are similar. Thus, compounds with homonuclear double bonds between all elements of Group 14 are now known.

Two- and three-dimensional photonic crystals made of macroporous silicon and liquid crystals

Variations of the refractive index can be utilized in order to shift the stop band in periodic structures, such as photonic crystals. We report on investigations about three-dimensional macroporous silicon structures that are filled with a liquid crystal. Fourier transform infrared measurements indicate that a shift of the photonic band edge can be induced by changing the temperature. The director field in macropores within the silicon structure is investigated by 2H-NMR spectroscopy and compared to director field simulations. The latter method indicates a preferred parallel orientation of the director in the nematic state. Based on this finding, we analyze the optical properties.

Silylene Reactions with Buta‐1,3‐diynes: Cycloadditions, Insertions, and Rearrangements

Di-tert-butylsilylene, generated by photolysis of hexa-tert-butylcyclotrisilane 1 or 1,1-di-tert-butyl-trans-2,3-dimethyl-silirane (2), reacts with the 1,3-diyne (tBu–C≡C–)29 to furnish the dialkynylsilane 11 via the isolable alkynylsilirene 10. Photolysis of excess 1 in the presence of 9 furnishes the C–C linked 2,2′-disilirene 12 which, upon prolonged irradiation, rearranges to the 2,5-disilabicyclo[2.2.0]hexa-1(6),3-diene (13). Treatment of 9 with diarylsilylenes, formed by irradiation of hexamethyl-2,2-dimesityltrisilane (3) or hexamethyl-2,2-bis(2,4,6-triisopropylphenyl)trisilane (4), gives the corresponding alkynylsilirenes 14 and 15, respectively. Photolysis of 1 or 2 in the presence of (Me3Si–C≡C–)216 yields the dialkynylsilane 17 which, on further reaction with 2, yields the 2,5-disilabicyclo[2.2.0]hexa-1(6),3-diene (18). Irradiation of 3 in the presence of 16 affords the cis- and trans-isomeric 1,3-dimethylene-2,4-disila-cyclobutane derivatives cis-21 and trans-21, presumably via a 1-silaallene intermediate. The structures of 12, 15, 18, cis-21, and trans-21 have been determined by X-ray crystallography.

Chalcogenatetrasilacyclopentenes: Five‐Membered Rings with Endocyclic Si−Si Double Bonds

Theformal[4+1]cycloaddition of the chalcogens S, Se, and Te to the tetrasilabuta-1,3-diene 1 furnishes the molecules 2–4, the first five-membered rings with endocyclic Si−Si double bonds. The new compounds are thermally stable and chemically inert. However, 4 is light-sensitive and decomposes in daylight with deposition of tellurium. R=2,4,6-iPr3C6H2.

1, 4‐Additions of HCl and HBr to a Tetrasilabutadiene: Formation of Unsymmetrically Substituted Disilenes [1]

The reactions of hexakis(2,4,6-triisopropylphenyl)tetrasilabuta-1,3-diene R2Si=SiR—SiR=SiR2 (1) with HCl and HBr, slowly generated from HSiCl3 or LiBr and CF3COOH, respectively, furnish the unsymmetrically substituted disilenes R2XSi—SiR=SiR—SiHR2, X = Cl (2), Br (3), by formal 1,4-addition of the hydrogen halides to 1. However, passing gaseous hydrogen halides over the solution of 1 yields the 1,4-dihalotetrasilanes by two-fold 1,2-additions to the double bonds of 1. The structures of 2 and 3 which crystallize isotypically with one another have been determined by X-ray crystallography. 1,4-Addition von HCl und HBr an ein Tetrasilabutadien: Bildung unsymmetrisch substituierter Disilene Die Reaktionen von Hexakis(2, 4, 6-triisopropylphenyl)tetrasilabuta-1,3-dien R2Si=SiR—SiR=SiR2 (1) mit HCl und HBr, die langsam aus HSiCl3 oder LiBr und CF3COOH erzeugt wurden, lieferten durch formale 1,4-Addition der Halogenwasserstoffe an 1 die unsymmetrisch substituierten Disilene R2XSi—SiR=SiR—SiHR2, X = Cl (2), Br (3). Uberleiten der gasformigen Halogenwasserstoffe uber Losungen von 1 ergibt hingegen 1,4-Dihalogentetrasilane als zweifache 1,2-Additionsprodukte an die Doppelbindungen von 1. Die miteinander isotypen Strukturen von 2 und 3 wurden aus Einkristallstruktur-Daten ermittelt.

Trichlorosilylation of chlorogermanes and chlorostannanes with HSiCl3/Net3 followed by base-catalysed formation of (Me3Ge)2Si(SiCl3)2 and related branched stannylsilanes

Abstract Chlorotrimethylgermane 1 and dichlorodimethylgermane 4 react with trichlorosilane and triethylamine to provide trichlorosilylgermanes Me4−nGe(SiCl3)n (n=1: 2; n=2: 5) in fair yields, as distillable liquids. The formation of 2 is followed by base-catalysed decomposition reactions leading to novel solid (Me3Ge)2Si(SiCl3)2 3. Chlorotrialkylstannanes 6a–c (6a: R=CH3, 6b: R=C2H5, 6c: R=n-C4H9) react with trichlorosilane and triethylamine providing the branched silylstannanes (R3Sn)2Si(SiCl3)2 7a–c and traces of silylstannanes R3SnSiCl3 8a–c. Only 7a was isolated in a pure state. Heating 7a or crude 7b and 7c with benzyl chloride leads to the formation of benzyltrichlorosilane (10). The constitution of compounds 2, 3, 5 and 7a was confirmed by MS, NMR and analytical data. The structures of C6D6-solvated 3 and C6H6-solvated 7a were determined by X-ray diffraction, and shown to be isotypic.

Ammonia and Chlorine Additions to a Tetrasilabuta‐1,3‐diene: Conglomerate versus Racemate Crystallization [1]

Treatment of hexakis(2,4,6-triisopropylphenyl)tetrasilabuta-1,3-diene (1), R2Si=SiR–SiR=SiR2, with ammonia and chlorine furnishes the correspondingly substituted 1,4-diaminotetrasilane (3) and 1,2,3,4-tetrachlorotetrasilane (6). While product 6 crystallizes as a racemate, 3 forms a conglomerate of enantiomerically pure crystals. The change of colors during the formation of 6 indicates a stepwise reaction sequence. Ammoniak- und Chloradditionen an ein Tetrasilabuta-1,3-dien: Konglomerat versus Racemat-Kristallisation [1] Die Reaktion von Hexakis(2,4,6-triisopropylphenyl)tetrasilabuta-1,3-dien R2Si=SiR–SiR=SiR2 mit Ammoniak oder Chlor ergibt das entsprechend substituierte 1,4-Diaminotetrasilan (3) und das 1,2,3,4-Tetrachlortetrasilan (6). Wahrend 6 als Racemat kristallisiert, bildet 3 ein Konglomerat enantiomerenreiner Kristalle. Der Farbwechsel wahrend der Bildung von 6 deutet auf eine schrittweise verlaufende Reaktionssequenz hin.

Chalkogenatetrasilacyclopentene: Fünfringe mit endocyclischen Si‐Si‐Doppelbindungen

Durch formale[4+1]-Addition der Chalkogene S, Se und Te an das Tetrasilabuta-1,3-dien 1 entstehen die Verbindungen 2–4 als erste Funfringe mit endocyclischen Si-Si-Doppelbindungen. Alle Verbindungen sind thermisch stabil und chemisch inert; lediglich 4 zersetzt sich an Licht unter Tellurabscheidung. R=2,4,6-iPr3C6H2.

A Zwitterionic Distannene and Two (RSnX)4 Cages with an Unusual Arrangement of the Sn4X4 Cluster Atoms (R = tBu3Si, × = Se, Te)

Reaction of tin(II) chloride with RNa(THF)2 (R = tBu3Si) in THF at –30 °C led to a complex reaction mixture, from which the compounds R4Sn4(THF)2, R2SnSnR2 (5), R–R (7), and a brownish black compound 6 were isolated. In toluene as solvent, the zwitterionic distannene 5 was obtained together with 7 and 6 which upon treatment with Et3PX, furnished the cluster compounds (RSnX)4 (10: × = Se; 11: × = Te). The X-ray structure analyses of the isotypic compounds 10 and 11 revealed that the tin atoms occupy the corners of an undistorted tetrahedron with weak tin–tin interactions. The chalcogen atoms form a plane which bisects the Sn4 tetrahedron.

From Nanosize Silica Spheres to Three-Dimensional Colloidal Crystals

Although a variety of preparation methods have been developed, the creation of high quality periodic 3D porous structures, preferably over large areas, uniformly and at low cost, is still a challenging problem. Problems associated with template assisted fabrication of porous structures include preparation of a high quality template, complete filling of the voids in the template and the minimization of shrinkage upon template removal by heating or etching. Since any of these factors can influence the final quality of the porous structure, all these requirements must be fulfilled at the same time.