Martin Dräger

Über zinn-haltige heterocyclen: VII. 2,2,6-trimethyl-1,3-dithia-6-aza-2-stannocan, ein 8-ring mit transannularer Sn ⋯ N-wechselwirkung

Abstract The crystal structure of 2,2,6-trimethyl-1,3-dithia-6-aza-2-stannocane has been determined and refined to R = 0.043. The transannular 1,5-distance Sn ⋯ N = 256.6(6) pm exceeds the respective single bond by 49 pm. A comparison with analogous eight-membered rings exhibits a clear-cut correlation of such differences with angle deformations in the transition tetrahedron to trigonal-bipyramid. The axial distance SnC is 2 pm longer than the equatorial one.

Asymmetric Aza Diels-Alder reactions of amino acid ester imines with Brassard's diene

Abstract Imines 1 obtained from aromatic, aliphatic or functionalized aldehydes and valine tert -butyl ester undergo Lewis acid catalyzed hetero Diels-Alder reactions with Brassards diene 2 . The cycloadducts are formed in good to high yields and with diastereomer ratios of 92:8 – 97:3. For the removal of the chiral auxiliary group a new method was developed whose principle consists in the conversion of the amino acid α-C-atom into an acetalic center employing a Curtius rearrangement as the key step.

Über polygermane: XIV. Polygermane als nebenprodukte der Grignard-reaktion von PhMgBr mit GeCl4

Abstract The synthesis of GePh4 and Ge2Ph6 by Grignard reaction in THF or ether/toluene leads to the by-products Ge3Ph8 (up to 11%) and Ge4Ph10 (up to 18%) which is dependant on using an excess of Mg. A quantitative analysis of the resulting products by HPLC and a semipreparative separation by column, flash, and HPL chromatography is described. The crystal structures of Ge3Ph8 (R = 0.075) and Ge4Ph10 · 2C6H6 (R = 0.054) have been determined. Ge4Ph10 has Ci symmetry and both chain conformations are well staggered (49–70° for Ge3Ph8, 53–66° for Ge4Ph10). The GeGe distances and GeGeGe angles are 244 pm and 121° (Ge3Ph8), and 246 pm and 118° (Ge4Ph10).

Über zinn-haltige heterocyclen : V. Sn-phenyk-substituierte stannocane, Übergänge von tetraedrischer 4-Zu trigonal-bipyramidaler 5-koordination

Abstract A complete series of diphenyl and mixed methyl/chlorine/bromine/iodinephenyl substituted oxadithia- and trithiastannocanes has been prepared by reactions between the respective disodium dithiolates and tin dihalides. The 13C NMR chemical shifts of these compounds and the coupling constants J(119Sn13C) are dependent upon the magnetic anisotropy of the substituents and the bond angles at the tin atom. The crystal structure of 2,2-diphenyl-1,3,6-trithia-2-stannocane has been determined and refined to R = 0.039. The environment of Sn is a monocapped tetrahedron (transannular distance Sn⋯S 324.6(1) pm). This type of coordination, intermediate between a tetrahedron and a trigonal bipyramid, is discussed quantitatively and compared with a series of analogous compounds. The eight-membered ring has the boat-chair conformation.

Über polygermane : VIII. Octaphenylcyclotetragerman (Ph2ge)4, ein germaniumhomocyclus mit D2d-symmetrie

Abstract The crystal structure of octaphenylcyclotetragermane, (Ph 2 Ge) 4 , has been determined and refined to an R value of 0.046. The symmetry of the molecule approximater D 2d . the Ge 4 ring is nearly planar and square (angle of pucker 3.9°, GeGe 246.5(5) pm). The 8 phenyl groups (GeC 196.2(10) pm) are arranged in two distinct sets (“parallel” touching and perpendicular to the Ge 4 ring) which exchange their positions in solution. The packing of the (Ph 2 Ge) 4 molecules in the crystal resembles a cubic body centred sphere packing. The homocyclic series (Ph 2 Ge) n with n  4, 5, 6 shows 13 C NMR signals in CDCl 3 solution monotonic dependent on the endocyclic GeGeGe angles.

Über gemischte Gruppe 14—Gruppe 14-Bindungen: IV. Hexa-p-tolylethan-analoga p-Tol6Sn2, p-Tol6PbSn und p-Tol6Pb2: Darstellung, Homöotype Strukturen, NMR-Kopplungen und Valenzschwingungen☆

p-Tol6PbSn has been synthesized by reaction of p-Tol3PbLi with p-Tol3SnI in THF/ether (1:2) at −78°C. The crystal structures of p-Tol4Pb (I4) and of p-Tol6Sn2, p-Tol6PbSn and p-Tol6Pb2 have been determined. The three dinuclear compounds crystallize not strickly isomorphous. They exhibit the same space group (R3 and rather similar unit cell dimensions. Yet according to the solvent of crystallization, two types with differing atomic position parameters can be distinguished (“homoeotypism with differences of parameters” in the definition of Laves). In both types, the individual molecules have a chiral C3-symmetric conformation and the non-chiral unit cell encloses both enantiomers. The metal—metal distances are SnSn = 2.777(1), PbSn = 2.813(2) and PbPb = 2.851(1) A. NMR (13C, 119Sn, 207Pb) and Raman data are given (1J(119Sn119Sn) = 4570, 1J(119Sn207Pb) = 3640 Hz; ν (SnSn) = 131, ν(PbSn) = 114, ν(PbPb) = 105 cm−1).

Über polystannane: IV. Vergleich von abständen d(SnSn), NMR-Kopplungen 1J(Sn) und Valenzschwingungen ν(SnSn) in acetat-verbrücketen distannanen Ph4Sin2(X3CCO2) (X = H, Cl, F)☆

Abstract The three compounds Ph4Sn2(X3CCO2)2 were synthesized from Ph2SnH2 and X3CCOOH (X = H, Cl) or by cleavage of two phenyl groups in Ph6Sn2 with Stoichiometric amounts of X3CCOOH (X = Cl, F). The crystal structures (R = 0.041, 0.030, 0.058) show that the Ph4Sn2 units are bridged by two isobidentate acetates resulting in five-coordinated tin atoms. Five crystallographically independent centrosymmetric molecules form three distinct conformers. Bonding parameters (compared with Ph6Sn2): distances d(SnSn) 269, 271, 272, 277 pm; NMR couplings (CDCl3 solution) 1J(SnSn) 16870, 9443, 12915, 4480 Hz; stretching vibrations ν(SnSn) 152, 155, 157, 159 cm−. The ion pairs [Ph4Sn2]2+ [(X3CCO2)2]2− are discussed.

Über polygermane: XIII. Pergerma-analoga von dioxan Ph8Ge4X2 und ethylenacetal Ph6Ge3X2 (X=O, S, Se)☆

Abstract [(Cl 3 CCOO)Ph 2 Ge] 2 reacts with wet acetone to give Ph 8 Ge 4 O 2 , and with dry H 2 S to give Ph 8 Ge 4 S 2 . With Na 2 S or NaHSe, Ph 4 Ge 2 Cl 2 yields Ph 8 Ge 4 S 2 and Ph 8 Ge 4 Se 2 , respectively. Only Ph 6 Ge 3 S 2 or Ph 6 Ge 3 Se 2 , but no Ph 6 Ge 3 O 2 , can be obtained from a mixture of Ph 4 Ge 2 Cl 2 , Ph 2 GeCl 2 and Na 2 S or NaHSe. The mass spectra show a high stability of the cations Ph 6 Ge 3 S 2 + and Ph 6 Ge 3 Se 2 + . The 13 C NMR phenyl signals for C( ipso ) shift to high field in the series O, S, Se and 6-membered, 5-membered rings. The crystal structures of Ph 8 Ge 4 O 2 ( R = 0.031) and Ph 6 Ge 3 S 2 ( R = 0.036) have been determined. The 6-membered ring Ge 4 O 2 has the chair conformation (total symmetry of the molecule is approximately C 2h , distances GeGe 244.8(1) and GeO 178–179 pm, angle GeOGe 126.9(1)°). The 5-membered ring Ge 3 Se 2 has the half-chair conformation (total symmetry of the molecule is approximately C 2 , distances GeGe 241.5(1) and GeSe 236–237 pm).

Strukturen von [Me4Sb]2[MeSbI4]MeSbI2, und [Me4Sb]I. Darstellung von Me3Sb · MeSbI2 und farbwechsel bei Me4Sb2 · Me2SbBr

Abstract The crystal structures of the complex [Me 4 Sb] 2 [MeSbI 4 ] ( 1 ) and its precursors MeSbI 2 ( 2 ) and [Me 4 Sb]I ( 3 ) are reported. In 1 there are tetrahedral cations and square pyramidal anions with Sb-I distances of 290–320 pm. The structure of 2 contains MeSbI 2 molecules. They associate via iodine bridges to form linear chains with alternating short and long Sb-I distances. The coordination around antimony is distorted tetragonal pyramidal. The tetrahedral coordination of the ions in 3 results in the formation of a wurtzite type structure with antimony-iodine distances of 406 and 435 pm. The novel adducts Me 3 Sb·Me 2 SbI 2 ( 4 ) and Me 2 SbSbMe 2 ·Me 2 SbBr ( 5 ) are formed by reaction of the components. They decompose easily with formation of antimony(V) compounds. Crystals of 5 are yellow but become reversibly black on cooling.

Über polygermane ☆: XV. Darstellung von phenylierten trigermanen in HMPT

Abstract The optimum conditions for the synthesis of the trigermanes Ge3Ph8 and Ge3Me2Ph6 according to R2GeCl2 + 2 Ph3GeAk (Ak = Li, K) in HMPT have been determined. The main difficulty is to repress a nucleophilic attack of Ph3Ge− at newly formed GeGe bonds. The mass spectrum of Ge3Me2Ph6 shows rearrangements of the GePh3 and Ph/Me groups. The 13C NMR phenyl signals of di-, tri- and tetra-germanes are nearly identical. Ge3Ph8 and Ge4Ph10 transform to the plastically-crystalline state before melting (ΔH 45.3 and 54.9 kJ mol−1). The crystal structure of Ge3Me2Ph6 has been determined. The molecule has C2 symmetry (GeGe 242.9(1) pm, GeGeGe 120.3(1)°).