Bernd Mathiasch

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.

Fourier transform nmr investigations of organotin compounds : IX. Tin-119 nmr spectra of organotin chalcogenides of the type R6Sn3X2 and R6Sn3X3 (X=S, Se, Te)

Abstract NMR spectra have been obtained for fiteen title compounds, mainly with R = Me. Tin chemical shifts were found to lie within the expected ranges, but to vary little with R or, apparently, with change in ring size. While the magnitute of 1 (SnSe) was as predicted, the of 1 (SnTe) was more than twice as large as that previously observed for (Me 3 Sn) 2 Te. In compounds Me 6 Sn( 3 X 3 , 2 J(SnMSn) varied systematically with variations in x, but within relatively narrow limits (195-250 Hz); a much more drastic variation was observed for Me 6 Sn 3 X 2 , possibly due to bond angle changes at Sn and X.

Formation of silicones mediated by the sponge enzyme silicatein-α

The sponge-restricted enzyme silicatein-α catalyzes in vivo silica formation from monomeric silicon compounds from sea water (i.e. silicic acid) and plays the pivotal role during synthesis of the siliceous sponge spicules. Recombinant silicatein-α, which was cloned from the demosponge Suberites domuncula (phylum Porifera), is shown to catalyze in vitro condensation of alkoxy silanes during a phase transfer reaction at neutral pH and ambient temperature to yield silicones like the straight-chained polydimethylsiloxane (PDMS). The reported condensation reaction is considered to be the first description of an enzymatically enhanced organometallic condensation reaction.

Über tetraaryl-methan-analoga in der gruppe 14: III. Ar4Sn/Pb (Ar Ph, p-, m-, o-Tol, 2,4-Xyl und 2,5-Xyl): Gegenüberstellung von bindungslängen und winkeln, von NMR chemischen verschiebungen und kopplungskonstanten und von schwingungsdaten☆

Abstract The title compounds have been synthesized by Grignard reactions or pyrolysis of diplumbanes respectively. The crystal structures of m -Tol 4 Pb and Ph 4 Pb (redetermination) have been determined. All eight compounds (Ph/Tol) 4 (Sn/Pb) are S 4 symmetric and contracted along this unique axis. The 13 C-NMR chemical shifts and the couplings 1 J ( 119 Sn/ 207 Pb 13 C) as well depend additively upon the methyl substituents. The ratios 1 K ( 207 Pb 13 C): 1 K ( 119 Sn 13 C) of the reduced coupling constants are all near to 1.61; a comparison with values from the literature for alkyl, alkenyl and alkinyl substituents is given. The ratio δ( 207 Pb):δ( 119 Sn) results in 2.28. IR (700 down to 200 cm −1 ) and Raman (700 down to 50 cm −1 ) data are given.

Tetramethylditin complexes: A general method for the preparation of a class of compounds with an unusual tintin bond

Abstract The preparation and physical and spectroscopic properties of eight compounds of the type Me4Sn2X2 (X  O2CR, S2CNR2, S2P(OR)2) are described, starting from Me4Sn2Cl2. The spectroscopic data indicate that X functions as an isobidentate ligand. The tintin coupling constants are extremely large (ca. 11–15 kHz), and can be correlated with the pKa values of the corresponding acids HX.

Über gemischte Gruppe 14-Gruppe 14-Bindungen: VII. Ein Inkrementsystem für 13C-NMR chemische Verschiebungen bei arylierten Gruppe 14-Verbindungen☆

Abstract To assign 13 C-NMR chemical shifts of aryl groups bonded to Group 14 elements, an incremental system for estimating such shifts is presented. The system gives consistent assignments for a broad range of linear compounds (Ar 4 M, Ar 6 M 2 , Ar 6 MM′, Ar m Ge n ) and also for some tin-sulphur and lead-sulphur heterocycles (Ar 2 MS) 3 . The influence of the Group 14 elements on the 13 C( ipso, ortho, meta, para ) chemical shifts is discussed.

Zinn—Chalkogen-heterocyclen : IX. Octamethyl-1,4-ditellura-tetrastanninan, (CH3)8Sn4Te2, darstellung, charakterisierung und lichtinduzierte zersetzung☆

Abstract The preparation of a new six-membered ring compound (CH 3 ) 8 Sn 4 Te 2 containing two SnSn bonds isolated by Te is described and its structure established by means of analytical vibrational and NMR spectroscopic data. The well crystallizing yellow compound undergoes light-induced disproportionation reactions showing the generation of dimethylstannylene, which can be trapped either by CH 3 I or by the parent compound itself. In the latter case the reaction leads to five-membered rings with Sn 3 Te 2 - and Sn 4 Te-skeletons, respectively.

Tetraaryl-methane analogues in group 14-4. Ph4−nM(p-Tol)n (n = 0–4, M = Si, Ge, Sn, Pb). Synthesis, structural and spectroscopic data, and semi empirical calculations: Mutual interaction of tetrahedral σ-orbitals (symmetry and electronegativity) and delocalized σ-lumos (π-Lewis acidity)☆

Abstract The 20 compounds mentioned in the title have been synthesized by lithium (M = Si) or Grignard methods (M = Ge, Sn, Pb). The crystal structure of Ph 3 Sn( p -Tol), a survey of the 10 known structures and spectroscopic data (NMR, Mossbauer, IR, Raman) are given. A change of the symmetry of the formally tetrahedral MC 4 backbone arises if M = Si and Ge (elongation along one S 4 or C 3 axis) are altered to M = Sn and Pb (contraction along one S 4 axis). The order of δ( 13 C- ipso ) points to a decrease in the electronegativities along Pb ⪢ Sn > Ge > Si. The 29 Si, 119 Sn and 207 Pb NMR chemical shifts exhibit a “sagging” along each series, which is described analytically in terms of a quadratic equation. The linear part of this equation is interpreted as an inductive contribution which changes its sign if M is changed from silicon to tin and lead. The quadratic part reflects the different population of a low-lying LUMO with charge given by the aromatic groups. This LUMO is slightly antibonding in the case of silicon and slightly bonding for tin and lead. The “π-acceptor” properties of M explain the upfield NMR shifts 29 Si/1 119 Sn/ 207 Pb of MAryl 4 compounds in comparison with MAlkyl 4 .

Die kopplungskonstanten nJ(SnC) und n+1J(SnH) ineinigen verbindungen mit der tetramethyldizinngruppe

Abstract Comparison of data on seven compounds containing the group tetramethylditin shows a variation in the coupling constants depending on the lone pair electrons of the substituents.

(MeSn)4Se6, Geometrie und Schwingungsformen eines Adamantan-Gerüstes aus Zinn-Selen-Bindungen / (MeSn)4Se6, Geometry and Vibrational Modes of an Adamantane Framework Formed by Tin-Selenium Bonds

Abstract The title compound has been synthesized by reaction of MeSnBr3 and NaHSe in aqueous solution. The X-ray structure determination showed adamantane-like molecules (Sn-Se 253(1), Sn-C 215(1) pm) arranged in a quasi hexagonal-close packing. The atomic coordinates were used for an analysis of the vibrational spectra, yielding information on the distribution of the potential energy for the normal modes in terms of internal co-ordinates and a set of force constants. The valence force constants f(Sn-Se) 154(6), f(Sn-C) 216(2) N/m) are compared with those in related monocyclic molecules.