Selective Si-C(sp3 ) Bond Cleavage in (Aminomethyl)silanes by Carbanionic Nucleophiles and Its Stereochemical Course.

Selective cleavage of a silicon-carbon bond in tetraorganosilanes is still a great challenge. A new type of Si-C(sp3 ) bond cleavage in bench-stable (aminomethyl)silanes with common organolithium reagents as nucleophiles has now been identified. Suitable leaving groups are benzyl, allyl, and phenylthiomethyl groups. A ß-donor function and polar solvents are essential for the reaction. Simple switching between α-deprotonation and substitution is possible through slight modifications of the reaction conditions. The stereochemical course of the reaction was elucidated by using a silicon-chiral benzylsilane. The new transformation proceeds stereospecifically with inversion of configuration and can be used for the targeted synthesis of enantiomerically pure tetraorganosilanes, which are otherwise difficult to access. Quantum chemical calculations provided insight into the mechanism of the new substitution.

A route to stereochemically pure benzyllithium reagents by stereocontrolled epimerisation.

Alkyllithium compounds are not generally stable at room temperature, therefore strategies were established to overcome this limitation. We present a systematic approach to obtain a stereochemically enriched benzyllithium compound, starting with the simple addition of a chiral auxiliary and ending by incorporation of the auxiliary in the substrate. Thereby, a very unusual dimer of a lithiated benzylsilane was obtained, which could be split into stereochemically enriched monomers by the addition of Lewis bases. Furthermore, we were able to understand the factors responsible for this stereochemical enrichment by using quantum chemical calculations and clarify the configuration of the lithiated compound and the corresponding trapping product by crystallisation. This enabled us to determine the stereochemical course of the deprotonation and the subsequent metathesis reaction.

{4-t-Bu-2,6-[P(O)(O-i-Pr)2]2C6H2Sn}2: an intramolecularly coordinated organotin(I) compound with a Sn-Sn single bond, its disproportionation toward a diorganostannylene and elemental tin, and its oxidation with PhI(OAc)2.

Syntheses of the intramolecularly coordinated organotin(I) compound {4-t-Bu-2,6-[P(O)(O-i-Pr)(2)](2)C(6)H(2)Sn}(2) (2), which crystallized in two different pseudopolymorphs 2 and 2·C(7)H(8), of the diorganostannylene {4-t-Bu-2,6-[P(O)(O-i-Pr)(2)](2)C(6)H(2)}(2)Sn (3) and of the organotin(II) acetate 4-t-Bu-2,6-[P(O)(O-i-Pr)(2)](2)C(6)H(2)SnOAc (4) are reported. The compounds were characterized by multinuclear NMR, IR (3 and 4), UV-vis spectroscopy (2), electrospray ionization mass spectrometry (3 and 4), and single-crystal X-ray diffraction analyses. Density functional theory calculations on compound 2 revealed the stabilizing effect of the intramolecular P═O → Sn coordination.

[µ-Bis(diphenyl-phosphan-yl)methane]-tricarbon-yl(µ-p-toluene-sulfonyl-meth-yl isocyanato)(triphenyl-phosphane)ironplatinum(Fe-Pt).

The title compound, [FePt(C(9)H(9)NO(2)S)(C(18)H(15)P)(C(25)H(22)P(2))(CO)(3)], represents a rare example of an isonitrile-bridged heterobimetallic complex (here Pt and Fe) and is an inter-esting precursor for the preparation of heterodinuclear µ-amino-carbyne complexes, since the basic imine-type N atom of the µ(2)-C=N-R ligand readily undergoes addition with various electrophiles to afford iminium-like salts. In the crystal, the almost symmetrically bridging µ(2)-C=N-R ligand (neglecting the different atomic radii of Fe and Pt) is strongly bent towards the Fe(CO)(3) fragment, with a C=N-R angle of only 121.1 (4)°.

Crystal structure and Hirshfeld surface analysis of 1-[(benzyl-dimethyl-sil-yl)meth-yl]-1-ethyl-piperidin-1-ium ethane-sulfonate.

The title mol-ecular salt, C17H30NSi+·C2H5O4S-, belongs to the class of a-amino-silanes and was synthesized by the alkyl-ation of 1-[(benzyl-dimethyl-sil-yl)meth-yl]piperidine using diethyl sulfate. This achiral salt crystallizes in the chiral space group P21. One of the Si-C bonds in the cation is unusually long [1.9075 (12) Å], which correlates with the adjacent quaternary N+ atom and was verified by quantum chemical calculations. In the crystal, the components are linked by weak C-H⋯O hydrogen bonds: a Hirshfeld surface analysis was performed to further investigate these inter-molecular inter-actions and their effects on the crystal packing.

Mechanistic insight into stereoselective carbolithiation.

This article addresses the mechanistic features of asymmetric carbolithiation of ß-methylstyrenes. While often the presence of functional groups is required to obtain high enantioselectivities in carbolithiation reactions, simple ß-methylstyrene also gives high selectivities in (-)-sparteine-mediated addition of alkyl lithium compounds. Computational studies on the carbolithiation of ß-methylstyrene with (-)-sparteine show that the observed selectivities are the result of repulsion effects in the diastereomeric transition states between the (-)-sparteine⋅alkyl lithium adduct and the ß-methylstyrene, upon approximation of the two reactants. In contrast, for the ortho-amino ß-methylstyrene (E)-benzyl(2-propenylphenyl)amine (4) X-ray structure analyses of intermediate lithium amides indicate a carbolithiation mechanism in which one side of the double bond is shielded by the amide moiety, leaving only one side free for approach of the chiral alkyl lithium adduct.

Crystal structures of di-aquadi-µ-hydroxido-tris-[tri-methyl-tin(IV)] diformatotri-methyl-stannate(IV) and di-µ-hydroxido-tris-[tri-methyl-tin(IV)] chloride monohydrate.

The title compounds, [Sn3(CH3)9(OH)2(H2O)2][Sn(CH3)3(CHO2)2] (1) and [Sn3(CH3)9(OH)2]Cl·H2O (2), are partially condensed products of hydrolysed tri-methyl-tin chloride. In the structures of 1 and 2, short cationic tris-tannatoxanes (C9H29O2Sn3) are bridged by a diformatotri-methyl-tin anion or a chloride anion, respectively. Hydrogen bridges are present and supposedly stabilize these structures against further polymerization to the known polymeric tri-methyl-tin hydroxide. Especially noteworthy is that the formate present in this structure was formed from atmospheric CO2.

Crystal structure of di-benzyl-dimethyl-silane.

In the title compound, C16H20Si, a geometry different from an ideal tetra-hedron can be observed at the Si atom. The bonds from Si to the benzylic C atoms [Si-C = 1.884 (1) and 1.883 (1) Å] are slightly elongated compared to the Si-Cmeth-yl bonds [Si-C = 1.856 (1) and 1.853 (1) Å]. The Cbenz-yl-Si-Cbenz-yl bond angle [C-Si-C = 107.60 (6)°] is decreased from the ideal tetra-hedral angle by 1.9°. These distortions can be explained easily by Bent's rule. In the crystal, mol-ecules inter-act only by van der Waals forces.

Crystal structure of benz-yl(meth-yl)phen-yl[(piperidin-1-ium-1-yl)meth-yl]silane bromide.

The title compound, C20H29NSi(+)·Br(-), contains a chiral silicon atom but crystallizes as a racemate. The C-Si-C bond angles in the range of 103.64 (8)-111.59 (9)° are usual for tetra-hedral geometry. The piperidine ring shows a regular chair conformation with an equatorially positioned exocyclic N-C bond. In the crystal, there is a hydrogen bond between the ammonium cation and the bromide anion. The crystal packing shows the dominant inter-molecular inter-action to be the electrostatic attraction between the ammonium cation and the bromide anion.