Frank Uhlig

Reaction pathways towards 1,1,2,2-tetratbutyldistannanes

Abstract 1,2-Dichlorotetratbutyldistannane (1) is synthesized as a byproduct in the reaction of tbutylmagnesium chloride with tin tetrachloride or by the reaction of ditbutyltindihydride with ditbutyltin dichloride in the presence of amines. Reaction of 1 with lithium aluminumhydride yielded the dihydrido derivative 2. The treatment of 2 with bromoform gave the dibromo distannane 3 nearly quantitatively. Reactions of 2 with one equivalent of LDA or KH yielded unsymmetrically substituted alkali metal distannanes of the type MtBu2SnSn(H)tBu2 (4, M=Li; 5, M=K). Reaction of either two equivalents of KH with 2, or one equivalent of KH with 5 gave the dipotassium distannide 6. The molecular structure of the dichloro derivative 1 was determined by X-ray diffraction.

Novel triphenyltin substituted derivatives of heavier alkaline earth metals

Abstract The synthesis and characterization of a family of novel alkaline earth metal stannides, in addition to tri- and pentastannanes are described. [Ba(18-crown-6)(HMPA) 2 ][SnPh 3 ] 2 ( 4 ), [Ca(18-crown-6)(HMPA) 2 ][Sn(SnPh 3 ) 3 ] 2 ( 5 ), and [Sr(18-crown-6)(HMPA) 2 ][Sn(SnPh 3 ) 3 ] 2 ( 6 ) were synthesized by insertion of the corresponding alkaline earth metals into the tintin bond of hexaphenyldistannane. Ph 3 SnSnPh 2 SnPh 3 ( 7 ), and Sn(SnPh 3 ) 4 ( 8 ) became available by treating 4 with diphenyldichlorostannane. All compounds were studied by NMR spectroscopy, and X-ray crystallography. The stannanes 7 and 8 were also characterized by elemental analysis.

Heavy alkali metal amides: role of secondary interactions in metal stabilization.

The coordination chemistry of the bis(diphenylmethylsilyl)amine ligand, HN(SiMePh(2))(2), with the heavy alkali metals potassium and rubidium has been investigated to study its effect on the structure of the resulting compounds. The compounds exhibit extensive intra- and intermolecular M-pi interactions, creating 1-D coordination polymers, [K{N(SiMePh(2))(2)}](infinity) (1) and [Rb{N(SiMePh(2))(2)}](infinity) (3). This motif is maintained in the presence of tetrahydrofuran (THF), as seen in [K{N(SiMePh(2))(2)}thf](infinity) (2). In contrast, use of the tridentate PMDTA allows isolation of a monomeric species, K(pmdta)N(SiMePh(2))(2) (4), which exhibits both agostic and M-pi interactions. The incorporation of macrocyclic 18-crown-6, results in the formation of a rare non-metal bound amido species, {[K(18-crown-6)N(SiMePh(2))(2)]}(infinity) (5), stabilized by M-pi interactions from adjacent [N(SiMePh(2))(2)](-) ligands propagating 1-D coordination polymers.

Zur darstellung von permethylierten cyclosilanylalkalimetall-derivaten

Abstract A simple way for the preparation of undecamethylcyclohexasilanylalkalimetal compounds is described by the reaction of dodecamethylcyclohexasilane with alkalimetal alcoholats in glyme solvents. Reactions of other cyclosilanes are also discussed. Some reactions of undecamethylcyclohexasilanylpotassium with element-halogen derivates and inorganic acids are described.

Synthesis and coordination ability of a partially silicon based crown ether

The first hybrid crown ether with two adjacent disilane fragments was synthesized through reaction of O(Si2Me4Cl)2 (3) with O(C2H4OH)2. By means of DFT calculations, the complexation ability of 1,2,4,5-tetrasila[12]crown-4 (7) towards Li+ was determined to be considerably higher compared to [12]crown-4.

Novel Si–Sn ring systems with distanna and tristanna moieties

Abstract The synthesis of new cyclic stannaoligosilanes 9, 10 and 11 with a bridging tin–tin unit [(tBu2Sn)2(SiMe2)n, n=2, 9; n=3; 10; n=4, 11] or an Sn3 moiety [(tBu2Sn)3(SiMe2)2] (12) are reported. All compounds are fully characterised by NMR, mass spectroscopy and elemental analysis. The structure of the five-membered ring 10 is determined by X-ray crystallography.

Cyclohexasilanes with exocyclic organogermanium, -tin or -lead groups

Abstract A new class of mono- ( 2 – 4 ) and bis(undecamethylcyclohexasilanyl) ( 5 – 9 ) substituted germanium, tin and lead compounds is described. These molecules are accessible by treatment of undecamethylcyclohexasilanyl potassium ( 1 ) with chlorogermanes, -stannanes or plumbanes. Attempts to generate bis(cyclohexasilanyl)methanes, -plumbanes or tris(cyclohexasilanyl)methylstannane starting from dihalomethanes, -plumbanes or methyltrichlorostannane and 1 result only in transmetallation reactions. The molecular structures of a mono- ( 3 ) and a dicyclohexasilanyl stannane derivative 5 were determined by single-crystal X-ray crystallography.

New cyclic stannyloligosilanes

Abstract The synthesis of new cyclic stannyloligosilanes [R 2 Sn(SiMe 2 ) n ] ( 2a , n =5, R=Ph; 2b , n =5, R=Me; 3a , n =6, R=Ph; 3b , n =6, R=Me) is reported. The compounds are fully characterised by mass spectrometry and NMR spectroscopy and in the case of 2a also by X-ray analysis.

A Raman spectroscopic study of the rotational isomerism of linear permethylated stannylsilanes Me3Sn(SiMe2)nSnMe3 with n=1, 2, 3, 4

Abstract The IR and Raman vibrational spectra of the methyl(trimethylstannyl)silanes Me 3 Sn(SiMe 2 ) n SnMe 3 with n =1 ( 1 ), 2 ( 2 ), 3 ( 3 ) and 4 ( 4 ) were recorded at various temperatures. Compound 2 consists of a mixture of two conformers, gauche (G) and anti (A), in the liquid state. By variable temperature Raman spectroscopy, the enthalpy difference Δ H = H gauche − H anti was determined from the relative intensities of the symmetric SiSn stretching bands as 0.8±0.3 kJ mol −1 . In the Raman spectrum of the crystalline solid, the lines of the G conformer disappear completely, facilitating the assignment of the fundamental vibrations for the A form. No indication of the presence of a third ( ortho ) conformer could be detected. HF-SCF ab initio calculations using electron core potentials for the heavy atoms predict the existence of three conformers on the potential surface. In the Raman spectra of 3 , the symmetric SiSn stretching vibration splits into three components, which can be assigned to the G + G + , GA and AA conformers. The G + G − rotamer could not be observed. As its energy is significantly larger than that for the other conformations due to repulsive four bond interactions between the SnMe 3 groups (pentane effect), the concentration in the equilibrium mixture is negligibly small. For 4 , eight (2 3 ) spectroscopically distinct (classical) conformations are possible. In the room temperature Raman spectrum, the SiSn stretching vibration consists of a line at 330 cm −1 with a broad shoulder at 320 cm −1 . In the solid (−60°C), a single rotamer (probably the all anti form) survives. Upon heating, several conformational states with higher energies are populated which could not be resolved by Raman spectroscopy.

Eine einfache Methode zur Darstellung von Alkalimetall-bis(trimethylsilyl)-phosphiden

Abstract A simple way for the preparation of alkali-bis(trimethylsilyl)-phosphides is described by the reaction of tris(trimethylsilyl)-phosphine with alkali-alcoholates.