Gas phase electron diffraction study of tetraphenyltin,Sn(C6H5)4

The geometrical parameters of the tetraphenyltin molecule have been determined by gas phase electron diffraction at about 310°. The S₄ and “open” D_2d molecular models with the tetrahedral bond configuration at tin were chosen for the structure analysis. The former gave the better fit. The thermal average bond lengths (r_g, in Å) are as follows:

The benzene ring geometry appears to be almost unaffected by bonding to tin. However, tin causes an increase in the endocyclic valence angle at the ipso-carbon atom to 121.0(0.9)° rather than a decrease of that angle as might be expected, tin being a σ-electron donor. The ring plane and the plane containing the

bond and S₄ axis make an angle, ?, of 34.1(2.1)°. The

bond length in tetraphenyltin is longer than not only the

bond in tetravinyltin (r_g = 2.117(4) Å) but also the

bond in tetramethyltin (r_g = 2.144(7) A).     

Molecular structures of acetylene derivatives of tin: Part IV. Gas-phase electron-diffraction study of tetraethynyltin,Sn(CCH)4, and triethynyltin iodide,ISn(CCH)3

The geometrical parameters of tetraethynyltin and triethynyltin iodide have been determined by gas-phase electron diffraction. Triethynyltin iodide was present as an admixture in both the tetraethynyltin samples studied. Because the samples differed significantly in percentage of the iodide (17.4 ± 4.0 and 47.1 ± 3.5 mol %, in samples A and B, respectively), it was possible to determine the structures of both molecules to a sufficient degree of accuracy.The r_α, structures were solved by the least-squares treatment of the molecular intensities, using mean amplitudes and shrinkage corrections calculated from the force fields of a number of tin derivatives.The T_d-symmetry model of Sn(CCH)₄ was refined to give the following parameters: Sn-C, 2.068(5); CC, 1.228(8); CH, 1.079(51). The structural parameters for ISn(CCH)₃ (on the basis of the C_3v model with linear Sn-CC-H fragments) are as follows: Sn-I, 2.646(4); Sn-C, 2.062(17); CC, 1.226(6); ∠ISnC 108.0(2.8). (The thermal average bond distances, r_g, are given in Å, and the valence angle, rα, in degrees; the values in paren- theses are three times the standard deviations, 3σ.)The Sn-C bonds in Sn(CCH)₄, and ISn(CCH)₃ are shorter than the corresponding bonds in the monoethynyltin derivatives, Me₃SnCCH and Me₃SnCCSnMe₃. The SnI bond in ISn(CCH)₃ is noticeably shorter than those in stannane iodide and trimethylstannane iodide.     

Reactions of Carbazoles with Hexacarbonyl Dicobalt Complexes of Propynol and 1,4-Butynediol

Metallopropargylation of a number of carbazoles was performed by dicobalt hexacarbonyl complexes with propargyl alcohol and 1,4-butynediol in the presence of boron trifluoride etherate. It was shown that depending on the substituents position in the carbazole ring occurred either N- of C-propargylation; with 1,4-butynediol formed also oligomeric products.     

Effect of “Stefan” currents of a solidifying melt on the process of thermal convection

The calculated results, represented by graphs, show that in the initial period of solidification the motion of a melt is fully determined by the shrinkage at the front of crystallization. The effect develops more strongly at lower Grashof numbers and higher Stefan numbers. As the rate of solidification and the temperature gradient decrease the process of natural thermal convection develops in the liquid phase. The calculated results are compared with experiment.     

Lewis acid stabilized group 13–15 element analogs of ethylene

Stabilization of hydrogen-substituted group 13–15 compounds H₂EE′H₂ (E = B, Al, Ga; E′ = P, As, Sb) by Lewis acids is considered at B3LYP/def2-TZVP, B3LYP-D3/def2-TZVP and M06-2X/def2-TZVP levels of theory. It is shown, that for many Lewis acids additional reactivity beyond the DA complex formation with H₂EE′H₂ monomer is expected. In case of complexation with E(C₆F₅)₃, F/H exchange reactions with group 13 bound hydrides are predicted to be exothermic and accompanied by the activation energies which are smaller than dissociation of the complex into components. In case of complex formation with transition metal (TM) carbonyls, additional O → Al, TM–C → Al interactions are observed, which in several cases lead to cyclic structures. The most promising candidates for the experimental studies have been identified. Synthetic approaches to the most promising LA-only stabilized compounds are recommended.     

A study of the electron-donating capacity of tin-containing amines by the IR-spectroscopic method

Conclusion The electron-donating capacities of tin-containing amines depend almost exclusively on the donor-acceptor properties and steric effects of the substituents at the N atom. The effect of d-p interaction in the Sn-N fragment of the tin-containing amines, unlike the analogous interaction in their silicon and germanium analogs, is hardly apparent. An increase in the number of trialkylstannyl radicals at the N atom leads to a fall in the donor capacity on passing from mono- to bis(trialkylstannyl)amines and to a considerable rise in this capacity in the tris(trialkylstannyl)amines. The donor properties of the dialkylamino-tannanes fall with an increase in the number of amino groups at the Sn atom.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1294–1298.     

Acyclic analogs of nucleosides. Synthesis of 1,5-dihydroxy-3-oxa-2-pentyl derivatives of nucleic bases

A convenient method for the synthesis of 1,5-dihydroxy-3-oxa-2-pentyl derivatives of nucleic bases, which consists in the condensation of trimethylsilyl derivatives of nucleic bases with 1,2,5-triacetoxy-3-oxapentane in the presence of SnCl₄, is proposed. Optically active derivatives — (R)- and (S)-1-(1,5-dihydroxy-3-oxa-2-pentyl)uracil, respectively — were obtained by periodate oxidation of -L- and -D-arabinopyranosyluracil.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 223–228, February, 1988.