Synthesis,molecular and crystal structures,and characteristic features of electronic structures of salicylamide-based B,Si-containing chelates

The reaction of 4-(2-hydroxybenzoyl)-2,2,6,6-tetramethyl-2,6-disilamorpholine with BF₃Et₂O afforded (O-B)-chelate 4-[2-(difluoroboroxy)benzoyl]-2,2,6,6-tetramethyl-2,6-disilamorpholine. Treatment of the latter with BF₃Et₂O or SOCl₂ gave rise to products of the disilamorpholine ring opening, viz., (O-B) chelate 2-(difluoroboroxy)-N,N-bis(dimethylfluorosilylmethyl)benzamide or 2-(difluoroboroxy)-N, N-bis(dimethylchlorosilylmethyl)benzamide, respectively. The structures of the compounds synthesized were confirmed by X-ray diffraction analysis and ¹H, ¹³C, and ²⁹Si NMR spectroscopy. High-precision X-ray diffraction study and quantum-chemical calculations demonstrated that the coordination OSi bond is absent in the two last-mentioned compounds.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1846–1853, September, 2004.     

Dynamic stereochemistry of hypervalent silicon, germanium and tin compounds containing amidomethyl C, O-chelating ligands

The results of NMR-spectroscopy studies of the structure, dynamic stereochemistry, and intermolecular interactions in solutions of organic derivatives of penta-and hexacoordinated silicon, germanium, and tin containing amidomethyl, lactamomethyl, and related bidentate ligands are surveyed. For the series of works “Dynamic stereochemistry of hypervalent compounds of silicon, germanium, and tin,” the author was awarded the Academia Europea Prize for young scientists from CIS in 1996. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1912–1934. November, 1997.     

Quantum-Chemical Study of the Relative Stability of N-Substituted Tetrazole Isomers

The enthalpies of formation and total energies of a series of 1- and 2-substituted tetrazoles in the gas phase and in solution were calculated by MNDO and AM1 semiempirical methods and by a set of nonempirical procedures. The effect of solvent on the relative stability of N-substituted tetrazoles was estimated in terms of the PCM, SM5, and SCRF models. The possibility for isomerization of N-substituted tetrazoles, depending on the substituent in position 1 or 2, was studied at the MP2/6-31G*//HF/6-31G* level. According to the results of nonempirical calculations, 2-substituted tetrazoles are more stable in the gas phase, in keeping with the experimental data for the corresponding isomers. The solvent nature is an important factor affecting isomerization of N-substituted tetrazoles: Rise in the solvent polarity leads to displacement of the equilibrium toward 1-substituted isomers.     

Unexpected formation of a dimeric cation-anionic complex of hypercoordinated tin in the reaction of bis[(2-oxopyrrolidino)methyl]tin dichloride with AgBF4

A new cation-anionic complex of hypercoordinated tin, {[L₂Sn(OH)]⁺ BF₄ ^?}₂ (L is a bidentate (2-oxopyrrolidino)methyl C,O-chelating ligand), was obtained by the reaction of L₂SnCl₂ with AgBF₄ and structurally characterized by X-ray diffraction analysis. In crystalline form, the BF₄ ^? anions are bound to the dications through O?H...F hydrogen bonds (the H?F distance is 1.78 Å). The octahedral coordination of the Sn atoms is strongly distorted because of a weak additional interaction with solvate molecules of dioxane (the Sn?O distance is 3.16 Å).     

Two new eudesmane derivatives from Verbesina virginica

<正>Two new eudesmane derivatives were isolated from the leaves and flowers of Verbesina virginica,along with the known 6-O-β-E -p-coumaroyl-4α-hydroxyeudesmane(1).Their structures were determined as 6-O-β-Z-p-coumaroyl-4α-hydroxyeudesmane(2) and 6-O-α-E-p-coumaroyl-1β-4α-dihydroxyeudesmane(3) by spectroscopic methods.     

Tribromogermyl monochelates — derivatives of N,N-disubstituted 2-hydroxycarboxylic amides

Reactions of GeBr₄ with N,N-dimethyl-2-trimethylsiloxypropionamide (2a), (S)-2-trime-thylsiloxypropionpyrrolidide ((S)-2b), and N,N-dimethyl-O-(trimethylsilyl)mandelamide (2c) afforded pentacoordinated neutral (O,O)-monochelates, viz., N,N-dimethyl-2-tribromoger-myloxypropionamide (3a), (S)-2-tribromogermyloxypropionpyrrolidide ((S)-3b), and N,N-dimethyl-O-(tribromogermyl)mandelamide (3c), respectively. X-ray diffraction study was performed for tribromides 3a, (S)-3b, and 3c, as well as for the N,N-dimethylmandelamide (1c) described earlier. According to the X-ray diffraction data, the Ge atom in tribromides 3a, (S)-3b, and 3c is pentacoordinated and has trigonal bipyramidal configuration with two halogen atoms and oxygen atom of the ether group in the equatorial positions and the halogen atom and the amide oxygen atom in the axial fragment, the bonds in which are somewhat longer as compared to the analogous bonds in tetracoordinated Ge compounds.     

Synthesis,structure, and stereochemical non-rigidity of bis[(2,2-dimethyl-4-oxo-2<Emphasis Type="Italic">H</Emphasis>-benzo[<Emphasis Type="Italic">e</Emphasis>][1,3]oxazin-3(4<Emphasis Type="Italic">H</Emphasis>)-yl)methyl] dichlorosilane and -germane

Bis[(2,2-dimethyl-4-oxo-2H-benzo[e][1,3]oxazin-3(4H)-yl)methyl]dichlorosilane (1) and -germane (2) were synthesized by the reaction of 2,2-dimethyl-3-(trimethylsilyl)-2H-benzo[e][1,3]oxazin-3(4H)-one with bis(chloromethyl)dichlorosilane and -germane, respectively, taken in a ratio of 2 : 1. The structures of these compounds were determined and their stereodynamic behavior in solution was studied by multinuclear (¹H, ¹³C, and ²⁹Si) and twodimensional (¹H, ¹³C COSY, HETCOR) NMR spectroscopy. The ²⁹Si NMR spectroscopic study of a solution of complex 1 provides evidence that the silicon atom in this complex is pentacoordinate. The X-ray diffraction study showed that the germanium atom in complex 2 in the solid state is hexacoordinate. The permutation isomerization in the coordination units of complexes 1 and 2 was found and investigated by dynamic ¹H NMR spectroscopy. Different mechanisms of stereodynamic transformations are suggested and discussed.     

Composition depth profile analysis of electrodeposited alloys and metal multilayers: the reverse approach

The reverse depth profile analysis is a recently developed method for the study of a deposit composition profile in the near-substrate zone. The sample preparation technique enables one to separate the deposit and a thin cover layer from its substrate, and the initial roughness of the sample is much smaller than in the conventional sputtering direction. This technique is particularly suitable to study the zones being formed in the early phase of the electrodeposition of alloys. It has been demonstrated with the reverse depth profile analysis that in many cases when one component of an alloy is preferentially deposited, an initial zone is formed that is rich in the preferentially deposited component. This phenomenon is demonstrated for Ni–Cd, Ni–Sn, Fe–Co–Ni, Co–Ni, and Co–Ni–Cu alloys. The composition change is confined to the initial 150-nm-thick deposit, and it is the result of the interplay of the deposition preference and the depletion of the electrolyte near the cathode with respect to the ion reduced preferentially. The reverse depth profile analysis made it possible to compare the measured and the calculated composition depth profile of electrodeposited multilayers. It has been shown that the decay in the composition oscillation intensity in Co/Cu multilayers with the increase of the sputtering depth can be derived from the roughness measured as a function of the deposit thickness.