Vad. V. Negrebetsky

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.

Synthesis and molecular and crystal structures of new cation-anionic hypervalent germanium complexes with 1,1,3,3-tetrakis(O—Ge)chelato-1,1,3,3-tetra(lactamomethyl)-1,3-digermoxane dications

The reaction of dichloride (L5)2GeCl2 with LiI·H2O under conditions, which did not exclude exposure to atmospheric oxygen, as well as hydrolysis of chloride triflate (L7)2Ge(Cl)OTf in the presence of Et3N and of perchlorate (L5)2Ge(Cl)OClO3 by atmospheric moisture afforded cation-anionic complexes containing the digermoxane dications of the general formula [(Ln)2GeOGe(Ln)2]2+ (Ln is a lactamomethyl n-membered bidentate C,O-coordinating ligand) with the triiodide, triflate, and perchlorate ions, respectively. According to the results of X-ray diffraction study, the digermoxane dications in these complexes contain two pentacoordinate Ge atoms each and occur as germylium ions stabilized by two O→Ge coordination bonds. In these complexes, the digermoxane dications are diastereomers in which the bischelate systems have opposite configurations.

Crystal and molecular structures of six-coordinate germanium difluorides and dibromides containing lactamomethyl C,O-chelating ligands

The structures of (O−Ge)-bischelate bis(lactamomethyl)difluoro- and-dibromogermanes [L(n)]2GeX2, where L is the bidentate lactamomethyl C,O-chelating ligand,n=5–7 (the size of the lactam ring), and X=F or Br, were studied by X-ray diffraction analysis. The six-coordinate Ge atom in these compounds is involved in two hypervalent X−Ge−O bonds whose parameters are compared with the corresponding values in analogous dichlorides and five-coordinate Ge derivatives. On going from difluorides to dichlorides and then to dibromides, the coordination environment about the Ge atom approaches the ideal octahedron. An analogous effect is observed as the size of the lactam ring increases.

Synthesis and crystal and molecular structures of six-coordinate tin dibromides and diiodides containing lactamomethyl C,O-chelating ligands

New (O−Sn)-bischelate bis(lactamomethyl)dibromo- and-diiodostannanes [L(n)]2SnX2 (L is the bidentate lactamomethyl C,O-chelating ligand;n is the size of the lactam ring, 5–7; X=Br or I) were prepared both by the direct method from metallic tin and the correspondingN-(halomethyl)lactams and by the reactions of dichlorides [L(n)]2SnCl2 with lithium halides. According to the data of X-ray diffraction analysis, the tin atom in [L(n)]2SnBr2 (n=5–7) and [L(n)]2SnI2 (n=5 or 6) adopts an octahedral configuration with the carbon atoms intrans positions and the coordinating oxygen and halogen atoms incis-positions with respect to each other. A comparison with the structures of analogous lactamomethyl halide derivatives of five-and six-coordinate Si, Ge, and Sn demonstrates that the spatial structures of the hypervalent fragments containing six-coordinate atoms are less sensitive to the replacement of the halide ligands and the central atom. The covalence of the M−Hal bond increases and the covalence of the M−O bond decreases in the series M=Si, Ge, and Sn.

Synthesis and structure of the first representative of pentacoordinate C,O-chelates with a dipeptide fragment, the fluorosilane Ts—Gly—( S )-Pro—N(Me)CH 2 SiMe 2 F

A reaction of bicyclic 2-sila-5-piperazinone, 2,2,4-trimethyl-1,4-diaza-2-silabicyclo-[4.3.0]nonan-5-one containing a proline moiety, and N-tosylglycine acyl chloride with subsequent hydrolysis of the primary unstable product to the intermediate disiloxane and its treatment with BF3•OEt2 furnished a first representative of pentacoordinate C,O-chelate halosilanes with a dipeptide fragment, namely, Ts—Gly—(S)-Pro—N(Me)CH2SiMe2F.

Donor-stabilized germylium cations. To the scheme of formation of bis(chelate) germylium ions using the complexes with lactamomethyl (С,О)-chelate ligand (enantolactam derivatives) as an example

Bis(chelate) dichlorogermane (L8CH2)2GeCl2 (1) with the monoanionic lactamomethyl (С,О)-chelate ligand based on enantolactam (L8H) was synthesized, and its molecular and crystal structures were studied. The germanium atom is characterized by the octahedral configuration with the mutual cis-arrangement of the Cl and O atoms and trans-arrangement of the C atoms. The scheme of transformation of dichlorogermane 1 into the bis(chelate) cationic complex (L8CH2)2Ge(Cl)OTf (2) was proposed. The H-bonded complexes of dichlorogermane 1 with HOSO2CF3 and HCl assumed to be intermediates in this process were studied by quantum chemical calculation. The energy necessary for the dissociation of the H-bonded complexes to the germylium cation and HCl2– and СlHOSO2CF3– anions depends on the relative arrangement of the Cl atoms in the coordination polyhedron of the Ge atom. In the case of the cis-arrangement of the Cl atoms in the H-bonded complexes, the dissociation energy was estimated as 11.5—16.1 kcal mol–1.

Synthesis and Some Chemical Properties of 2,2-Dimethyl-4-R-1-oxa-4-aza-2-sila-5-benzocycloheptanones

One-pot synthesis of 2,2-dimethyl-4-R-1-oxa-4-aza-2-sila-5-benzocycloheptanones (R = Me, CH2SiMe2Cl) from the N-methylamide of salicylic acid and salicylamide, respectively, by treatment of these amides with a mixture of hexamethyldisilazane and dimethylchloromethylchlorosilane was developed. The hydrolysis and other nucleophilic substitution reactions of the resultant seven-membered silacyclanes were studied. In the case of the silacyclane with R = Me, hydrolysis leads to the corresponding disiloxane, while the silacyclane with R = CH2SiMe2Cl gives either 2,2,6,6-tetramethyl-4-(2-hydroxybenzoyl)-2,6-disilamorpholine or its hydrochloride, depending on the reaction conditions. The chlorine atom was replaced by fluorine in the silacyclane with R = CH2SiMe2Cl. The structures of 2,2,6,6-tetramethyl-4-(2-hydroxybenzoyl)-2,6-disilamorpholine and its hydrochloride as well as 2,2-dimethyl-4-R-1-oxa-4-az! a-2-sila-5-benzocycloheptanones (R = CH2SiMe2Cl, CH2SiMe2F) were confirmed by X-ray diffraction.

New disiloxane based on N-acetylvaline: synthesis and structure

Silylmethylation of N-acetylvaline with the ClCH2SiMe2Cl—(Me3Si)2NH system gave the previously unknown 2-silamorpholin-6-one derivative, whose hydrolysis in aqueous ethanol produced bis-acetylvaline-containing disiloxane. The X-ray diffraction study and quantum chemical calculations demonstrated that both silicon atoms in the final product are four-coordinated.

Synthesis and structural features of new pentacoordinated monofluorosilanes containing C,O-chelate ligands based on 2-amino acid N-methylamides

Pentacoordinated monofluorosilanes R1SO2NHCHR2C(O)N(Me)CH2SiMe2F containing moieties of N′-methyl-N-(organosulfonyl)-2-amino acid amides of glycine, alanine, and leucine as C,O-chelating ligands were synthesized via the reaction of corresponding disiloxanes with BF3•Et2O. The structures of obtained compounds were investigated by single-crystal X-ray diffraction analysis.

Lactamomethyl derivatives of diphenols: synthesis, structure, and potential biological activity

A series of mono-, bis-, and tris-substituted lactamomethyl derivatives of diphenols were synthesized. The solution and solid-state structures of these compounds were confirmed by IR and NMR spectroscopy and X-ray diffraction. The in silico evaluation indicated a high probability that these compounds have various biological activities.