A. G. Shipov

Stereochemical rearrangements of dibromides of hexacoordinated germanium containing amidomethyl and lactamomethyl chelate ligands

For the first time a slow (on the NMR time scale) dynamic exchange between two diastereomers of hexacoordinated dibromogermanes containing two amidomethyl and lactamomethyl C,O-chelate ligands has been observed at room temperature in solution. The influence of temperature and solvent on the ratio of diastereomers was studied. At higher temperatures only one set of signals of the products were detected in the NMR spectra. Based on the dynamic NMR and quantum-chemical calculations (ab initio FR 3-21G), as well as on the structures determined for these compounds in the solid state, a cis-configuration of monodentate ligands was proposed for one of the diastereomers and an all-trans-configuration for the other. At low temperatures interconversion of enantiomers in the cis-diastereomer was observed. In the case of bis[(N-methylacetamido)methyl]dibromogermane the activation and thermodynamic parameters of enantiomerization (DeltaG(298)(#) 12.0+/-0.1 kcal mol(-1), DeltaH(#) 10.7+/-0.3 kcal mol(-1), DeltaS(#) -4.6+/-2.5 cal mol(-1) K-1) and diastereomeric exchange OcCtBrcreversible arrowOtCtBrt (DeltaG(298)(#), 15.0+/-0.1 kcal mol(-1); DeltaH(#) 0.1+/-0.8 kcal mol(-1); DeltaS(#) -50.0+/-5.8 cal mol(-1) K-1; DeltaG(298)degrees -0.2+/-0.1 kcal mol(-1); DeltaHdegrees -0.8+/-0.8 kcal mol(-1); DeltaSdegrees -2.6+/-1.0 cal mol(-1) K-1) were determined

Synthesis, crystal structure and stereochemical non-rigidity of (O-Sn)-bischelated bis(lactamomethyl)dichlorostannanes

Previously unknown (0-Sn)-bischelated bis(lactamomethyl)dichlorostannanes have been synthesized by a direct method from metallic tin and N-chloromethyllactams. According to X-ray structural analysis data, in the solid state in these compounds the tin atom is hexacoordinated and has an octahedral configuration with the two carbon atoms in the transposition, and both coordinating oxygen atoms and the two halogen atoms in thecis-position. A comparison to Ge-analogs indicates that the replacement of the central atom of the coordination unit MCl2O2C2 has inconsistent effects on the parameters of the latter. According to1H and1191 Sn NMR data, the hexacoordination of tin and the geometry of the coordination unit are also retained in solution at low temperatures. At higher temperatures a dynamic process takes place resulting in isochronisms of the protons signals of the NCH2Sn groups. Quantum-chemical calculations of isomeric bis(lactamomethyl)dichlorostannanes by MNDO and MNDO/PM3 methods have been discussed.

N,N -bis-(dimethylfluorosilylmethyl)amides of N -organosulfonylproline and sarcosine: synthesis, structure, stereodynamic behaviour and in silico studies

(O→Si)-Chelate difluorides R3R2NCH(R1)C(O)N(CH2SiMe2F)2 (9a–c, R1R2 = (CH2)3, R3 = Ms (a), Ts (b); R1 = H, R2 = Me, R3 = Ms (c)), containing one penta- and one tetracoordinate silicon atoms were synthesized by silylmethylation of amides R3R2NCH(R1)C(O)NH2, subsequent hydrolysis of unstable intermediates R3R2NCH(R1)C(O)N(CH2SiMe2Cl)2 (7a–c) into 4-acyl-2,6-disilamorpholines R3R2NCH(R1)C(O)N(CH2SiMe2O)2 (8a–c) and the reaction of the latter compounds with BF3·Et2O. The structures of disilamorpholines 8a,c and difluoride 9a were confirmed by an X-ray diffraction study. According to the IR and NMR data, the O→Si coordination in solutions of these compounds was weaker than that in the solid state due to effective solvation of the Si–F bond. A permutational isomerisation involving an exchange of equatorial Me groups at the pentacoordinate Si atom in complexes 9a–c was detected, and its activational parameters were determined by 1H DNMR. In silico estimation of possible pharmacological effects and acute rat toxicity by PASS Online and GUSAR Online services showed a potential for their further pharmacological study.

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.

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).