E. P. Kramarova

The reaction of N-trimethylsilyl-amides and -lactams with dimethyl(chloromethyl)chlorosilane. Kinetically controlled formation of (NSi) chelate intermediates, O-[(dimethylchlorosilyl)methyl]imidates and their rearrangement to final(OSi) chelate N-[(dimethylchlorosilyl)methyl]amides and lactams

The multistage character of the reaction of dimethyl(chloromethyl)chlorosilane (I) with N-trimethylsilyl-amides and -lactams (II) was shown by NMR monitoring. Interaction of the reactants starts with transsilylation, leading to Me3SiCl and the corresponding N-[dimethyl(chloromethyl)silyl]amide or -lactam (III). The second stage, intramolecular (dimethylchlorosilyl)methylation of unstable III, proceeds in two directions. A kinetically controlled transformation of III affords previously unknown O-(dimethylchlorosilyl)methylated intermediates, O-[(dimethylchlorosilyl) methyl]imidates (IV) containing a hypervalent ClSiN bond. The already known products, (OSi) chelate N-[(dimethylchlorosilyl)methyl]amides (V), arise from the reaction carried out under thermodynamic control. The same compounds are also formed via the Chapman rearrangement of the intermediates (IV).

Synthesis and crystal structure of enantiomeric N-(dimethylfluorosilylmethyl) and N-(dimethylchlorosilylmethyl)-[N-(S)-1-phenylethyl)] acetamides

Abstract Synthesis of the first optically active compounds containing asymmetric carbon and pentacoordinated silicon has been carried out. The enantiomeric (O-Si)-chelate N-(dimethylhalogenosilylmethyl) acetamides, MeC(O)N(CH(Ph)Me)CH2SiMe2 X (X = F, Cl), obtained are the model compounds in studies of the stereodynamic processes at the trigonal-bipyramidal silicon atom and asymmetric induction. An X-ray structural investigation confirmed a 3 + 2 pentacoordination of the Si atom in the title compounds and an axial arrangement of the oxygen and halogen atoms. The geometrical parameters of hypervalent moieties are in good agreement with relations established earlier.

Interaction of the (O → Ge)-chelate bis-(lactamo-N-methyl)-cis-dichlorogermanes with trimethyltriflate. Synthesis of bis-(lactamo-N-methyl)-trans-(trifluoromethylsulfonyloxy)chlorogermanes

Abstract Regardless of the ratio of reagents, the interaction of the (O→Ge)-chelate,bis-(lactamo- N -methyl)- cis -dichlorogermanes with trimethylsilyltriflate in acetonitrile, proceeds with substitution of one chlorine atom by the triflate group resulting in products with an inversion of configuration at the germanium atom, viz. (O→Ge)-chelate bis-(lactamo- N -methyl)- trans -(trifluorosulfonyloxy) chlorogermanes. This result as well as conductometric studies allow us to suppose an easy ionization of the final products with formation of a triflate anion and a cation with a pentacoordinated germanium atom. According to X-ray structural studies of the prepared compounds, the Ge atom has an octahedral coordination strongly distorted towards a capped trigonal bipyramid configuration. The GeCl bond (2.13–2.17 A) is the shortest among those observed by us in hypervalent germanium compounds and the GeOTf bond is, on the contrary, the longest (3.02–3.36 A).

Reactions of silamorpholinones and acylsilamorpholines with electrophilic reagents. X-ray structure of products including a pentacoordinated silicon compound

Reactions of 2-sila-5-morpholinones, 4-acyl-2-silamorpholines and 4-acyl-2,6-disilamorpholines with electrophilic reagents generally lead to the opening of the sila- or disilacycle by cleavage of the Si–O bond with subsequent rearrangement to form five-membered chelate derivatives where the amide oxygen atoms coordinate with the silicon to form pentacoordinate silicon species. Multinuclear NMR spectroscopy and X-ray diffraction studies were used for structural investigation of the products. 4-Acyl-2,6-disilamorpholines initially form adducts with strong acids where the amide oxygen is protonated by the acid as demonstrated by X-ray crystallography.

Molecular and crystal structure of N-(fluorodimethylsilylmethyl)pyrrolidone-2

Abstract An X-ray diffraction study of N -(fluorodimethylsilylmethyl)pyrrolidone-2 was carried out ( R = 0.077 for 2256 reflections with I ⩾ 2σ( I . The Si atom has distorted trigonal-bipyramidal [4 + 1] coordination with the F and O atoms in axial positions. The SiF and Si ← O distances in four independent molecules are 1.630–1.665(7)( and 2.316–2.461(8) A, respectively.

Pentacoordinated chlorosilanes with C,O-chelate ligands derived from N-methyl-N'-organosulfonyl-prolinamides*

The reaction of amides RSO2-Pro-NHMe with ClCH2SiMe2Cl in the presence of (Me3Si)2NH gave pentacoordinated chlorosilanes RSO2-Pro-N(Me)CH2SiMe2Cl with an organosulfonyl group (R = Me, Ph, 4-ClC6H4, 4-BrC6H4, 4-MeC6H4, and 4-O2NC6H4) attached to the proline nitrogen atom. An alternative method for the preparation of these compounds comprises the cyclosilylmethylation of proline methylamide by dimethylchloromethylchlorosilane to give the previously unreported heterocyclic 2-sila-5-piperazinone system in the first step. The bicyclic silacyclane synthesized is 2-sila5-piperazinone condensed with a proline residue. The action of sulfonyl chlorides RSO2Cl leads to cleavage of the sila ring Si–N bond to give the desired chlorosilanes. The hydrolysis of these products, depending on the reaction conditions, gives either silyloxonium chlorides [RSO2-ProN(Me)CH2SiMe2OH2]Cl or disiloxanes [RSO2-Pro-N(Me)CH2SiMe2]2O. X-ray diffraction structural analysis showed that the silicon atom in the chlorides and silyloxonium chlorides is pentacoordinated due to an intramolecular O → Si bond and has distorted trigonal-bipyrimidal configuration. 29Si NMR spectroscopy showed that the disiloxanes and bicyclic sila-5-piperazinone have a tetracoordinated silicon atom.

Stereochemical non-rigidity of N-(dimethylhalogenosilylmethyl)-N-(1-phenylethyl) acetamides in solutions

Abstract The structure and dynamic behavior of (O-Si)-chelate N -(dimethylhalogenosilyl)methyl acetamides of the type MeC(O)N(CH(Ph)Me)CH 2 SiMe 2 X, where X = F, Cl, Br with the OSiC 3 X coordination set, were studied by multinuclear ( 1 H, 13 C, 17 O, 29 Si) and dynamic 1 H NMR spectroscopy. Ligand permutation at silicon was detected. The observed influence of the solvent, nucleofugacity of the X substituent and the external nucleophile on the calculated values of the free energies of activation testify to the dissociative and/or associative mechanisms of the process, but including the stages in which the regular (pseudo-rotation or ‘turnstile’) mechanism takes place. At lower temperatures (up to −90°C) the 1 H, 13 C, 29 Si NMR spectra of N -(dimethylchlorosilyl)methyl acetamide contain the signals of two species of unequal intensity. This effect was explained by an equilibrium between monomers containing the intramolecular O → Si bond and dimers with a hexacoordinate silicon and the bridging chlorine atoms.

Crystal and molecular structure of 1-(iododimethylsilylmethyl)piperidone-2

Abstract Crystal structure study of 1-(iododimethylsilylmethyl)piperidone-2 ( R = 0.018 from 1665 reflections) was performed. A donor-accepted Si ← I Interaction, at a distance of 3.734(1) A, was detected for the first time. The Si atom is distinguished by a distorted trigonal-bipyramidal coordination with O and I atoms in the axial positions.

Scheme of hydrolysis of five-coordinate chlorosilanes by X-ray diffraction data

Hydrolysis of monochelate five-coordinate chlorosilanes MeC(O)N(Me)CH2SiMe2Cl (Ia), L7CH2SiMe2Cl (Ib), L8CH2SiMe2Cl (Ic), PhtImCH2SiMe2Cl (Id), MeC(O)N(Me)CH2SiMePhCl (IIa), and Im5CH2SiMePhCl (IIe), containing a monoanionic C,O-chelating ligand LCH2 [L is an amide, n-membered lactam (Ln), imide (Imn), or phthalimide (PhtIm) residue]. The structures of the starting chlorides and their hydrolysis products were established by means of X-ray diffraction analysis. Based on experimental and published data, a general scheme of hydrolysis of mono-C,O-chelate chlorosilanes was suggested, including initial formation of silyloxonium chlorides III and subsequent formation of disiloxane dihydrochlorides IV.

Six- and seven-membered 1-oxa-4-aza-2-silacyclanes as possible correctors of adaptational mechanisms.

The biological activity of eight 1-oxa-4-aza-2-silacyclanes with the OSiCH2N fragment including 6-membered 2-sila-5-morpholinones (1–3) and 4-acyl-2-silamorpholines (4–6)and previously unknown 7-membered derivatives of salicylic acid (7, 8) was studied. Compounds 1 and 3–6 show the certain antihypoxic action. Compounds 2 (40 mg/kg), 4 (20 mg/kg), 6 (40 mg/kg), 7 (20 mg/kg) and 8 (40 mg/kg) reduce the physical serviceability of intact animals. Compound 1 (20 mg/kg) influences the physical serviceability in a moderate-positive way on the background of chlorophos-poisoning. Compounds 5–8 displayed protective properties against chlorophos-poisoning at the LD50 dose and compounds 2, 4, 5, 7 at the LD100 dose. Influence of compounds 1 and 2 on the emotional-research behavior of mice was studied.