Yu. I. Baukov

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.

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).

Crystal and molecular structures of (O-Ge)-chelate 1-(dimethylchlorogermylmethyl)pyrrolidone-2 and 1-(dimethylchlorogermylmethyl)piperidone-2, and of (N-Ge)-chelate O-(dimethylchlorogermylmethyl)-δ-valerolactim and 2-(chlorodimethylgermylmethylthio)-pyrrolidine-1. Structural correlations between derivatives of four- and five-coordinated germanium

Abstract An X-ray study of (O-Ge)-chelate 1-(dimethylchlorogermylmethyl)pyrrolidone-2 ( 1 ), 1-(dimethylchlorogermylmethyl)piperidine-2 ( 2 ), (N-Ge)-chelate O -(dimethylchlorogermylmethyl)-δ-valerolactim ( 3 ), and 2-(chlorodimethylgermylmethylthio)pyrrolidine-1 ( 4 ) has been carried out ( R = 0.033, 0.062, 0.097 and 0.048 for 1241, 2351, 1242 and 1838 reflections, respectively). The Ge atom has a distorted trigonal-bipyramidal [3 + 2] coordination with the axial Cl and O atoms in 1 and 2 or Cl and N atoms in 3 and 4 . The axial distances are Ge-Cl 2.324(2), 2.354(2), 2.458(8) and 2.566(2) A, Ge ← O 2.311(4) and 2.194(2), Ge ← N 2.148(18) and 2.064(5) A in 1 – 4 respectively. Correlation between structural parameters of the compounds of five- and four-coordinated germanium have been considered.

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).

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.

Crystal and molecular structure of compounds containing a hypervalent O−Si(C3)−O fragment. Parametrization in the description of the coordination environment of the silicon atom

We have carried out an X-ray structural investigation of four pentacoordinated silicon compounds with a hypervalent O−Si(C3)−O fragment. In their molecules, the axial Si−O bond lengths range from 1.711 to 2.785 Å. Analysis of the geometry of such fragments containing other atoms in axial positions shows that the main parameter determining the state of the hypervalent fragment is deviation of the Si atom from the plane of equatorial substituents. Some consequences of this study for structural modeling of nucleophilic substitution reactions are discussed.

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.

Reaction of silyl- and germyl-ketenes with silyldiazomethanes

Abstract The reaction of trialkylsilyl- and trialkylgermyl-ketenes with trialkylsilyldiazomethanes proceeds stereoselectively to give one of two feasible stereoisomers, the Z -2,3-bis(Si,Ge)-substituted cyclopropanone. The addition of nucleophilic reagents such as benzyl alcohol, LiAlH 4 or (trimethylsilyl)dialkylphosphites is highly stereoselective and is a convenient method for assigning the stereochemical configuration of 2,3-substituted cyclopropanones.