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A novel organosilicon complex of N-acetylvaline was synthesized by the reaction of the relative disiloxane derivative with BF3 etherate. According to X-ray and NMR data, the silicon atom of the final product is pentacoordinated in both the solid state and solution. The coordination state of silicon was correctly predicted by quantum-chemical calculations.

Halogen exchange reactions between hexacoordinate tin dihalides (LnCH2)2SnX2 and (LnCH2)2SnY2 (LnCH2 = C,O-chelate n-membered lactamomethyl ligand, n = 5–7, X, Y = Cl, Br, I) produce mixed dihalides (LnCH2)2SnXY. Along with the signals of original complexes, NMR 119Sn spectra of solutions containing two different homodihalides show the third signal with a median chemical shift. The results of NMR monitoring studies, conductivity data and quantum-chemical calculations suggest that mixed dihalides readily form in solutions, although these complexes have not been isolated as individual compounds.

The structures and stereodynamic behavior of (O→Si)-chelate methyldifluorosilanes in solutions were studied by multinuclear (1H, 13C, 19F, 29Si) and 2D (COSY, HETCOR 1H, 13C) NMR spectroscopy. The range of studied complexes included amides RC(O)N(R')CH2SiMeF2 [R = Ph, R' = H (1a); R = R' = Me (1b); R = Me, R' = CHMePh (1c)], lactams LCH2SiMeF2 (L = 2-oxoazepan-1-yl (2a), 2,2-dimethyl-4-oxo-2H-benzo[1,3]oxazin-3-yl (2b) or 4-methyl-2-oxoquinolin-1-yl (2c)] and the six-membered imide Im6CH2 [2,6-dioxopiperidin-1-yl (3)]. The pentacoordination of silicon atoms in all studied compounds was confirmed by NMR study in solutions and single-crystal X-ray studies of complexes 1c, 2a, 2c and 3. The temperature dependency observed for the 19F NMR signals in solution was explained by the ligand exchange in the coordination environment of silicon atoms (permutational isomerization) and used for determining the activation parameters of this process by 19F DNMR. Quantum-chemical calculations for various isomers of complexes 1c, 2a, 2c and 3 suggested the "turnstile rotation" as the most likely mechanism for the observed stereodynamic processes.

(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.

Regioselective reaction of N-trimethylsilyl-N-acetylglycine N’,N’-dimethylamide with chloro(chloromethyl)dimethylsilane yields chlorosilane MeC(O)N(CH2SiMe2Cl)CH2C(O)NMe2 with a five-membered C,O-chelate ring involving the N-acetyl group rather than the six-membered ring involving the N’,N’-dimethylamide fragment. According to X-ray data, the pentacoordinate silicon atom in the product has a TBP environment with the halogen and oxygen atoms in axial positions.

The (O→Si)-chelate N′-(dimethylfluorosilylmethyl))-N′-methyl-N-(organosulfonyl)prolinamides RSO2-Pro-N(Me)CH2SiMe2F (2a–f, R = Me (a), Ph (b), 4-MeC6H4 (c), 4-ClC6H4 (d), 4-BrC6H4 (e), 4-NO2C6H4 (f)) were synthesized from the corresponding disiloxanes 1a–f using Et2O·BF3. According to the NMR and IR data, the extent of dimerization of fluorosilanes 2a–f in solution is negligible, while the O→Si coordination in solution is weaker than that in the solid state. Comparative CP/MAS NMR and X-ray diffraction studies revealed that in solution the coordination Si–O bond length varies in a narrow range (2.22–2.24 A) that is 0.02–0.11 A longer than in the crystalline state. Dynamic NMR (DNMR) studies of the fluorides revealed a fine structure of the 19F signals in the 0–20 °C temperature range, which was related to the structural features of the coordination set in these complexes. The temperature dependence of the SiMe2 signals in the 1H DNMR spectra was attributed to a permutational isomerization process involvin...

Reactions of ethyltrichlorostannane with N,N-dimethylamides of 2-(trimethylsilyl)glycolic (2a), 2(S)-lactic [(S)-2b] and mandelic (2c) acids led to the first representatives of tin(IV) O,O-monochelates containing the five-membered SnOCC(O) monoanionic chelate cycles as a result of the substitution of one halogen atom. According to the X-ray data, in the case of the derivatives of glycolic and mandelic acids, the isolated complexes have dimeric structures {EtCl2Sn[OCH(R)C(O)NMe2]}2 [R = H (3a), Ph (3c)] with the bridge oxygen atoms and hexacoordinated tin atoms. By contrast, in the case of the derivative of lactic acid (S)-2b, the product of the reaction is the cationic–anionic complex 2EtCl2Sn[OCH(Me)C(O)NMe2]·HCl (4), which is the adduct of two molecules of the respective monomeric complex with HCl. In addition, N,N-dimethylamide of O-triethylstannylglycolic acid (5) with tetracoordinated tin is described. To analyze the stability of complex 4, the experimental charge density study and the quantum chemical calculations [PBE0/6-311G(d,p)] were carried out. Topological analysis of the experimental and calculated electron density distribution functions allowed us to conclude that the strong OH···O bond with pronounced covalent contribution stabilizes the dimeric structure of 4 to a greater extent than the bridged SnCl bonds. Copyright © 2010 John Wiley & Sons, Ltd.

Substituted N-(silatran-1-ylmethyl)acetamides, N-methyl-N-[1-(3′,7′,10′-trimethylsilatran-1-yl)methyl]acetamide (2a) and N-(2-hydroxyethyl)-N-[1-(3′,7′,10′-trimethylsilatran-1-yl)methyl]acetamide (2b) were prepared by the reactions of triisopropanolamine with N-methyl-N-(trimethoxysilylmethyl)acetamide (1a) and 2,2-dimethoxy-4-acetyl-1-oxa-4-aza-2-silacyclohexane (1b), respectively. According to X-ray data, the structures of the silatrane moieties are superpositions of unsymmetrical and symmetrical stereoisomers. The O Si coordination between the central atom and exocyclic substituent is absent in both compounds. Silatranes 2a and 2b are partial muscarinic agonists which demonstrate submaximal effect and mimic the effect of acetylcholine by binding directly to cholinoreceptors of the ileal smooth muscle. Copyright © 2009 John Wiley & Sons, Ltd.

Bischelate complexes of germanium with different chelate rings were prepared by double transmetallation. The earlier reported (O,O)-chelate [from the reaction of trichloro(chloromethyl)germane and N,N-dimethyl-2-(trimethylsilyloxy)-2-phenylacetamide (1)], 2-[dichloro(chloromethyl)germyloxy]-N,N-dimethyl-2-phenylacetamide (2) was reacted with trimethylsilylamides, 2,2-dimethyl-3-trimethylsilylbenzo[2H]-1,3-oxazin-4-one (5, B–SiMe3) and 4-methyl-1-trimethylsilylquinolin-2-one (6, Q–SiMe3) resulting in mixed (O,O),(C,O)bischelate complexes, 2-[dichloro[(2,2-dimethyl-4-oxo-2H-benzo[e][1,3]oxazin-3(4H)yl)methyl]germyloxy]-N,N-dimethyl-2-phenylacetamide (7) and 2-[dichloro[(4-methyl-2oxoquinolin-1(2H)-yl)methyl]germyloxy]-N,N-dimethyl-2-phenylacetamide (8). Crystallographic analyses established pentacoordination of germanium in 2 and hexacoordination in 7 and 8; the latter two compounds are the first reported mixed (O,O), (C,O)-bischelate complexes with two O→Ge coordinate bonds.

The novel compounds, N -(trifluorosilylmethyl)-[ N -( S )-(1-phenylethyl)]-acetamide ( 1a ) and 1-(trifluorosilylmethyl)-2-oxoperhydroazepine ( 1b ) have been prepared from the corresponding NH-compounds using ClCH 2 SiCl 3 /Et 3 N or ClCH 2 SiCl 3 /(Me 3 Si) 2 NH followed by methanolysis or hydrolysis of the reaction mixture in the presence of Lewis bases, and then BF 3 etherate. Potassium-(18-crown-6)-(2-oxoperhydroazepinomethyl)tetrafluorosilicate ( 2 ) was synthesized by reaction of the trifluoride ( 1b ) with KF in the presence of 18-crown-6. Using 19 F, 29 Si NMR and X-ray diffraction techniques it was established that the silicon atom is pentacoordinate in the trifluorides ( 1a , b ) and hexacoordinate in the adduct 2 . Thus the internal coordination of the O → Si bond present in the trifluoride ( 1b ) is retained in the adduct 2 . The stereochemical non-rigidity of the trifluorides ( 1a , b ) and the N -(trifluorosilylmethyl)- N -methylacetamide ( 1c ) was investigated using dynamic 19 F NMR spectroscopy. The activation barriers for permutational isomerization are in the range 9.5–10 kcal mol −1 . Lower values of Δ G # for permutation of trifluorides ( 1a – c ) compared to the monofluorides with the coordination core OSiC 3 F together with small negative values for the activation entropy implies a non-dissociative mechanism. Quantum-chemical analysis suggests a mechanism involving a turnstile rotation.

The reaction of (ClCH2)2SiCl2 (4) with O-Me3Si-hydrazides (3) yields three new types of products: a 1:2 reagent ratio leads to a neutral hexacoordinate dichelate with two six-membered rings each containing an N+−N- ylide structure, as well as to the corresponding dissociated pentacoordinate dichelate siliconium chloride salt. These products readily undergo partial hydrolysis to form a dinuclear complex: dicationic disiloxane dichloride. All three product types have been characterized by means of single-crystal structure analysis. Nonempirical ab initio calculations were carried out to determine the atomic charges. Natural bond order (NBO) calculations show that there are no significant charge accumulations on either the ammonium or the imidate nitrogen in the ylide moieties and that the net charge on silicon (which could formally be −2) is between +1.8 and +2.1 e in all species, regardless of overall molecular charge.

Eleven new silicon-substituted N-(dimethylsilylmethyl)- and N-(methylphenylsilylmethyl)amides and -lactams bearing a chiral carbon in the amide or lactam fragment, and containing the OSiC3X (X = Hal, OTf) coordination fragment have been synthesized and their structures determined in solution by spectroscopic means. These structures are consistent with the hypervalency model. Quantum chemical calculations adequately reflect correlations between the type of monodentate ligand X and the geometric parameters of the N–Ci?½O–Sii?½X fragments. The activation parameters for enantiomerization and diastereomerization in these new compounds and the other related compounds were determined by the dynamic NMR (DNMR) method using full line-shape analysis. The free activation energy values in the absence of external nucleophiles vary from 9 to 27 kcal mol?1. The entropies of activation (?S#) are negative (?20 to ?50 cal mol?1 K?1) in all cases except for the chloride derivatives of 4-phenyl-2-pyrrolidone and 4-oxazolidinone that have weaker intramolecular O ? Si coordination. Irregular mechanisms of permutational isomerization were proposed on the basis of the DNMR data and the results of quantum-chemical calculations carried out by ab initio (HF) and DFT (PBE, B3PW91, 6-311++G(d,p)). Depending on the coordination environment at silicon, the mechanisms proposed involve either the dissociation of the Si–X bond followed by the Berry pseudorotation or similar in the intermediate or the cleavage of intramolecular O–Si bond with subsequent inversion at the silicon atom. The apparently simple pseudorotation mechanism involving only the pentacoordinate structures 1–21 does not appear to be favoured in any of the examples studied.

(C,O)-chelate silanol hydrohalides RC(O)NHCH2SiMe2OH · HHal (2a,b and 5b), and their precursors, (C,O)-chelate chlorosilanes RC(O)NHCH2SiMe2Cl (6a,b) and disiloxanes [RC(O)NHCH2SiMe2]2O (8a,b) (R = Me (a), Ph (b); Hal = Cl (2), Br (5)), were obtained by several routes. The original scheme of hydrolysis of the above chlorides was discussed in detail. X-ray analysis has shown that the silanol hydrohalogenides PhC(O)NHCH2SiMe2OH · HX (2b and 5b) in the crystal exist in the form of cation–anion pairs [PhC(O)NHCH2SiMe2(OH2)]+ · X− (14b · Cl− and 14b · Br−) assembled by H-bonds in a 3D framework. The Si atom in the cation has a trigonal bipyramidal configuration with the oxygen atom of the carbonyl group and protonated hydroxyl exo-substituent in axial positions. The endocyclic Si–O bonds are equal with an average of 1.905 A while the exocyclic Si–O bonds are 1.979 and 2.009 A, for Hal = Cl and Br, respectively. Quantum chemical calculations have shown that the cation [PhC(O)NHCH2SiMe2(OH2)]+ (14b) is stable only in the crystal. Based on a high-resolution X-ray study and a quantum chemical calculation, it was found that the chemical bonding pattern in the OSiO axial fragment of the cation 14b corresponds to a three-centred four electron interaction. The cation 14b should be considered as a silylium cation stabilized by coordinated H2O molecules rather than a silyloxonium ion.

A general scheme of reactions between chloro(chloromethyl)dimethylstannane and N-trimethylsilylamides and -lactams was established by NMR and IR techniques. The reactions proceed via transmetallation followed by transformation of the N-stannylated intermediate (1) into (N–Sn)-coordinated O-stannylmethyl (2) and (O–Sn)-coordinated N-stannylmethyl (3) derivatives. In the cases of 2-piperidone and 2-hexahydroazepinone these products were isolated as individual compounds (2b,c and 3b,c). X-ray diffraction study of 1-(chlorodimethylstannylmethyl)-2-piperidone (3b) confirmed (3 + 2)-coordination state of the tin atom and axial positions of oxygen and halogen atoms. The experimental and quantum-chemically calculated structural parameters are discussed in comparison with those of related trigonal bipyramidal (TBP) silicon, germanium and tin derivatives. Calculation at the MP2/LanL2DZ/D95 level reveals that the stability of the (O–M)chelates increases in the following order: (O–Si)

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. (C) 2003 Published by Elsevier Science B.V.

Solution 1 J SiF and 2 J CF NMR coupling constant and 19 F-NMR chemical shift data have been analysed in a series of pentacoordinate silyl monofluoride complexes used to model nucleophilic substitution at silicon. Patterns in the data reveal strong correlations between both coupling constants and 19 F-NMR chemical shifts and the degree of substitution displayed by each. Excellent correlation is obtained between the new data and our previous 13 C- and 29 Si-NMR studies to further confirm the validity of the NMR technique for structural correlation in solution. By pooling the X-ray crystal structures of a large number of compounds of this class from both our own results and the literature we are able to provide a possible explanation for some of the trends in the NMR data we observe in solution.

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.

In the title compound, [Ge(C(8)H(14)NO)(2)Cl]CF(3)SO(3), which is the first complex containing an eight-membered lactam (enantholactam) as ligand, the coordination polyhedron of the Ge(IV) atom is intermediate between trigonal-bipyramidal and square-pyramidal. Quantum chemical calculations of the crystal structure indicate the absence of additional coordination bonding between the Ge(IV) atom and the trifluoromethanesulfonate anion.

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.

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.

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.

The coordinate structure of N -methyl- and N -phenyl- N -(dimethylchlorosilylmethyl) acetamide in solutions is investigated by multinuclear 1 H, 13 C, 17 O, and 29 Si NMR spectroscopy. At low temperatures (up to −90°C), two pentacoordinated silicon species are detected for the first time as an example of compounds including the coordinative OSiC 3 Cl unit. At higher temperatures their fast (on the NMR time scale) interconversions are observed. On the basis of concentration, solvent and temperature dependence we assume that one species contains the intramolecular coordination O → Si bond, while the other includes the intermolecular coordination O → Si bond.

Synthesis and X-ray diffraction study of cationic bischelates MeSi(SCH(2)CONMe(2))(2)(+)Cl(-) and MeGe(SCH(2)CONMe(2))(2)(+)Br(-) are reported. According to X-ray data, the Si and Ge atoms in these compounds have distorted TBP environments with two coordinating oxygen atoms in axial positions.

1 Introduction and Outline 2 Self-Associates 3 Pentacoordinate Anionic Compounds 4 Pentacoordinate Intermolecular Neutral Compounds 5 Pentacoordinate Intramolecular Neutral Germanium Compounds 6 Pentacoordinate Intramolecular Neutral Tin and Lead Compounds 7 Pentacoordinate Cationic Compounds 8 Hexacoordinate Anionic Compounds 9 Hexacoordinate Neutral Compounds 10 Hexacoordinate Cationic Tin Compounds 11 Acknowledgments Keywords: pentacoordinate anionic compounds; hypervalent germanium reactivity; stoichiometry of complexes and nature of organometallic halides; pentacoordinate intermolecular neutral compounds; pentacoordinate intramolecular germanium complexes; hypervalent compounds of organic germanium, tin and lead; AMPAC and HyperChem software; Quantum-chemical calculations of trichloroorganogermanes

1 Introduction and Outline 2 Self-Associates 3 Pentacoordinate Anionic Compounds 4 Pentacoordinate Intermolecular Neutral Compounds 5 Pentacoordinate Intramolecular Neutral Germanium Compounds 6 Pentacoordinate Intramolecular Neutral Tin and Lead Compounds 7 Pentacoordinate Cationic Compounds 8 Hexacoordinate Anionic Compounds 9 Hexacoordinate Neutral Compounds 10 Hexacoordinate Cationic Tin Compounds 11 Acknowledgments Keywords: pentacoordinate anionic compounds; hypervalent germanium reactivity; stoichiometry of complexes and nature of organometallic halides; pentacoordinate intermolecular neutral compounds; pentacoordinate intramolecular germanium complexes; hypervalent compounds of organic germanium, tin and lead; AMPAC and HyperChem software; Quantum-chemical calculations of trichloroorganogermanes

Reactions of 1-(trimethoxysilylmethyl)-2-piperidone with glycolic and (R,R)-tartaric acids in the presence of dicyclohexylamine afford cation–anionic complexes with different coordination states of the Si atoms.