Nearly planar nonsolvated monomeric silyl- and germyllithiums as a result of an intramolecular CH-Li agostic interaction

Pale-yellow crystals of the nonsolvated monomeric silyl- and germyllithiums, tris[di-tert-butyl(methyl)silyl]silyllithium 2a and tris[di-tert-butyl(methyl)silyl]germyllithium 2b, were obtained by one-electron reduction of the corresponding silyl and germyl radicals with lithium in hexane. The crystal structure analysis of both 2a and 2b showed almost planar geometry around the anionic centers, due to both intramolecular CH-Li agostic interactions and steric reasons. However, the free anions [(tBu2MeSi)3Si-][Li+(THF)4] 3a and [(tBu2MeSi)3Ge-][Li+(THF)n] (n = 3, 4) 3b no longer showed a planar geometry, because of the absence of the intramolecular CH-Li agostic interaction. A temperature-dependent 1H NMR study of 2a showed that the CH-Li interaction is weak.     

Mechanism of palladium-catalyzed diene cyclization/hydrosilylation: direct observation of intramolecular carbometalation

The results of kinetic, deuterium-labeling, and low-temperature NMR studies have established a mechanism for the palladium-catalyzed cyclization/hydrosilylation of dimethyl diallylmalonate (1) with triethylsilane involving rapid, irreversible conversion of the palladium silyl complex [(phen)Pd(SiEt(3))(NCAr)](+) [BAr(4)](-) [Ar = 3,5-C(6)H(3)(CF(3))(2)] (4b) and 1 to the palladium 5-hexenyl chelate complex [(phen)Pd[eta(1),eta(2)-CH(CH(2)SiEt(3))CH(2)C(CO(2)Me)(2)CH(2)CH=CH(2)]](+) [BAr(4)](-) (5), followed by intramolecular carbometalation of 5 to form the palladium cyclopentylmethyl complex trans-[(phen)Pd[CH2CHCH2C(CO2Me)2CH2CHCH2SiEt3](NCAr)]+ [BAr4]- (6), and associative silylation of 6 to release 3 and regenerate 4b.     

A versatile nanobuilding precursor for the effective architecture of well-defined organic/inorganic hybrid via click chemistry

A novel octazido substituted nanobuilding precursor,octakis[dimethy（p-azidomethylene）siloxyl]octasilsesquioxane（ODA）, was prepared by the conventional diazo-transfer reaction of octakis[dimethy（p-chloromethylene）silyl]octasilsesquioxane（ODC） with NaN₃,and its structure was characterized by FT-IR,¹H,¹³C,²⁹Si NMR and MALDI-TOF MS,respectively.The structural rearrangement of POSS core in the synthesis strategy of ODA developed in this work was effectively prohibited in comparison with traditionary azidization process.The resultant ODA was not only soluble in common solvents such as CHCl3,THF,toluene,DMF and DMSO,but also could effectively serve as a versatile nanobuilding precursor for the architecture of well-defined organic-inorganic hybrids via click chemistry.     

Synthesis, structure, and ethene polymerisation catalysis of 1- or 2-silyl substituted bis[indenyl]zirconium(IV) dichlorides

The systematic syntheses of 1- and 2-substituted silylindenes, with a wide variety of substitution patterns on the silyl moiety, and their corresponding zirconocene dichlorides are presented. The rac- and meso-diastereomers of the 1-substituted zirconocene dichlorides can in most cases be separated. Instable zirconocenes were observed for certain substitution patterns. Two of the obtained zirconocene dichlorides, bis[2-(dimethylsilyl)indenyl]zirconium dichloride (4a) and bis[2-(trimethylsilyl)indenyl]zirconium dichloride (4b), were characterised by single crystal X-ray diffraction. On the basis of DFT results, the two compounds are geometrically similar, i.e. the additional methyl group on the silyl moiety only affects the conformational energy profile. Differences in their catalyst performance in the homopolymerisation studies with ethane are thus attributed to conformational control. For the remaining complexes, sterically less demanding silyl groups seem to be favoured with respect to the catalyst performance. All the 2-isomers have lower polymerisation activities than the unsubstituted bis[indenyl]zirconium dichloride/MAO system. Curiously, the rac-bis[1-(dimethylphenylsilyl)indenyl]zirconium dichloride/MAO system is found to be the most active catalyst in ethene homopolymerisations.     

Synergic Synthesis and Characterization of tert-Butyl 4-[(E)-But-1-en-3-yn-1-yl]-3-{[tert-butyl(dimethyl)silyl]oxy}-1H-indole-1-carboxylate

Russian Journal of Organic Chemistry - tert-Butyl 4-[(E)-but-1-en-3-yn-1-yl]-3-{[tert-butyl(dimethyl)silyl]oxy}-1H-indole-1-carboxylate has been synthesized with a good yield and selectivity...     

Mechanistic study of the enantiomeric recognition of a basic compound with negatively charged single-isomer gamma-cyclodextrin derivatives using capillary electrophoresis,nuclear magnetic resonance spectroscopy,and infrared spectroscopy

The possible mechanisms for the chiral recognition of 2-(R)-N-[1-(6-aminopyridin-2-ylmethyl)piperidin-4-yl]-2-[(1R)-3,3-difluorocyclopentyl]-2-hydroxy-2-phenylacetamide (RR-M3), and its enantiomer (SS-M3) with octakis(2,3-di-O-acetyl-6-sulfo)-gamma-cyclodextrin (ODAS-gamma-CD) and octakis(6-sulfo)-gamma-cyc?pdextrom enantiomer; (OS-gamma-CD), were investigated using capillary electrophoresis (CE), proton ((1)H), fluorine ((19)F) and carbon ((13)C) nuclear magnetic resonance spectroscopy (NMR), and infrared (IR) spectroscopy. Clear evidence for the formation of diastereomeric complexes between the enantiomers and the two CDs was observed. NMR spectra suggest that the phenyl and difluorocyclopentyl rings are involved in the complexation. The phenyl ring on the guest molecule is deeply penetrated into the cavity of OS-gamma-CD, but it is not included into the cavity of ODAS-gamma-CD. The continuous variation plots built based on the (1)H NMR and IR spectra indicate a 1:1 complex stoichiometric ratio of the M3 enantiomers for both CDs. The affinity of the enantiomers for the two CDs is opposite.     

Alkylation of 2-methylimidazole with iodomethylsilanes

2-Methyl-1,3-bis[(1-methylsilolan-1-yl)methyl]-1H-imidazolium triiodide, 1,3-bis{[dimethyl-(phenyl)silyl]methyl}-2-methyl-1H-imidazolium iodide and triiodide, and cyclic 3,3,5,5,10-pentamethyl-4-oxa-7-aza-1-azonia-3,5-disilabicyclo[5.2.1]deca-1(10),8-diene iodide were synthesized by solvent-free reactions of 2-methyl-1H-imidazole with 1-(iodomethyl)-1-methylsilolane, (iodomethyl)(dimethyl)phenylsilane, and ethynyl(iodomethyl)(dimethyl)silanes, respectively, in the absence of base catalyst.     

Novel acyclic and macrocyclic highly unsaturated silahydrocarbons

Two novel silicon-containing acetylenic synthons, 1-[dimethyl(ethynyl)silyl]-2-[ethynyl(methyl)-(vinyl)silyl]ethyne and bis[(ethynyldimethylsilyl)ethynyl](methyl)vinylsilane, were obtained by the reaction of diethynyl(methyl)vinylsilane with ethylmagnesium bromide and ethynylfluorodimethylsilane. The reaction of magnesium derivatives of the products and diethynyl(methyl)vinylsilane with organylhalosilanes gave macrocyclic polyunsaturated silahydrocarbons containing numerous endo- and exocyclic miltiple bonds.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1612–1616.Original Russian Text Copyright © 2004 by O. Yarosh, Zhilitskaya, N. Yarosh, Istomina, Albanov, Chuvashev, Voronkov.This revised version was published online in April 2005 with a corrected cover date.     

Novel metal-to-metal silyl-migration reactions in heterometallic complexes

An unprecedented, intramolecular metal-to-metal silyl ligand migration reaction has been discovered in a series of phosphido-bridged iron-platinum complexes and which may be triggered by an external nucleophile. Thus, reaction of solutions of [(OC)3-(R1/3Si)Fe(mu-PR2R3)Pt(1,5-COD) (1a R1 = OMe, R2 = 3 = Ph; 1b R1 = OMe, R2 = R3 = Cy; 1c R1 = Ph, R2 = R3 = Ph; 1d R1 = Ph, R2 = R3 = Cy; 1e R1 = Ph, R1 = H, R3 = Ph) in CH2Cl2 with CO rapidly afforded the corresponding complexes [(OC)4Fe(mu-PR2R3)Pt(SiR1/3)-(CO)] (2a-e) in which the silyl ligand has migrated from Fe to Pt, while two CO ligands have been ligated, one on each metal. When 1a or 1c was slowly treated with two equivalents of tBuNC at low temperature, quantitative displacement of the COD ligand was accompagnied by silyl migration from Fe to Pt and coordination of an isonitrile ligand to Fe and to Pt to give [(OC)3-(tBuNC)Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)] (3a) and [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[SiPh3](CNtBu)] (3c). Reaction of 2a with one equivalent of tBuNC selectively led to substitution of the Pt-bound CO to give [(OC)4-Fe(mu-PCy2)Pt[Si(OMe)3](CNtBu)] (4b), which reacted with a second equivalent of tBuNC to give [(OC)4Fe(mu-PCy2)-Pt[Si(OMe)3](CNtBu)2] (5b) in which the metal-metal bond has been cleaved. Opening of the Fe-Pt bond was also observed upon reaction of 3a with tBuNC to give [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)2] (6). The silyl ligand migrates from Fe, in which it is trans to mu-PR2R3 in all the metal-metal-bonded complexes, to a position cis to the phosphido bridge on Pt. However, in 5a,b and 6 with no metal-metal bond, the Pt-bound silyl ligand is trans to the phosphido bridge. The intramolecular nature of the silyl migration, which may be formally viewed as a redox reaction, was established by a cross-over experiment consisting of the reaction of 1a and 1d with CO; this yielded exclusively 2a and 2d. The course of the silyl-migration reaction was found to depend a) on the steric properties of the -SiR1/3 ligand, and for a given mu-PR2R3 bridge (R2 = R3 = Ph), the migration rate decreases in the sequence Si(OMe)3> SiMe2Ph> SiMePh2>SiPh3; b) on the phosphido bridge and for a given silyl ligand (R1 = OMe), the migration rate decreases in the order mu-PPh2 > mu-PHCy; c) on the external nucleophile since reaction of 1c with two equivalents of P(OMe)3, P(OPh)3 or Ph2PCH2C(O)Ph led solely to displacement of the COD ligand with formation of 11a-c, respectively, whereas reaction with two equivalents of tBuNC gave the product of silyl migration 3c. Reaction of [(OC)3-[(MeO)3Si]Fe(mu-PPh2)Pt(PPh3)2] (7a) with tBuNC (even in slight excess) occurred stereoselectively with replacement of the PPh3 ligand trans to mu-PPh2, whereas reaction with CO led first to [(OC)3((MeO)3Si)Fe(mu-PPh2)Pt(CO)-(PPh3)] (8a), which then isomerized to the migration product [(OC)4Fe(mu-PPh2)Pt[Si(OMe)3](PPh3)] (9a). Most complexes were characterized by elemental analysis, IR and 1H, 31P, 13C, and 29Si NMR spectroscopy, and in five cases by X-ray diffraction.     

Hydrosilylation of methylenecyclopropane and methylenecyclobutane with dichloro(methyl)silane and synthesis of novel acetylenic silahydrocarbons from the reaction products

Hydrosilylation of methylenecyclopropane with dichloro(methyl)silane involves not only addition to the multiple bond, but also results in opening of the three-membered ring to form dichloro(cyclopropylmethyl)methylsilane and 1,4-bis(dichloromethylsilyl)butane. Dichloro(cycloalkylmethyl)methylsilanes were converted into the corresponding (cycloalkylmethyl)(diethynyl)methylsilanes by reaction with ethynylmagnesium bromide. The reaction of bis(bromomagnesioethynyl)(cyclobutylmethyl)methylsilane with dichlorodimethylsilane leads to cyclotetrasilaethyne framed with methyl and cyclobutyl groups. From 1,4-bis-[dichloro(methyl)silyl]butane and bis[(bromomagnesioethynyl)dimethylsilyl]ethyne or -ethene, 22-membered macrobicyclic highly unsaturated silahydrocarbons with an endocyclic tetramethylene bridge were synthesized.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1608–1611.Original Russian Text Copyright © 2004 by O. Yarosh, Zhilitskaya, N. Yarosh, Albanov, Voronkov.This revised version was published online in April 2005 with a corrected cover date.     

Total synthesis of 2-(β-D-ribofuranosyl)thiazole-4-carboxamide (Tiazofurin) and of precursors of ribo-C-nucleosides

(1R,2S,4R)-2-Cyano-7-oxabicyclo[2.2.1]hept-5-en-2-yl (1S′)-camphanate ( 5 ) was transformed into (?)-methyl 2,5-anhydro-3,4,6-O-tris[(tert-butyl)dimethylsilyl]-D -allonate ( 2 ), (+)-1,3-diphenyl-2-{2′,3′,5′-O-tris[(tert-butyl)dimethylsilyl]-β-D -ribofuranosyl}imidazolidine ( 3 ), and the benzamide 20 of 1-amino-2,5-anhydro-1-deoxy-3,4,6-O-tris-[((tert-butyl)dimethylsily)]-D -allitol. Compound 2 was converted efficiently into optically active tiazofurin ( 1 ).     

Functionalization of the periphery of calix[4]resorcinarenes with P(III)-containing substituents via hydroxy,trimethylsiloxy, and ethoxy-tethered trimethylsiloxy intermediates

Unlike C-undecylcalix[4]resorcinarene, C-methylcalix[4]resorcinarene 1 reacted with chlorodifluorophosphine in the absence of an auxiliary base to give the unstable octakis(difluorophosphite)-substituted derivative 2. The existence of two conformational isomers of 2 in solution was observed by ¹⁹F and ³¹P NMR spectroscopy. Attempts to react the octakis(trimethylsilyl)calix[4]resorcinarene 3 and its tetrabromo derivative 4 with phosphorus trichloride and chlorodifluorophosphine were unsuccessful. The ethoxy-tethered C-methyl-octakis(trimeth-ylsilyl)calix[4]resorcinarene 5 was allowed to react with 2-chloro-1,3,5-trimethyl-1,3,5-triaza-2σ³λ³-phosphorin-4,6-dione and chlorodifluorophosphine. By substitution of all trimethylsilyl groups, the octakis(phosphorus(III))-substituted compounds 6 and 7 were formed. As for 2, dynamic behavior in solution was observed for 6 and 7, arising from the equilibrium between different conformational isomers. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:553–558, 1998     

Highly diastereoselective 7-endo radical cyclization of ethyl α-methylene-γ-(bromomethyl)dimethylsiloxycarboxylates

The 7-endo radical cyclization of (bromomethyl)dimethylsilyl ethers derived from ethyl γ-hydroxy-α-methylenecarboxylates bearing a bulky γ-substituent such as isopropyl, cyclohexyl, and tert-butyl groups in tetrahydrofuran gave preferentially cyclic silyl ethers bearing the ethoxycarbonyl group anti to the γ-substituents in high yields. Treatment of the cyclic silyl ethers with silica gel gave acyclic ethyl γ-hydroxy-α-[2-(hydroxydimethylsilyl)ethyl]carboxylates. The reduction of the cyclization products with DIBAL followed by Tamao oxidation gave the corresponding acyclic triols.     

Cyclization/hydrosilylation of functionalized 1,6-diynes catalyzed by cationic platinum complexes containing bidentate nitrogen ligands

A 1:1 mixture of the platinum dimethyl diimine complex [PhN[double bond]C(Me)C(Me)[double bond]NPh]PtMe(2) (4a) and B(C(6)F(5))(3) catalyzed the cyclization/hydrosilylation of dimethyl dipropargylmalonate (1) and HSiEt(3) to form 1,1-dicarbomethoxy-3-methylene-4-(triethylsilylmethylene)cyclopentane (3) in 82% isolated yield with 26:1 Z:E selectivity. Platinum-catalyzed diyne cyclization/hydrosilylation tolerated a range of functional groups including esters, sulfones, acetals, silyl ethers, amides, and hindered ketones. Diynes that possessed propargylic substitution underwent facile cyclization/hydrosilylation to form silylated 1,2-dialkylidene cyclopentanes as mixtures of regioisomers. Diynes that possessed an electron-deficient internal alkyne underwent cyclization/hydrosilylation in moderate yield to form products resulting from silyl transfer to the less substituted alkyne. The silylated 1,2-dialkylidenecyclopentanes formed via diyne cyclization/hydrosilylation underwent a range of transformations including protodesilylation, Z/E isomerization, and [4 + 2] cycloaddition with dieneophiles.     

Hydrolytic polycondensation of sodiumoxymethyl(dialkoxy)silanes as a method for producing linear poly[(sodiumoxy)methylsilsesquioxane]

Polyfunctional linear poly[(sodiumoxy)methylsilsesquioxanes] are obtained via the hydrolytic polycondensation of sodiumoxymethyl(dialkoxy)silanes. Blocking of sodiumoxy groups with vinyl(dimethyl)chlorosilane is employed to obtain vinyl(dimethyl)siloxane replicas of polyfunctional matrices. The linear structure of the polymers is studied by GPC, NMR spectroscopy, and elemental analysis. The specific properties of poly[vinyl(dimethylsiloxy)methylsilsesquioxane] are investigated and are shown to be primarily related to an abnormally dense organization of polymer coils in solutions.     

Understanding the reactivity of strained sandwich compounds with aluminum or gallium in bridging positions: experiments and DFT calculations

The aluminum and gallium dichlorides (Mamx)ECl(2)1a (E = Al; 82%) and 1b (E = Ga; 79%) (Mamx = 2,4-di-tert-butyl-6-[(dimethylamino)methyl]phenyl) reacted with dilithioferrocene or dilithioruthenocene to give [1]ferrocenophanes (2a, 2b) and [1]ruthenocenophanes (3a, 3b), respectively. The galla[1]ruthenocenophane 3b could be isolated from the reaction mixture through precipitation into hexane (50%), while 2a, 2b, and 3a underwent ring-opening polymerization under the reaction conditions of their formation reactions to give metallopolymers (M(w) (DLS) between 8.07 and 106 kDa). Monomer 3b was polymerized using Karstedt's catalyst resulting in an M(w) of 28.6(±6.3) kDa. In order to get an indication of the structure of polymers, bis(ferrocenyl) compounds (Mamx)EFc(2) (E = Al (4a), 51%; E = Ga (4b), 49%) were prepared and characterized by single crystal X-ray analysis. DFT calculations shed some light on the unexpected high reactivity of these new strained sandwich species. Optimized geometries of known aluminum and gallium-bridged [1]ferrocenophanes (Al(Pytsi) (6a), Ga(Pytsi) (6b); Pytsi = [dimethyl(2-pyridyl)silyl]bis(trimethylsilyl)methyl) and [1]ruthenocenophanes (Al(Me(2)Ntsi) (7a), Ga(Me(2)Ntsi) (7b); Me(2)Ntsi = [(dimethylamino)dimethylsilyl]bis(trimethylsilyl)methyl) matched very well with experimental molecular structures. Geometries of species 2a, 2b, 3a, and 3b were optimized (BP86/TZ2P) and the structural influence of the tBu group of the Mamx ligand in ortho position was evaluated by optimizing molecular structures of the four unknown species where the ortho-tBu group was replaced by an H atom (2a(H), 2b(H), 3a(H), and 3b(H)). The most pronounced structural effect was seen as a change of the orientation of the bridging moiety with respect to the sandwich unit. As the tBu group was removed, the aromatic ligand moved toward the freed-up space. The energetics (ΔE, ΔH(298K), and ΔG(298K)) accompanied by the structural changes were evaluated by a hydrogenolysis reaction of strained species resulting in Cp(2)M (M = Fe, Ru) and respective aluminum and gallium dihydrides. This nonisodesmic reaction showed that [1]metallocenophanes equipped with the ortho-tBu group were on average 5.5 kcal/mol higher strained (ΔH(298K)) than species where the tBu group was lacking. The investigation of the isodesmic reaction between strained species and Cp(2)M yielding bis(metallocenyl) compounds revealed that the ortho-tBu group sterically interacts with one of the metallocenyl units. The bis(metallocenyl) compounds are model compounds for the respective metallopolymers and one can conclude that even though the ortho-tBu group imposes additional strain on the starting metallocenophanes, this effect cancels out in ROPs because the ortho-tBu group imposes a similar strain on the resulting polymers. The uncovered steric repulsion between the ortho-tBu group and the sandwich moieties probably causes the ortho-tBu to act as an unusually sensitive NMR probe of the tacticity of the polymers.     

Synthesis and characterization of new soluble fluorinated seco-porphyrazines

Magnesium porphyrazinate substituted with eight 3,5-bis(trifluoromethyl)phenyl groups on the peripheral positions has been synthesized by the cyclotetramerization of 3,4-[3,5-bis(trifluoromethyl)phenyl]pyrroline-2,5-diimine in the presence of magnesium butanolate. Acid-mediated demetallation of the magnesium porphyrazine resulted in peripheral oxidation of one pyrrole ring to reveal the seco-porphyrazine, octakis[3,5-bis(trifluoromethyl)phenyl]-2-seco-porphyrazine-2,3-dione. Further reaction of this product with copper (II) acetate, zinc (II) acetate and cobalt (II) acetate has led to the metallo-derivatives, {octakis[3,5-bis(trifluoromethyl)phenyl]-2-seco-2,3-dioxoporphyrazinato} M(II) [M = Cu(II), Zn(II), Co(II)]. These new soluble complexes were characterized by elemental analysis, together with FT-IR, ¹H NMR, ¹³C NMR, ¹⁹F NMR, UV-Vis and mass spectral data.     

Synthesis and NMR spectroscopy of N,N-dialkyl-N' -(dimethyl-chlorosilylmethyl) ureas with an intramolecular Si←O bond

The reaction of N,N-dialkyl-N' -trimethylsilylureas with dimethyl (chloromethyl)-chlorosilane gave N,N-dialkyl-N'-(dimethylchlorosilylmethyl)ureas with an intramolecular SiO bond. Relatively stable N,N-dialkyl-N' -[dimethyl (chloromethyl) silyl]ureas are intermediates. The structures of the compounds obtained were demonstrated by NMR spectroscopy.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2841–2843, December, 1989.     

The chemistry of O-silylated ketene acetals: an efficientstereocontrolled synthesis of N-benzoyl L-daunosamine

N-Benzoyl L-daunosamine was synthesized with high stereoselectivity utilizing a 1,3-addition of ketene silyl acetal (3a) to the chiral nitrone,(Z)-[(4R)-trans-2,2,5-trimethyl-1,3-dioxolan-4-yl]methylene[(1S)-1-phenylethyl]amine N-oxide (4c) accompanied by a silyl group-transfer in acetonitrile under mild conditions.     

1,3,5-三[(4’-乙炔基苯基)乙炔基]苯的合成

设计了多种合成路线制备芳香炔基树枝状化合物中间体1,3,5-三[(4’-乙炔基苯基)乙炔基]苯,通过一系列的合成路线和反应条件的对比,发现多官能团的端基炔化合物与芳基溴化合物之间发生多重Sonogashira反应时,常会生成不同取代程度的极性相似化合物,因而难以分离.采用多官能团的端基炔化合物与芳基碘化合物反应可以避免这种情况.最终确定以1,3,5-三溴苯和2-甲基-3-丁炔-2-醇为原料,制得中间产物1,3,5-三乙炔基苯;再以对碘苯胺和三甲基硅乙炔为原料,经重氮化化、卤代反应制得4-三甲基硅乙炔基碘苯;后者与1,3,5-三乙炔苯经Sonogashira反应、裂解去保护反应,制得化合物1,3,5-三[(4’-乙炔基苯基)乙炔基]苯.用1H NMR,13C NMR,元素分析等表征手段确认了中间体及最终产物的结构.