Mechanism of formation of macrocyclic siloxanes with a benzimidazole fragment by reaction of benzimidazole with 1,3-bis(iodomethyl)-1,1,3,3-tetramethyldisiloxane

The formation of macrocyclic polysiloxane system containing a benzimidazole fragment by reaction of benzimidazole with 1,3-bis(iodomethyl)-1,1,3,3-tetramethyldisiloxane was studied at the B3LYP/6-31G(d,p) level of theory. The calculations showed that expansion of siloxane ring involves thermodynamically controlled insertion of four silanone molecules generated by thermal decomposition of the complex derived from the initial siloxane and hydrogen triiodide.     

New halogen-containing polyimides based on 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxane dianhydride

Previously undescribed halogen-containing polyimides are synthesized via the interaction of 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxane dianhydride with aromatic diamines containing hexafluoroisopropylidene and dichloroethylene groups. The influence of tetramethyldisiloxane, hexafluoroisopropylidene, and dichloroethylene groups incorporated into these polymers on their solubility, heat resistance, thermal stability, and film-forming properties is investigated.     

Structure of 1,1,3,3-bis(trimethylene)-1,3-di-α-naphthyldisiloxane

Conclusions 1,1,3,3-Bis(trimethylene)-1,3-di--naphthyldisiloxane is a centrosymmetric dimer with a linear SiOSi group. The silacyclobutane fragment has a folded conformation with flexure angle =28.9°. The transannular Si...C distance is 2.350(3) Å. The presence of an electronegative substituent (oxygen atom) at the silicon atom leads to a contraction of the Si-C bonds in the heterocycle to 1.863(2) Å.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1030–1034, May, 1985.     

Main group complexes incorporating 1,3-bis(furyl)-1,1,3,3-tetramethyldisilazide ligands

The lithium salt of the bis-furyl substituted disilazide anion, Li{i} [{i} = N(SiMe₂R)₂ where R = 2-methylfuryl] has been examined as a ligand transfer reagent for the synthesis of group 2 (magnesium) and group 13 (aluminium) compounds. Salt metathesis between Li{i} and AlMe₂Cl afforded the expected dimethyl species, Al{i}Me₂ (1), which was isolated as a colourless oil. In contrast the corresponding aluminium dichloride, synthesized from Li{i} and AlCl₃, gave crystalline products as both the THF adduct Al{i}Cl₂(THF) (2a) and the base-free derivative, Al{i}Cl₂ (2b). The homoleptic magnesium bis(amide) Mg{i}₂ (3) was also synthesized. X-ray crystallographic analysis of 2a reveals a four-coordinate distorted tetrahedral metal, in which neither of the furyl-substituents interact with the metal. In contrast, the aluminium in the base-free dichloride 2b is five-coordinate, containing the first structurally characterized example in which the amide binds with a κ¹N,O,O′-bonding mode, involving coordination of both furyl-substituents at the N-bound metal.     

Reductive halogenation of epoxides induced by halosilanes and 1,1,3,3-tetramethyldisiloxane (TMDS)

Synthesis of alkyl halides from epoxides and halosilanes together with silicon hydrides is briefly described.     

Efficient hydrosilylation of carbonyl compounds by 1,1,3,3-tetramethyldisiloxane catalyzed by Au/TiO2

1,1,3,3-Tetramethyldisiloxane (TMDS) is a highly reactive reducing reagent in the Au/TiO₂-catalyzed hydrosilylation of carbonyl compounds relative to monohydrosilanes. The reduction of aldehydes or ketones with TMDS can be performed on many occasions at ambient conditions within short reaction times and at low loading levels of gold, whereas typical monohydrosilanes require excess heating and prolonged time for completion. The product yields are excellent, while almost stoichiometric amounts of carbonyl compounds and TMDS can be used. It is postulated that the enhanced reactivity of TMDS is attributed to the formation of a gold dihydride intermediate. This intermediate is also supported by the fact that double hydrosilylation of carbonyl compounds by TMDS is a negligible pathway.     

Synthesis and reactions of 2-chloro-1,3-bis(trimethylsilyloxy)-1,3-butadienes

The reaction of 2-chloro-1,3-bis(trimethylsilyloxy)-1,3-butadienes with various electrophiles allows a convenient synthesis of chlorinated molecules which are not readily available by other methods.     

Deactivation pathways of ethylene polymerization catalysts derived from titanium and zirconium 1,3-bis(furyl)-1,1,3,3-tetramethyldisilazide complexes

The stoichiometric reaction between the previously described lithium amide salts, LiN(SiMe2R)2 [Li{i}, R = furyl, Li{ii}, R = 2-methylfuryl] and titanium(iv)chloride at low temperature afforded the mono-amide compounds Ti{i}Cl3 (1a) and Ti{ii}Cl3 (1b). The analogous zirconium derivatives Zr{i}Cl3 (3a) and Zr{ii}Cl3 (3b) were accessed via the reaction of excess trimethylsilylchloride with the mixed tetra-amide species, Zr{i}(NMe2)3 (2a) and Zr{ii}(NMe2)3 (2b). The bis-amide complexes Ti{ii}2Cl2 (4b), Zr{i}2Cl2 (5a) and Zr{ii}2Cl2 (5b) were synthesized in a straightforward salt metathesis reaction employing two equivalents of Li{i} or Li{ii} with the metal salts, MCl4(THF)2. The reactivity of the halide compounds 1 and 3-5 with a variety of alkylating agents was studied, with ligand transfer from the transition-element to the main group metal-alkyl reagent being the predominant reaction pathway. The reaction of 4b with MeLi was, however, partially successful affording the titanium(III) complex, Ti{ii}2X (X = Cl/Me, 6b'); this compound was subsequently made as the pure chloride from the reaction of two equivalents of Li{iii} with TiCl3(THF)3. The targeted dialkyl species, Ti{ii}Me2 (7b), was successfully isolated from the reaction between the dichloride 4b and dimethylmagnesium. The molecular structures of 1a, 1b, [3a]2 [3b]2, 4b, 5b and 6b have been solved using single-crystal X-ray diffraction techniques, indicating varying nuclearity of the complexes and hapticities for the amide ligands in the solid-state. The catalytic activity of selected complexes in the polymerization of ethylene is reported.     

An efficient synthesis of 1,3-bis(1,4,7-triazacyclonon-1-yl)-2-hydroxypropane, [1,3-bis(TACN)-2-propanol]

Abstract

An efficient synthesis of 1,3-bis(1,4,7-triazacyclonon-1-yl)-2-hydroxypropane is described. In contrast to earlier procedures, an improved synthetic strategy led to the selection of suitable reagents and conditions that afforded the title compound in excellent overall yield with improved process efficiency and scalability. Moreover, the mildness and synthetic efficiency of the chosen conditions were particularly well-suited for the large-scale synthesis of the title compound, which is in increasing demand for a variety of applications, including the preparation of stationary phases for immobilized metal-ion affinity chromatography of recombinant proteins.     

New π-electron donors: Ethanediylidene-2,2′-bis(1,3-diselenole) and ethanediylidene-2-(1,3-dithiole)-2′-(1,3-diselenole)

This communication describes synthesis and electrochemical properties of new type of π-donors containing 1,3-diselenole ring, ethanediylidene-2,2′-bis(1,3-diselenole)(1a) and ethanediylidene-2-(1,3-dithiole)-2′-(1,3-diselenole)(2a). The conductivities of the charge-transfer complexes of these donors with tetracyanoquinodimethane (TCNQ) are also demonstrated.     

Synthesis of functionalized 2-alkylidenetetrahydrofurans by cyclization of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with epoxides

The Lewis acid mediated cyclization of epoxides with 1,3-bis(trimethylsilyloxy)-1,3-butadienes, electroneutral equivalents of 1,3-dicarbonyl dianions, results in the formation of 2-alkylidenetetrahydrofurans with a great variety of substitution patterns and functional groups. This includes the synthesis of 2,3'-bifuranylidenes and 7-oxabicyclo[4.3.0]nonanes. The cyclization of dienes with functionalized epoxides containing base-labile groups proceeds with good chemoselectivity. In all reactions, good regio- and E diastereoselectivities are observed. Based on the stereoselectivities observed for reactions of 1,2-disubstituted epoxides, a working hypothesis for the mechanism of the reaction is suggested.     

Synthesis of 1,3-bis(acetylacetonyloxy)- and 1,3-bis(benzoylacetonyloxy)benzene and their complexation with lanthanide ions

Claisen condensation of 1,3-bis(methoxycarbonylmethoxy)benzene with acetone and acetophenone afforded new chelating ligands consisting of two β-diketonate fragments, viz., 1,3-bis(acetylacetonyloxy)benzene and 1,3-bis(benzoylacetonyloxy)benzene, which are linked to each other through the resorcinol spacer. In the crystal, 1,3-bis(acetylacetonyloxy)benzene, unlike the starting ester, adopts a planar conformation and exists in the enol form. The acidities of these compounds and their complexation with lanthanide ions in aqueous ethanolic solutions were studied by pH-potentiometry. Depending on the concentration conditions and pH, the La³⁺, Gd³⁺, and Lu³⁺ ions form 1 : 1, 1 : 2, or 1 : 3 complexes with bis(β-diketones). The stability of the complexes increases as the atomic number of the lanthanide increases (La³⁺ < Gd³⁺ ≤ Lu³⁺). The complexation constants and selectivity of complexation substantially increase with increasing degree of deprotonation of the ligands, which indicates that both chelate groups of the ligands are simultaneously involved in coordination. The Ph substituents in bis(β-diketone) have a considerable effect on the composition and stability of complexes with lanthanide ions due to additional noncovalent inner-sphere interactions.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 614–622, March, 2005.     

Synthesis of benzyl halides from aldehydes promoted by halosilanes and 1,1,3,3-tetramethyldisiloxane (TMDS).

Direct synthesis of monoalkyl halides from aldehydes by a new reductive halogenation method is briefly described.     

Synthesis of 1-azaxanthones by condensation of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with 3-(cyano)benzopyrylium triflates and subsequent domino ‘retro-Michael/nitrile-addition/heterocyclization’ reaction

Functionalized 1-azaxanthones (5-oxo-5H-[1]-benzopyrano[2,3-b]pyridines) were prepared by TMSOTf-mediated condensation of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with 3-cyanochromones and subsequent base-mediated domino ‘retro-Michael/nitrile-addition/heterocyclization’ reaction.