On the formation of permethylcyclopolysilanes in the würtz-type reaction of Me2SiCl2: The influence of solvent and complexing agent

Permethylcyclopolysilanes are most often prepared by Würtz-type coupling of Me₂SiCl₂ with Na K alloy in THI: When nonpolar solvents like benzene were used, only linear polysilanes (Me₂Si)_n were produced, but the addition of a catalytic amount of crown ether 18-crown-6 was found to increase significantly the amount of cyclic oligomers. The ratio of (Me₂Si)₆ to (Me₂Si)₅ decreased from 18:1 to 6:1 in the presence of crown ether in a typical synthesis in THF. An explanation based on solvated electron theory has been proposed.     

The influence of cation complexation in NaClO3 and KClO3 by crown ethers on the electronic structure of salts studied by 35Cl-N.Q.R. method

Me^⊕ (Me = Na; K) cations in MeClO₃ chlorates were complexed by crown ethers (CE): 12C4, 15C5 and 18C6 in solution. In the solid phase we could obtain only Na(15C5)ClO₃ and K(18C6)ClO₃ complexes significant shift in ³⁵Cl-n.q.r. frequency with respect to the frequency of pure sodium and potassium chlorates was observed. The shifts at 77K were –2.879 MHz for Na(15C5)ClO₃ and –1.004 for K (18C6)ClO₃. For other reaction mixtures the ³⁵Cl-n.q.r. frequencies observed were the same as for the appropriate pure chlorates which confirmed that the expected complexation in the solid phase had not occurred. The investigation described in this paper proved a rapid increase in selectivity of crown ethers at the transition from the solution to the solid state. Moreover, in the solid phase of Me(CE)ClO₃ complexes a significant increase was found in the shielding effect of the Me^⊕ cation by the surrounding crown ether.     

SYNERGIC EXTRACTION OF COBALT(II) BY STRUCTURALLY RELATED CROWN ETHERS AND THENOYLTRIFLUOROACETONE

ABSTRACT

Cobalt (II) was extracted from perchlorate aqueous media by thenoyltrifluoroacetone (HTTA)alone and mixed with 12-Crown-4 (12C4) 15-Crown-5 (15C5) 18-Crown-6 (18C6)dibenzo-18-Crown-6 (Dbl8C6)dicyclohexyl-18-Crown-6 (Dchl8C6) or dicyclohexyl-24-Crown-8 (Dch24C8), in chloroform. The extraction constant of the chelate (K20) the extraction constant of the mixed species (K21), the synergic factor (S.F.) and the formation constant of the extracted adducts (β₂₁) were evaluated. The adduct stoichiometry was found to have the general formula Co(TTA)₂CE, irrespective of the crown ether (CE) used. It was found that no specific cavity size is required for the adduct formation. The synergic values K₂₁, S.F., and β₂₁as related to the crown ether took the order Dch24C8 > 18C6 > Dchl8C6 > 15C5 > Dbl8C6 > 12C4, which could be explained in terms of the crown ether basicity rather than the correspondence between the cavity size of the crown ether and the cobalt(II) crystal radii. The sequence 18C6 > Dchl8C6 > Dbl8C6 was interpreted in terms of the withdrawing ability of Dch and Db as substitutes in reducing the basic character of the adjacent crown ether oxygen donors.     

Functionalization of polymethylhydrosiloxane gels with an allyl ureido benzocrown ether derivative: Complexation properties

Crosslinked polymethylhydrosiloxane (PMHS) thin films prepared by sol–gel polycondensation have been functionalized by Pt‐catalyzed hydrosilylation of SiH groups with an allyl ureido crown ether precursor. To this purpose, both 4′‐allylurea‐benzo‐15‐crown‐5 ( 1 ) and 1‐allyl‐3‐propyl‐urea ( 2 ) were synthesized and characterized. We have shown that competitive side‐reactions occurred following hydrosilylation due to the hydrolysis of part of the SiH groups resulting in the formation of new crosslinks Si(CH₃)O_3/2 as shown by solid‐state ²⁹Si‐NMR. This is explained by the deactivation of the Pt catalyst toward hydrosilylation by amide groups. For thin films (～ 1 μm) prepared on silicon wafers, a quantitative method based on FT‐IR transmission spectroscopy was used to measure the crosslinking density of the network, and the percentage of functionalization (SiC %) following hydrosilylation. The results are discussed in relation to the mesh size of the network, and the diffusion of alkenes and water molecules within lightly crosslinked PMHS gels obtained by varying the amount of triethoxysilane crosslinker (mol %) from 15 to 1%. The self‐organization properties of ureido groups by H‐bonding were studied by FT‐IR for the functionalized thin films. The complexation properties of the crown ether 1 ‐functionalized thin films were evidenced by using FT‐IR following diffusion‐reactions of NaSCN and KSCN salts in CHCl₃ : MeOH solvent mixtures within thin films. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Controlled synthesis of lanthanide–lithium inverse crown ether complexes

An ytterbium–lithium inverse crown ether complex stabilized by amine-bridged bis(phenolate) ligands (LYbBr)₂(μ₄-O)(μ₃-Li) (1) [L = Me₂NCH₂CH₂N{CH₂-(2-O- C₆H₂-Bu^t₂-3,5)}₂] was isolated as a byproduct from the reaction of LYbCl(THF) with CH₃Li in THF in a very low isolated yield. Further study revealed that the inverse crown ether complexes can be synthesized in a controlled manner by the reaction of bis(phenolate) lanthanide chloride with an in situ mixture of n-BuLi with water in THF. A second inverse crown ether complex (L′YbCl)₂(μ₄-O)(μ₃-Li) (2) [L′ = Me₂NCH₂CH₂N{CH₂-(2-O-C₆H₂-Bu^t-3-Me-5)}₂] was prepared in high isolated yield and well characterized.     

Synthesis, characterization, and oxygen permeability of homo- and copolymers from p-[tris(trimethylsilyl)silyl]-phenylacetylene

Summary Homopolymerization of p-[tris(trimethylsilyl)silyl]phenylacetylene [p(Me₃Si)₃SiPA] by Rh catalyst provided insoluble polymer. On the other hand, copolymerization of p(Me₃Si)₃SiPA with p-(trimethylsilyl)phenylacetylene (pMe₃SiPA) at 80:20, 50:50, and 20:80 feed ratios afforded high molecular weight copolymers (M _w > 1×10⁶), all of which were soluble in common solvents such as toluene and chloroform. The mole ratios of p(Me₃Si)₃SiPA to pMe₃SiPA unit in copolymers were close to those in the feeds. The oxygen permeability increased monotonously with increasing p(Me₃Si)₃SiPA content of copolymer in correspondence with fractional free volume; the value of the copolymer for the 80:20 feed ratio reached 770 barrers. Received: 30 August 2000/ Accepted: 6 September 2000     

Supramolecular assemblages from uranyl complexes of calixarenes and potassium complexes of 18-crown-6 or dibenzo-18-crown-6

Reaction of uranyl nitrate with p-tert-butyl[3.1.3.1]homocalixarene (L¹H₄) or p-tert-butylcalix[8]arene (L²H₈) has been carried out in the presence of KOH and 18-crown-6 (18C6) or dibenzo-18-crown-6 (db18C6), giving the supramolecular assemblages [K(db18C6)(H₂O)₂]₃ [{UO₂(L¹)}₂K(H₂O)₅] (1) and [K(18C6)(OH)₂][{(UO₂)₂(L²H₅)(OH)}{K(18C6)}] (2). Compound 1 comprises a sandwich, “complex-within-complex” assemblage in which two uranyl/calixarene complexes encompass a potassium/crown ether guest. A direct bond between uranyl and K(18C6) is present in 2, in which a columnar arrangement of alternate dimetallic calixarene complexes and potassium/crown ether species is formed.     

Spacer-chromoionophores — polymethine dye substituted aza-crown ethers with increased complexation ability

Aromatic aldehyde derivatives of N-phenyl-aza-15-crown-5 ( 2 ), N-phenyl-aza-18-crown-6 ( 8 ), and benzo-15-crown-5 ( 10 ) are condensed with malononitrile and 2-amino-1,1,3-tricyano-1-propene to give light yellow to orange colored crown ether derivatives 4 , 5a , 9a , 11 , and 12 . 5a and 9a were acylated with ethyl chloroformate to give the magenta colored dyes 5b and 9b , respectively. By condensation of N-(4-nitrosophenyl)-aza-15-crown-5 3 with 2-amino-1,1,3-tricyano-1-propene the magenta dye 6a is obtained. Acylation of 6a with ethyl chloroformate leads to the deep blue colored dye 6b . In these derivatives the nitrogen or oxygen atoms of the crown ethers are part of the chromophoric system, and binding properties are affected. Further chromophoric derivatives of aza-crown ethers are studied in which these are separated from the chromophoric moiety by a spacer. N-(ω-chloroalkyl)-N-alkylanilines 14a-c were attached to aza-15-crown-5 13a-c and aza-18-crown-6 13b-c to yield the spacer crown ether derivatives 15a-c and 16a-c , respectively. The formylated spacer crown ether derivatives 17a-c and 18b were condensed with 2-amino-1,1,3-tricyano-1-propene to give the orange spacer-chromoionophores 19a-c and 20 . In these crown ether derivatives the extended conjugation is interrupted by the spacer, and good binding properties are obtained. The complex formation constants of the crown ether derivatives with Na⁺ and K⁺ are determined using ¹H NMR spectroscopy.     

Study on the adsorption properties of novel crown ether crosslinked chitosan for metal ions

We first synthesized N‐benzylidene chitosan (CTB) by the reaction of benzaldehyde with chitosan (CTS). Chitosan‐dibenzo‐18‐crown‐6 crown ether bearing Schiff‐base group (CTBD) and chitosan‐dibenzo‐18‐crown‐6 crown ether (CTSD) were prepared by the reaction of 4,4′‐dibromodibenzo‐18‐crown‐6 crown ether with CTB and CTS, respectively. Their structures were confirmed by Fourier transform infrared spectral analysis and X‐ray powder diffraction analysis. These novel crown ether crosslinked CTSs have space net structures with embedded crown ethers and contain the double structures and properties of CTS and crown ethers. They have stronger complexation with and better selectivity for metal ions than corresponding crown ethers and CTS. Moreover, these novel CTS derivatives can be used to separate and preconcentrate heavy or precious metal ions in aqueous environments. From this practical viewpoint, we studied the adsorption and selectivity properties of CTB, CTBD, and CTSD for Ag⁺, Cu²⁺, Pb²⁺, and Ni²⁺. The experimental results showed that CTBD had better adsorption properties and higher selectivity for metal ions than CTSD. For aqueous systems containing Pb²⁺–Ni²⁺ and Pb²⁺–Cu²⁺, the selectivity coefficients of CTSD and CTBD were K/Ni²⁺ = 24.4 and K/Cu²⁺ = 41.4 and K/Ni²⁺ = 35.5 and K/Cu²⁺ = 55.3, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 29–34, 2002; DOI 10.1002/app.10180     

Phenylcalcium iodides with silyl substituents in para-position

The reduction of silyl substituted iodobenzenes 4-Ph₃Si–C₆H₄–I (1) and Me₂Si(–C₆H₄–4–I)₂ (2) with activated calcium yields sparingly soluble 4-Ph₃Si–C₆H₄–Ca(thf)₄I (3) and moderate soluble Me₂Si[–C₆H₄–4-Ca(thf)₄I]₂ (4). The molecular structures of 1 and 2 and a structural motif of 4 are presented.