Asymmetric induction in forming poly(olefin sulphone)s

Poly(1-olefin sulphone)s have been prepared from olefins with a chiral centre at the carbon atom adjacent to the double bond. In ¹³C and ¹H NMR studies on the polymers obtained by free radical copolymerisation it has been found that the chirality of a main chain methine carbon that forms part of the backbone depends upon the chirality of the carbon initially present within the same hydrocarbon residue. The introduction of bulky groups into the chiral group of the monomeric olefin increased the ratio of diastereoisomers formed within the residue. In the most favoured case 69% of the backbone chiral centres were fixed with reference to the side chain structures. By employing a simple theory based upon an enumeration of steric interactions and upon the γ-gauche effect on carbon chemical shifts, it was deduced that the main chain chiral centre preferred to adopt the opposite stereochemistry to that of the side chain when that carries an ethyl group, a methyl group and a hydrogen atom. A bias was also found at the backbone when the monomer chiral centre contained polar acid or ester groups.     

Chiral Bis(N‐sulfonylamino)phosphine‐ and TADDOL‐Phosphite‐Oxazoline Ligands: Synthesis and Application in Asymmetric Catalysis

A series of N,P‐ligands has been prepared, containing a chiral oxazoline ring and as a second chiral unit a bis(N‐sulfonylamino)phosphine group embedded in a diazaphospholidine ring or a cyclic phosphite group derived from TADDOL. These modular ligands are readily synthesized from chiral amino alcohols and chiral 1,2‐diamines or TADDOLs. Palladium and iridium complexes derived from these ligands were found to be efficient catalysts for enantioselective allylic alkylation and olefin hydrogenation, respectively.     

Asymmetric anionic polymerization of n-diphenyl-methylitaconimide with chiral ligand-organometal complex

Summary Asymmetric anionic polymerizations of achiral N-diphenylmethylitaconimide (DPII) were performed with chiral ligand — organometal complexes in toluene. The obtained poly(DPII)s exhibited molecular weights of 1.5 × 10³ to 6.3 × 10³ and specific rotation between +7.5 to −18.4° (THF). The chirality of polymer was significantly affected by the organometals and chiral ligands. The poly(DPII) obtained with (4S)-2,2′-(1-ethylpropylidene)bis(4-benzyl-4,5-dihydrooxazole) (Bnbox) / n-butyllithium (n-BuLi) exhibited the highest specific rotation (−18.4°). The optical activities of the poly(DPII)s were attributed to configurational chirality of the main chain more than conformational chirality, judged from NMR, circular dichroism (CD) and GPC analyses using UV and polarimetric detectors. Received: 10 January 2002/ Revised: 12 April 2002/ Accepted: 22 April 2002     

Synthesis and chiroptical properties of liquid crystalline copolymers containing azobenzene chromophores

A series of new liquid crystalline copolymers, poly[((S)‐2‐methyl‐1‐butyl methacrylate)‐co‐(6‐(4‐(4‐cyanophenylazo)phenoxy)hexyl methacrylate)], with different contents of chiral units of 17, 36, 54 and 78 mol% were synthesized. The structures and properties of the copolymers were characterized and evaluated using infrared, ¹H NMR and UV spectroscopy, differential scanning calorimetry, gel permeation chromatography and circular dichroism (CD). The CD results suggested that absorptions of azobenzene chromophores were observed in films of copolymer containing 17, 36 or 54 mol% chiral units, but not in the film of copolymer containing 78 mol% chiral units. Also, CD values of the copolymeric films decreased with increasing chiral content. After irradiation with linear polarized light at 442 nm, CD values were changed in all the copolymeric films, and the CD values increased with decreasing chiral content in a nonlinear way, while the photoinduced change of chirality of the copolymers increased in a linear way with decreasing chiral content. The results are discussed in terms of interactions between structures and chiroptical properties. Copyright © 2007 Society of Chemical Industry     

Four chiral Ag(I) complexes with dual chiral components: Effect of positional isomerism,luminescence and SHG response

Four chiral Ag(I) complexes with dual chiral components have been synthesized by using a series of (1R,2R)-N¹,N²-bis(pyridinylmethyl)cyclohexane-1,2-diamine ligands with different N-positions of pyridyl rings. The circular dichroism (CD) spectra and second-harmonic generation (SHG) efficiency measurements confirmed that they are of structural chirality in the bulk samples. The luminescence properties indicated that they may have potential applications as optical materials. The formation of discrete mononuclear and binuclear complexes and one-dimensional chains may be attributed to positional isomerism of the ligands.     

Self‐induced short chain branching in homopolymers and 1‐hexene copolymers of ethylene produced with amido functionalized ansa half‐sandwich complexes as catalysts

Amido ansa 3‐substituted indenyl complex precursors can be activated with methylaluminoxane and used for prepolymerization with ethylene to give a heterogeneous catalyst for olefin polymerization. Homo polymerization of ethylene with 1‐(3‐pent‐4‐enylindenylidene) dimethylsilyl'butylamidotitaniumdichloride (1), 1‐(3‐hex‐5‐enylindenylidene)dimethylsilyl'butylamidotitanium‐dichloride (2), and 1‐(3‐pent‐4‐enylindenylidene) (oct‐7‐enyl)methylsilyl'butylamidotitaniumdichloride (3) produces polyethylenes that contain ethyl branches. The ethyl branching in the polymers made with complexes 1 and 2 is barely above the ¹³C NMR detection limit, but the level observed in the polymer made with complex 3 is 17 times greater. Copolymerization of ethylene and 1‐hexene using prepolymerized 3 yields copolymers containing both ethyl and butyl branches. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 734–739, 2006     

Application of Δ- and Λ-Isomerism of Octahedral Metal Complexes for Inducing Chiral Nematic Phases

The Δ- and Λ-isomerism of octahedral metal complexes is employed as a source of chirality for inducing chiral nematic phases. By applying a wide range of chiral metal complexes as a dopant, it has been found that tris(β-diketonato)metal(III) complexes exhibit an extremely high value of helical twisting power. The mechanism of induction of the chiral nematic phase is postulated on the basis of a surface chirality model. The strategy for designing an efficient dopant is described, together with the results using a number of examples of Co(III), Cr(III) and Ru(III) complexes with C₂ symmetry. The development of photo-responsive dopants to achieve the photo-induced structural change of liquid crystal by use of photo-isomerization of chiral metal complexes is also described.     

Control of Polymer Composition in Pd‐Catalyzed CO/Olefin Terpolymerization Reactions

The CO/tert‐butylstyrene/ethylene terpolymerization catalyzed by Pd‐(N‐N′) complexes was studied. The results evidence that the olefin preferentially inserted in the terpolymer chain is strictly related to the nature of the nitrogen ligand, mainly to its steric constraints, and not to the kind of ligand. Indeed, slight variations in the backbone of the nitrogen ligands coordinated to palladium allow for the synthesis of terpolymers with a controlled composition.     

Copolymerization of ethylene/α‐olefins over (2‐MeInd)2ZrCl2/MAO and (2‐BzInd)2ZrCl2/MAO systems

Ethylene homopolymerization and ethylene/α‐olefin copolymerization were carried out using unbridged and 2‐alkyl substituted bis(indenyl)zirconium dichloride complexes such as (2‐MeInd)₂ZrCl₂ and (2‐BzInd)₂ZrCl₂. Various concentrations of 1‐hexene, 1‐dodecene, and 1‐octadecene were used in order to find the effect of chain length of α‐olefins on the copolymerization behavior. In ethylene homopolymerization, catalytic activity increased at higher polymerization temperature, and (2‐MeInd)₂ZrCl₂ showed higher activity than (2‐BzInd)₂ZrCl₂. The increase of catalytic activity with addition of comonomer (the synergistic effect) was not observed except in the case of ethylene/1‐hexene copolymerization at 40°C. The monomer reactivity ratios of ethylene increased with the decrease of polymerization temperature, while those of α‐olefin showed the reverse trend. The two catalysts showed similar copolymerization reactivity ratios. (2‐MeInd)₂ZrCl₂ produced the copolymer with higher M_w than (2‐BzInd)₂ZrCl₂. The melting temperature and the crystallinity decreased drastically with the increase of the α‐olefin content but T_m as a function of weight fraction of the α‐olefins showed similar decreasing behavior. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 928–937, 2000     

Synthesis of Optically Active Dendrimers Having Chiral Bisphosphine as a Core

Summary First and second generation chiral dendrimers P-1G1, P-2G1, P-1G2 and P-2G2 containing chiral bisphosphine as a core were synthesized via a reaction of chiral bisphosphine compound (S,S)-1 with benzyl ether dendrons. This is the first example of chiral dendrimers containing chiral phosphorus atoms. To investigate the effect of chiral phosphorus atoms on their conformations, optically inactive dendrimer P′-2G1 was synthesized as well using optically inactive initiator 1′ which was the mixture of rac-1 ((S,S)-1 and (R,R)-1) and meso-1. Their structures were characterized by ¹H, ¹³C, ³¹P NMR, and HRMS. According to CD measurement, optically active dendrimers exhibited the Cotton effect induced by the chirality of phosphorus atoms, while optically inactive dendrimer P′-2G1 showed no Cotton effect.     

Preparation of a topologically linked branch polymer containing cyclodextrin

Macromolecules containing topological linkages made of α‐cyclodextrin (αCD) and poly(ethylene glycol) (PEG) were prepared by condensation of mono‐6‐O‐deoxy‐mono‐6‐amino‐α‐cyclodextrin (NH₂‐αCD) with PEG dicarboxylic acid (PEG‐diCOOH) having one carboxyl group at both chain ends. The analysis of ¹H NMR and ¹³C NMR spectra of the condensation products showed completion of the condensation reaction between NH₂ and COOH groups, and the absence of ester linkages, thus indicating that all of the PEG chains carried one αCD molecule at both chain ends through amide linkages. Gel permeation chromatography analysis of these condensation products showed that NH₂‐αCD formed inclusion complexes with PEG‐diCOOH prior to condensation, resulting in macromolecules having topological linkages. In addition, the amount of the topological linkages increased with the increase of molecular weight of PEG‐diCOOH. This result shows that the complexation equilibrium of NH₂‐αCD with PEG‐diCOOH depends on the concentration of ethylene glycol units. Copyright © 2007 Society of Chemical Industry     

Catalytic Asymmetric Epoxidation of Unfunctionalized Olefins by Supported Cu(II)-Amino Acid Complexes

Polymer-supported Cu(II) complexes with L-phenyl alanine and L-valine were used as chiral catalysts for asymmetric epoxidation of nonfunctionalized straight-chain terminal olefins viz. 1-octene, 1-hexene, 2-methyl-1-pentene and 4-methyl-1-pentene using m-chloroperbenzoic acid (m-CPBA) as oxidant giving high conversions and selectivity. Enantiomeric yields, though moderate, are comparable with the best-reported ees using homogeneous catalysts. All catalysts displayed good recycling efficiency. Variations in percent ee have been discussed on the basis of the structural geometry of the supported catalysts and the trajectory of the olefin approach to the active oxo-intermediate.     

Chirality delivery through multiple and helical H-bonding from chiral coordination complex to its supramolecular architecture

The path of the chirality delivery in the crystalline and chiral nucleotide–Co(II) complex, [Co(GMP)(H₂O)₅]·3H₂O (GMP = guanosine-5′-monophosphate), has been studied based on X-ray single crystal diffraction analysis, liquid- and solid-state circular dichroism (CD) spectroscopy. The multiple and helical H-bonding is a distinctive way of chirality delivery from the discrete molecules to three-dimensional supramolecular architecture.     

Kinetics and mechanism of olefin methylation reactions on zeolites

Ethylene and propylene methylation rates increased linearly with olefin pressure but did not depend on dimethyl ether (DME) pressures on proton-form FER, MFI, MOR, and BEA zeolites at low conversions (<0.2%) and high DME/olefin ratios (30:1) in accordance with a mechanism that involves the zeolite surface being predominantly covered by DME-derived species reacting with olefins. Higher first-order reaction rate constants for both ethylene and propylene methylation were observed over H-BEA and H-MFI compared with H-FER and H-MOR, indicating that olefin methylation reaction cycles involved in the conversion of methanol-to-gasoline over zeolitic acids are propagated to varying extents by different framework materials. Systematically lower activation barriers and higher rate constants were observed for propylene methylation in comparison with ethylene methylation over all frameworks studied, reflecting the increased stability of reaction intermediates and activated complexes with increasing olefin substitution. A binomial distribution of d₀/d₃/d₆ in unreacted DME upon introduction of equimolar protium- and deuterium-form DME under steady-state reaction conditions of ethylene methylation over H-MFI suggests the presence and facile formation of reactive surface-bound methoxide species and the absence of C–H bond cleavage.     

Resolution of Racemic Propranolol in Liquid Membranes Containing TA‐β‐cyclodextrin

Abstract

The pharmacological properties of propranolol enantiomers are quite different, the β‐adrenergic blocking activity resides in the (S)‐(?) isomer, while the (R)‐(+)‐enantiomer has only a membrane stabilizing effect. The inherent chirality of cyclodextrins (CDs) allows them to form diastereomeric complexes. In this work, a peracetylated β‐CD (TA‐β‐CD) that preferentially interacts with the (S)‐(?) isomer of propranolol was used. Two liquid membranes, bulk liquid membrane (BLM) and supported liquid membrane (SLM) were tested. A recovery of 30% and a enantiomeric excess of 12% were obtained, using a SLM with 10 mM of propranolol and a pH gradient between feed and stripping phases.     

An effective method to identify the type and content of α‐olefin in polyolefine copolymer by Fourier Transform Infrared–Differential Scanning Calorimetry

A new method for identification of ethylene/α‐olefin copolymer was established by Fourier Transform Infared (FTIR)–Differential Scanning Calorimetery (DSC) in this article. DSC and FTIR spectroscopy techniques were used to analysis the type and content of α‐olefin in polyolefine copolymer. FTIR was available to identify the structures of polyethylene and copolymers of ethylene with different α‐olefins. The type of polyethylene can be determined by the peak position of 1378 and 1369 cm^?1. According to the peak location of 770, 784, and 895 cm^?1, the type of α‐olefin can also be determined. DSC method was used to decide the position of melting peaks. The quantitative investigation of the content of α‐olefin in polyethylene was calculated by the formula: ?ln(CH₂ mol fraction) = ?0.331+135.5/T_m. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Binaphthol-strapped chiral bis(porphyrinato) cerium double-decker complexes

(R)-(+)- or (S)-(−)-1,1′-bi-2-naphthol (BINOL) was applied as a remote chiral auxiliary to connect the two facing porphyrin rings, resulting in the BINOL-strapped chiral bis(porphyrinato) cerium double-decker complexes (R)-/(S)-1 and (R)-/(S)-2, which were carefully characterized by a range of spectroscopic and electrochemical methods. Perfect mirror images were observed in their circular dichroism (CD) spectra with a negative sign in the Soret band for (R)-enantiomers and a positive sign for (S)-enantiomers, which suggests the C₂-chirality of a BINOL strap is transcribed to the double-decker core as a defined chiral twist in the inter-porphyrin arrangement. Furthermore, the CD intensities of (R)-/(S)-1 are always larger than those of (R)-/(S)-2, indicating that the intramolecular chirality transfer efficiency can be finely tuned by changing the length of interlocking moieties.     

Functionalized assembly of solid membranes for chiral separation using polyelectrolytes and chiral ionic liquid

The successful assembly of a new solid membrane for chiral separation, assembled via the formation of complexes of a polyelectrolyte and β‐cyclodextrins chiral ionic liquid (β‐CD‐IL) is presented. Before the assembly, the β‐CD‐IL, used as a chiral selector, was synthesized and characterized by ¹H NMR. To tune the chiral separation capability of the solid membrane, β‐CD‐IL was subsequently immobilized on to porous supporting membranes through layer‐by‐layer assembly of the β‐CD‐IL and polyelectrolytes. The resulting membrane was used in the chiral separation of D, L‐tryptophan racemate enantiomer. The membrane structure and surface morphologies were systematically analyzed by FT‐IR, UV–vis, SEM and AFM. The effects of layer number on the chiral separation were investigated. It was found that the more β‐CD‐IL was immobilized on the membranes; the higher average separation factor could be obtained. The stability of the multilayer membrane was improved by coating with crosslinked polymer layer. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4772–4779, 2013     

Detection of chirality of poly(glycerol methacrylate)s after derivatization by 1H NMR spectroscopy

Chiral poly(glycerol methacrylate)s (PGMAs) are synthesized via ATRP using enantiopure solketal methacrylates followed by acidic hydrolysis. The optical activity of the polymers is confirmed by measurements of the circular dichroism. Furthermore, the chirality of the PGMAs containing repeat units with diol groups is determined via ¹H NMR spectroscopy employing a three-component chiral derivatizing process, involving the treatment of enantiopure polymers with 2-formylphenylboronic acid and enantiopure α-methylbenzylamine (MBA), which yields cyclic boronate diastereoisomers on the pendant groups. The detection of the chirality of the PGMAs is based on the anisotropic shielding/deshielding effect of the phenyl group in (R)- or (S)-MBA. The main advantage of this method is its simplicity as it only involves the mixing of all the components without any further purification steps. This procedure has been applied here for the first time to chiral polymers.     

Pirouetting in chiral [2]catenanes

One of the best known classes of mechanically interlocked molecules is the category of [ 2 ]catenanes, which exhibit donor-acceptor interactions between the 1,5-dioxynaphthalene (DNP) units in a crown ether and the bipyridinium units in the tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺). In order to gain an in-depth understanding and appreciation of the stereochemistry and dynamic behavior of these [ 2 ]catenanes, chiral analogues—having both the DNP ring, which is capable of displaying planar chirality, and the axially chiral binaphthol (BINAP) moiety (as both enantiomers and as the racemic modification), in a crown ether, in addition to the CBPQT⁴⁺ cyclophane—have been synthesized using a template-directed protocol. Dynamic ¹H NMR spectroscopy shows that (i) the presence of immutable axial chirality, arising from the BINAP moiety in the crown ether component, leads to no induction of diastereoselectivity—the chiral catenanes exist as a mixture of diastereoisomers in solution at low temperatures in the approximate ratio of 1:1, (ii) the barrier (ΔG_cD̊) to the interconversion between these two diastereoisomers is 7.9 ± 0.1 kcal mol⁻¹ at 171 K, and (iii) no induction of diastereoselectivity is observed upon the addition of a chiral solvating agent to the chrial catenanes. The pattern of behavior in the variable temperature ¹H NMR spectra and the low ΔTG_cD̊ value indicates that the dynamic process involving the interconversion between these two diastereoisomers is one of a pirouetting nature. Of the four possible diastereoisomers, only two, (R)-(pR/pS) or (S)-(pR/pS), are shown to exist in solution.