Zirconium phosphonate immobilized chiral amino alcohol for heterogeneous enantioselective addition of diethylzinc to benzaldehyde

The chiral (1R,2S)-(−)-2-amino-1,2-diphenylethanol and (1S,2R)-(+)-2-amino-1,2-diphenylethanol had been immobilized on the layered frame of zirconium phosphate to obtain zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b. The enantioselective addition of Et₂Zn to benzaldehyde using zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b as heterogeneous catalysts yielded secondary alcohol in 80.1% yield and e.e. values of up to 54.3%, which was only 7.6% e.e. lower than that using the corresponding ligands (1R,2S)-(−)-2a and (1S,2R)-(+)-2b as homogeneous catalysts. The zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b were characterized by IR, SEM, XRD and TG analysis. SEM and XRD data showed that the catalysts (1S,2R)-(+)-4b and (1R,2S)-(−)-4a were in aggregate and mesopore structure with the same interlayer spacing 2.48 nm and pore diameter 5.6 nm.     

Homo- and R/S-copolymerizations of chiral methylpropargyl esters carrying pyrene moieties, and optical properties of the formed polymers

Pyrene-functionalized chiral methylpropargyl esters, (R)-3-butyn-2-yl-1-pyrenebutyrate [(R)-1], (S)-3-butyn-2-yl-1-pyrenebutyrate [(S)-1], (R)-3-butyn-2-yl-1-pyrenecarboxylate [(R)-2], and 3-butyn-2-yl-1-pyrenecarboxylate [(R,S)-2] were polymerized with (nbd)Rh⁺[η⁶-C₆H₅B⁻(C₆H₅)₃] to obtain the corresponding polymers with moderate molecular weights (M_n: 10?500-66?500) in good yields (82-97%). All the polymers were soluble in CHCl₃, CH₂Cl₂, and THF. The polarimetric and CD spectroscopic data indicated that poly[(R)-1], poly[(S)-1], and poly[(R)-2] existed in a helical structure with predominantly one-handed screw sense in these solvents. The helical structure of poly[(R)-1] and poly[(S)-1] was stable upon heating and addition of MeOH, while that of poly[(R)-2] changed upon MeOH addition. The copolymerization of (R)-1 with (S)-1 was also conducted to obtain the copolymers satisfactorily. Poly[(R)-1], poly[(S)-1], and poly[(R)-2] emitted fluorescence smaller than the corresponding racemic copolymers. The fluorescence intensity was tuned by the addition of MeOH to THF solutions of the polymers.     

A fluorescence sensor based on chiral polymer for highly enantioselective recognition of phenylalaninol

The chiral polymer P-1 incorporating (S)-2,2′-binaphthol (BINOL) and (S)-2,2′-binaphthyldiamine (BINAM) moieties in the main chain of the polymer backbone was synthesized by the polymerization of (S)-6,6′-dibutyl-3,3′-diformyl-2,2′-binaphthol (S-M-1) with (S)-2,2′-binaphthyldiamine (S-M-2) via nucleophilic addition-elimination reaction, and the chiral polymer P-2 could be obtained by the reduction reaction of P-1 with NaBH₄. The fluorescence intensity of the chiral polymer P-1 exhibits gradual enhancement upon addition of (d)- or (l)-phenylalaninol and keeps nearly a linear correlation with the concentration molar ratios of (d)- or (l)-phenylalaninol. The value of enantiomeric fluorescence difference ratio (ef) is 6.85 for the chiral polymer on (d)-phenylalaninol. On the contrary, the chiral polymer P-2 shows no obvious fluorescence response toward either (d)- or (l)-phenylalaninol.     

Zirconium phosphonate immobilized chiral amino alcohol for heterogeneous enantioselective addition of diethylzinc to benzaldehyde

The chiral (1R,2S)-(−)-2-amino-1,2-diphenylethanol and (1S,2R)-(+)-2-amino-1,2-diphenylethanol had been immobilized on the layered frame of zirconium phosphate to obtain zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b. The enantioselective addition of Et₂Zn to benzaldehyde using zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b as heterogeneous catalysts yielded secondary alcohol in 80.1% yield and e.e. values of up to 54.3%, which was only 7.6% e.e. lower than that using the corresponding ligands (1R,2S)-(−)-2a and (1S,2R)-(+)-2b as homogeneous catalysts. The zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b were characterized by IR, SEM, XRD and TG analysis. SEM and XRD data showed that the catalysts (1S,2R)-(+)-4b and (1R,2S)-(−)-4a were in aggregate and mesopore structure with the same interlayer spacing 2.48 nm and pore diameter 5.6 nm.     

Polybinaphthyls incorporating chiral (R) or (S)-2,2′-binaphthyland oxadiazole moieties by Stille reaction

Chiral polymers P-1 and P-2 were prepared by the polymerization of (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-1) and (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-1) with 2,5-bis[(4-tributylstannyl)phenyl]-1,3,4-oxadiazole (M-2) via Pd(PPh₃)₄ catalyzed Stille coupling reaction. 1,3,4-Oxadiazole unit not only has high electron affinity, high thermal and oxidative stability, but also serves as a good chromophore. Polymers have strong blue fluorescence due to the efficient energy migration from the extended π-electronic structure of the polymers to the chiral binaphthyl core and can be expected to have potential application in the materials of fluorescent sensors. Circular dichroism (CD) spectra of polymers P-1 and P-2 are almost identical except that they gave opposite signals at each wavelength. The long wavelengths CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and a high rigidity of the polymer backbone.     

Fluorescence sensors based on chiral polymer for highly enantioselective recognition of phenylglycinol

Chiral polymer P-1 incorporating (R,R)-salen-type unit was synthesized by the polymerization of (R,R)-1,2-diaminocyclohexane with 2,5-dibutoxy-1,4-di(5-tert-butylsalicyclaldehyde)-phenylene (M-1) via nucleophilic addition-elimination reaction, and chiral polymer P-2 incorporating (R,R)-salan-type unit could be obtained by the reduction reaction of P-1 with NaBH₄. The fluorescence response of two chiral polymers P-1 and P-2 on (R)- or (S)-phenylglycinol were investigated by fluorescence spectra. The fluorescence intensities of two chiral polymers P-1 and P-2 show gradual enhancement upon addition of (R)- or (S)-phenylglycinol and keeps nearly linear correlation with the concentration molar ratios of (R)- or (S)-phenylglycinol. But both P-1 and P-2 exhibited more sensitive response signals for (S)-phenylglycinol. The values of enantiomeric fluorescence difference ratio (ef) are 1.84 and 2.05 for P-1 and P-2, respectively. The results also showed that two chiral polymers P-1 and P-2 can also be used as fluorescence sensors for enantiomer composition determination of phenylglycinol.     

Polybinaphthyls incorporating chiral 2,2′-binaphthyl and isoquinoline moieties by Sonogashira reaction

Polymers P-1, P-2, P-3, P-4 and P-5 were synthesized by the polymerization of 5,8-bis(ethynyl)isoquinoline (M-1) with (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-2), (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-2), (R)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-3), (S)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-3), and rac-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl (M-4) under Sonogashira reaction, respectively. Both monomers and polymers were analyzed by NMR, MS, FT-IR, UV-vis spectroscopy, DSC-TGA, fluorescence spectroscopy, GPC and circular dichroism (CD) spectroscopy. CD spectra of polymers P-1 and P-2, P-3 and P-4 are almost identical except that they gave opposite signals at each wavelength. The long wavelength CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and the helical backbone in the polymer chain. All five polymers have strong blue-green fluorescence due to the efficient energy migration from the extended π-electronic structure of the repeating unit of the polymers to the chiral binaphthyl core and are expected to provide understanding of structure-property relationships of the chiral conjugated polymers.     

Circular dichroism enhancement by the coordination of different metal ions with a pair of chiral tripodal ligands

The coordination of metal ions with a pair of chiral tripodal ligands (R or S)-2-(2-((bis(pyridin-2-ylmethyl)amino)methyl)phenoxy)-N-(1-phenylethyl)acetamide (R- or S-L) results in the circular dichroism (CD) enhancement distinctly, giving fingerprint information among different metals. Specifically, the CD signals show more obvious magnification upon coordination with Ln^3 + compared with Zn^2 + and other metals. Structural analyses show that in Eu-complex (1), the Eu^3 + metal center is surrounded in a 10-coordinating geometry and the ligand takes fan-like configuration, while in Zn-complex (2), Zn^2 + is surrounded in a 7-coordinating geometry and the ligand takes pincer-like configuration. These differences in the coordination structure as well as intramolecular packing effects are responsible for the variation in CD signal responses of different metal-coordinated systems.     

Ca–O Binding of Poly[1-carboxylate-2-(N-t- butylcarbamoyl)ethylene-alt-ethylene] and Calcium Carbonate Composites

A novel poly(carboxylate) ligand was synthesized as a ligand for a crystalline CaCO₃-organic composite. Poly[1-carboxylate-2-(N-t-butylcarbamoyl)ethylene-alt-ethylene] has a 7-membered ring with an intramolecular NH·O hydrogen bond between the carboxylate group and the neighboring amide NH proton in the anionic carboxylate form. The configuration of the polymer ligand was estimated with polymer repeat-unit models, (S,S)- or (R,R)-2-(N-t-butylcarbamoyl)-cyclohexanecarboxylic acid ((S,S)- or (R,R)-TBCA) and (S,R)- 2-(N-t-butylcarbamoyl)-cyclohexanecarboxylic acid ((S,R)-TBCA). The proton NMR spectum of the carboxylate anion of (S,S)- or (R,R)-TBCA exhibits a non-hydrogen bonded NH signal at 7.31 ppm in Me₂SO-d ₆. (S,R)-TBCA shows a strongly NH·O hydrogen-bonded NH signal at 8.50 ppm. The observation of one strongly NH·O hydrogen bonded NH signal at 11.3 ppm indicates that the polymer anion has a threo-form in the zigzag polymer main chain. Moreover, a polymer ligand-CaCO₃ composite was synthesized. The composite was characterized by ¹³C cross polarization/magic angle spinning (CP/MAS) and scanning electron microscopy (SEM). The polymer ligand stabilizes the Ca–O (carboxylate) bond in the CaCO₃ composite. This prevents dissociation due to pK_a shifts of the NH·O hydrogen bond and controls the crystal growth toward metastable vaterite.     

Synthesis and properties of helical polyacetylenes containing carbazole

Novel acetylene monomers containing carbazole with chiral menthyl and bornyl groups, 9-(1R,2S,5R)-menthyloxycarbonyl-2-ethynylcarbazole (1), 9-(1S,2R,5S)-menthyloxycarbonyl-2-ethynylcarbazole (2), 9-(1R,2S,5R)-menthyloxycarbonyl-3-ethynylcarbazole (3) and 9-(1S)-bornyloxycarbonyl-2-ethynylcarbazole (4) were synthesized and polymerized with a Rh catalyst to give the corresponding polymers [poly(1)-poly(4)] with moderate M_n value of (11.5-92.2) × 10³ in good yields (77-89%). CD spectroscopic studies revealed that poly(1), poly(2) and poly(4) took predominantly one-handed helical structure in CHCl₃, THF, toluene, and CH₂Cl₂, while poly(3) did not. Addition of methanol to CHCl₃ solutions of poly(1) and poly(2) resulted in the formation of aggregates showing smaller CD signals at 275 and 320 nm. The helical structure of poly(1) and poly(2) was very stable against heating. The polymers emitted fluorescence in 0.40-2.90% quantum yields. Poly(4) exhibited an obvious oxidation peak at 1.10 V. The polymers were thermally stable below 300 °C.     

Synthesis,structure, and reactivity of yttrium complexes with chiral biaryldiamine-based N4-ligands

The chiral biaryl-based N₄-ligands, (R)-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-bis(pyrrol-2-ylmethyleneamino)-1,1′-binaphthyl (1H₂) and (S)-2,2′-bis(pyrrol-2-ylmethyleneamino)-6,6′-dimethyl-1,1′-biphenyl (2H₂), can effectively stabilize the chiral rare earth metal chloride complexes such as 1-YCl(dme) (3) and 2-YCl(dme) (4), which offers important intermediates for the preparation of chiral rare earth catalysts containing the M–C or M–X (X = heteroatom) bonds. For example, treatment of 3 with half equiv of 1Na₂ in THF gives the binuclear complex 1-Y(thf)-1-Y(thf)-1 (5) in 70% yield. These complexes have been characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses. The complex 5 is an active catalyst for the ring-opening polymerization of rac-lactide, affording isotactic-rich polylactides.     

Toward chiral iron(II) spin-crossover grafted resins with imidazole Schiff-base ligands

Using chiral imidazole Schiff-base as ligands, two couples of mononuclear iron(II) enantiomeric complexes fac-Λ-[Fe(R-L)₃](ClO₄)₂·H₂O (1), fac-Δ-[Fe(S-L)₃](ClO₄)₂·H₂O (2), fac-Λ-[Fe(R-L)₃](BF₄)₂·H₂O (3), fac-Δ-[Fe(S-L)₃](BF₄)₂·H₂O (4) (L = 1-(2-naphthyl)-N-((1-methyl-imidazol-2-yl)methylene)ethanamine) have been successfully synthesized and characterized. The CD spectra of 1 and 2, 3 and 4, were basically mirror images confirming their enantiomers. X-ray crystallography revealed that complexes 1–4 all crystallized in the chiral space group P2₁3 with the iron(II) center surrounded by three bidentate ligands. Magnetic measurements revealed incomplete spin transition for 1, and gradual spin crossover (T_1/2 = 150 K) for 3. However, the spin-crossover behaviors were vanished after grafting 1–4 to the Merrifield's peptide resin, and the iron(II) centers in the resin remained in a high-spin state in the temperature range of 2–300 K.     

One-pot diastereoselective assembly of helicates based on a chiral salen scaffold

The one-pot reaction of (1S,2S)-(+)-1,2-diaminocyclohexane, 3-tert-butyl-2-hydroxybenzaldehyde and Zn(OAc)₂·1.5H₂O in methanol under reflux gives the diastereoselective formation of the first zinc(II)-salen double helicate, P-(S, S)-1, which adopts a right-handed helicity. The stereochemistry of the helicates can be readily tuned through varying the chiral diamine backbone.     

Synthesis and characterization of macrocyclic nickel(II) complexes with α-methylbenzyl groups as chiral pendants

Novel nickel(II) hexaaza macrocyclic complexes, [Ni(L^R,R)](ClO₄)₂ (1) and [Ni(L^S,S)](ClO₄)₂ (2), containing chiral pendant groups have been synthesized by an efficient one-pot template condensation and characterized (L^R,R/S,S = 1,8-di((R/S)-α-methylbenzyl)-1,3,6,8,10,13-hexaazacyclotetradecane). The crystal structures of 1 and 2 were determined by single-crystal X-ray analysis. Each complex has a square-planar coordination environment for the nickel(II) ion, and is either an R or an S enantiomorph depending on the pendant groups. The circular dichroism spectrum of 1 showed a negative, positive and negative peak at 345, 440, and 492 nm, respectively, and that of 2 exhibited an enantiomeric pattern.     

Perylene diimide-appended mixed (phthalocyaninato)(porphyrinato) europium(III) double-decker complex: Synthesis, spectroscopy and electrochemical properties

Treatment of sandwich-type mixed (phthalocyaninato)(porphyrinato) metal complex [HEu^III{Pc(α-3-OC₅H₁₁)₄}{TriBPP(NH₂)}] (3) [Pc(α-3-OC₅H₁₁)₄ = 1,8,15,22-tetrakis(3-pentyloxy)-phthalocyaninate, TriBPP(NH₂) = 5,10,15-tris(4-tert-butylphenyl)-20-(4-aminophenyl)porphyrinate] with N-n-butyl-1,6,7,12-tetra(4-tert-butylphenoxyl)perylene-3,4-dicarboxylate anhydride-9,10-dicarboxylate imide (2) in the presence of imidazole in toluene afforded the novel perylene diimide-appended mixed (phthalocyaninato)(porphyrinato) europium(III) double-decker complex (5). Porphyrin-PDI dyad 4 was also obtained by similar method. The electronic absorption spectroscopic and electrochemical properties of PDI-appended double-decker 5 and the model compounds 2, 3, and 4 were studied, the results indicated that there was no considerable ground-state interaction between the double-decker unit and the PDI unit in 5. The fluorescence measurements revealed that the emission of PDI unit was effectively quenched by the double-decker unit, suggesting remarkable intramolecular interaction in 5 under excited state.     

Polymerization of cysteine functionalized thiophenes

Different synthetic pathways leading to polythiophenes (PTs) containing units derived from methyl N-(tert-butoxycarbonyl)-S-3-thienyl-l-cysteinate (1) and methyl N-(tert-butoxycarbonyl)-S-(2-thien-3-ylethyl)-l-cysteinate (2) were investigated. The oxidative coupling with FeCl₃ applied to N-deprotected monomer 1 generates a chemically fleeting PT, whereas when applied to N-deprotected monomer 2 generates a mixture of oligomers. Two co-polymers bearing cysteine moieties, poly{[methyl N-(tert-butoxycarbonyl)-S-3-thienyl-l-cysteinate]-co-thiophene} (co-PT1) and poly{[methyl N-(tert-butoxycarbonyl)-S-(2-thien-3-ylethyl)-l-cysteinate]-co-thiophene} (co-PT2), were eventually synthesized through Stille coupling of 2,5-bis(trimethylstannyl)thiophene and 2,5-dibromo derivative of compound 1 and through the post-functionalization with protected cysteine of a tosylate co-polymer, poly{[2-(3-thienyl)ethyl 4-methylbenzenesulfonate]-co-thiophene} (co-PTTs). UV-vis, CD, NMR and GPC analyses evidenced that these polymers are able to form chiral self-assembling structures, due to the formation of a hydrogen bond network and to π-stacks, not only in the solid state but also in solution.     

Synthesis of a novel chiral Schiff base of (R,R)-11,12-diamino-9,10-dihydro-9,10-ethanonanthracene and its application as ligand in Ti(IV) complex catalyzed asymmetric silylcyanation of aldehydes

A novel chiral salen ligand (R,R)-2 was synthesized through the condensation of (R,R)-11,12-diamino-9,10-dihydro-9,10-ethanoanthracene and 3,5-di-tert-butylsalicylaldehyde. The (salen)Ti(IV) complex formed in situ upon the treatment of ligand 2 and Ti(OPr-i)₄ was proved to be an efficient catalyst for the asymmetric trimethylsilylcyanation of aldehydes. The corresponding cyanohydrins were obtained in high yields (75–97%) with moderate to good enantioselectivities (48–76%).     

Ruthenium-catalyzed asymmetric hydrogenation of N-(3,4-dihydro-2-naphthalenyl)-acetamide

The enantioselective hydrogenation of a challenging enamide (N-(3,4-dihydro-2-naphthalenyl)-acetamide, 1) bearing an endocyclic trisubstituted carbon-carbon double bond has been performed using cis-fac-Δ-[Ru^IICl{(R)-(bpea)}{(S)-(BINAP)}]BF₄, cis-fac-Δ-(R)-(S)-3, as catalyst achieving good conversions and enantioselectivities up to 74%. Furthermore, the study of the influence of different reaction parameters during the hydrogenation reaction has been performed, showing a strong influence of the coordinating ability of the solvent on the reaction rate.     

Sensitivity of antennae of male and femaleIps paraconfusus (Coleoptera: Scolytidae) to its pheromone and other behavior-modifying chemicals

The antennal sensitivities of both male and femaleIps paraconfusus were found generally to be greatest for conspecific aggregation pheromones (ipsdienol, ipsenol); intermediate for an additional conspecific pheromone (cis-verbenol), an aggregation synergist (2-phenylethanol), and pheromones/allomones of sympatric species (trans-verbenol, verbenone, and frontalin); and lowest for both host terpenes (alpha-pinene and myrcene) and other bark beetle-produced odorants (exo-brevicomin and linalool). Of the enantiomeric compounds tested, antennae of both sexes did not differ in sensitivity between thetrans-verbenol enantiomers at low dosage levels; but at higher dosages, the conspecific-produced enantiomer, (1R,4S,5R)-(+)-trans-verbenol, elicited larger mean EAG responses than its antipode, (1S,4R, 5S)-(?)-trans-verbenol. At the mid-dosage range, female antennae tended to be slightly more responsive to (S)-(?)-verbenone than to (R)-(+)-verbenone, while male antennae were equally responsive to stimulations by either verbenone enantiomer. In field bioassays there was a large and significant reduction in trap catches ofI. paraconfusus on traps where the (S)-(?)- or (R)-(+)-enantiomers of verbenone were evaporated beside logs containing boring conspecific males. Only when the (S)-(?)-enantiomer of verbenone was evaporated beside logs containing boring males did the sex ratio ofI. paraconfusus trapped shift from female-dominated to male-dominated attraction. Thus both physiological and behavioral data suggest a differential chiral sensitivity of female beetles for the verbenone enantiomers. The relative sensitivities between different chiral compounds derived from one or the other of the common precursoral host terpenes, (S)-(?)- and (R)-(+)alpha-pinene or myrcene, are discussed.     

Asymmetric hydrodimerization of styrene by a chiral zirconium complex containing a tetradentate [OSSO]-type bis(phenolato) ligand

The chiral non racemic (Λ,R,R)-[OSSO]Zr(CH₂Ph)₂ (1a) activated by methylaluminoxane (MAO) and in presence of H₂ produces the chiral hydrodimer (S)-1,3-diphenylbutane with good selectivity respect to the achiral 1,4-diphenylbutane. The absolute configuration of the chiral dimer and the effect of the hydrogen pressure on the ratio between 1,3-diphenylbutane and 1,4-diphenylbutane give useful information about the regiochemistry and stereochemistry of insertion of the styrene into the Zr–H bond.