Ring-opening metathesis polymerization of amino acid-functionalized norbornene diester monomers

Amino acid-derived novel norbornene diester derivatives, 5-norbornene-endo,endo-2,3-dicarboxylic acid bis((S)-2-N-(tert-butoxycarbonyl)aminopropyl) ester (1a), 5-norbornene-exo,exo-2,3-dicarboxylic acid bis((S)-2-N-(tert-butoxycarbonyl)aminopropyl) ester (1b), bis(N-α-(tert-butoxycarbonyl)-l-alanine) 5-norbornene-2,3-endo,endo-dimethyl ester (2a), bis(N-α-(tert-butoxycarbonyl)-l-alanine) 5-norbornene-2,3-exo,exo-dimethyl ester (2b) were synthesized and polymerized by the Grubbs catalyst, 2nd generation. Ring-opening metathesis polymerization of the monomers satisfactorily proceeded to give the polymers with fairly high molecular weights in good yields. The polymerization rate was not affected by the stereostructure of the monomers, endo,endo- and exo,exo-, while largely affected by solvents. The order of polymerization rate was as follows: acetone-d₆ > benzene-d₆ > DMF-d₇ ≈ CD₂Cl₂ > CDCl₃.     

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.     

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 of poly(1,4-naphthylene) bearing crown ether side chain by asymmetric oxidative coupling polymerization

The oxidative coupling polymerization of racemic-, (R)-, and (S)-2,2′,3,3′-tetrahydroxy-1,1′-binaphthyl derivatives bearing a crown ether moiety was carried out in the presence of a Cu(I) or Cu(II) catalyst with various ligands, such as N,N,N′,N′-tetramethylethylenediamine, (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine, (−)-sparteine [(−)Sp], and (S)-(−)-2,2′-isopropylidenebis(4-phenyl-2-oxazoline). Methanol-insoluble poly(binaphthyl crown ether) with a molecular weight up to M_n=4.1×10³ was synthesized in moderate yields. Polymerization using (−)Sp proceeded in an S-selective manner; the polymer with the highest negative specific rotation was obtained with the (S)-monomer. The obtained polymers exhibited characteristic abilities for chiral recognition toward amino acids, such as 2-phenylglycine hydrochloride and 2-phenylglycine methyl ester hydrochloride.     

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.     

Oxidative addition of Se–X bonds and reductive elimination of Se–C bonds in platinum compounds containing hydrocarbyl ligands

The oxidative addition of PhSe–X molecules (X=Cl or Br) to Pt(II) complexes of formula [PtR(R^′)(N,N-chelate)] [R, R^′=Me, CH(CO₂Me)₂, CH(CO₂Me)(CN); N,N-chelate=4,4^′-(tert-butyl)₂-2,2^′-bipyridine] is described. The reaction quantitatively affords octahedral products [PtR(R^′)(SePh)(X)(N,N-chelate)], and is highly selective, since only the isomers with -X and -SePh in trans position are obtained. When R=R^′=CH(CO₂Me)₂ or R=R^′=CH(CO₂Me)₂(CN) an irreversible reductive elimination takes place in solution, giving rise to Pt(II) compounds [PtR(X)(N,N-chelate)] and organoselenium molecules PhSeR^′.     

Zirconium complexes of amino(polyphenolic) ligands and their hydrolytic stability

Three amino(polyphenolic) ligands, N,N′-bis(5-tert-butyl-2-hydroxybenzyl)-1,2-diaminoethane 1, tris(5-tert-butyl-2-hydroxy-3-methylbenzyl)amine 3, its 3-chloro analogue 4 and their Zr^IV complexes have been synthesised. The crystal structure of the Zr^IV complex of tris(5-tert-butyl-3-chloro-2-hydroxybenzyl)amine, shows this to be [Zr(4-2H)₂] in which both ligands exists in a zwitterionic form with one alkylammonium and three phenolate groups. The complexes are stable in a two phase, chloroform/water, system at high pH, but the zirconium is stripped at pH < 2.5. The pH value needed to strip 50% of the Zr^IV from the complex [Zr(1-4H)] of the tetraphenolic ligand is ∼2.0 whilst the complexes [Zr(3-2H)₂] and [Zr(4-2H)₂] of the triphenolic ligands are slightly more stable with pH_1/2 values of ∼1.4. We were unable to use the ligands to extract zirconium from low pH aqueous zirconium oxychloride solutions into an organic phase under a variety of conditions.     

Protection of mild steel corrosion with Schiff bases in 0.5 M H2SO4 solution

Three new Schiff bases, viz., N,N′-ethylen-bis (salicylidenimine) [S₁], N,N′-isopropylien-bis (salicylidenimine) [S₂], and N-acetylacetone imine, N′-(2-hydroxybenzophenone imine) ortho-phenylen [S₃] have been investigated as corrosion inhibitors for mild steel in 0.5 M H₂SO₄ using Tafel polarization and electrochemical impedance spectroscopy (EIS). The three Schiff bases function as good inhibitors reaching inhibition efficiencies of ∼97-98% at 300 ppm concentration. The fraction <theta> of the metal surface covered by the inhibitor is found to increase with inhibitor concentration. Of the three Schiff bases, the S2 shows better efficiency than the other two Schiff bases. The adsorption of the inhibitor follows Langmuir isortherm. Thermodynamic calculations indicate the adsorption to be physical in nature.     

Supramolecular assembly of a dinuclear Ag(I) complex with discreet Ag2S2 centers

The NS chelate N,N′-(thiodiethane-2,1-diyl)bis(1-methyl-1H-imidazole-2-carboxamide) and its silver(I) complex have been synthesized and characterized by X-ray crystallography. The complex displays a supramolecular structure consisting of discreet Ag₂S₂ centers stacked in columns along the a-axis via π-interactions. Individual Ag₂S₂ cores are isolated with no significant interactions between Ag ions.     

Terminal defined chain-growth polycondensation of 4-chloropyridine

This work examines the polycondensation of 4-chloropyridine derivatives using an N-(4-tert-butylbenzyl)-4-chloropyridinium (BPymCl) initiator and ion exchange reagents NaBPh₄, NaBF₄, and TBABF₄. The ¹H NMR spectra demonstrate that the product quantity is proportional to the total conversion of the monomer and the initiator. The MALDI-TOF MS spectrum shows that the product contains more than 9 monomer units. The polymerization was well-terminated via the addition of dimethylaminopyridine. These results indicate that the polycondensation proceeds in a chain-growth manner. This polycondensation could be a new example of a controlled polymerization with a well-defined end group.     

Carbon dioxide/propylene oxide coupling reaction catalyzed by chromium salen complexes

A series of chromium/Schiff base complexes N,N′-bis(salicylidene)-1,2-phenylenediamino chromium^III X were prepared and employed for the alternating copolymerization of carbon dioxide with racemic propylene oxide in the presence of (4-dimethylamino)pyridine. The effect of the complex structure and reaction conditions on the catalytic activity, the poly(propylene carbonate)/cyclic carbonate (PPC/PC) selectivity, and the polymer head-to-tail linkages was examined. The experiments indicated that N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-phenylenediamino chromium^III (NO₃) exhibited the highest PPC/PC selectivity as well as polymer head-to-tail linkages and N,N′-bis(3,5-dichlorosalicylidene)-1,2-phenylenediimino chromium^III (NO₃) possessed the highest catalytic activity among these chromium/Schiff base complexes. The structure of the produced copolymer was characterized by the IR, ¹H NMR, and ¹³C NMR measurements. Almost 100% carbonate content of the resulting polycarbonate were obtained with the help of these effective catalyst systems under facile conditions.     

34 GHz e.p.r. study of vanadyl complexes in various asphaltenes: Statistical correlative model of the coordinating ligands

High precision 34 GHz e.p.r. measurements were performed to study the coordination of vanadyl complexes in various asphaltenes. The spin-Hamiltonian parameter analysis indicates that the asphaltenes can be classified into those which have g- and A-parameters nearly identical to those for the vanadyl tetraphenyl porphyrins doped in carbonaceous materials and those for which these parameters are nearly identical to those for the vanadyl etioporphyrins. Quantitative statistical analysis of the parameters for model compounds with coordination N₄, N₂S₂, NS₃, S₄, S₂O₂, N₂O₂ and O₄ shows that these parameters cannot be used to predict the coordination for various asphaltenes. It is found that g₀ is a better parameter than A₀ to predict the coordination, although it cannot resolve the N₄, S₄ and S₂O₂ coordinations. However, the spin-Hamiltonian parameter resolution was sufficient to distinguish between those vanadyl complexes present in porphyrins, humates and minerals. The importance of high precision e.p.r. measurement at 34 GH_z or higher frequencies for model compounds and chromatographically-separated fractions is discussed.     

Ru/ZIF-8 with a chiral modifier for asymmetric hydrogenation of acetophenone

A series of Ru/ZIF-8 (Zeolitic imidazolate framework) catalysts was prepared in the different impregnation solvents and characterized by ICP, XRD, TEM, and N₂ adsorption. The obtained catalysts exhibited different catalytic performances in the presence of achiral modifier triphenylphosphine (TPP) and chiral modifier (1S,2S)-1,2-diphenylethylenediamine [(1S,2S)-DPEN] for asymmetric hydrogenation of acetophenone. Ethanol was found to be the most effective impregnation solvent, while low activity and enantioselectivity were observed for water. The prepared Ru/ZIF-8 catalyst was stable and could be reused at least five times without significant loss in activity and entantioselectivity.     

Highly Enantioselective Phase‐Transfer Catalytic α‐Alkylation of α‐tert‐Butoxycarbonyllactams: Construction of β‐Quaternary Chiral Pyrrolidine and Piperidine Systems

A new enantioselective α‐alkylation of α‐tert‐butoxycarbonyllactams for the construction of β‐quaternary chiral pyrrolidine and piperidine core systems is reported. α‐Alkylations of N‐methyl‐α‐tert‐butoxycarbonylbutyrolactam and N‐diphenylmethyl‐α‐tert‐butoxycarbonylvalerolactam under phase‐transfer catalytic conditions (solid potassium hydroxide, toluene, −40 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐3,3′,5,5′‐tetrahydro‐2,6‐bis(3,4,5‐trifluorophenyl)‐4,4′‐spirobi[4H‐dinaphth[2,1‐c:1′,2′‐e]azepinium] bromide [(S,S)‐NAS Br] (5 mol%) afforded the corresponding α‐alkyl‐α‐tert‐butoxycarbonyllactams in very high chemical (up to 99%) and optical yields (up to 98% ee). Our new catalytic systems provide attractive synthetic methods for pyrrolidine‐ and piperidine‐based alkaloids and chiral intermediates with β‐quaternary carbon centers.     

Synthesis of PAA-g-PNIPAM well-defined graft polymer by sequential RAFT and SET-LRP and its application in preparing size-controlled super-paramagnetic Fe3O4 nanoparticles as a stabilizer

A series of well-defined double hydrophilic graft copolymers, poly(acrylic acid)-g-poly(N-isopropylacrylamide) (PAA-g-PNIPAM), was employed as a novel water-soluble coating for constructing superparamagnetic iron oxide nanoparticles. The copolymer was synthesized via a three-step procedure: firstly, a well-defined hydrophobic PtBA-based backbone, poly(tert-butyl 2-((2-chloropropanoyloxy)-methyl)acrylate)-co-poly(tert-butyl acrylate), (PtBCPMA₁₉-co-PtBA₁₈), was prepared through RAFT copolymerization of a new trifunctional acrylic monomer, tert-butyl 2-((2-chloropropanoyloxy)methyl)acrylate and tert-butyl acrylate; secondly, taking this backbone as a macroinitiator to initiate SET-LRP of N-isopropylacrylamide resulted in well-defined (poly(tert-butyl 2-((2-chloropropanoyloxy)methyl)-acrylate)-co-poly(tert-butyl acrylate))-g-poly(N-isopropylacrylamide) ((PtBCPMA-co-PtBA)-g-PNIPAM) amphiphilic graft copolymers with relatively narrow polydispersities (M_w/M_n ≤ 1.31); thirdly, handling (PtBCPMA-co-PtBA)-g-PNIPAM in acidic conditions afforded PAA-g-PNIPAM graft copolymers. The resulting PAA-g-PNIPAM copolymers were directly utilized as a polymeric stabilizer in the preparation of superparamagnetic Fe₃O₄ nanoparticles. The particle size can be readily tuned in the range of 12.1–23.2 nm by varying the amount of PAA-g-PNIPAM copolymer or the length of PNIPAM side chain. Besides, the structure and properties of prepared Fe₃O₄/polymer nanocomposites were characterized by XRD, FT-IR, TGA, TEM, and magnetic measurement in detail.     

Remarkable asymmetric induction from remote stereocenters in conjugate addition chemistry for the synthesis of alkyl-branched α, ω-diaminoazelates

Conjugate addition of aryl Grignard reagents to (2S, 5E, 8S)-di-tert-butyl 4-oxo-2,8-bis-[N-(PhF)amino]non-5-enedioate ( 6 , PhF = 9-(9-phenyl-fluorenyl)) in THF proceeded with complete chemoselectivity and >9:1 stereoselectivity to provide predominantly (2S,6S,8S)-6-aryl 4-oxo-2,8-diamino-azelates 7 . In the presence of magnesium dibromide, diastereoselectivity in the addition of PhMgBr to enone 6 was improved to 15:1 in favor of the 6S-isomer. Although lower chemoselectivity and stereoselectivity were obtained from the analogous reaction of 6 with isopropyl magnesium bromide in the absence of MgBr₂, both were improved significantly when the addition reaction was performed in the presence of MgBr₂. In contrast, the corresponding higher-order cyanocuprates reacted with low diastereoselectivity on 6 by a 1,4-addition pathway. In an attempt to identify the source of the high selectivity in the conjugate addition chemistry with 6 and Grignard reagents, the syntheses of enones 12 and 13 provided model systems in which one of the two amino carboxylate moieties of 6 was replaced by a branched alkyl substituent. Conjugate addition reactions on 12 and 13 demonstrated that chemoselectivity with Grignard reagents in the 1,4-addition reaction was contingent on the presence of an amino carboxylate moiety near the ketone of the enone system. Furthermore, because diastereoselectivity with Grignard reagents was significantly lower in additions to amino enones 12 and 13 relative to diamino enone 6 , the presence of both amino carboxylate moieties has been highlighted as an important factor for remarkable asymmetric induction in the conjugate addition of Grignard reagents.     

Confidence limits for Weibull parameters estimated using linear least squares analysis

Confidence limits (at selected levels of 68.27%, 90%, 95% and 99%) for unbiased estimation of Weibull parameters obtained using linear least squares (LLS) analysis were investigated in this paper. A Monte Carlo procedure was used to obtain probability distributions for unbiased estimates of Weibull modulus, m, and Weibull scale parameter, S_o, as a function of total specimen number, N (10 ≤ N ≤ 200), and m (1 ≤ m ≤ 25). Inspection of the probability distributions indicated that confidence limits for m depended only on N whereas those for S_o depended on both N and m. Whilst the determination of confidence limits for m proved to be relatively straightforward, the respective values for S_o were obtained by fitting an empirical equation to the S_o probability distributions approximated by a Gaussian curve. Example values of m and S_o confidence limits for selected N have been presented in this work.     

A selective and convenient synthesis of gemini surfactants over heterogeneous basic catalyst

Tri-ethanolamine (C₆H₁₅O₃N) and fatty acid (C₁₀H₂₀O₂, C₁₂H₂₄O₂, C₁₄H₂₈O₂ and C₁₆H₃₂O₂) using MgO–ZrO₂ selectively gave the corresponding 2-(bis(2-hydroxyethyl)amino)ethyl alkanoate in good yield. Further the reaction of 2-(bis(2-hydroxyethyl)amino)ethyl alkanoate with epichlorohydrin or 1,2-dichloroethane (in the presence of the 2-(alkanoyloxy)-N,N-bis(2-hydroxyethyl)ethanaminium chloride) over same heterogeneous catalysis to afford novel N,N-bis(2-(alkanoyloxy)ethyl)-N,N,N,N-tetrakis(2-hydroxyethyl) propane-1,3-diaminium or N,N-bis(2-(alkanoyloxy)ethyl)-N,N,N,N-tetrakis(2-hydroxyethyl)ethane-1,2- diaminium (gemini surfactants), respectively. The ease of the diaminium reaction was found to be due to the neighboring-group participation (NGP) in the quaternization step. Results of esterification and diaminium reactions, reported herein were optimized for several catalytic effects to understand the probable mechanism. The catalysts can be easily separated from reaction and showed good recyclability.     

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.     

Dealkylation of N,N-dimethylaniline with sulphur and hydrogen sulphide

N,N-Dimethylaniline successively demethylates at 425 °C in the presence of hydrogen and hydrogen sulphide or sulphur to give successively N-methylaniline and aniline. For the dealkylation reaction, the rank order of promotors is S >SH₂ >H₂S >H₂SH₂ >H₂.