Highly cis-1,4 selective polymerization of dienes with homogeneous Ziegler-Natta catalysts based on NCN-pincer rare earth metal dichioride precursors

The first aryldiimine NCN-pincer ligated rare earth metal dichlorides (2,6-(2,6-C6H3R2N=CH)(2)C6H3)LnCl(2)(THF)(2) (Ln = Y, R = Me (1), Et (2), Pr (3); R = Et, Ln = La (4), Nd (5), Gd (6), Sm (7), Eu (8), Tb (9), Dy (10), Ho (11), Yb (12), Lu (13)) were successfully synthesized via transmetalation between 2,6-(2,6-C2H3-R2N=CH)(2)-C6H3Li and LnCl(3)(THF)(1 similar to 3.5). These complexes are isostructural monomers with two coordinating THF molecules, where the pincer ligand coordinates to the central metal ion in a kappa C:kappa N: kappa N' tridentate mode, adopting a meridional geometry.

Study on the cyclization of cis-1,4 polybutadiene in various solvents and its mechanism

The cyclization of cis-1,4 polybutadiene in various solvents (mesitylene,xylene, toluene,benzene and cyclohexane) with the catalyst composed of CH2=CHCH2Cl-AlEt2Cl was studied. The infrared spectra of the cyclized products were investigated. It was shown that the products produced in cyclohexane and mesitylene have infrared spectra identical with those of the original cis-1,4-polybutadiene and the products obtained in other aromatics have infrared spectra different from each other and distinguishing with those of the parent cis-1,4 polybutadiene. The analyses of infrared spectra came to the conclusion that the molecules of aromatic solvent participate in cyclization of cis-1,4 polybutadiene at the given condition. A possible reaction scheme involving an electrophilic substitution of carbonium ions for Ar-H of aromatic solvents was proposed. Some experimental facts were explained with great satisfaction on the basis of the above mechanism.

Metal dependent control of cis-/trans-1,4 regioselectivity in 1,3-butadiene polymerization catalyzed by transition metal complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine

Fe(III), Cr(III), Fe(II), Co(II) and Ni(II) chloride complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine have been synthesized and characterized along with single crystal X-ray diffraction. These complexes, in combination with MAO, have been examined in butadiene polymerization. The catalytic activity and regioselectivity are strongly controlled by metal center and cocatalyst (MAO/Co ratio dependent in the case of Co(II) complex). The activity decreases in the order of Fe(III) > Co(II) > Cr(III) approximate to Ni (II) complexes, in consistent with the space around the metal center. Polybutadiene with different microstructure content, from high trans-1,4 units (88-95% for iron(III) and Cr(III)), medium trans-1,4 and cis-1,4 units (55% and 35%, respectively, for iron(II)) to high cis-1,4 units 79% for Co(II) and 97% for Ni(II) call be easily achieved by varying of the metal center.

Comparação entre os intumescimentos de borracha natural e polibutadieno com alto teor 1,4-cis em solventes (n-octano, ciclo-hexano e esqualeno) e em soluções poliméricas

Amostras de borracha natural foram reticuladas por meio de radiação gama (doses de 2, 4, 6 e 8 MRad) e intumescidas: a) em n-octano, ciclo-hexano e esqualeno; b) em polibutadieno líquido (Mn=1830 g/mol; alto teor 1,4- cis) a 45°C; C) em solução de polibutadieno de baixo peso molecular (M,= 1830 g/mol; alto teor 1,4-cis) em n-octano e ciclo-hexano; d) em solução de polibutadieno de alto peso molecular (Mn= 175.000 g/rnol; alto teor 1,4-cis) emn-octano e ciclo-hexano ; e) em solução de borracha natural (Mn=779.000 g/mol) em ciclo- hexano, a 25°C. Amostras de polibutadieno (alto teor 1,4-cis) foram reticuladas por meio de radiação gama (doses de 1,s; 18 e 25 MRad) e intumescidas: a) em n-octano, ciclo-hexano e esquaieno. Salvo quando mencionado em contrário, as amostras de borracha natural e de polibutadieno foram intumescidas nas temperaturas de 25, 35 e 45°C. A partir dos ensaios de intumescirnento acima mencionados, foram determinadas as solubilidades de borracha natural e de polibutadieno em n-octano, ciclo-hexano e esqualeno através dos parâmetros de Flory-Huggins, calculados com o emprego da equação de Flory-Rehner. Verificou-se a influência da temperatura e da concentração de polimero no gel sobre o valor do parâmetro de Flory-Huggins. Também através desse parâmetro procurou-se determinar a compatibilidade entre borracha natural e polibutadieno. Foi demonstrado que cadeias lineares de baixo peso molecular de polibutadieno conseguem penetrar em amostras reticuladas de borracha natural, quando o peso molecular das cadeias lineares for bem inferior ao do arco de rede Mc das amostras reticuladas. Cadeias lineares de polibutadieno e de borracha natural com peso molecular superior ao do arco de rede da borracha natural reticulada, entretanto, não conseguem penetrar no retículo. Quranto mais alta a concentração da solução externa em moléculas de alto peso molecular, tanto menor é o grau de intumescimento da amostra reticulada.

Comparative Study on the Technological Properties of Latex and Natural Rubber from Hancornia speciosa Gomes and Hevea brasiliensis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Stereospecific construction of multiple contiguous quaternary carbons. Total synthesis of (±)-cis,anti,cis-1,8,12,12-tetramethyl-4-oxatricyclo[6.4.0.02,6]dodecan-3-ol, a thapsane isolated from Thapsia villosa var minor

The details of the first total synthesis of a natural thapsane lg containing three contiguous quaternary carbon atoms, starting from cyclogeraniol (9) '5 described. The Claisen rearrangement of 9 with methoxypropene in the presence of a catalytic amount of propionic acid produced ketone 10. Rhodium acetate-catalyzed intramolecular cyclopropanation of a-diazo-&keto ester 12, obtained from 10 via 8-keto ester 8, furnished cyclopropyl keto ester 7. Lithium in liquid ammonia reductive cleavage of cyclopropyl compound 7 gave a 1:l mixture of hydrindanone 6 and keto1 13. Wittig methylenation of 6 furnished ester 21. Epoxidation of 21, followed by BF3-OEt2-catalyzed rearrangement of epoxide 23 afforded hemiacetal 25. Treatment of hemiacetal 25 with triethylsilane in trifluoroacetic acid furnished lactone 22, a degradation product of various thapsanes. Finally, DIBAH reduction of lactone 22 generated the thapsane

syn-Benzene dioxides: chemoenzymatic synthesis from 2,3-cis-dihydrodiol derivatives of monosubstituted benzenes and their application in the synthesis of regioisomeric 1,2- and 3,4-cis-dihydrodiols and 1,4-dioxocins

cis-2,3-Dihydrodiol metabolites of monosubstituted halobenzenes and toluene have been used as synthetic precursors of the corresponding 3,4-cis-dihydrodiols. Enantiopure syn-benzene dioxide intermediates were reduced to the 3,4-cis-dihydrodiols and thermally racemised via the corresponding 1,4-dioxocins. The syn-benzene dioxide-1,4-dioxocin valence tautomeric equilibrium ratio was found to be dependent on the substituent position. The methodology has also been applied to the synthesis of both enantiomers of the 1,2-(ipso)- and 3,4-cis-dihydrodiols of toluene. This chemoenzymatic approach thus makes available, for the first time, all three possible cis-dihydrodiol regioisomers of a monosubstituted benzene.

Enzyme-catalysed synthesis and absolute configuration assignments of cis-dihydrodiol metabolites from 1,4-disubstituted benzenes

A series of ten cis-dihydro-diol metabolites has been obtained by bacterial biotransformation of the corresponding 1,4-disubstituted benzene substrates using Pseudomonas putida UV4, a source of toluene dioxygenase (TDO). Their enantiomeric excess (ee) values have been established using chiral stationary phase HPLC and H-1 NMR spectroscopy. Absolute configurations of the majority of cis-dihydrodiols have been established using stereochemical correlation and X-ray crystallography and the remainder have been tentatively assigned using NMR spectroscopic methods but finally confirmed by circular dichroism (CD) spectroscopy. These configurational assignments support and extend the validity of an empirical model, previously used to predict the preferred stereochemistry of TDO-catalysed cis-dihydroxylation of ten 1,4-disubstituted benzene substrates, to more than twenty-five examples.

Novel manganese (III) porphyrin containing peripheral [RuCl(dppb)(X-bipy)](+) cations [dppb=1,4-bis(diphenylphosphino) butane and X = -CH3, -OMe, -Cl]. X-ray structure of the cis-[RuCl(dppb)(bipy)(4-Mepy)]PF6 complex

New tetraruthenated manganese (III) porphyrins were synthesized and characterized (P-31 NMR, cyclic voltammetry, UV-Vis). This new system presents four units of cationic ``[RuCl(dppb)(X-bipy)](+)``. The electrochemical and catalytic properties of the central manganese (III) show dependence on the characteristics of the peripheral ruthenium complexes as evidenced by the Mn-(III)/Mn-(II) reduction potential. The catalytic oxidation reactions of olefins, cyclohexene and cyclohexane, were carried out in the presence of tetrapyridyl manganese (III) porphyrins containing cationic ruthenium complex and using iodosylbenzene as oxygen donor. The performance of these new tetraruthenated porphyrins systems were evaluated and compared with the manganese porphyrin. (C) 2007 Elsevier Ltd. All rights reserved.

Synthesis and characterization of the mer-[RuCl3(NO)(dppb)] isomer. X-ray structures of fac-[RuCl3(NO)(dppm)], cis-[RuCl2(dppm)2] and mer-[RuCl3(NO)(dppb)] [dppm=1,2-Bis(diphenylphosphino)methane and dppb=1,4-Bis(diphenylphosphino)butane]

The fac-[RuCl3(NO)(dppm)] (1) and cis-[RuCl2(dppm)2] (2) complexes were obtained with co-crystallization in the solid state from the reaction of RuCl3(NO) with the diphosphine in dichloromethane. mer-[RuCl3(NO)(dppb)] (3) was obtained from [RuCl3(dppb)(H2O)] by bubbling NO for 30 min in the same solvent. The crystal and molecular structures of these three compounds have been determined from X-ray studies. © Elsevier Science Ltd.

Structure of 1 lct-Hydroxyeon-1,4,18-trienine-3-one

C21H27NO2, Mr=325.5 , orthorhombic,P21212,, a = 7.516 (2), b = 13.430 (2), c =18.047 (2) A, U= 1821.79 A 3, Z = 4, D x =1.186 Mg m -a, 2(Cu Ka) = 1.5418 A, # = 0.56 mm -1, F(000) = 704, T= 293 K, final R = 0.04 for 1892 reflections with I _> 3a(I). Ring A is planar, and rings B and C adopt a chair conformation. Rings D and E are envelopes, with C(14) and C(17) displaced from their respective planes by 0.643 (3) and 0.482 (3)A. The ring system A/B shows quasi-trans fusion, whilst ring systems B/C and C/D are trans fused about C(8)-C(9) and C(13)-C(14) respectively. The D/E junction shows cis fusion.

The structure of 11[alpha]-hydroxycon-1,4-dienine-3-one monohydrate

C22H31NO2.H2 O, M r = 359" 5, orthorhombic,P2~212 ~, a= 10.032 (1), b= 11.186 (1), C = 17.980 (1)/~,, U= 2017.48/~3, Z = 4, D x = 1.276 Mg m -a, 2(Cu Kct) = 1.5418/~, # = 0.69 mm -~,F(000) = 784, T = 293 K. Final R = 0.05 for 1972 unique reflections with I > 3o(/). Ring A is planar, and rings B and C adopt a chair conformation. Rings D and E are envelopes, with C(14) and C(20) displaced from their respective ring planes by 0-616 (2) and 0.648 (3)/~. The A/B ring junction is quasi-trans,whilst ring systems B/C and C/D are trans fused about the bonds C(8)-C(9) and C(13)-C(14) respectively.The D/E junction shows cis fusion.