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  • 1. Gao, Aiping
    et al.
    Wang, Mei
    Shi, Jicheng
    Wang, Dongping
    Tian, Wei
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Asymmetric oxidation of sulfides catalyzed by chiral (salen)Mn(III) complexes with a pyrrolidine backbone2006Inngår i: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 20, nr 12, s. 830-834Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Catalytic properties of a series of chiral (pyrrolidine salen)Mn(III) complexes for asymmetric oxidation of aryl methyl sulfides were evaluated. Moderate activity, good chemical selectivity and low enantioselectivity were attained with iodosylbenzene as a terminal oxidant. Enantioselectivity of sulfide oxidation was affected slightly by polar solvent and the sulfoxidation carried out in THF for thioanisole and in CH3CO2Et for electron-deficient sulfides gave better enatioselctivities. The addition of the donor ligand PPNO (4-phenylpyridine N-oxide) or MNO (trimethylamine N-oxide) only has a minor positive effect on the enantioselectivity. Also explored was the steric effect of the N-aza-substituent in the backbone of (pyrrolidine salen)Mn(III) complexes on the enantioselectivity of sulfide oxidation. The sulfides' access pathway is discussed based on the catalytic results.

  • 2. Liu, Haibin
    et al.
    Wang, Mei
    Wang, Ying
    Yin, Ran
    Tian, Wei
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Influence of substituents in the salicylaldehyde-derived Schiff bases on vanadium-catalyzed asymmetric oxidation of sulfides2008Inngår i: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 22, nr 5, s. 253-257Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A series of chiral Schiff bases (L-1-L-5) with different substituents in the salicylidenyl unit were prepared from condensation of 3-aryl-5-tert-butylsalicylaldehyde derivatives and optically active amino alcohols. Bromination of 3-phenyl-5-tert-butylsalicylaldehyde gave an unexpected product 3-(4-bromophenyl)-5-bromosalicylaldehyde, from which the corresponding Schiff base ligands L-6 and L-7, derived from (S)-valinol and (S)-tert-leucinol, respectively, were prepared. Ligands L-1-L-7 were applied to the vanadium-catalyzed asymmetric oxidation of aryl methyl sulfides. Under the optimal conditions, the oxidation of the thioanisole with H2O2 as oxidant in CH2Cl2 catalyzed by VO(acac)(2)-L-1-L-7 gives good yields (74-83%) with moderate enantioselectivity (58-77% ee). Ligand L-7, containing a 4-bromophenyl group on the 3-position and a Br atom on the 5-position of the salicylidenyl moiety, displays an 80-90% ee for vanadium-catalyzed oxidation of methyl 4-bromophenyl sulfide and methyl 2-naphthyl sulfide.

  • 3. Scholz, S. M.
    et al.
    Vacassy, R.
    Lemaire, L.
    Dutta, Joydeep
    Swiss Fed. Inst. Technol. Lausanne, Switzerland; Balzers Process Systems, Display Technology Division, Liechtenstein.
    Hofmann, H.
    Nanoporous Aggregates of ZnS Nanocrystallites1998Inngår i: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 12, nr 5, s. 327-335Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During the synthesis of ZnS powders by wet chemical precipitation, the formation of nanoporous spheres is observed. The powders have been investigated using thermogravimetric analysis, X-ray diffraction and optical spectroscopies. Nanopore formation can be explained by several stages of growth. The formation of nanoparticles as primary particles is followed by their agglomeration forming secondary particles. These secondary particles are monodispersed spheres with a considerable porosity, because the agglomeration of the nanoparticles is unlikely to be volume-filling. The voids or nanopores formed by this agglomeration process in the secondary particles is estimated to comprise around 35% of the sphere volume. They are mainly filled with water and the residues of the chemical reagents. Water in the pores partially reacts with ZnS and forms hydrated sulphates. The chemical reagents used for the precipitation reactions are also found to be bound to the nanocrystallite's surfaces as ligands in some cases. Depending on the reaction conditions and reagents, the agglomeration of the nanoparticles can also be modified or hindered by the use of complexing agents acting as a sterically stabilizing surface layer on the nanocrystallites. The agglomeration of nanoparticles to larger units being a general phenomenon, this use of complexing agents to control pore formation and agglomerate size should be applicable to other nanocrystalline systems.

  • 4. Shi, Yu
    et al.
    Li, Xiaoyu
    Liu, Jianhui
    Jiang, Wenfeng
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    A Suzuki-type cross-coupling reaction of arylacetylene halides with arylboronic acids2011Inngår i: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 25, nr 7, s. 514-520Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A PdCl(2)-catalyzed direct alkynylation of arylboronic acids to give diarylacetylenes is described. The optimal conditions using PdCl(2) as catalyst, MeOH-PhMe-H(2)O as solvent and K(2)CO(3) as base effectively suppressed the formation of homo-coupling product and afforded moderate to good yield of the desired unsymmetrical coupling product. This reaction represents a Suzuki-type sp(2)(C-B)-sp(C-X) cross-coupling.

  • 5. Sun, Hongfei
    et al.
    Wang, Mei
    Li, Fei
    Li, Ping
    Zhao, Zhenbo
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Synthesis and structure of a mu-oxo diiron(III) complex with an N-pyridylmethyl-N,N-bis(4-methylbenzimidazol-2-yl)amine ligand and its catalytic property for hydrocarbon oxidation2008Inngår i: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 22, nr 10, s. 573-576Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A mu-oxo diiron(III) complex [{Fe(pbba)Cl}(2)(mu-O)]Cl-2 (1, pbba = N-pyridylmethyl-N,N-bis(4-methylbenzimidazol-2-yl)amine) bearing multi-imidazolyl motifs was synthesized and characterized by X-ray crystallography to closely mimic the structural features of methane monooxygenase. As shown by its X-ray crystal structure, complex 1 is a centrosymmetric dimer with an Fe-O-Fe angle of 180 degrees, and pseudo-octahedral around each iron(III) center. The catalytic ability of title compound in the oxidation of alkane and alkene is investigated by employing tert-butylhydroperoxide and m-chloroperbenzoic acid as oxidants under mild conditions. The catalytic oxidation results showed that radical intermediate dominates the oxidation process.

  • 6. Wang, M.
    et al.
    Sun, H. F.
    Wang, Y.
    Wang, X.
    Li, F.
    Sun, Licheng C.
    Preparation, characterization and catalytic oxidation properties of tris 2-(2-pyridyl)benzimidazole iron(II) complexes2004Inngår i: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 18, nr 6, s. 277-281Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Complexes [Fe(Hpbi)(3)](ClO4)(2) (1) and [Fe(Hpbi)(3)](SbF6)(2) (2) (Hpbi = 2-(2-pyridyl)benzimidazole) were prepared by a modified method and characterized by IR, H-1 and C-13 NMR, mass spectrometry, electron paramagnetic resonance spectra and elemental analysis. The catalytic activities of 1 and 2 were evaluated for the oxidation of cyclohexene, cyclohexane, ethylbenzene and adamantane with tert-butylhydroperoxide or H2O2 as oxidant, and the results were compared with the properties of their analogue [Fe(bpy)(3)](SbF6)(2) (3). Complexes 1 and 2 both afforded the ketonization product for the oxidation of ethylbenzene and the hydroxylation product for adamantane.

  • 7. Wang, Ying
    et al.
    Wang, Mei
    Wang, Lin
    Wang, Yu
    Wang, Xiuna
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Asymmetric oxidation of sulfides with H2O2 catalyzed by titanium complexes of Schiff bases bearing a dicumenyl salicylidenyl unit2011Inngår i: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 25, nr 5, s. 325-330Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The sterically hindered Schiff bases (L-3-L-5), prepared from 3,5-dicumenyl salicylaldehyde and chiral amino alcohols, were used in combination with Ti(OiPr)(4) for asymmetric oxidation of aryl methyl sulfides with H2O2 as terminal oxidant. Among the ligands L-3-L-5, L-4 with a tert-butyl group in the chiral carbon of the amino alcohol moiety gave the best result with 89% yield and 73% ee for the sulfoxidation of thioanisole under optimal conditions [with 1 mol% of Ti(OiPr)(4) in a molar ratio of 100 : 1 : 1.2 : 120 for sulfide : Ti(OiPr)(4) : ligand : H2O2 in CH2Cl2 at 0 degrees C for 3 h]. The reaction afforded good yield (84%) with a moderate enantioselectivity (62% ee) even with a lower catalyst loading from 1.0 to 0.5 mol%. The oxidations of methyl 4-bromophenyl sulfide and methyl 4-methoxyphenyl sulfide with H2O2 catalyzed by the Ti(OiPr)(4)-L-4 system gave 79-84% yieldsand54-59% ee of the corresponding sulfoxides in CH2Cl2 at 20 degrees C. The chiral induction capability of the cumenyl-modified sterically hindered Schiff bases for sulfoxidation was compared with the conventional Schiff bases bearing tert-butyl groups at the 3,5-positions of the salicylidenyl unit.

  • 8. Zhang, Xiang
    et al.
    Wang, Dong-Ping
    Jia, Yin-Bao
    Lu, Xiao-Bing
    Wang, Hui
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Asymmetric epoxidation of chromenes catalyzed by chiral pyrrolidine SalenMn(III) complexes with an anchored functional group2008Inngår i: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 22, nr 10, s. 592-597Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Chiral pyrrolidine SalenMn(III) complexes with an anchored functional group at the N-aza-substituent in the pyrrolidine backbone were synthesized, and used as catalysts for asymmetric epoxidation of substituted chromenes. The complex 1 with an anchored imidazole as acceptor could effectively catalyze epoxidation of substituted chromenes in the absence of expensive additive 4-phenyl pyridine N-oxide (PPNO) by the coordination of the anchored organic base to the central manganese ion. Complexes 2 and 3 with a quaternary ammonium salt unit at the Naza-substituent in the pyrrolidine backbone displayed higher activities than Jacobsen catalyst and the analogous complex 4 without anchored functional group in the aforementioned reaction.

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