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- Bornschein, Christoph, et al.
(författare)
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Evaluation of Fe and Ru Pincer-Type Complexes as Catalysts for the Racemization of Secondary Benzylic Alcohols
- 2016
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Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 22:33, s. 11583-11586
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Tidskriftsartikel (refereegranskat)abstract
- Fe and Ru pincer-type catalysts are used for the racemization of benzylic alcohols. Racemization with the Fe catalyst was achieved within 30 minutes under mild reaction conditions, with a catalyst loading as low as 2 mol %. This reaction constitutes the first example of an iron-catalyzed racemization of an alcohol. The efficiency for racemization of the Fe catalyst and its Ru analogue was evaluated for a wide range of sec-benzylic alcohols. The commercially available Ru complex proved to be highly robust and even tolerated the presence of water in the reaction mixture.
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- Duan, Lele, 1982-
(författare)
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Artificial Water Splitting: Ruthenium Complexes for Water Oxidation
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns the development and study of Ru-based water oxidation catalysts (WOCs) which are the essential components for solar energy conversion to fuels. The first chapter gives a general introduction about the field of homogenous water oxidation catalysis, including the catalytic mechanisms and the catalytic activities of some selected WOCs as well as the concerns of catalyst design. The second chapter describes a family of mononuclear Ru complexes [Ru(pdc)L3] (H2pdc = 2,6-pyridinedicarboxylic acid; L = pyridyl ligands) towards water oxidation. The negatively charged pdc2− dramatically lowers the oxidation potentials of Ru complexes, accelerates the ligand exchange process and enhances the catalytic activity towards water oxidation. A Ru aqua species [Ru(pdc)L2(OH2)] was proposed as the real catalyst. The third chapter describes the analogues of [Ru(terpy)L3]2+ (terpy = 2,2′:6′,2′′-terpyridine). Through the structural tailor, the ligand effect on the electrochemical and catalytic properties of these Ru complexes was studied. Mechanistic studies suggested that these Ru-N6 complexes were pre-catalysts and the Ru-aqua species were the real WOCs. The forth chapter describes a family of fast WOCs [Ru(bda)L2] (H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid). Catalytic mechanisms were thoroughly investigated by electrochemical, kinetic and theoretical studies. The main contributions of this work to the field of water oxidation are (i) the recorded high reaction rate of 469 s−1; (ii) the involvement of seven-coordinate Ru species in the catalytic cycles; (iii) the O-O bond formation pathway via direct coupling of two Ru=O units and (iv) non-covalent effects boosting up the reaction rate. The fifth chapter is about visible light-driven water oxidation using a three component system including a WOC, a photosensitizer and a sacrificial electron acceptor. Light-driven water oxidation was successfully demonstrated using our Ru-based catalysts.
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- Johansson, Mikael, 1978-
(författare)
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Development of Biomimetic Catalytic Systems for Selective Oxidations with H2O2 and O2
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Four different catalytic systems were studied for biomimetic coupled oxidations using H2O2 or O2. In the first example, osmium tetroxide works as a substrate-selective catalyst for dihydroxylation of olefins. Electron transfer to H2O2 is facilitated by electron transfer mediators (ETMs). In one case VO(acac)2 or MeReO3 was used as ETM; in the other case a combination of flavin and tertiary amine was used as ETMs. These three systems were immobilized in the ionic liquid [bmim]PF6 for the purpose of recycling of the catalyst.In the second example, an organocatalyst (a flavin) was used for the oxidation of sulfides to sulfoxides and this catalytic system was recycled and reused in an ionic liquid.In the third example, primary aromatic amines were oxidized by H2O2 to nitroso compounds in a selenium-catalyzed oxidation. The nitrosoarenes were used in a one-pot hetero Diels-Alder reaction with dienes forming 1,2-oxazines.In the fourth example, a cobalt salophen complex was immobilized in different zeolites. The catalyst was used in aerobic oxidation of p-hydroquinone and the zeolite catalyst could be reused. The oxidative carbocyclization of ene-allenes was tested successfully using the triple catalytic system consisting of palladium(II), p-benzoquinone, and the immobilized catalyst for O2 activation.All these systems gave mild and selective oxidations with environmentally friendly and inexpensive terminal oxidants.
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- Nilsson, Peter, 1971-
(författare)
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Selectivity in Palladium- and Enzyme-Catalyzed Reactions : Focusing on Enhancement of Reactivity
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Catalysis has a profound impact on all living species on the earth. Nature’s catalysts, the enzymes, have the ability to selectively promote a specific bio-chemical transformation, given the required substrate. As well as being highly selective, enzymes enhance the speed of these reactions, helping them to run at temperatures much lower than normally required, i.e. at body temperature. In comparison, reactions used in the production of new materials such as polymers, medicines, fragrances, petrochemicals, etc. are often catalyzed by transition metals. This thesis describes how the selectivity and activity of these catalysts can be influenced via two conceptually different methods: chelation control and microwave heating. The thesis primarily focuses on regio- and stereochemical aspects of the palladium-catalyzed arylation of olefins, i.e. the Heck reaction. Reaction rate enhancement of both palladium and enzyme (polymerase chain reaction [PCR]) catalysis by microwave heating is also discussed. Novel chelation-controlled palladium-catalyzed multi- and asymmetric arylations of vinyl ethers were performed, resulting in tetra-substituted olefins as well as chiral quaternary carbon centers with excellent optical purity. In addition, a new synthetic route to diarylated ethanals, relying on a double chelation-controlled regioselective arylation followed by hydrolysis, has been discovered. High temperature conditions, using microwave heating, substantially reduce the reaction time for ligand-controlled asymmetric Heck arylations, while retaining levels of enantioselectivity in most cases. In addition, a potentially useful fast synthetic protocol for the employment of aryl boronic acids in oxidative Heck arylation was developed. Finally, microwave-assisted PCR was described for the first time; this method allows reductions in the run time of 50%.
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- Yang, Bin, 1987-
(författare)
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Catalytic Stereoselective Formation of C–O, C–C and C–B Bonds : A Voyage from Asymmetric Reactions Enabled by Lipases to Stereoselective Palladium-Catalyzed Oxidative Transformations of Enallenes
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis has been focused on enzymatic kinetic resolutions and stereoselective oxidative transformations of enallenes catalyzed by PdII.In the first part of the thesis, a detailed discussion on Candida antarctica lipase B (CALB)-catalyzed kinetic resolution (KR) of δ-functionalized alkan-2-acetates is shown. We gained a deeper insight into the mechanism of enzyme-substrate recognition. Changing from an anhydrous solvent to water or a water-containing organic solvent enhanced the enantioselectivity. The effect of –OH was also confirmed by a lipase mutant suggesting that the water molecule mentioned above can be partly mimicked.In the second part of the thesis, we developed an efficient KR for allenic alcohols. On this basis, a novel synthesis of optically pure 2-substituted 2,3-dihydrofurans from allenic alcohols via a Ru-catalyzed cycloisomerization was reported. The developed protocol enabled us to assemble an optically pure precursor for total synthesis with three chiral centers from readily available allenol in 2 days.In the third part, we reported a class of reactions involving C–H cleavage under mild conditions: PdII-catalyzed oxidative transformations of enallenes. These reactions are particularly attractive since a number of meticulous structures have been achieved from readily accessible starting materials. The directing effect of an unsaturated hydrocarbon was found to be key for these transformations.In the final part, we developed the carbonylative insertion reaction discussed in the third part of the thesis into an asymmetric version. By using this methodology, a number of cyclopentenone compounds were obtained in good to excellent enantioselectivity.
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