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The term quasi-homogeneous (it is also known as colloidal or soluble heterogeneous or soluble hybrid heterogeneous-homogeneous) was introduced first by Schmid [105]. It means that the catalyst forms the same (homogeneous) phase with the reaction mixture i.e. it is soluble in the used solvent however catalyst is not consisting of molecules or complexes like e.g. mentioned above binap-Ru catalyst is. The quasi-homogeneous catalysis consists of small particles (generally few nm in size) which are soluble since their surface is modified by a specific ligand. Colloidal catalysts are of interest for two reasons. Firstly the support effect is eliminated and secondly, it is possible to better control the morphology (size and shape) of the metal particles compared to classical supported catalysts. Among several studies, where Pt and other colloids were used for the cinchonidine-modified hydrogenation of pyruvates, diketones [106-112] and trifluoroacetophenone [113] we would like to mark the works of Bönneman [114, 115] since in his work dihydrocinchonidine was used as chiral modifier and stabilizer, simultaneously, that has allowed to investigate this system and compare with conventional supported Pt catalysts. Others interesting works [106, 116, 117] where Pt colloidal catalyst stabilized by PVP (poly-N-vinyl-2- pyrrolidone) (about stabilization see the next chapter) demonstrated the maximum obtained 98 % ee in methyl pyruvate hydrogenation. Very recently Pd colloids modified with specific chiral ligands demonstrated up to 98 % of ee in allylic alkylation reaction [118]. Similar rate acceleration [109] and solvent effect [106] which are known for conventional Pt/Al 2 O 3 were observed for colloidal systems. The very interesting questions arise, wherever the size of Pt nanoparticles influence on ee or not and how adsorption of cinchonidine on small ~1-2 nm nanoparticles is different from adsorption of big macroscopic Pt support (plane). Thus, in the current thesis these questions will be under focus of our attention. 17
Chapter 2 Introduction to the nanoscale materials 2.1 General information and definitions Introduction Colloidal metal (originally called "sols") particles are known at lease since work [119] of Hans Heinrich Helcher (1718) about gold colloids. In the Middle Ages glass-blower workers used gold and other metals in colloidal form in order to make coloured glass (Fig. 2-1) which were used e.g. as stained-glass window in churches or as service dishes. In 1857, Faraday reported the formation of deep red solutions of colloidal Au by reduction of an aqueous solution of AuCl 4 using phosphorus in CS 2 (a two-phase system) in a well-known work [120]. Fig. 2-1. Red coloured glass based on gold colloids. Both pictures were found via google.com Now the field of nanomaterials is booming with scientific investigations and application of the different areas of technology. In fact, for example the catalytic properties and the electronic structure of the nanomaterials can be considered from changing the cluster size, composition and structure [121, 122]. Herein, we will provide an overview of colloidal methods and properties as well as the approaches being used to bridge the fields of nanotechnology and catalysis. In our opinion, it is better to start acquaintance with nanomaterials from definitions developed by Schmid (Table 2-1) [123] as well standardized by IUPAC [124]. Classification Nanoparticles are constituted of several tens or hundreds of atoms or molecules and can have a variety of sizes and morphologies (amorphous, crystalline, spherical, needles, etc.). According to the IUPAC definition the term colloidal refers to a state of subdivision, implying that the molecules or polymolecular particles dispersed in a medium have at least in one direction a dimension, roughly between 1 nm and 1µm, or that in a system discontinuities are found at distances of that order [124]. Table 2-1. Classification of nanoscale materials. 18
Page 1 and 2: Preparation and Characterization of
Page 3 and 4: 5.4 Summary 66 Chapter 6 Cinchonidi
Page 5 and 6: Abstract Studies of the interaction
Page 7 and 8: many compounds are biologically act
Page 9 and 10: Fig. 1-7. Hexahelicene [3]. 7. Chir
Page 11 and 12: R H COOH C OH CH 3 H COO - Bricine-
Page 13 and 14: Catalyst activity, expressed in the
Page 15 and 16: In fact, there are only two heterog
Page 17 and 18: similar way as relative abundance o
Page 19 and 20: surface concentration of cinchonidi
Page 21: site on Pt surface formed by a adso
Page 25 and 26: Triangular prism 5 4 Comments: A -
Page 27 and 28: precursors and building-up. This me
Page 29 and 30: 2.3 Preparation of nanoclusters on
Page 31 and 32: Paris Marseille Ljubljana Synphos Q
Page 33 and 34: Chapter 4 Cinchonidine modified Pt
Page 35 and 36: dihydrocinchonidine (355 mg or 1.2
Page 37 and 38: Table 4-1. Comparison between 5 % P
Page 39 and 40: widening can be used in estimation
Page 41 and 42: 1 Absorbance 0.1 2 1600 1400 1200 1
Page 43 and 44: the focus of these prior experiment
Page 45 and 46: Fig. 4-11. Tilted adsorbed cinchoni
Page 47 and 48: sci., QL. comp. 768 (str) 756 (str)
Page 49 and 50: Conversion, % 100 80 60 40 ITP time
Page 51 and 52: 6A c 10 19.5 B, 20 61 0 3 0.18 0.51
Page 53 and 54: pressure, exposing time, cinchonidi
Page 55 and 56: Fig. 4-16. Linear relationship betw
Page 57 and 58: 1 , 1209 cm -1 and 1382 cm -1 remai
Page 59 and 60: Our results are in line with previo
Page 61 and 62: eaction. The stability of the catal
Page 63 and 64: Table 5-1. Ee and reaction rate ind
Page 65 and 66: Enantiomeric excess, % 85 80 75 A2
Page 67 and 68: 35 30 Before After Percent of parti
Page 69 and 70: catalyst activation seems to indica
Page 71 and 72: Table 5-3. Assignment of some vibra
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6.2 Experimental Materials Cinchoni
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Fig. 6-3. TEM image of cinchonidine
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From the results of EP and EB hydro
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enhancement. However the exact fact
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Further, this family of man-made li
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Fig. 7-2. TEM of quiphos modified P
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of quiphos adsorbed on Pt and Pd an
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Fig. 7-8 Flat adsorbed quiphos via
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comp., H 11,12,13,14 2 C b., 2 P 11
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Chapter 8 “Quiphos-spider” modi
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flat crystal surface due to the hig
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Chapter 9 Diphos and diop modified
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Table 9-1. Average crystal size of
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Fig. 9-4. Conformation of diphos mo
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ings. Due to these reasons we can n
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Fig. 9-9. Proposed orientation of a
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The model of adsorption of diop on
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The calculation of energy of formin
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For the preparation of synphos modi
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1 2 20 40 60 80 2Θ Fig. 10-3. XRD
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The DRIFT spectra of synphos (Fig.
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peaks which can be used for analysi
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References [1] G.E. Tranter, J. Che
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[64] A. Szabo, N. Kunzle, T. Mallat
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[128] J.D. Aiken III, R.G. Finke, J
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[189] K. Umezawa, T. Ito, M. Asada,
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I declare that the current Ph.D. th
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