1576 (sh) 1567 (med) 1571 (med) 1622 C-Qu. strch., H- Qu. b. 1514 (str) 1507 (str) 1502 (str) 1556 C-Qu. strch., H- Qu. b. 1463 (str) 1452 (str) - 1494 1427 (sh) 1420 (med) 1431 (wk) 1445 15,17,22 CH 2 - QL. sci. 2,3 C strch., C-H-Qu., ip. def., 15 CH 2 , HO 2 C sci., H 2 C b. 1208 (med) 1207 (med) - 1240 C-H-Qu. ip. b., 2,3 C strch., HO, 2 CH b., QL. comp. 1179 (wk) 1180 (wk) - 1223 1168 (wk) 1163 (wk) - 1189 30 H-Qu., 23,24 H b., H- 17 C-Ql. comp. 25,26,30 H- Qu. ip. b., 23,24 H b., QL. comp. 1145 (wk) 1133 (wk) - 1143 H-Qu. ip. b., 23,24 H b., Ql. comp. 1118 (med) 1099 (wk) - 1128 H-Qu. ip. b., O 2 C strch., QL. comp. 856 (med) 862 (wk) - 873 29,10 H-Qu. oop. wag., QL. comp. 831 (med) 823 (med) 807 (str) 843 H-Qu. oop. wag, H 20 2 C sci., QL. Comp. 809 (med) 803 (med) 787 (str) 824 H-Qu. oop. Wag., 40,41 H 20 C sci., QL. comp. 782 (str) 778 (wk) 761 (wk) 791 H-Qu. oop. wag., 40,41 H 20 C Tilted , flat Tilted Tilted Flat Tilted Flat Flat, tilted Flat Flat Flat Flat Flat Flat 41
sci., QL. comp. 768 (str) 756 (str) 740 (str) 775 25,26,27,28 H- Flat Qu. oop. wag. Comments: sh. – shoulder, med. – medium, wk – weak, st. – strong., 15C –carbon atom number 15. Qu – quinoline, QL – quinuclidine. C-Qu. – only carbons in quinoline, H- Qu. – only hydrogens in quinoline, skel. – skeleton, comp. – complex: more then one type <strong>of</strong> vibrations (stretching, wagging, rocking, <strong>and</strong> scissoring) are present, def. – deformation, C-H-QL. – carbons <strong>and</strong> hydrogens in quinuclidine, b. – bending, strch. – stretching, sci. – scissoring, wag. – wagging, ip.- in plane, oop. – out <strong>of</strong> plane vibration. As it is seen from the Table 4-3, cinchonidine on Pt nanoclusters was found in both the ‘flat’ <strong>and</strong> ‘tilted’ adsorption modes. Here, we did not differentiate between the two types <strong>of</strong> tilted adsorption modes, the so called “N-lone pair bonded” <strong>and</strong> “α-H abstracted" because we found assignment <strong>of</strong> the corresponding species is somewhat ambiguous <strong>and</strong> since the flat adsorption mode is more determinant in enantioselective catalysis. It is very important to compare the adsorbed modes <strong>of</strong> cinchonidine on macroscopic <strong>and</strong> nanocluster surfaces <strong>of</strong> Pt. In fact, through comparison <strong>of</strong> IR investigations <strong>of</strong> cinchonidine adsorbed on bulk Pt crystals (ATR, RAIRS) <strong>and</strong> on Pt nanoclusters (DRIFTS) we found no principal difference in the spectra as well in the spectra <strong>of</strong> sample D <strong>and</strong> cinchonidine modified conventional Pt/Al 2 O 3 (the only difference we found was in the quality <strong>of</strong> the spectra). However, in the spectra <strong>of</strong> cinchonidine on Pt nanoclusters small shifts <strong>of</strong> the spectra from free cinchonidine were found <strong>and</strong> between the spectra <strong>of</strong> cinchonidine adsorbed on Pt. For example: in case <strong>of</strong> free cinchonidine, the peak at 1593 cm -1 in work <strong>of</strong> Ferri [76] was observed at 1590 cm -1 in the current thesis <strong>and</strong> 1591 cm -1 in the work <strong>of</strong> Zaera [77]; in case <strong>of</strong> cinchonidine on Pt, the peak at 1458 cm -1 in work <strong>of</strong> Ferri was found at 1463 cm -1 in the current work <strong>and</strong> at 1463 cm -1 in the work <strong>of</strong> Zaera. It seems most likely that these small shifts are due to the role <strong>of</strong> solvents/purity <strong>of</strong> cinchonidine used <strong>and</strong> other secondary effects. Another difference is that the spectra <strong>of</strong> the lig<strong>and</strong>s on nanoclusters contains less noise <strong>and</strong>, mostly, have better quality with respect to the spectra <strong>of</strong> lig<strong>and</strong>s on bulk metal. The reason for this may be due to the high surface area <strong>of</strong> nanoclusters <strong>and</strong> thus higher concentration <strong>of</strong> adsorbed lig<strong>and</strong> in the IR beam. If size <strong>of</strong> the cinchonidine supported Pt nanoclusters (2.3 nm sample D, or 4 nm conventional Pt/Al 2 O 3 ) is bigger than typical size <strong>of</strong> molecule (about 0.5 nm, the length <strong>of</strong> the quinoline anchor), the support can be considered as a plane <strong>and</strong> molecule behaves similarly as to being adsorbed on a continuous surface <strong>of</strong> a (bulk) metal crystal. However, if the size <strong>of</strong> the clusters becomes comparable with the size <strong>of</strong> the molecule, as we have in case <strong>of</strong> cinchonidine on Pt (1.2 nm in sample B) the lig<strong>and</strong> might behave differently (especially in terms <strong>of</strong> enantioselectivity) <strong>and</strong> would be expected to experience less steric hindrance due to the curvature <strong>of</strong> the surface. In fact, Yang <strong>and</strong> co-authors [106] reported enantiomeric excess in hydrogenation <strong>of</strong> methyl pyruvate to be 90 % over 1.2 nm Pt cluster <strong>and</strong> 85 % over 3.4 nm under 40 bar <strong>of</strong> H 2 pressure. They explained this difference as a size effect resulting from cinchonidine <strong>and</strong> methyl pyruvate forming a half-hydrogenated complex which is adsorbed on different crystal faces. However, these authors did not focus on stability <strong>of</strong> Pt nanoclusters during hydrogenation <strong>and</strong> changes in size, especially after removal <strong>of</strong> 42
- Page 1 and 2: Preparation and Characterization of
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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