The adsorption and the two-dimensional ͑2D͒ ordering of chloro͓subphthalocyaninato͔boron͑III͒ ͑SubPc͒ on Ag͑111͒ has been studied in detail by combined scanning tunneling microscopy and photoelectron spectroscopy at room temperature. SubPc is a polar, highly symmetric molecule, consisting of an extended aromatic system and a central B-Cl bond. When growing on Ag͑111͒ an interesting phase behavior is observed for the first molecular layer of SubPc. At low coverage, below Ϸ0.2 monolayer ͑ML͒, a 2D lattice gas is present, whereas at medium coverage ͑on the order of 0.2-0.5 ML͒, 2D condensed molecular islands are observed in coexistence with the 2D lattice gas. In these condensed islands, the molecules assemble into a well-ordered honeycomb pattern. At higher coverage ͑approximately 0.5-0.9 ML͒ the molecules organize into a 2D hexagonal close-packed ͑hcp͒ pattern, in equilibrium with a dense 2D gas phase. In the honeycomb and in the hcp pattern, individual molecules are imaged with submolecular resolution, giving information on their orientation. For both the honeycomb and hcp patterns, islands with two different orientations of the superstructures with respect to the Ag͑111͒ substrate are observed. In case of the honeycomb pattern, the two superstructures are enantiomorphic. The chirality of these layers originates in the loss of the symmetry of the metal surface upon adsorption of SubPc, while the molecules alone are intrinsically achiral. Based on different photoelectron spectroscopy experiments we conclude that the SubPc molecule is adsorbed on Ag͑111͒ with its Cl atom towards the substrate and that the molecule remains intact. Finally, several aspects of the observed 2D condensed phases and the thermodynamic phase behavior are discussed with respect to the charge distribution and the adsorption physics and chemistry of the SubPc molecules.
[reaction: see text] Peptides containing a secondary amine and a carboxylic acid in a specific orientation to each other are presented as highly efficient catalysts for asymmetric aldol reactions: (1) their activity is considerably higher compared to that of proline, and (2) the enantioselectivity of the peptidic catalysts can be changed from (R)- to (S)-selectivity by simple modifications of the secondary structure.
Enantioselective syntheses O 0031Increased Structural Complexity Leads to Higher Activity: Peptides as Efficient and Versatile Catalysts for Asymmetric Aldol Reactions. -Tripeptides (I) and (II) are significantly more active than proline as catalysts for asymmetric aldol reactions. Equally high catalytic activities are observed with a variety of aldehydes under otherwise identical conditions. Compared to proline, similar yields are obtained using 10 mol% of (I) and only 1 mol% of (II). The catalysts generate aldol products with opposite absolute configurations, thus showing the possibility for tuning the enantioselectivity by simple modifications in the secondary structure. -(KRATTIGER, P.; KOVASY, R.; REVELL, J. D.; IVAN, S.; WENNEMERS*, H.; Org. Lett. 7 (2005) 6, 1101-1103; Dep. Chem., Univ. Basel, CH-4056 Basel, Switz.; Eng.) -R. Steudel 33-030
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