Showing papers by "Dong Wang published in 2004"

Adsorption and coordination of tartaric acid enantiomers on Cu(111) in aqueous solution.

Abstract: Chiral modifiers have gained much attention because they can induce high enantioselectivity on reactive metal surface in heterogeneous enantioselective catalysis. The high enantioselectivity is attributed to that the chirality of modifiers is bestowed onto the metal surface upon adsorption. Much study on the adsorption of modifiers on metal surface has been performed in an ultrahigh vacuum. In this paper, the adsorption of tartaric acid on Cu(111) has been studied by electrochemical scanning tunneling microscopy (STM) in aqueous solution. It is found that (R,R)-tartaric acid and (S,S)-tartaric acid can form a well-ordered adlayer on the Cu(111) surface with a (4 x 4) symmetry. A dimeric structure is proposed in the temporary model from STM observation.

Direct STM Investigation of Cinchona Alkaloid Adsorption on Cu(111)

Abstract: Scanning tunneling microscopy (STM) combined with cyclic voltammetry has been employed to investigate the adsorption of cinchonine on Cu(111). Similar to cinchonidine, cinchonine forms a long-range ordered adlayer with (4 × 4) symmetry on the substrate. The structural details on molecular adsorption were obtained by high-resolution STM images. On the basis of the previous results and obtained STM images, the quinoline ring is proposed to lie parallel to Cu(111) and serve as an anchoring group. The chiral quinuclidine moiety extends out of the surface to facilitate the interaction with the prochiral reactants.

Absolute configuration of monodentate phosphine ligand enantiomers on Cu(111).

Abstract: Scanning tunneling microscopy (STM) has been employed to investigate the chirality of monophosphine compounds that are highly efficient chiral ligands in transition-metal-catalyzed organic transformations. The absolute configuration of 1-(2-diphenyphosphino-1-naphthyl)isoquinoline enantiomers with axial chirality was discriminated directly by the “marker” group, PPh2 substitutes. Although the two enantiomer molecules adsorb on a Cu(111) surface and form well-defined (4 × 4) structures, the positions of PPh2 substitutes in the molecular adlayers are different. The mirror symmetry between two adlayers is demonstrated. On the basis of STM results, structural models are proposed to interpret the chiral adsorption. The results presented here supply a straightforward method for axial chirality analysis in adsorbed adlayers by STM.

Synthesis of enatiomerically enriched β-amino alcohol derivatives via chiral base mediated-asymmetric deprotonation of (benzyl methyl ether) tricarbonylchromium(0) complex and electrophilic trapping with imines:

Abstract: Deprotonation of (benzyl methyl ether)tricarbonylchromium(0) complex 1 by chiral base 2 followed by quenching reaction with imines 3 and subsequent decomplexation give β-amino alcohol derivatives 5...