|
Catalysis at Self-Assembled Monolayers
Chiral rhodium diphosphine complexes have been incorporated into self assembled thiolate monolayers
(SAMs) on gold colloids. Catalysts of this type are of interest because they combine properties of
homogeneous and heterogeneous systems. In addition, it should be possible to influence the catalytic
properties of the metal center by the neighboring thiolate molecules.
Colloids with a diameter of ca. 3 nm, coated with a mixed monolayer of n octanethiolates and thiolates
with chiral rhodium PYRPHOS end groups were studied as hydrogenation catalysts (Figure 1). With methyl
a acetamido cinnamate as substrate, virtually the same enantioselectivities (up to 93% ee) and full
conversion were obtained as with the corresponding homogeneous [Rh(COD)(PYRPHOS)]BArF catalyst. The
colloids were easily recovered by filtration and reused as catalysts three times without loss of
enantioselectivity.
STM studies of analogous SAMs on Au(111) gave a detailed picture of the structure and dynamics of
mixed monolayers of this type (Figure 2). The STM images showed that the catalyst bearing thiolates
are distributed statistically on the surface and that the ordered structure of the n octanethiolate
SAM can be retained during incorporation of the catalyst bearing thiols using the place exchange methodology.
Figure 1
Figure 2: STM-Image of ligands 8 embedded in a n-octanethiolate monolayer on Au(111) in
which the ligands appear as protrusions.
Immobilization of Rhodium Complexes at Thiolate Monolayers on Gold Surfaces: Catalytic and Structural Studies
Thomas Belser, Meike Stöhr and Andreas Pfaltz
J. AM. CHEM. SOC. 2005, 127, 8720-8731
Contact:
Andreas Pfaltz |
|
|
 |
|
|
Department of Chemistry
University of Basel
Switzerland
|
|
