Immobilization of Rhodium Complexes at Thiolate Monolayers on Gold Surfaces:  Catalytic and Structural Studies

• Published in: Journal of the American Chemical Society Vol. 127; no. 24; pp. 8720 - 8731
• Main Authors: Belser, Thomas, Stöhr, Meike, Pfaltz, Andreas
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 22-06-2005
• Subjects: Chemistry; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; General and physical chemistry; Physics; Solid-fluid interfaces; Solid-liquid interface; Surface physical chemistry; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Atomic force microscopy; Gold; Liquid solid interface; Catalyst selectivity; Organic ligand; Crystal face; Transition metal Complexes; Exchange reaction; Surface topography; Experimental study; Surface structure; Mixed monolayer; Scanning tunneling microscopy; Rhodium Complexes; Complexes Mixed; Ditertiary phosphine; Platinoid Complexes; Catalyst activity
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0500714

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. With methyl α-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. 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.