Catalyst combinatorial chemistry complexes

Immobilized catalysts on solid supports inherently have benefits because of their easy separation from the products and the possibility of recycling. They are also expected to be useful for combinatorial chemistry and high-throughput experimentation. The polystyrene-bound BINAP/DPEN-Ru complex (beads) in the presence of (CH3)3COK catalyzes the hydrogenation of l -acetonaphthone with an SCR of 12 300 in a 2-propanol-DMF mixture (1 1, v/v) to afford the chiral alcohol in 97% ee (Fig. 32.35) [113]. This supported complex is separable... 

Adsorption on silica gel surfaces or silica gels coated with water or thin layers of ionic liquids has been used to immobilize transition metal complexes % ionic interactions and hydrogen bonding. Reversed-phase silica gels were used to retain catalysts by hydrophobic interactions. Support of catalysts on fluorous reversed-phase silica gel by the solvophobic nature of perfluoroalkyl chains is a new and promising approach with potential in catalysis and combinatorial chemistry. 

As carbene complexes have become proficient catalysts, their incorporation into recyclable catalyst systems has grown into a field of its own. The most common strategy for recovering a catalyst for subsequent use is to append it to a heterogeneous support (e.g., a PS bead), and both Fischer carbenes and NHCs have been incorporated into polymers for this purpose. The first polymer-bound Fischer carbene complexes were reported by Mariorana and Seneci in 1999 [51], for use in soHd-phase organic synthesis for combinatorial chemistry. These materials were prepared via the attachment of chromium carbene complexes to a polymer resin... 

Another synthetic area which has experienced the advantageous introduction of sol-gel encapsulation is that of combinatorial chemistry. The recently developed combinatorial approach to many complex synthetic efforts may benefit from sol-gel encapsulation in so-called one-pot reactions. Different reagents such as multiple catalysts may be encapsulated ( site-isolated ) in a sol-gel matrix, thereby offering the possibility of performing two or more successive or simultaneous reactions in a single vessel. One-pot synthesis may result in more sustainable synthetic routes as long as catalyst selectivity can be maintained at a level sufficient to allow good control over the succession of the different reactions [105]. 

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