Rapid screening and combinatorial methods in homogeneous organometallic catalysis

Abstract

Methods are discussed for rapid screening of soluble and polymer-bound homogeneous catalysts for activity. A polymer-bound phosphine library is synthesized, and a modular tridentate pincer CNC bis-carbene Pd complex is described. The possibility of C-bound His in metalloenzymes is raised.Homogeneous catalysis has much to offer Green Chemistry. By allowing reactions to occur at lower temperature and pressure, energy is saved. By enhancing selectivity, waste is avoided. Waste can even be essentially eliminated if catalysis allows atom-economic processes to be used. These are reactions like eq. 1 in which all the atoms of the reagents are incorporated into the product [1,2]. This particular rhodium-catalyzed reaction-the Monsanto Process-is a commercially important route to acetic acid [3]. In contrast, much conventional industrial chemistry still goes via reactions that produce stoichiometric amounts of inorganic salts or tainted water as byproducts. MeOH + CO = MeCOOH(1)For each new application, new homogeneous catalysts may well need to be identified and optimized, then understood mechanistically. Mechanization and computerization, now becoming more readily available and efficient, can help with all these goals. Combinatorial chemistry [4][5][6][7], together with rapid catalyst screening [8,9], has potential value in identification and optimization. The latest methods of computational and theoretical chemistry can give very valuable mechanistic information in ruling out otherwise plausible pathways and predicting structural information for transient species and transition states [10]. Here, we naturally discuss only the title topic, although by doing so we do not intend to detract from the importance of mechanistic understanding.The principles of combinatorial chemistry have been covered in several recent monographs and reviews [11][12][13][14][15][16]. In summary, the concept involves creating a large number of chemically distinct species-called a library-in a controlled way. This library is then assayed by a suitable rapid screening protocol to see if a desired response is elicited. The library members showing a good response, termed "hits", are then analyzed to determine the chemical structure responsible for the desired response.The field has its intellectual roots in an understanding of how the immune system works and in Merrifield's [17] approach to polypeptide synthesis. The immune system has the task of tagging foreign biomolecules to label them for attack. To do this, it creates a library of polypeptides of variable structure, then senses when one of these peptides by chance binds strongly to a foreign target, such as the surface of an invading bacterium, for example. The successful immune system peptide is then synthesized on a large scale to carry out its defense role in the body.

Self-Assembled Complexes of Non-cross-linked Amphiphilic Polymeric Ligands with Inorganic Species: Highly Active and Reusable Solid-Phase Polymeric Catalysts

“…6). PdAS-V 3 assembled from (NH 4 ) 2 PdCl 4 and poly[(N-isopropylacrylamide) 5 -co-diphenylphosphinostyrene] provides recycling system of itself for Mizorogi-Heck reaction. TiSS 4 made from Ti(O-i-Pr) 4 and poly(styryl-linked binaphtholate-co-styrene) promotes an enantioselective carbonyl-ene reaction as a recyclable catalyst.…”

“…[1][2][3][4][5][6][7][8][9] The simple recovery of catalysts by filtration and their reuses resulted in enhancing the economical evaluation of the reaction. At the same time, there is a prospect that the environmental pollution caused by residual metals in the waste fluid will be decreased.…”

“…In this review, I describe the development of self-assembled catalysts PWAA (poly{PW 12 O 40 3Ϫ [(N-isopropylacrylamide)-co-(acrylamide with ammonium salt)] 3 }) (1), PdAS (poly{PdCl 2 [(N-isopropylacrylamide) 10 -co-diphenylphosphinostyrene] 2 }) (2), PdAS-V (poly{PdCl 2 [(N-isopropylacrylamide) 5 -co-diphenylphosphinostyrene] 2 }) (3), and TiSS (poly(Ti styryl-linked binaphtholate-co-styrene)) (4) prepared from metal ions and non-cross-linked amphiphilic (except 4) polymers, and their application to the heterogeneous organic synthetic reactions. These catalysts showed outstanding stability in any reaction media such as water, aqueous or anhydrous organic solvents and was reused as follows.…”

Crossing the divide between homogeneous and heterogeneous catalysis in water oxidation

“…Research in heterogeneous catalysis continues to flourish (9-15) but iterative design and modification are restricted by limitations in materials preparation and experimental access to surface mechanisms. By contrast, synthetic modification of molecular catalysts is possible by readily available routes; a variety of experimental techniques is available for monitoring rates and mechanism in solution for the investigation of homogeneous catalysis (16)(17)(18)(19)(20)(21)(22)(23). Transferring this knowledge and the reactivity of homogeneous molecular catalysts to a surface could open the door to heterogeneous applications in fuel cells, dye sensitized photoelectrochemical cells, and multiphase industrial reactions.…”

Solid-phase synthesis of chiral 3,4-diazaphospholanes and their application to catalytic asymmetric allylic alkylation

“…9-13) of phosphine ligands is a recent phenomenon (14)(15)(16)(17)(18)(19)(20)(21)(22)(23) natorial synthesis of achiral phosphine ligand collections have been reported by LaPointe (14) and by Portnoy and coworkers (16). Most relevant to this work, Gilbertson's group has pioneered the synthesis of phosphinated polypeptides (20)(21)(22), both in solution and in the solid phase, based on unnatural phosphinefunctionalized amino acids.…”