Catalyst substrate complex, schematic

Figure 10. Schematic of the proposed catalyst-substrate complex, before and in the activated state. The increase of the chain end-to-end distance possibilities is represented by the bases of the cones.

Figure 1.2 Schematic representation of the modes of coordination of the double bond in the catalyst-substrate complexes 9,10,12. (From Gridnev, I. D., /. Synth. Org. Chem. Jpn., 74, 1250-1264,2014. With permission.)...

The schematic phase behaviour of C02 depicted in Figure 8.1 is only valid for the pure compound. The phase behaviour of mixtures is much more complex [6], being a function of composition, and the actual phase diagram can vary considerably even for seemingly similar components. Reaction systems contain at least three substances (substrate, product and catalyst), but in most cases more components are present and a... 

Since poly(S-)ysine) — copper(II) complex at pH = 10.5 assumes aTielical conformation while it is random coiled at pH = 6.9, the selective catalysis towards the entantiomeric substrates is considered to be related to the a-helical conformation of the catalyst. This was confirmed also by the comparison of the oxidation rates of R-DOPA and S-DOPA at varkius temperatures in relation to the a-helical content of the catalyst as obtained by the circular diduroic analysis. From these and other (4>servations (SO), a schematic model of the intermediate of the oxidation reacticm has been proposed (Fig. 8) (SI). In this bifunctional coordination of DOPA, the... 

Figure 9.1b shows a schematic catalytic cycle. The active catalyst, M is often rather unstable and is only formed in situ from the catalyst precursor (or precatalyst), M. If during the reaction we observe the system, for example, by NMR, we normally see only the disappearance of S and the appearance of P. Decreasing the substrate concentration [S] and increasing the metal concentration [M] may allow us to see the complex. We may still see only... 

In Figure 9.2 D, the catalyst binds to the substrate, and the complex is lower in energy than free substrate. In this scenario, however, the binding between the catalyst and transition state is even stronger. Now the activation energy is lowered relative to the uncatalyzed path, and the reaction rate increases. We show this schematically in Figure 9.3 with a binding pocket where more contacts with the catalyst are formed with the transition state than with the substrate or product. 

Figure 9.1 h shows a schematic catalytic cycle. The aclive catalyst M is often rather unstable and is only formed in situ from the catalyst precursor (or precatalyst), M. If during the reaction we observe the system, for example, by NMR, we normally see only the disappearance of S and the appearance of P. Decreasing the substrate concentration [S] and increasing the metal concentration [M] may allow us to see the complex. We may still see only M because only a small fraction of the metal is likely to be on the loop at any given time. Even if an observed species appears to be an intermediate, we still cannot be sure it is not M S, an off-loop species. If a. species builds up steadily during the reaction, it might be a catalyst deactivation product M", in which case the catalytic rate will fall as [M"] rises. Excellent reviews are available on the determination of mechanism in catalytic reactions. ... 

Another example of asymmetric catalysis involving optically active polymers is provided by the work of Plate et al. [89, 90]. They first reported the asymmetric hydrogenation of keto groups of polymeric j3-ketoesters, using nickel catalysts treated with solutions of optically active compounds (such as L-glutamic acid or D-tartaric acid). Although in these examples the catalysts are low molecular weight compounds the catalytic action is ascribed to their complexation with the polymeric substrate. Reactions, usually carried out at 60—80 atm. of H2, at 60—80°C, in methanol, chloroform or dimethyl-formamide, can be shown schematically as follows ... 

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