Activation of COS

When the selectivity of a reaction is controlled by differences in the way molecules are activated on different sites, the probability of the presence of different sites becomes important. An example again can be taken from the activation of CO. For methanation, activation of the CO bond is essential. This will proceed with low barriers at step-edge-type sites. If one is interested in the production of methanol, catalytic surfaces are preferred, which do not allow for easy CO dissociation. This will typically be the case for terrace sites. The selectivity of the reaction to produce methanol will then be given by an expression as in Eq. (1.29a) ... 

Alberto, R. Motterlini, R. Chemistry and biological activities of CO-releasing molecules (CORMs) and transition metal complexes. Dalton Trans., 1651-1660 (2007). 

Figure 2 shows one possible explanation of the CO and C-H activation found in this synthesis. Activation of CO by insertion into the Sm-C... 

Ge, Q., and Neurock, M. 2006. Adsorption and activation of CO over flat and stepped Co surfaces A first principles analysis. J. Phys. Chem. B 110 15368-80. 

Cyanoaminecobaltate(II) catalysts (/, p. 150) were initially studied in relation to the well-known activity of Co(CN)53 (/, p. 106). Use of such catalysts with optically active amines (1,2-propanediamine and N.N-dimethyl-1,2-propanediamine), thought to be bridged in complexes such as [(CN4)Co-amine-Co(CN4)]4 , led to asymmetric hydrogenation of atro-pate [Eq. (55)] to a 7% ee (309). 

Our work on the bifunctional activation of CO insertion was prompted by the thought that strong molecular Lewis acids should be more effective and more general than simple cations. It already had been observed that molecular Lewis acids would promote a molecular Fischer-Tropsch type reaction (5), and that iron diene complexes can be converted to polycyclic ketones by the action of aluminum halides, equation 7,(18), but information on the course of these reactions was sketchy. 

B. Activation of Hydrogen. Activation of hydrogen is clearly as important for the catalytic processes under consideration as the activation of CO. For Co and Mn the hydrogen activation mechanism is the equilibrium ... 

A comparison of the initial rates obtained with various cobalt complexes (Table I) reveals that the chelate complexes of Co(II) are more efficient than the simple salts, the catalytic activity of Co(III) is lower than that of Co(II) and the reaction becomes slower by increasing the number of N atoms in the coordination spheres in both oxidation states. In general, the addition of amine derivatives increased the activity of the catalysts. 

Catalytic Activity of Co(II) and Co(III) Complexes in Autoxidation of DI-ferf-P,UTYI,CATECHOL (52) ... 

Otsuka and coworkers—addition of ligands to Pt and Rh complexes to facilitate water activation. Most researchers in the water-gas shift field focused their research primarily on the activation of CO through coordination that facilitated the nucleophilic attack by OH- or H20. In addition to this, Ostuka and coworkers28,40,47,55,56 added a new approach. It was based on a strategy that induces two-electron transfer from a low valent metal compound to a H20 molecule that leads to a hydrido-hydroxo-metal species, M + H20 <-> MH(OH). In so doing, they predicted that nucleophilic attack by the OH- on the coordinated CO would be more facile relative to the neutral H20 molecule. 

Recent advances include alkyl iodides as substrates that can be activated by metal complexation. Also Jt-allyl "anions", when co-ordinated to palladium, are activated toward attack by nucleophiles. This is very similar to the activation of co-ordinated alkenes and it shows the very high electrophilicity of palladium. The valence state of palladium, and/or the charge on palladium, and therefore also the ligands attached to it are very important ... 

Fig. 21. Influence of thermal activation on the electrocatalytic activity of Co-N4-complexes...

The higher activity of Co-Mo-S supported on carbons may also be due to increased access to the active sites, as it is postulated that the MoS2 slabs... 

Table 1. Catalytic activities of CO, reforming of methane over supported Ni Catalysts3.

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