Reaction classification insertion reactions

Three prominent types of reactions fall in this classification cyclizations by condensation, metal-mediated cyclizations and nitrenoid insertion reactions. 

The mechanistic conclusions may be summarized as follows, reference being made to the classification of processes at the beginning of Section X,A,1. The basic reactions are five heterolytic dissociative adsorptions and one reaction analogous to a ligand insertion reaction. The first five reactions below represent reaction of Cr3+(cus) + 02 (cus) with deuterium or a hydrocarbon. 

The la type classification also applies to a group of reactions attributable to nitrene or related (nitrenoid) intermediates. Although not as prominent as carbonyl condensation reactions, these reactions are especially useful for carbazole synthesis. These are formally insertion reactions but mechanistic scrutiny frequently reveals that the reactions are more complicated than a one step insertion process (Scheme 29). 

While major advances in the area of C-H functionalization have been made with catalysts based on rare and expensive transition metals such as rhodium, palladium, ruthenium, and iridium [7], increasing interest in the sustainability aspect of catalysis has stimulated researchers toward the development of alternative catalysts based on naturally abundant first-row transition metals including cobalt [8]. As such, a growing number of cobalt-catalyzed C-H functionalization reactions, including those for heterocycle synthesis, have been reported over the last several years to date (early 2015) [9]. The purpose of this chapter is to provide an overview of such recent advancements with classification according to the nature of the catalytically active cobalt species involved in the C-H activation event. Besides inner-sphere C-H activation reactions catalyzed by low-valent and high-valent cobalt complexes, nitrene and carbene C-H insertion reactions promoted by cobalt(II)-porphyrin metalloradical catalysts are also discussed. 

Figure 2.1 Classification of electrochemical electron transfer reaction on metal electrodes. (See color insert.)...

In the present chapter, a classification of the hydrogenation reaction mechanisms according to the necessity (or not) of the coordination of the substrate to the catalyst is presented. These mechanisms are mainly classified between inner-sphere and outer-sphere mechanisms. In turns, the inner-sphere mechanisms can be divided in insertion and Meerweein-Ponndorf-Verley (MPV) mechanisms. Most of the hydrogenation reactions are classified within the insertion mechanism. The outer-sphere mechanisms are divided in bifunctional and ionic mechanisms. Their common characteristic is that the hydrogenation takes place by the addition of H+ and H- counterparts. The main difference is that for the former the transfer takes place simultaneously, whereas for the latter the hydrogen transfer is stepwise. 

All of the proposed phase behavior classification schemes describe liquids and gases. However, many of the systems related to reactions in SCFs involve solids, e.g., the reactant and especially the catalyst may be solid. One could imagine the added complexity of inserting solid-phase transitions into just the six types. 

FIGURE 9.5 Classification of the structure dependence of catalytic reactions. In each case, the transition state scaling lines for activation and removal are shown for two different sites. Below the transition state scaling fines, the resulting volcano types are shown. Case 1 both activation and removal exhibit structural dependence. Case 2 activation is independent of structure, but removal shows structural dependence. Case 3 activation is structure dependent but removal is not. Case 4 neither activation nor removal shows structural dependence. Adapted from Nprskov et al. (2008). (See insert for color representation of the figure.)... 

As discussed above, the mechanism of reaction can be classified into two general categories which we have designated as "insertion and "abstraction". The classification is a purely geometrical one... 

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