Catalysis cooperative dual

Since the last decades, chemists have described a huge variety of multi-catalytic systems and cooperative effects [6]. First of all, it has been shown that cooperative effects can appear by combining two catalytic functions within the same molecule (bifunctional catalysis) [7] or in two separate molecules (cooperative dual catalysis) [8,9], Both can participate to the same catalytic cycle by activating together the same substrate (double-activation catalysis) or its own substrate. The two catalytic centers can also activate simultaneously different substrates in two directly coupled catalytic reactions for giving a product (synergistic catalysis) [10]. Tandem reactions have been also described [11, 12]. In that case, the two catalytic centers operate consecutively in two independent catalytic cycles, the second catalytic cycle using the product of the first one as an intermediate and converts it as final product. The second catalytic function may also not interact with the substrates but contributes to the stability of the active metal center and acts as redox partner (restorative catalysis) [8]. 

In a fifth contribution, Pierre Le Gendre et al. review the catalytic performances of early-late bimetallic complexes. After an introduction dealing with bifunctional and cooperative dual catalysis in which the cooperative effects arise from two catalytic functions present in the same or two different molecules, this paper focuses on an inventory of early-late heterobimetallic complexes in catalysis. It includes those where the two metal centers belong to the same complex, with bridging ligands as in the following example in which the chiral information is provided by the titanium metal center ... 

Fig. 13.9 [(salen)AI]20 Complex and (PyBOXJErCE complex for intermolecular cooperative dual catalysis. 

In 2013, Riant et al. developed a novel enantioselective domino conjugate reduction-allylic allylation reaction based on a cooperative dual catalysis involving a chiral copper catalyst and an achiral palladium catalyst. The reaction occurred between cyclic a-substituted a,(3-unsaturated ketones and ally methylcarbonate, providing the corresponding chiral cyclic a-allylic... 

In order to extend this chemistry for the synthesis of other types of indoles besides 2-alkylindoles, the same group disclosed an efficient synthesis of N-protected indoles 48 fromiV-arylhydroxamic acidsW-aryl-Af-hydroxycarbamates 47 and a variety of alkynes via gold and zinc cooperative catalysis (Scheme 12.23) [27]. They found that catalytic Zn(OTf)2 enhances the nucleophilicity of these hydroxylamine derivatives via the formation of deprotonated chelates, which is similar to the metal ion catalysis in metalloenzymes. This chemistry is a rare example of cooperative dual catalysis involving gold catalyst. 

Are heterogeneous catalysts appropriate platforms to construct cooperativity Cooperative catalysis can occm in homogeneous catalysis. For example, Kanemasa and Ito [3] have reported a two-catalyst system that leads to the dual activation of an electrophile and a nucleophile by a Lewis acid and amine base, respectively. 

Abstract By combining an ever-increasing number of catalysts or catalytic functions, cooperative catalysis is a research area that grows fast. In the field, early-late heterobimetallic complexes are rather old objects but they still continue to fasdnate chemists because of their latent reactivity. After a brief and ccaicise overview of cooperative catalysis, this review focuses on early-late heterobimetallic complexes that were used in catalysis over the last decades. Examples of dual catalysis using early and late metal partners are also described. This chapter ends with an opening towards therapeutic applications of early-late heterobimetallic complexes. 

Keywords Bifunctional catalysis Bimetallic complexes Cooperative catalysis Dual catalysis Early-late heterobimetallic complexes... 

NHCs are also regarded as good candidates to promote organic transformations via cooperative or dual catalysis. In this way, a dual secondary amine/NHC catalytic system has been developed for the formation of highly functionalized cyclopentanones... 

By taking advantage of the (salen)AlCl complex s ability to activate imide and of the lanthanide-PyBOX complex s ability to activate cyanide, intermolecular heterobimetallic dual cooperative catalysis was investigated. The dual catalyst system, that is, the combination of bench-stable (S,S)-[(salen)Al]20 complex and (S,S)-ErCl3-PyBOX complex, afforded distinctly superior results compared with (salen)AlCl complex alone (Table 13.33) [105]. Reaction times (from 26-48 to 8-14 hours), the amount of TMSCN (from 2.5-4 equiv to 2 equiv), and total catalyst loading (f rom 10 to 15 mol% to 7 mol%) decreased significantly. Reaction proceeded... 

A simple and practical method for the one-pot synthesis of nitroalkenes has been developed using a cooperative catalysis system involving piperidine and iron(III) chloride. This dual catalytic protocol simultaneously activates both electrophile and nucleophile. 

In the same year, Xu et al developed an efficient example of asymmetric cooperative catalysis applied to a domino oxa-Michael-Mannich reaction of salicylaldehydes with cyclohexenones. The proeess was eatalysed by a combination of two chiral catalysts, such as a chiral pyrrolidine and amino acid D-tert-leucine. The authors assumed that there was protonation of the aromatic nitrogen atom of the pyrrolidine catalyst by u-te/t-leucine, which spontaneously led to the corresponding ion-pair assembly (Scheme 2.6). This self-assembled catalyst possessed dual activation centres, enabling the catalysis of the electrophilic and nucleophilic substrates simultaneously. The domino oxa-Michael-Mannich reaction provided a range of versatile chiral tetrahydroxanthenones in high yields and high to excellent enantioselectivities of up to 98% ee, as shown in Scheme 2.6. 

---