Cooperative catalytic systems

Functionalization of the matrix allows incorporation of a variety of catalytic activities into the material. Recently, procedures were developed to add functional groups that are electrostatically or hydrophobically attractive to the ammonium surfactant head groups and are able to compete with silicate anions during self-assembly. This has led to a class of mesoporous materials that are functionalized only on the inside of the pores. Highly selective polymerization and cooperative catalytic systems have been developed from these materials.3 Furthermore, by incorporating caps onto the pores, chemical reagents can be stored in the channels,... 

A further example of a cooperative catalytic system is a bifunctionalized mesoporous silica nanosphere material (MSN) containing the ureidopropyl group (UDP) and 3-[2-(2-aminoethylamino)ethylamino]propyl group (AEP). All catalysts were synthesized by a sol-gel procedure similar to the previously mentioned one by using different AEP/UDP molar ratios. The MSN-AEP/ UDP catalyst was employed for the aldol, Henry and cyanosilylation reactions (Scheme 3.8 R = NO2, R" = H, Schemes 3.35 and 3.36, respectively) and TON values were compared with those observed by using MSN-AEP and MSN-UDP catalysts (Table 3.10). 

Baylis-Hillman reactions. BINOL and a teriary phosphine (e.g., BujP) constitute a cooperative catalytic system to promote the reaction (higher rates and yields). Application to catalytic asymmetric synthesis is indicated. 

In addition to THIQs that could act as the typical substrates for the asymmetric CDC reactions, glycine derivatives were also well tolerated in this kind of transformation. Xie and Huang reported a facile approach to iV-aryl amino acid derivatives via the CDC reactions between Af-substituted glycine esters with unmodified ketones under the cooperative catalytic system consisting of Cu(0Ac)2 H20 and pyrrolidine. TBHP and DDQ were proved to... 

In 2010, Huang and co-workers reported an AFC alkylation of indoles with P-aryl a -hydroxy enones catalyzed by a cooperative catalytic system involving an iron salt and a chiral phosphoric acid (Scheme 6.34). Good to excellent... 

Figure 6.100 Use of the NH bond acidity in a cooperative catalytic system based on a thiourea. ...

Optically active trifluoromethyl-substituted tetrahydroimidazo[l, 5-c] quinazoline derivatives 44 were synthesized by Zhao and coworkers via a diastereo- and enantioselective Mannich-type cyclization cascade reaction of a-aryl isocyanoacetates and trifluoromethyl-substituted cyclic ketimines, using a multihydrogen-bonding donor squaramide/AgOAc cooperative catalytic system in THF at 0°C (Scheme 30) (140L4566). The products were obtained in 76—99% yield with a diastereomeric ratio of greater than 15 1 and 58-98% enantiomeric excess. 

Among all catalysts containing phenol groups, the best results in terms of yields and asymmetric inductions were obtained with molecules containing a binaphthol scaffold. Inspired by the seminal work of Yamada et on the Morita-Baylis-Hillman reaction between cyclic enones and aldehydes promoted by a cooperative catalytic system of tributylphosphine and phenols (including rac-BINOL), McDougal and Schaus reported the first example of an asymmetric Morita-Baylis-Hillman reaction using chiral BINOL and binaphthol derivatives 38 as catalysts, in the presence of triethylphosphine as nucleophilic promoter (Scheme 24.15). 

Recently, we reported on a new cooperative catalytic system comprised of a series of bifunctionalized mesoporous silica nanosphere materials with various relative... 

N. Sakai, N. Uchida, T. Konakahara, Synlett 2008, 1515-1519. Facile and selective synthesis of propargylic amines and 1,6-diynes one-pot three-component coupling reactions of alkynylsilanes, aldehydes and amines by a cooperative catalytic system comprised of CuCl and Cu(OTf)j. 

Although a large number of transformations exist for N-heterocyclic carbene catalysis, until recently there was no knowledge about their compatibility with metals as catalysts and their workability in presence of each other. ° In 2010, Scheidt et al. reported the first enantioselective cooperative catalytic system, consisting of Mg(Ot-Bu)2 and a chiral N-heterocyclic carbene, which was applied in the presence of a base, such as 1,5,7-triaza-bicyclo[4.4.0]dec-5-ene (TBD), to a diastereo- and enantioselective synthesis... 

To resolve this reactivity problem, we explored the possibility of employing a Lewis acid to activate the iV-acyl hydrazone by lowering its LUMO energy (Scheme 22) [145-147]. If successful, such an achievement would expand the possibilities for the development of new NHC reactions. The most important challenge to this idea is the known ability of carbenes to act as ligands and form stable complexes, particularly with late transition metals such as palladium and copper [148-151]. We hypothesized that early metals would react reversibly with NHCs, allowing for the development of a cooperative catalytic system. After... 

Quinazolines have been synthesized by a variety of methods. However, due to the harsh conditions employed in earlier protocols, development of more efficient and environment-friendly methods is in demand. Recently, Kobayashi et al. [56] have developed a methodology based on the application of the cooperative catalytic system of metal nanoclusters (NCs) and catechol derivatives as redox-active organocatalysts for the synthesis of quinazoline derivatives. Here a metalloenzyme-like cooperative catalytic system of heterogeneous bimetallic Pt/Ir alloy NCs were used for the syntiresis of quinazoline derivatives xmder mild conditions (Scheme 36). 

The synthetically useful quinazoline-2-carbaldehyde was prepared and was employed as a useful precursor for the synthesis of symmetric 2,2 - bis-quinazoline using this cooperative catalytic system. Applying the strategy for the synthesis of heterocycles using Pl/CB-Pt catalysts xmder aerobic oxidative conditions, bis-heterocyclic compotmds were obtained in excellent yields (Scheme 37). These compotmds may serve as potentially useful ligands or materials with unique properties. The heterogeneous catalyst was recovered and reused for five times without loss of reactivity and the leaching of the metals. 

H. Yuan, W.-J. Yoo, H. Miyamura, S. Kobayashi, A cooperative catalytic system of platinum/iridium alloyed nanoclusters and a dimeric catechol derivative an efficient synthesis of quinazolines through a sequential aerobic oxidative process, Adv. Synth. Catal. 354 (2012) 2899-2904. 

Aldol condensations are universal reactions in organic chemistry, from the synthesis of small molecules to the well-designed intermediates of drugs. Among the many organocatalysts for aldol condensation that have been developed so far are the aminofunctional group, i-proline, and ILs. lin and coworkers reported a new cooperative catalytic system comprising a series of bifunctionalized... 

The multi-component systems developed quite recently have allowed the efficient metal-catalyzed stereoselective reactions with synthetic potential [75-77]. Multi-components including a catalyst, a co-reductant, and additives cooperate with each other to construct the catalytic systems for efficient reduction. It is essential that the active catalyst is effectively regenerated by redox interaction with the co-reductant. The selection of the co-reductant is important. The oxidized form of the co-reductant should not interfere with, but assist the reduction reaction or at least, be tolerant under the conditions. Additives, which are considered to contribute to the redox cycle directly, possibly facilitate the electron transfer and liberate the catalyst from the reaction adduct. Co-reductants like Al, Zn, and Mg are used in the catalytic reactions, but from the viewpoint of green chemistry, an electron source should be environmentally harmonious, such as H2. 

Selective aromatic functionalization has been a permanent object of research since the ninenteenth century. Catalysis has offered a powerful tool to achieve this goal. Over the years we have worked out a complex catalytic system consisting of an inorganic compound such as a palladium salt and an organic molecule containing a strained double bond such as norbomene (1,2). We have seen that these two catalysts cooperatively react with an aromatic iodide, an alkyl iodide and a terminal olefin. The following equation reports an example (L = solvent and/or olefin) (3). 

Cooperative catalysis between multiple metal centers is considered to be common in enzymatic systems,96 and using this idea for designing catalytic systems... 

During our investigations of the reactions mediated by LASCs, we have found that addition of a small amount of a Bronsted acid dramatically increased the rate of the aldol reaction (Eq. 5).[191 This cooperative effect of a LASC and an added Bronsted acid was also observed in the allylation ofbenzalde-hyde with tetraallyltin in water.1201 Although, from a mechanistic point of view, little is known about the real catalytic function of scandium and proton, this cooperative effect of a Lewis acid and a Bronsted acid provides a new methodology for efficient catalytic systems in synthetic chemistry. 

Catalysts used to convert ethylene to vinyl acetate are closely related to those used to produce acetaldehyde from ethylene. Acetaldehyde was first produced industrially by the hydration of acetylene, but novel catalytic systems developed cooperatively by Farbwerke Hoechst and Wacker-Chemie have been used successfully to oxidize ethylene to acetaldehyde, and this process is now well established (7). However, since the largest use for acetaldehyde is as an intermediate in the production of acetic acid, the recent announcement of new processes for producing acetic acid from methanol and carbon monoxide leads one to speculate as to whether ethylene will continue to be the preferred raw material for acetaldehyde (and acetic acid). 

The combination of surface-associated reactants with surface-bound H-atoms, occasionally leads to poor photoinduced hydrogenation of the reactant and parallelly to inhibition of H2-evolution. For such systems, tailored bifunctional heterogeneous catalysts have been developed [141], where cooperative catalytic effects are observed in the photohydrogenation reactions. Substitution of ethylene by acetylene, C2H2, in the photosystem composed of Ru(bpy) +/MV2+/Na2EDTA and the Pt colloid results in inefficient hydrogenation of acetylene to ethylene,

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We can easily predict that cascade and sequential catalytic reactions will be the subject of important investigations not only by promoting the cooperation of several metal catalysts but also by organizing the tolerance and the cooperative work of metal and organo catalysts, and of metal and enzyme catalysts. This will be possible through a deep understanding of the mechanisms of each catalytic system, so as to organize their mutual tolerance. 

Cooper (145) recently reported the use of dye-containing substrates as screening tools for the rapid evaluation of different catalytic systems. Hydrosilylation was chosen as... 

While it is often reported that, generally, polypropylene produced with any industrial process presents broad MWD (Q = 8-12) with any type of catalytic system, and that in order to obtain a narrow MWD a polymer visbreaking process should be used, studies on the control of MWD by means of high yield catalytic systems are being more and more frequently announced. Such systems, developed by Montedison in cooperation with Mitsui Petrochemical are formed of MgCl -electron donor-TiCl and AIR3. 

Hu et al. developed a system that involved cooperative catalysis by a chiral phosphoric acid and an achiral rhodium complex (Scheme 3.37) [81]. They applied the binary catalytic system to a three component coupling reaction among a diazoesters, primary alcohols, and aldimines. The steric bulkiness of the primary alcohol had a significant effect on both diastereo and enantioselectivities. The sterically demanding 9 anthracenemethanol was the best component to give p amino a alkoxy esters with excellent stereoselectivities under the combined and cooperative catalysis by phosphoric acid ll and the rhodium complex. 

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