Selective hybrid catalysts

Selective Hybrid Catalysts Based on Nucleic Acids... 

Moreau J. J.E., Wong Chi Han M. The design of selective catalysts from hybrid silica-based materials. Coordin. Chem. Rev. 1998 178 1073-1084... 

Metalloporphyrinosilicas as a new class of hybrid organic-inorganic materials were prepared by polymerization of 3- er -butyl-5-vinylsalicylaldehyde with styrene and divinylbenzene and used as selective biomimetic oxidation catalyst.27 Synthesis and structural characterization of rare-earth bisfdimethyl-silyl)amides and their surface organometallic chemistry on mesoporous silicate MCM-41 have been reported.28... 

The description of pure quantum mechanics (QM) methods presented in Section 3 has shown how in most cases they provide an accurate description of the electronic subtleties involved at the transition metal center of a catalytic process, but that they are unable to introduce the whole bulk of the catalyst substituents, which can be critical for selectivity issues. The description of pure molecular mechanics (MM) methods presented in subsection 4.1 has shown how these methods can easily introduce the steric bulk of the substituents, and accurately describe their steric interactions, but that they struggle badly when trying to describe properly the transition metal center and its immediate environment. The logical solution to this complementary limitations is to divide the chemical system in two regions, and to use a different description for each of them, QM for the metal and its environment, MM for the rest of the system. This is precisely the basic idea of hybrid quantum mechanics / molecular mechanics (QM/MM) methods. 

Tab. 15.3 Selected examples for nanocarbon-inorganic hybrid catalysts.

He got a Habilitation a diriger les recherches in 2008 and he is now developing his own project that consists of the elaboration of new hybrid metalloprotein catalysts for selective oxidation reactions, by insertion of metal cofactors into xylanases. He then studies their peroxidase, catalase, and monooxygenase activities, in particular in the selective oxidation of sulfides, alkanes, and alkenes. 

Elaboration of new hybrid metalloproteins catalysts for selective oxidation reactions. 

The perfluoroacetamide catalysts, rhodium(II) trifluoroacetamidate [Rh2(tfm)4] and rhodium(II) perfluorobutyramidate [Rh2(pfbm)4], are interesting hybrid molecules that combine the features of the amidate and perfluorinated ligands. In early studies, these catalysts were shown to prefer insertion over cycloaddition [30]. They also demonstrated a preference for oxindole formation via aromatic C-H insertion [31], even over other potential reactions [86]. In still another example, rhodium(II) perfluorobutyramidate showed a preference for aromatic C-H insertion over pyridinium ylide formation, in the synthesis of an indole nucleus [32]. Despite this demonstrated propensity for aromatic insertion, the perfluorobutyramidate was shown to be an efficient catalyst for the generation of isomtinchnones [33]. The chemoselectivity of this catalyst was further demonstrated in the cycloaddition with ethyl vinyl ethers [87] and its application to diversity-oriented synthesis [88]. However, it was demonstrated that while diazo imides do form isomtinchnones under these conditions, the selectivity was completely reversed from that observed with rhodium(II) acetate [89, 90]. 

Isoalkanes can also be synthesized by using two-component catalyst systems composed of a Fischer-Tropsch catalyst and an acidic catalyst. Ruthenium-exchanged alkali zeolites288 289 and a hybrid catalyst290 (a mixture of RuNaY zeolite and sulfated zirconia) allow enhanced isoalkane production. On the latter catalyst 91% isobutane in the C4 fraction and 83% isopentane in the C5 fraction were produced. The shift of selectivity toward the formation of isoalkanes is attributed to the secondary, acid-catalyzed transformations on the acidic catalyst component of primary olefinic (Fischer-Tropsch) products. 

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