Synthèse critique de la caractérisation électrochimique de zéolithes et d'aluminophosphates chimiquement modifiés

1998 ◽  
Vol 76 (12) ◽  
pp. 1886-1909 ◽  
Author(s):  
Lionel Roué ◽  
Emmanuel Briot ◽  
Fethi Bedioui
Keyword(s):  
Transition Metal ◽  
Transition Metal Complexes ◽  
Molecular Sieves ◽  
Inorganic Compounds ◽  
Electrochemical Process ◽  
Porous Network ◽  
Chemically Modified ◽  
Framework Species ◽  
Dimerization Process ◽  
Electrolyte Effects

Zeolites that have been chemically modified by incorporating transition metal complexes in their porous network and molecular sieves chemically modified by incorporating transition metal in their framework have led to numerous applications of which the most widespread is undoubtfully catalysis. However, the catalytic activity of these inorganic compounds is still not well understood and there is a lack of evidence concerning the encapsulation efficiency of complexes within the zeolites and the location of transition metals inside the framework of molecular sieves. Numerous studies have shown that zeolite encapsulation has an influence on the redox behaviour of these complexes, such as in preventing aggregation or the dimerization process. Moreover, analysis of the electrochemical process at this type of modified electrode demonstrates solvant and electrolyte effects on the electroactivity of the encapsulated complexes. However, these different studies highlighted the unsatisfactory electrochemical accessibility of intrazeolitic or framework species. Thus, we undertake here a discussion of the different strategies reported in the literature aimed at promoting the electroactivity of these molecular materials.

C-Methylation Of Organic Substrates: A Comprehensive Overview. Part Ii. Methanol As Methylating Agent. A Case Of Catalysis Versatility

2020 ◽  
Vol 17 ◽  
Author(s):  
Saad Moulay
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Molecular Sieves ◽  
Acid Sites ◽  
Lewis Base ◽  
Molar Ratio ◽  
Organic Substrates ◽  
Solid Catalysts ◽  
The Impact

: The present account surveys the results of the myriad of works on C-methylation of organic substrates with methanol as an eco-friendly methylating agent. The innumerable reports on this issue reveal the widespread use of a set of solid catalysts such as molecular sieves, zeolites, metal phosphates, metal oxides and transition metal complexes, to accomplish such methylation. One related facet was the impact of the numbers of Brønstëd acid sites, of Lewis acid sites, and of Lewis base sites present in solid catalysts, such as zeolites, their ratios, and their strengths that affect the distribution of the methylation products and their selectivities. Also, specific surface area and porosity for some solid catalysts such as zeolites play additional roles in the overall reaction. Not only these properties of a catalyst that influence the methylation outcome but also the temperature, space velocity (WHSV, LHSV, GSHV), weight of catalyst per reactant flow rate (W/F), time of stream (TOS), and methanol/substrate molar ratio. The treated substrates herein discussed were aromatic hydrocarbons (benzene, biphenyls, naphthalenes, toluene, xylenes), alkenes, phenolics (phenol, cresols, anisole), N-heteroarenes, carbonyls, alcohols, and nitriles. Methylation of benzene affords not only toluene as main product but also polymethylated benzenes (xylenes, pseudocumene, hexamethylenebenzene, and also ethylbenzene as a sidechain product). Also, toluene is sensitive to the reaction conditions, giving rising to ring methylation and to sidechain one (ethylbenzene and styrene), besides the formation of benzene as a disproportionation product. Wealth of results from the methylation of phenolic compounds bears witness to the interest of different investigators in this special research. As to these phenolics, concurrent O-methylation inevitably parallels the C-methylation, and the selectivity of the latter one remains depended on the above-cited factors; ortho-cresol and 2,6-xylenol have been the main C-ring methylated phenols. Methylation of olefins with methanol over solid catalysts, leading to higher olefins, is of a great interest. The chemistry involved in the methylation of N-heteroarenes such as pyridines, indoles, and pyrroles is significant. Application of the methylation protocols, using methanol as a reagent and transition metal complexes as catalysts, to ketones, esters, aldehydes, nitriles, and alcohols, ends up with some important molecules such as acrylonitrile (a monomer) and isobutanol (a biofuel).

C-methylation of organic substrates: A comprehensive overview. Part iiia. Methanol as a methylating agent. A case of catalysis versatility

2021 ◽  
Vol 18 ◽  
Author(s):  
Saad Moulay
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Molecular Sieves ◽  
Acid Sites ◽  
Lewis Base ◽  
Side Chain ◽  
Organic Substrates ◽  
Solid Catalysts ◽  
The Impact

: The present account surveys the results of the myriad of works on the C-methylation of organic substrates with methanol as an eco-friendly methylating agent. The innumerable reports on this issue reveal the widespread use of a set of solid catalysts such as molecular sieves, zeolites, metal phosphates, metal oxides and transition metal complexes to accomplish such methylation. One related facet was the impact of the numbers of Brønstëd acid sites, Lewis acid sites, and Lewis base sites present in solid catalysts, such as zeolites, ratios, and strengths that affect the distribution of the methylation products and their selectivities. Moreover, specific surface area and porosity for some solid catalysts, such as zeolites, play additional roles in the overall reaction. Not only do these catalyst properties influence the methylation outcome, but the temperature, space velocity (WHSV, LHSV, GSHV), weight of catalyst per reactant flow rate (W/F), time of stream (TOS), and methanol/substrate molar ratio also do. The treated substrates herein discussed were aromatic hydrocarbons (benzene, biphenyls, naphthalenes, toluene, xylenes), alkenes, phenolics (phenol, cresols, anisole), N-heteroarenes, carbonyls, alcohols, and nitriles. Methylation of benzene affords not only toluene as the main product but also polymethylated benzenes (xylenes, pseudocumene, hexamethylenebenzene, and also ethylbenzene as a side-chain product). Furthermore, toluene is sensitive to the reaction conditions, giving rise to ring methylation and side-chain one (ethylbenzene and styrene), besides the formation of benzene as a disproportionation product. A number of results from the methylation of phenolic compounds bear witness to the interest of different investigators in this special research. As to these phenolics, concurrent O-methylation inevitably parallels the C-methylation, and the selectivity of the latter one remains dependent on the above-cited factors; ortho-cresol and 2,6-xylenol have been the main C-ring methylated phenols. Methylation of olefins with methanol over solid catalysts, leading to higher olefins, is of great interest. The chemistry involved in the methylation of N-heteroarenes, such as pyridines, indoles, and pyrroles, is significant. Application of the methylation protocols, using methanol as a reagent and transition metal complexes as catalysts to ketones, esters, aldehydes, nitriles, and alcohols, ends up with some important molecules such as acrylonitrile (a monomer) and isobutanol (a biofuel).

Mechanochemical changes on cyclometalated Ir(iii) acyclic carbene complexes – design and tuning of luminescent mechanochromic transition metal complexes

2020 ◽  
Vol 7 (3) ◽  
pp. 786-794 ◽  
Author(s):  
Jingqi Han ◽  
Kin-Man Tang ◽  
Shun-Cheung Cheng ◽  
Chi-On Ng ◽  
Yuen-Kiu Chun ◽  
...  
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Carbene Complexes ◽  
New Class

A new class of luminescent cyclometalated Ir(iii) complexes with readily tunable mechanochromic properties derived from the mechanically induced trans-to-cis isomerization have been developed.

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