A Computational Study on Fluxional Behavior of Group 6 and 7 Transition-metal Complexes of Borane–Lewis Base Adducts

2006 ◽  
Vol 35 (6) ◽  
pp. 568-569 ◽  
Author(s):  
Yasuro Kawano ◽  
Taeko Kakizawa ◽  
Kazunori Yamaguchi ◽  
Mamoru Shimoi
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Computational Study ◽  
Lewis Base ◽  
Group 6

scholarly journals Frustration across the periodic table: heterolytic cleavage of dihydrogen by metal complexes

2017 ◽  
Vol 375 (2101) ◽  
pp. 20170002 ◽  
Author(s):  
R. Morris Bullock ◽  
Geoffrey M. Chambers
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Molecular Complexes ◽  
Main Group ◽  
Lewis Base ◽  
Metal Compounds ◽  
Metal Catalysis ◽  
Heterolytic Cleavage ◽  
Lewis Pairs

This perspective examines frustrated Lewis pairs (FLPs) in the context of heterolytic cleavage of H 2 by transition metal complexes, with an emphasis on molecular complexes bearing an intramolecular Lewis base. FLPs have traditionally been associated with main group compounds, yet many reactions of transition metal complexes support a broader classification of FLPs that includes certain types of transition metal complexes with reactivity resembling main group-based FLPs. This article surveys transition metal complexes that heterolytically cleave H 2 , which vary in the degree that the Lewis pairs within these systems interact. Many of the examples include complexes bearing a pendant amine functioning as the base with the metal functioning as the hydride acceptor. Consideration of transition metal compounds in the context of FLPs can inspire new innovations and improvements in transition metal catalysis. This article is part of the themed issue ‘Frustrated Lewis pair chemistry’.

Synthetic, Structural, NMR, and Computational Study of a Geminally Bis(peri-substituted) Tridentate Phosphine and Its Chalcogenides and Transition-Metal Complexes

2013 ◽  
Vol 52 (8) ◽  
pp. 4346-4359 ◽  
Author(s):  
Matthew J. Ray ◽  
Rebecca A. M. Randall ◽  
Kasun S. Athukorala Arachchige ◽  
Alexandra M. Z. Slawin ◽  
Michael Bühl ◽  
...  
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Computational Study

scholarly journals Should External Heavy-Atom Effects be Expected in Transition Metal Complexes?

2018 ◽  
Author(s):  
Justin Lomont ◽  
Son Nguyen ◽  
Charles Harris
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Spin State ◽  
Computational Study ◽  
Heavy Atom ◽  
Minimum Energy ◽  
Free Energy Barrier ◽  
Heavy Atom Effect ◽  
Atom Effect

Spin state changes frequently play a key role in the reactivity of transition metal complexes. The rates of spin-forbidden reactions are mediated both by the free energy barrier connecting reactants and products, as well as the strength of spin-orbit coupling (SOC) between the relevant electronic states. Since the 1950’s, there have been numerous demonstrations of external heavy-atom effects on organic molecules, in which a heavy atom, not chemically bonded to the molecule undergoing a change in spin state, perturbs the strength of SOC via an intermolecular effect. However, the potential role of external heavy atom effects on the rates of reactions involving transition metal complexes remains almost entirely unexplored. We report a computational investigation into the changes in SOC that occur along a bimolecular reaction coordinate when an incoming atom coordinates to the prototypical triplet reaction intermediate Fe(CO)4. The calculated changes in SOC are compared for molecules containing atoms ranging in atomic number from Z = 8 to Z = 53 approaching the Fe center (ZFe =26). No evidence for an external heavy atom effect was found, and the changes in SOC with the approach of each incoming group were similar in magnitude. In fact, when taking into account the different minimum energy crossing point geometries for the different incoming groups, the opposite of an external heavy atom effect trend is predicted for this reaction. The results of this computational study suggest that external heavy atom effects are unlikely to have a significant effect on the rates of spin-forbidden reactions for transition metal complexes. <br>

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).

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