Definitive Evidence for the Insertion of Terminal Alkynes into ArylSPt Bonds: “o-Halogen Effect” in Stoichiometric and Catalytic Reactions

2007 ◽  
Vol 46 (31) ◽  
pp. 5929-5933 ◽  
Author(s):  
Hitoshi Kuniyasu ◽  
Fumikazu Yamashita ◽  
Jun Terao ◽  
Nobuaki Kambe
Keyword(s):  
Catalytic Reactions ◽  
Terminal Alkynes ◽  
Definitive Evidence ◽  
Halogen Effect

Metalloporphyrin catalysts for organic synthesis

2004 ◽  
Vol 08 (09) ◽  
pp. 1166-1171 ◽  
Author(s):  
Gérard Simonneaux ◽  
Pietro Tagliatesta
Keyword(s):  
Organic Synthesis ◽  
Enantiomeric Excess ◽  
Catalytic Reactions ◽  
Terminal Alkynes ◽  
Asymmetric Oxidation ◽  
Carbene Transfer ◽  
Catalytic Asymmetric ◽  
Chiral Systems ◽  
Metalloporphyrin Catalysts

Novel chiral systems for the catalytic asymmetric oxidation and cyclopropanation of olefins based on metalloporphyrins containing iron, ruthenium and manganese, have been recently introduced. High catalyst turnover numbers and sometimes high enantiomeric excess were observed. New catalytic reactions with metalloporphyrins have recently been reported; these are the olefination of aldehydes and cyclotrimerization of terminal alkynes. Dendrimers and polymers containing metalloporphyrins, have also been found to be efficient catalysts for oxidation and carbene transfer.

Catalytic Reactions of Terminal Alkynes Using Rhodium(I) Complexes Bearing 8-Quinolinolate Ligands

ACS Catalysis ◽  
2018 ◽  
Vol 8 (7) ◽  
pp. 6127-6137 ◽  
Author(s):  
Fumitoshi Kakiuchi ◽  
Shotaro Takano ◽  
Takuya Kochi
Keyword(s):  
Catalytic Reactions ◽  
Terminal Alkynes

Activation of cytochrome c to a peroxidase compound I-type intermediate by H2O2: relevance to redox signalling in apoptosis

2004 ◽  
Vol 71 ◽  
pp. 97-106 ◽  
Author(s):  
Mark Burkitt ◽  
Clare Jones ◽  
Andrew Lawrence ◽  
Peter Wardman
Keyword(s):  
Cytochrome C ◽  
Hydroxyl Radical ◽  
Redox Regulation ◽  
Chemotherapeutic Agents ◽  
Tyrosyl Radical ◽  
Compound I ◽  
Definitive Evidence ◽  
Enhanced Production ◽  
Physico Chemical

The release of cytochrome c from mitochondria during apoptosis results in the enhanced production of superoxide radicals, which are converted to H2O2 by Mn-superoxide dismutase. We have been concerned with the role of cytochrome c/H2O2 in the induction of oxidative stress during apoptosis. Our initial studies showed that cytochrome c is a potent catalyst of 2′,7′-dichlorofluorescin oxidation, thereby explaining the increased rate of production of the fluorophore 2′,7′-dichlorofluorescein in apoptotic cells. Although it has been speculated that the oxidizing species may be a ferryl-haem intermediate, no definitive evidence for the formation of such a species has been reported. Alternatively, it is possible that the hydroxyl radical may be generated, as seen in the reaction of certain iron chelates with H2O2. By examining the effects of radical scavengers on 2′,7′-dichlorofluorescin oxidation by cytochrome c/H2O2, together with complementary EPR studies, we have demonstrated that the hydroxyl radical is not generated. Our findings point, instead, to the formation of a peroxidase compound I species, with one oxidizing equivalent present as an oxo-ferryl haem intermediate and the other as the tyrosyl radical identified by Barr and colleagues [Barr, Gunther, Deterding, Tomer and Mason (1996) J. Biol. Chem. 271, 15498-15503]. Studies with spin traps indicated that the oxo-ferryl haem is the active oxidant. These findings provide a physico-chemical basis for the redox changes that occur during apoptosis. Excessive changes (possibly catalysed by cytochrome c) may have implications for the redox regulation of cell death, including the sensitivity of tumour cells to chemotherapeutic agents.

Tunable Carbon Surface from Mono- to Multi-Metallic Single Atoms

2020 ◽  
Author(s):  
Weihong Lai ◽  
Heng Wang ◽  
Quan jiang ◽  
Zichao Yan ◽  
Hanwen Liu ◽  
...  
Keyword(s):  
Synergistic Effects ◽  
Structural Evolution ◽  
Charge Compensation ◽  
Catalytic Reactions ◽  
Single Atom ◽  
Carbon Surface ◽  
Hydrogen Electrode ◽  
Single Atoms ◽  
Mass Activity ◽  
Co Doped

<p>Herein, we develop a non-selective charge compensation strategy to prepare multi-single-atom doped carbon (MSAC) in which a sodium p-toluenesulfonate (PTS-Na) doped polypyrrole (S-PPy) polymer is designed to anchor discretionary mixtures of multiple metal cations, including iron (Fe<sup>3+</sup>), cobalt (Co<sup>3+</sup>), ruthenium (Ru<sup>3+</sup>), palladium (Pd<sup>2+</sup>), indium (In<sup>3+</sup>), iridium (Ir<sup>2+</sup>), and platinum (Pt<sup>2+</sup>) . As illustrated in Figure 1, the carbon surface can be tuned with different level of compositional complexities, including unary Pt<sub>1</sub>@NC, binary (MSAC-2, (PtFe)<sub>1</sub>@NC), ternary (MSAC-3, (PtFeIr)<sub>1</sub>@NC), quaternary (MSAC-4, (PtFeIrRu)<sub>1</sub>@NC), quinary (MSAC-5, (PtFeIrRuCo)<sub>1</sub>@NC), senary (MSAC-6, (PtFeIrRuCoPd)<sub>1</sub>@NC), and septenary (MSAC-7, (PtFeIrRuCoPdIn)<sub>1</sub>@NC) samples. The structural evolution of carbon surface dictates the activities of both ORR and HER. The senary MSAC-6 achieves the ORR mass activity of 18.1 A·mg<sub>metal</sub><sup>-1</sup> at 0.9 V (Vs reversible hydrogen electrode (RHE)) over 30K cycles, which is 164 times higher than that of commercial Pt/C. The quaternary MSAC-4 presented a comparable HER catalytic capability with that of Pt/C. These results indicate that the highly complexed carbon surface can enhance its ability over general electrochemical catalytic reactions. The mechanisms regarding of the ORR and HER activities of the alternated carbon surface are also theoretically and experimentally investigated in this work, showing that the synergistic effects amongst the co-doped atoms can activate or inactivate certain single-atom sites.</p>

Mechanistic Study and Development of Catalytic Reactions of Sm(II)

2018 ◽  
Author(s):  
Sandepan Maity ◽  
Robert Flowers
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Proton Donor ◽  
Catalytic Reactions ◽  
Mechanistic Study ◽  
Mechanistic Studies ◽  
Cyclization Reactions ◽  
Mechanistic Approach ◽  
Donor Source

Despite the broad utility and application of SmI<sub>2</sub>in synthesis, the reagent is used in stoichiometric amounts and has a high molecular weight, resulting in a large amount of material being used for reactions requiring one or more equivalents of electrons. We report mechanistic studies on catalytic reactions of Sm(II) employing a terminal magnesium reductant and trimethyl silyl chloride in concert with a non-coordinating proton donor source. Reactions using this approach permitted reductions with as little as 1 mol% Sm. The mechanistic approach enabled catalysis employing HMPA as a ligand, facilitating the development of catalytic Sm(II) 5-<i>exo</i>-<i>trig </i>ketyl olefin cyclization reactions.

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