scholarly journals Switching the O-O Bond Formation Pathways of Ru-pda Water Oxidation Catalyst by Third Coordination Sphere Engineering

Research ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yingzheng Li ◽  
Shaoqi Zhan ◽  
Lianpeng Tong ◽  
Wenlong Li ◽  
Yilong Zhao ◽  
...  
Keyword(s):  
Coordination Sphere ◽  
Water Oxidation ◽  
Density Functional ◽  
Electrochemical Polymerization ◽  
Bond Formation ◽  
Kinetic Studies ◽  
Oxidation Catalyst ◽  
Nucleophilic Attack ◽  
Formation Pathway ◽  
Axial Ligands

Water oxidation is a vital anodic reaction for renewable fuel generation via electrochemical- and photoelectrochemical-driven water splitting or CO2 reduction. Ruthenium complexes, such as Ru-bda family, have been shown as highly efficient water-oxidation catalysts (WOCs), particularly when they undergo a bimolecular O-O bond formation pathway. In this study, a novel Ru(pda)-type (pda2– =1,10-phenanthroline-2,9-dicarboxylate) molecular WOC with 4-vinylpyridine axial ligands was immobilized on the glassy carbon electrode surface by electrochemical polymerization. Electrochemical kinetic studies revealed that this homocoupling polymer catalyzes water oxidation through a bimolecular radical coupling pathway, where interaction between two Ru(pda)–oxyl moieties (I2M) forms the O-O bond. The calculated barrier of the I2M pathway by density-functional theory (DFT) is significantly lower than the barrier of a water nucleophilic attack (WNA) pathway. By using this polymerization strategy, the Ru centers are brought closer in the distance, and the O-O bond formation pathway by the Ru (pda) catalyst is switched from WNA in a homogeneous molecular catalytic system to I2M in the polymerized film, providing some deep insights into the importance of third coordination sphere engineering of the water oxidation catalyst.

scholarly journals From Ru-bda to Ru-bds: a step forward to highly efficient molecular water oxidation electrocatalysts under acidic and neutral conditions

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jing Yang ◽  
Lei Wang ◽  
Shaoqi Zhan ◽  
Haiyuan Zou ◽  
Hong Chen ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Density Functional ◽  
Bond Formation ◽  
Density Functional Theory Calculations ◽  
Oxidation Catalyst ◽  
Nucleophilic Attack ◽  
Molecular Water ◽  
Formation Mechanisms ◽  
Equatorial Position ◽  
Neutral Conditions

AbstractSignificant advances during the past decades in the design and studies of Ru complexes with polypyridine ligands have led to the great development of molecular water oxidation catalysts and understanding on the O−O bond formation mechanisms. Here we report a Ru-based molecular water oxidation catalyst [Ru(bds)(pic)2] (Ru-bds; bds2− = 2,2′-bipyridine-6,6′-disulfonate) containing a tetradentate, dianionic sulfonate ligand at the equatorial position and two 4-picoline ligands at the axial positions. This Ru-bds catalyst electrochemically catalyzes water oxidation with turnover frequencies (TOF) of 160 and 12,900 s−1 under acidic and neutral conditions respectively, showing much better performance than the state-of-art Ru-bda catalyst. Density functional theory calculations reveal that (i) under acidic conditions, the high valent Ru intermediate RuV=O featuring the 7-coordination configuration is involved in the O−O bond formation step; (ii) under neutral conditions, the seven-coordinate RuIV=O triggers the O−O bond formation; (iii) in both cases, the I2M (interaction of two M−O units) pathway is dominant over the WNA (water nucleophilic attack) pathway.

Ligand Geometry Directs OO Bond-Formation Pathway in Ruthenium-Based Water Oxidation Catalyst

2012 ◽  
Vol 124 (24) ◽  
pp. 6069-6072 ◽  
Author(s):  
Somnath Maji ◽  
Laura Vigara ◽  
Francesca Cottone ◽  
Fernando Bozoglian ◽  
Jordi Benet-Buchholz ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Bond Formation ◽  
Oxidation Catalyst ◽  
Formation Pathway

scholarly journals Two-transition-metal water oxidation catalysts. Faster rates via electronic structure tuning

2021 ◽  
Author(s):  
Craig Hill ◽  
Meilin Tao ◽  
Qiushi Yin ◽  
Alexey Kaledin ◽  
Natalie Uhlikova ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Active Sites ◽  
Density Functional ◽  
Molecular Model ◽  
Kinetic Studies ◽  
Oxidation Catalyst ◽  
Molecular Water ◽  
Oxidation Catalysts ◽  
Order Of Magnitude ◽  
Cobalt Nickel Oxide

Abstract Mixed 3d-metal oxides are some of the most promising water oxidation catalysts (WOCs), but it is very difficult to know the active site structures and thus structure-catalytic activity correlations at the molecular level in such insoluble materials. This study reports a molecular water oxidation catalyst, [Co2Ni2(PW9O34)2]10- (Co2Ni2P2), that constitutes a molecular model of the heterogeneous WOC, cobalt-nickel oxide. Both Co2Ni2P2 and its isostructural analogue, [Co4(PW9O34)2]10- (Co4P2), have the same CoO5(H2O) active sites but Co2Ni2P2 is an order of magnitude faster than Co4P2. Co2Ni2P2 is prepared by a new synthesis, and both the location and percent occupancy of Co and Ni in Co2Ni2P2 (Co outside and Ni inside the central belt are >97% for each) is confirmed by multiwavelength synchrotron X-radiation anomalous dispersion scattering (synchrotron XRAS), a technique applied for the first time to such complexes. Density functional theory (DFT) studies predicated and reveal that Co4P2 and Co2Ni2P2 have greatly altered frontier orbitals, while stopped-flow kinetic studies and DFT calculations indicate that water oxidation by both complexes follows analogous multi-step mechanisms, including Co-OOH formation, with the energetics of most steps being lower for Co2Ni2P2 than for Co4P2.

Ligand Geometry Directs OO Bond-Formation Pathway in Ruthenium-Based Water Oxidation Catalyst

2012 ◽  
Vol 51 (24) ◽  
pp. 5967-5970 ◽  
Author(s):  
Somnath Maji ◽  
Laura Vigara ◽  
Francesca Cottone ◽  
Fernando Bozoglian ◽  
Jordi Benet-Buchholz ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Bond Formation ◽  
Oxidation Catalyst ◽  
Formation Pathway

scholarly journals Understanding the reaction mechanism of the regioselective piperidinolysis of aryl 1-(2,4-dinitronaphthyl) ethers in DMSO: Kinetic and DFT studies

2021 ◽  
Vol 46 ◽  
pp. 146867832110274
Author(s):  
Yasmen M Moghazy ◽  
Nagwa MM Hamada ◽  
Magda F Fathalla ◽  
Yasser R Elmarassi ◽  
Ezzat A Hamed ◽  
...  
Keyword(s):  
Carbon Atom ◽  
Density Functional ◽  
Function Analysis ◽  
Density Functional Theory Method ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Nucleophilic Attack ◽  
Common Mechanism ◽  
Slow Step ◽  
Rate Determining Step

Reactions of aryl 1-(2,4-dinitronaphthyl) ethers with piperidine in dimethyl sulfoxide at 25oC resulted in substitution of the aryloxy group at the ipso carbon atom. The reaction was measured spectrophotochemically and the kinetic studies suggested that the titled reaction is accurately third order. The mechanism is began by fast nucleophilic attack of piperidine on C1 to form zwitterion intermediate (I) followed by deprotonation of zwitterion intermediate (I) to the Meisenheimer ion (II) in a slow step, that is, SB catalysis. The regular variation of activation parameters suggested that the reaction proceeded through a common mechanism. The Hammett equation using reaction constant σo values and Brønsted coefficient value showed that the reaction is poorly dependent on aryloxy substituent and the reaction was significantly associative and Meisenheimer intermediate-like. The mechanism of piperidinolysis has been theoretically investigated using density functional theory method using B3LYP/6-311G(d,p) computational level. The combination between experimental and computational studies predicts what mechanism is followed either through uncatalyzed or catalyzed reaction pathways, that is, SB and SB-GA. The global parameters of the reactants, the proposed activated complexes, and the local Fukui function analysis explained that C1 carbon atom is the most electrophilic center of ether. Also, kinetics and theoretical calculation of activation energies indicated that the mechanism of the piperidinolysis passed through a two-step mechanism and the proton transfer process was the rate determining step.

scholarly journals Iron-TAML Complexes: A Computational Approach to Improving Stability

2021 ◽  
Author(s):  
◽  
Kevin Tuano
Keyword(s):  
Water Oxidation ◽  
Density Functional ◽  
Prolonged Exposure ◽  
Computational Study ◽  
Macrocyclic Ligand ◽  
Oxidation Mechanism ◽  
Nucleophilic Attack ◽  
Functional Theory ◽  
The Stability ◽  
Oxidation Chemistry

<p>Researchers at the Institute for Green Oxidation Chemistry of the Carnegie Mellon University developed a group of catalysts called tetra amido macrocyclic ligand (TAML) activators. The purpose of that research was that TAML activators would breakdown pollutants in the presence of a sacrificial oxidant. Furthermore, the catalyst was designed to decompose on a required timescale, as to not damage the environment by prolonged exposure. Since the initial designs from the 1980’s, the TAML structure has undergone significant changes to increase efficiency or selectivity. Other uses of this group of catalysts have been explored, namely, the oxidation of water to molecular oxygen.  This work presents a computational study using Density Functional Theory (DFT) which addresses the issue regarding the stability of certain iron-TAML intermediates in the water oxidation mechanism. Hence, the work seeks to explore how changing certain groups on the TAML ring can affect the stability of the reactive intermediates and the activation energy of the nucleophilic attack within the mechanism. The work highlights the importance of the fluorinated tail of the TAML structure in the accessibility of the desired transition state.</p>

N-Heterocyclic Carbene-Catalyzed Synthesis of Ynones via C–H Alkynylation of Aldehydes with Alkynyliodonium Salts

2019 ◽  
Author(s):  
Adam A. Rajkiewicz ◽  
Natalia Wojciechowska ◽  
Marcin Kalek
Keyword(s):  
Density Functional ◽  
Bond Formation ◽  
Kinetic Studies ◽  
Density Functional Theory Calculations ◽  
Hypervalent Iodine ◽  
Functional Theory ◽  
Leaving Group ◽  
13C Labelling ◽  
Reaction Proceeds ◽  
Mechanism Of The Reaction

Alkynylation of aldehydes with alkynyl(aryl)iodonium salts catalyzed by an N-heterocyclic carbene (NHC) has been developed. The application of the organocatalyst and the hypervalent iodine group-transfer reagent allowed for metal-free C–H functionalization and C–C bond formation. The reaction proceeds under exceptionally mild conditions, at –40 ⁰C and in the presence of an amine base, providing access to an array of heteroaryl-propargyl ketones containing various substituents in good to excellent yields. The mechanism of the reaction was investigated by means of both experiments and density functional theory calculations. 13C-labelling and computations determined that the key alkynyl transfer step occurs via an unusual direct SN2 substitution of iodine-based leaving group by Breslow intermediate nucleophile at an acetylenic carbon. Moreover, kinetic studies revealed that the turnover-limiting step of the catalytic cycle is the generation of the Breslow intermediate, whereas the subsequent C–C bond-formation is a fast process. These results were fully reproduced and rationalized by the computed full free energy profile of the reaction, showing that the largest energy span is located between protonated NHC and the transition state for the carbene attack on the aldehyde substrate.<br>

The Mechanism of OO Bond Formation in Tanaka’s Water Oxidation Catalyst

2011 ◽  
Vol 124 (5) ◽  
pp. 1247-1250 ◽  
Author(s):  
Soumya Ghosh ◽  
Mu-Hyun Baik
Keyword(s):  
Water Oxidation ◽  
Bond Formation ◽  
Oxidation Catalyst
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