Dendritic polarizing agents for DNP SENS

Liao, Wei‐Chih; Ong, Ta‐Chung; Gajan, David; Bernada, Florian; Sauvée, Claire; Yulikov, Maxim; Pucino, Margherita; Schowner, Roman; Schwarzwälder, Martin; Buchmeiser, Michael R.; Jeschke, Gunnar; Tordo, Paul; Ouari, Olivier; Lesage, Anne; Emsley, Lyndon; Copéret, Christophe

doi:10.1039/c6sc03139k

Cited by 41 publications

(49 citation statements)

References 55 publications

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“…The term “radical dendrimers” has been used in the case of highly functionalized dendrimers with organic radicals . Nowadays there is an increasing interest for the application of radical dendrimers as contrast agents in Magnetic Resonance Imaging (MRI), Dynamic Nuclear Polarization (DNP), as additive or active materials in organic solar cells for solar energy conversion, and environmentally friendly organic electronic applications . Another possible application of radical dendrimers might be as the electrode material for rechargeable organic batteries (ORBs), where stable organic radicals function as electrochemically active pendant groups…”

Section: Introductionmentioning

confidence: 99%

Tuning Spin‐Spin Interactions in Radical Dendrimers

et al. 2018

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Two generations of polyphosphorhydrazone (PPH) dendrimers were synthesized and fully functionalized with TEMPO radicals via acrylamido or imino group linkers to evaluate the impact of the linker substitution on the radical-radical interactions. A drastic change in the way that the radicals interacted among them was observed by EPR and CV studies: while radicals in G -imino-TEMPO dendrimers presented a strong spin-spin interaction, in the G -acrylamido-TEMPO ones they acted mainly as independent radicals. This shows that these interactions could be tuned by the solely substitution of the radical linker, opening the perspective of controlling and modulating the extension of these interactions depending on each application. The chemical properties of the linker strongly influence the spin-spin exchange between pendant radicals.

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Section: Introductionmentioning

confidence: 99%

Tuning Spin‐Spin Interactions in Radical Dendrimers

et al. 2018

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“…Our simulations focusedo no ptimizing the factorst hat can be alteredb yf inetuning the chemical structureo ft he polarizing agent such as the orientation of the radicals,t he length of the linker,a nd the size and rigidity of the molecule (which affects the electron relaxationt imes). [57,58,59] Computational Details All calculations were performed using the software developed by Ivanov and co-workers. Research into better performingp olarizing agentss hould then focus on:( 1) the synthesis of new polarizing agents having narrow EPR lines, such as trityl radicals [32,53] and paramagnetic metal centers, [54][55][56] and (2) biradical formulations that minimize sample quenching as well as the reactions between the polarizing agent and the material.…”

Section: Discussionmentioning

confidence: 99%

In Silico Design of DNP Polarizing Agents: Can Current Dinitroxides Be Improved?

2017

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Numerical calculations of enhancement factors offered by dynamic nuclear polarization in solids under magic angle spinning (DNP-MAS) were performed to determine the optimal EPR parameters for a dinitroxide polarizing agent. We found that the DNP performance of a biradical is more tolerant to the relative orientation of the two nitroxide moieties than previously thought. Generally, any condition in which the g tensor components of both radicals are perpendicular to one another is expected to have near-optimal DNP performance. Our results highlight the important role of the exchange coupling, which can lessen the sensitivity of DNP performance to the inter-radical distance, but also lead to lower enhancements when the number of atoms in the linker becomes less than three. Lastly, the calculations showed that the electron T value should be near 500 μs to yield optimal performance. Importantly, the newest polarizing agents already feature all of the qualities of the optimal polarizing agent, leaving little room for further improvement. Further research into DNP polarizing agents should then target non-nitroxide radicals, as well as improvements in sample formulations to advance high-temperature DNP and limit quenching and reactivity.

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“…Immobilization of [W(O)(IMes)(CHCMe 2 Ph)(OCH(CF 3 ) 2 ) + B(ArF) 4 − ] on silica 700 yielded [(≡SiO)W(=O)(=CHCMe 2 Ph)(IMes)][B(Ar F ) 4 ] (Scheme ) . Its structure was also unambiguously confirmed by dynamic nuclear polarization (DNP) 13 C cross‐polarization (CP) NMR . This silica‐supported catalyst exhibited the highest productivity in the homometathesis of propene ever reported for a molecular catalyst (TON>1.2×10 6 ).…”

Section: Immobilization Of Tungsten Oxo Alkylidene Nhcs On Silica700 mentioning

confidence: 95%

Molybdenum Imido, Tungsten Imido and Tungsten Oxo Alkylidene N‐Heterocyclic Carbene Olefin Metathesis Catalysts

Buchmeiser

2018

Chemistry A European J

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This article outlines the fundamental concept to molybdenum imido, tungsten imido and tungsten oxo alkylidene N-heterocyclic carbene (NHC) catalysts for olefin metathesis. Starting from Mo(NR)(CHCMe R')(OTf) ⋅DME (R=alkyl, aryl; R'=CH , Ph; OTf=CF SO ; DME=1,2-dimethoxyethane), W(NR)(CHCMe Ph)X (X=pyrrolide, OR'', SiPh ) and W(O)Cl (CHCMe Ph)(PMe Ph) , respectively, the neutral, pentacoordinated 16-valence electron (VE) complexes became accessible. These serve as precursors for the corresponding cationic, tetracoordinated 14-VE catalysts. This class of olefin metathesis catalysts based on group 6 metal alkylidene NHCs is characterized by a broad structural variability, high activity, high productivity and, in tailored systems, high functional group tolerance even vs. protic groups including alcohols and carboxylic acids. Also, high regio- and stereoselectivity is achieved, both in ring-opening metathesis polymerization (ROMP) and in the cyclopolymerization of α,ω-diynes. Fundamentals concerning the influence of the imido/oxo ligand, the different NHCs and the anionic ligands on catalyst performance and stability as well as reaction pathways are summarized. Also, the concepts for catalyst immobilization, whether via the NHC or by substitution of an alkoxide, are presented. Finally, special features such as the use of betaine-type anionic ligands (alkoxides and sulfonates), which offer access to ionic catalysts for use biphasic reaction setups, are briefly outlined.

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Dendritic polarizing agents for DNP SENS

Abstract: Dendrimer-shielded polarizing agents for the application of DNP SENS to reactive surfaces.

Cited by 41 publications

References 55 publications

Tuning Spin‐Spin Interactions in Radical Dendrimers

Tuning Spin‐Spin Interactions in Radical Dendrimers

In Silico Design of DNP Polarizing Agents: Can Current Dinitroxides Be Improved?

Molybdenum Imido, Tungsten Imido and Tungsten Oxo Alkylidene N‐Heterocyclic Carbene Olefin Metathesis Catalysts

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