- Discovery and Elucidation of Counteranion Dependence in Photoredox Catalysis
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Over the past decade, there has been a renewed interest in the use of transition metal polypyridyl complexes as photoredox catalysts for a variety of innovative synthetic applications. Many derivatives of these complexes are known, and the effect of ligand modifications on their efficacy as photoredox catalysts has been the subject of extensive, systematic investigation. However, the influence of the photocatalyst counteranion has received little attention, despite the fact that these complexes are generally cationic in nature. Herein, we demonstrate that counteranion effects exert a surprising, dramatic impact on the rate of a representative photocatalytic radical cation Diels-Alder reaction. A detailed analysis reveals that counteranion identity impacts multiple aspects of the reaction mechanism. Most notably, photocatalysts with more noncoordinating counteranions yield a more powerful triplet excited state oxidant and longer radical cation chain length. It is proposed that this counteranion effect arises from Coulombic ion-pairing interactions between the counteranion and both the cationic photoredox catalyst and the radical cation intermediate, respectively. The comparatively slower rate of reaction with coordinating counteranions can be rescued by using hydrogen-bonding anion binders that attenuate deleterious ion-pairing interactions. These results demonstrate the importance of counteranion identity as a variable in the design and optimization of photoredox transformations and suggest a novel strategy for the optimization of organic reactions using this class of transition metal photocatalysts.
- Farney, Elliot P.,Chapman, Steven J.,Swords, Wesley B.,Torelli, Marco D.,Hamers, Robert J.,Yoon, Tehshik P.
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supporting information
p. 6385 - 6391
(2019/05/02)
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- Efficient method for varying the anions in quaternary onium halides
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Quaternary onium salts of halides can be efficiently converted into the corresponding quaternary onium salts of various anions [NO3 -, BF4-, PF6-, CF 3SO3-, CH3SO3 -, ClO4-, p-CH3C6H 4SO3-, CF3CO2 -, 2,4-(NO2)2C6H3O -] by treating the onium halide with trimethyl phosphate under neat condition in the presence of an equivalent amount of conjugate acid of the desired anion.
- Jeon, Jong Yeob,Varghese, Jobi Kodiyan,Park, Ji Hae,Lee, Suck-Hyun,Lee, Bun Yeoul
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experimental part
p. 3566 - 3569
(2012/08/14)
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- POSITIVE RESIST COMPOSITION AND PATTERNING PROCESS
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A positive resist composition comprises (A) a resin component which becomes soluble in an alkaline developer under the action of an acid and (B) an acid generator. The resin (A) is a polymer comprising recurring units containing a non-leaving hydroxyl group represented by formula (1) wherein R1 is H, methyl or trifluoromethyl, X is a single bond or methylene, m is 1 or 2, and the hydroxyl group attaches to a secondary carbon atom. The composition is improved in resolution when processed by lithography.
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- THE CHEMISTRY OF FUNCTIONAL GROUP ARRAYS. ELECTROSTATIC CATALYSIS AND THE "INTRAMOLECULAR SALT EFFECT"
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Ionic groups and salt bridges in the active sites of enzymes are thought to have important effects upon substrate reactivity.This paper describes the evaluation of an ion pair as an intramolecular effector of reaction rate for an addition reaction.The results reveal that in chloroform the intramolecular salt effect can lead to very large rate enhancements.It is proposed that in this case the local effect of the ion pair probably depends upon two factors: the electrostatic effects of the salt pair and, to a lesser extent, an intramolecular hydrogen bond.This observation of large rate enhancements in nonpolar solvents provides evidence of the substantial effects that ion pairs within the active sites of enzymes could have on reaction rates.The most specific and strongest synthetic molecular associations have been reported for host-guest systems in chloroform, and it is foreseen that hydrogen bond based host-guest systems will be combined with the intramolecular salt effect to bring within reach a large class of new shape selective specific synthetic catalysts and molecular effectors.
- Smith, Paul J.,Wilcox, Craig S.
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p. 2617 - 2628
(2007/10/02)
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- CORRELATION OF THE RATES OF REACTION OF ARENESULFONATE IONS WITH THE TRIMETHYLOXONIUM ION IN ACETONITRILE
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The kinetics of the reactions between trimethyloxonium hexafluorophosphate and a series of tetra-n-butylammonium arenesulfonates have been studied in acetonitrile at -23.4 deg C.With the oxonium salt concentration at about 0.01 M, two series of runs were carried out; Hammett plots of the second-order rate coefficients led to ρ values of -1.18 +/- 0.04 for 0.04 M arenesulfonate salt and -1.07 +/- 0.02 for 0.16 M arenesulfonate salt.Solvolysis kinetics for the trimethyloxonium ion in acetonitrile are also reported.
- Kevill, Dennis N.,Lin, Gloria Meichia L.,Wang, An
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p. 715 - 717
(2007/10/02)
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