Charge transfer complexation of N,N-dimethyl-p-toluidine with nitrogen heteroaromatic cations as a model for association complexes in hydride transfer reactions

Bunting, John W.; Luscher, Mark A.

doi:10.1139/v88-397

Cited by 5 publications

(3 citation statements)

References 21 publications

(48 reference statements)

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“…Using the Benesi–Hildebrands method, 63 we estimate the equilibrium constant K DA to be 0.96 M –1 . When applied to the conditions used in the spectroscopic analysis of Figure 4 b, an additional 0.3 μM 9 + · can be accounted for as originating from a donor–acceptor complex.…”

Section: Results and Discussionmentioning

confidence: 99%

Mechanistic Insight into the Photoredox Catalysis of Anti-Markovnikov Alkene Hydrofunctionalization Reactions

2014

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We describe our efforts to understand the key mechanistic aspects of the previously reported alkene hydrofunctionalization reactions using 9-mesityl-10-methylacridinium (Mes-Acr+) as a photoredox catalyst. Importantly, we are able to detect alkene cation radical intermediates, and confirm that phenylthiyl radical is capable of oxidizing the persistent acridinyl radical in a fast process that unites the catalytic activity of the photoredox and hydrogen atom transfer (HAT) manifolds. Additionally, we present evidence that diphenyl disulfide ((PhS)2) operates on a common catalytic cycle with thiophenol (PhSH) by way of photolytic cleaveage of the disulfide bond. Transition structure analysis of the HAT step using DFT reveals that the activation barrier for H atom donation from PhSH is significantly lower than 2-phenylmalononitrile (PMN) due to structural reorganization. In the early stages of the reaction, Mes-Acr+ is observed to engage in off-cycle adduct formation, presumably as buildup of PhS− becomes significant. The kinetic differences between PhSH and (PhS)2 as HAT catalysts indicate that the proton transfer step may have significant rate limiting influence.

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Section: Results and Discussionmentioning

confidence: 99%

Mechanistic Insight into the Photoredox Catalysis of Anti-Markovnikov Alkene Hydrofunctionalization Reactions

2014

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“…In fact a weak charge-transfer complex has been shown (19) to be formed immediately upon mixing 1-benzyl-1,4-dihydronicotinamide and the lo-methylacridinium cation, with the rate of disappearance of this complex being identical to the rate of hydride transfer between these two species. A fuller exploration of the association of neutral aromatic species with the various heteroaromatic cations of this study is reported in the accompanying paper (52).…”

Section: Discussionmentioning

confidence: 99%

Kinetics of hydride transfer between nitrogen heteroaromatic cations

Bunting¹,

Luscher²

1988

Can. J. Chem.

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. 66,2524 (1988).The kinetics of the reduction of the 3-cyano-1-methylquinolinium, 4-cyano-2-methylisoquinolinium, and 2-methyl-5-nitroisoquinolinium cations by 9,lO-dihydro-10-methylacridine, and also the reduction of these same three cations as well as the 10-methylacridinium cation by 5,6-dihydro-5-methylphenanthridine, have been investigated in 20% acetonitrile -80% water, ionic strength 1.0, 25°C. The reactions of the 2-methyl-5-nitroisoquinolinium cation with both reductants, and also of the 4-cyano-2-methylisoquinolinium cation with 9,lO-dihydro-10-methylacridine, display kinetic saturation effects in the pseudo-first-order rate constants as a function of heterocyclic cation concentration. These effects are consistent with the formation of 1: 1 association complexes between hydride donor and acceptor prior to the rate-determining step of the reduction. The second-order rate constants for these reactions, and also those for analogous heterocyclic catibn reductions by 1,4-dihydronicotinamides, show systematic variations as a function of the hydride donor and acceptor species. JOHN W. BUNTING et MARK A. LUSCHER. Can. J. Chem. 66,2524Chem. 66, (1988 OpCrant A 25"C, ti une force ionique de 1,0, dans une solution d'acktonitrile dans l'eau 20:80, on a CtudiC la cinCtique de la reduction des cations cyano-3 mtthyl-1 quinolinium, cyan04 mCthyl-2 isoquinolinium et methyl-2 nitro-5 isoquinolinium par la dihydro-9,10 methyl-10 acridine ainsi que la reduction de ces trois mCme cations ainsi que celle du cation methyl-10 acridinium par la dihydro-5,6 mkthyl-5 phenanthridine. Les reactions du cation methyl-2 nitro-5 isoquinolinium avec chacun des reactifs ainsi que celle du cation cyano-4 methyl-2 isoquinolinium avec la dihydro-9,10 mtthyl-10 acridine presentent des effets de saturation cinCtique des constantes de vitesse du pseudo premier ordre en fonction de la concentration de cation hCtCrocyclique. Ces effets sont en accord avec la formation de complexes d'association 1: 1 entre le donneur et l'accepteur d'hydrure avant 1'Ctape qui determine la vitesse de la reduction. Les constantes de vitesse du deuxibme ordre de ces reactions, ainsi que celles des rkductions analogues de cations hCterocycliques par les dihydro-1,4 nicotinamides, presentent des variations systimatiques en fonction des espkces qui donne ou qui accepte l'hydrure.[Traduit par la revue]

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“…other workers have also concluded that such charge-transfer species may lie on the reaction coordinate for these formal hydride transfer processes (3,30). It should be noted that it has been established (32)(33)(34) that the order of charge-transfer absorption maxima (A,,,) with a common donor species follows the order: xanthylium > tropylium > 10-methylacridinium > 1-methylquinolinium > ' l,5-Dihydro-3,10-dimethyl-5-deazaisoalloxazine …”

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confidence: 95%

Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

Bunting¹,

Conn²

1990

Can. J. Chem.

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, 537 (1990). The pH-dependences of the apparent second-order rate constants (k2PP) for the reduction of 2,4,6-cycloheptatrien-1-01 and 9-xanthydrol by each of 1-benzyl-1,4-dihydronicotinamide (BNH) and 10-methyl-9,lO-dihydroacridine (MAH) have been measured in 20% acetonitrile -80% water, at 25OC and ionic strength 1.0. For each of these reactions, the pH-dependence of kyp is only consistent with reduction occurring via the aromatic cation (either tropyliurn or xanthylium) that is present in equilibrium with these alcoholic species. The relative second-order rate constants (k2BNH/kYAH) for reductions by these two reducing agents (1700 for tropylium and 770 for xanthyliurn) are similar for these two cations. These ratios are also similar to those observed for a variety of nitrogen heteroarornatic hydride acceptors, even though the absolute magnitudes of these rate constants vary by 10''-fold. The second-order rate constants for the reductions of the tropyliurn and xanthyliurn cations are predicted reasonably well by their pKR+ values, with the latter cation being (7 x lo5)-fold more reactive than its T-isoelectronic N-methyl acridiniurn cation. The xanthyliurn cation has the greatest k!NH/koH ratio yet observed for any heteroarornatic cation, and this value further extends the known range of this ratio as a function of reactivity.Key words: hydride transfer, kinetics of reduction, 1,4-dihydropyridine derivatives, tropyliurn cation, xanthyliurn cation. 537 (1990). Operant h 25°C et a une force ionique de 1,0, dans des solutions contenant 20% d'acetonitrile et 80% d'eau, on a mesure la relation qui existe entre le pH et les constantes apparentes de vitesse du deuxikrne ordre (kyp) pour la reduction du cyclohepta-2,4,6-trikn-1-01 et du xanthydr-9-01 soit par le I-benzyl-l,4-dihydronicotinamide (BNH) ou par la 10-methyl-9,10-dihydroacridine (MAH). Pour chacune de ces reactions, la relation entre le pH et le kyP ne correspond qu'h celle attendue pour une reduction se produisant par le biais d'un cation aromatique (soit tropyliurn ou xanthylium) qui est present l'equilibre dans ces espkces alcooliques. Les constantes relatives des vitesses de reaction du second ordre (k2BNH/kyAH) pour les reductions par ces deux agents riducteurs (1700 pour le tropyliurn et 770 pour le xanthyliurn) sont sernblables pour ces deux cations. MCme si les valeurs absolues de ces constantes de vitesse varient par des facteurs allant jusqu'h 101°, ces rapports sont aussi similaires h ceux observes pour un grand nornbre de derives hCtCroaromatiques azotks accepteurs d'hydrure. Utilisant les valeurs des pKR+ des cations, on peut aussi predire assez correcternent les constantes de vitesse du deuxikrne ordre pour les reductions des cations tropyliurn et xanthylium; ce dernier cation est environ 7 X lo5 fois plus rkactif que le cation N-methyl acridinium qui lui est T-isoelectronique. La valeur du rapport k!NH/koH du cation xanthyliurn est la plus ClevCe avoir Ct C observee jusqu'h rnaintenant et cette valeur Clargit la plage connue de ce rapport ...

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Charge transfer complexation of N,N-dimethyl-p-toluidine with nitrogen heteroaromatic cations as a model for association complexes in hydride transfer reactions

Cited by 5 publications

References 21 publications

Mechanistic Insight into the Photoredox Catalysis of Anti-Markovnikov Alkene Hydrofunctionalization Reactions

Mechanistic Insight into the Photoredox Catalysis of Anti-Markovnikov Alkene Hydrofunctionalization Reactions

Kinetics of hydride transfer between nitrogen heteroaromatic cations

Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

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