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Lattke YM, Corbin DA, Sartor SM, McCarthy BG, Miyake GM, Damrauer NH. Interrogation of O-ATRP Activation Conducted by Singlet and Triplet Excited States of Phenoxazine Photocatalysts. J Phys Chem A 2021; 125:3109-3121. [PMID: 33826326 DOI: 10.1021/acs.jpca.1c00855] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Organocatalyzed ATRP (O-ATRP) is a growing field exploiting organic chromophores as photoredox catalysts (PCs) that engage in dissociative electron-transfer (DET) activation of alkyl-halide initiators following absorption of light. Characterizing DET rate coefficients (kact) and photochemical yields across various reaction conditions and PC photophysical properties will inform catalyst design and efficient use during polymerization. The studies described herein consider a class of phenoxazine PCs, where synthetic handles of core substitution and N-aryl substitution enable tunability of the electronic and spin characters of the catalyst excited state as well as DET reaction driving force (ΔGET0). Using Stern-Volmer quenching experiments through variation of the diethyl 2-bromo-2-methylmalonate (DBMM) initiator concentration, collisional quenching is observed. Eight independent measurements of kact are reported as a function of ΔGET0 for four PCs: four triplet reactants and four singlets with kact values ranging from 1.1 × 108 M-1 s-1, where DET itself controls the rate, to 4.8 × 109 M-1 s-1, where diffusion is rate-limiting. This overall data set, as well as a second one inclusive of five literature values from related systems, is readily modeled with only a single parameter of reorganization energy under the frameworks of the adiabatic Marcus electron-transfer theory and Marcus-Savéant theory of DET. The results provide a predictive map where kact can be estimated if ΔGET0 is known and highlight that DET in these systems appears insensitive to PC reactant electronic and spin properties outside of their impact on the driving force. Next, on the basis of measured kact values in selected PC systems and knowledge of their photophysics, we also consider activation yields specific to the reactant spin states as the DBMM initiator concentration is varied. In N-naphthyl-containing PCs characterized by near-unity intersystem crossing, the T1 is certainly an important driver for efficient DET. However, at DBMM concentrations common to polymer synthesis, the S1 is also active and drives 33% of DET reaction events. Even in systems with low yields of ISC, such as in N-phenyl-containing PCs, reaction yields can be driven to useful values by exploiting the S1 under high DBMM concentration conditions. Finally, we have quantified photochemical reaction quantum yields, which take into account potential product loss processes after electron-transfer quenching events. Both S1 and T1 reactant states produce the PC•+ radical cation with a common yield of 71%, thus offering no evidence for spin selectivity in deleterious back electron transfer. The subunity PC•+ yields suggest that some combination of solvent (DMAc) oxidation and energy-wasting back electron transfer is likely at play and these pathways should be factored in subsequent mechanistic considerations.
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Affiliation(s)
- Yisrael M Lattke
- Department of Chemistry, University of Colorado, Boulder, Colorado 80309, United States
| | - Daniel A Corbin
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States
| | - Steven M Sartor
- Department of Chemistry, University of Colorado, Boulder, Colorado 80309, United States
| | - Blaine G McCarthy
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States
| | - Garret M Miyake
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States
| | - Niels H Damrauer
- Department of Chemistry, University of Colorado, Boulder, Colorado 80309, United States
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Costentin C, Louault C, Robert M, Teillout AL. Sticky Dissociative Electron Transfer to Polychloroacetamides. In-Cage Ion−Dipole Interaction Control through the Dipole Moment and Intramolecular Hydrogen Bond. J Phys Chem A 2005; 109:2984-90. [PMID: 16833619 DOI: 10.1021/jp0442549] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The reductive cleavage of chloro- and polychloroacetamides in N,N-dimethylformamide gives new insights into the nature of the in-cage ion radical cluster formed upon dissociative electron transfer. Within the family of compounds investigated, the electrochemical reduction leads to the successive expulsion of chloride ions. At each stage the electron transfer is concerted with the breaking of the C-Cl bond and acts as the rate-determining step. The reduction further leads to the formation of the corresponding carbanion with the injection of a second electron, which is in turn protonated by a weak acid added to the solution. From the joint use of cyclic voltammetric data, the sticky dissociative electron-transfer model and quantum ab initio calculations, the interaction energies within the cluster fragments (*R, Cl-) resulting from the first electron transfer to the parent RCl molecule are obtained. It is shown that the stability of these adducts, which should be viewed as an essentially electrostatic radical-ion pair, is mainly controlled by the intensity of the dipole moment of the remaining radical part and may eventually be strengthened by the formation of an intramolecular hydrogen bond, as is the case with 2-chloroacetamide.
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Affiliation(s)
- Cyrille Costentin
- Laboratoire d'Electrochimie Moléculaire, Université de Paris 7, Denis Diderot, UMR CNRS 7591, Case Courrier 7107, 2 place Jussieu, 75251 Paris Cedex 05, France.
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3
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Lorance ED, Kramer WH, Gould IR. Barrierless electron transfer bond fragmentation reactions. J Am Chem Soc 2004; 126:14071-8. [PMID: 15506771 DOI: 10.1021/ja030438+] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The ultrafast N-O bond fragmentation in a series of N-methoxypyridyl radicals, formed by one-electron reduction of the corresponding N-methoxypyridiniums, has been investigated as potentially barrierless electron-transfer-initiated chemical reactions. A model for the reaction involving the electronic and geometric factors that control the shape of the potential energy surface for the reaction is described. On the basis of this model, molecular structural features appropriate for ultrafast reactivity are proposed. Femtosecond kinetic measurements on these reactions are consistent with a kinetic definition of an essentially barrierless reaction, i.e., that the lifetime of the radical is a few vibrational periods of the fragmenting bond, for the p-methoxy-N-methoxypyridyl radical.
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Affiliation(s)
- Edward D Lorance
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604, USA
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Sakamoto M, Cai X, Hara M, Tojo S, Fujitsuka M, Majima T. Competitive Marcus-Type Electron Transfer and Energy Transfer from the Higher Triplet Excited State. J Phys Chem A 2004. [DOI: 10.1021/jp046892x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Masanori Sakamoto
- The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
| | - Xichen Cai
- The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
| | - Michihiro Hara
- The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
| | - Sachiko Tojo
- The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
| | - Mamoru Fujitsuka
- The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
| | - Tetsuro Majima
- The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
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Sakamoto M, Cai X, Hara M, Fujitsuka M, Majima T. Intermolecular Electron Transfer from Naphthalene Derivatives in the Higher Triplet Excited States. J Am Chem Soc 2004; 126:9709-14. [PMID: 15291574 DOI: 10.1021/ja049948+] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Intermolecular electron transfer (ELT) from a series of naphthalene derivatives (NpD) in the higher triplet excited states (T(n)) to carbon tetrachloride (CCl(4)) in Ar-saturated acetonitrile was observed using the two-color two-laser flash photolysis method. The ELT efficiency depended on the driving force of ELT. Since the ELT from the T(n) state occurred competitively with the internal conversion (IC, T(n) --> T(1)) and the triplet energy transfer (ENT), the ELT became apparent only when sufficient free energy change of ELT was attained. On the other hand, ELT from the T(1) state was not observed, although ELT from the T(1) state with sufficiently long lifetime has a slightly exothermic driving force. The fast ELT from the T(n) state and lack of the reactivity of the T(1) state were explained well by the "sticky" dissociative electron-transfer model based on one-electron reductive attachment to CCl(4) leading to the C-Cl bond cleavage.
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Affiliation(s)
- Masanori Sakamoto
- The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
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Argüello JE, Peñéñory AB. Fluorescent quenching of the 2-naphthoxide anion by aliphatic and aromatic halides. Mechanism and consequences of electron transfer reactions. J Org Chem 2003; 68:2362-8. [PMID: 12636403 DOI: 10.1021/jo026518y] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The fluorescent excited state of the 2-naphthoxide ion (1) is quenched by aliphatic and aromatic halides according to an electron-transfer mechanism, with generation of the corresponding alkyl and aryl radicals by a concerted or consecutive C-X bond fragmentation reaction. Whereas bromo- and iodobenzene follow a concerted ET mechanism (C-X, BDE control), 1-bromonaphthalene exhibits a stepwise process (pi LUMO control). The photoinduced reaction of anion 1 with 1-iodoadamantane (2) in DMSO affords substitution products on C3, C6, and C8, 1-adamantanol, 1-adamantyl 2-naphthyl ether, and adamantane (3.2, 13.2, 12.2, 2.8, 2.5, and 14.1% yields, respectively). A complex mixture is also observed in the photochemical reaction of neopentyl iodide (3) with anion 1, which renders substitution on C1, C3, C6, C8, and 2-naphthyl neopentyl ether (8.1, 1.3, 19.1, 31.1, and 2.8% yields, respectively). The absence of reaction in the dark and the inhibition of the photoinduced reaction by the presence of the radical traps di-tert-butylnitroxide (DTBN) and 1,4-cyclohexadiene are evidence of a radical chain mechanism for these substitutions. On the other hand, only coupling at C1 is achieved by the photostimulated reaction of anion 1 with iodobenzene (5), to afford 41.9% of 1-phenyl-2-naphthol and 5.4% of disubstitution product. The regiochemistry of these reactions can be ascribed to steric hindrance and activation parameters.
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Affiliation(s)
- Juan E Argüello
- INFIQC, Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000 Córdoba, Argentina
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Rossi RA, Pierini AB, Peñéñory AB. Nucleophilic substitution reactions by electron transfer. Chem Rev 2003; 103:71-167. [PMID: 12517182 DOI: 10.1021/cr960134o] [Citation(s) in RCA: 339] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Roberto A Rossi
- INFIQC, Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000 Córdoba, Argentina
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Cardinale A, Isse AA, Gennaro A, Robert M, Savéant JM. Dissociative electron transfer to haloacetonitriles. An example of the dependency of in-cage ion-radical interactions upon the leaving group. J Am Chem Soc 2002; 124:13533-9. [PMID: 12418908 DOI: 10.1021/ja0275212] [Citation(s) in RCA: 125] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The reductive cleavage of the haloacetonitriles (Cl, Br, I) in DMF provides additional examples of the formation of a fragment cluster upon dissociative electron transfer, which is able to survive in this polar solvent thanks to the electron-withdrawing character of the cyano group. The remarkable sensitivity of the activation energy to small changes of the interaction energies allows, with help of the "sticky" dissociative electron-transfer model, the precise determination of interaction energies down to a few millielectronvolts from the cyclic voltammetric data. The interaction energy rapidly decreases from Cl to Br and to I, correlated with the increase of the halide radius. These observations add to the previously gathered evidence to confirm the existence of such interactions and to highlight their electrostatic character. This is further corroborated by the quantum chemical computation of the potential energy profiles, which exhibit a long-distance energy minimum. This revisiting of the notion of sigma-ion radicals and of their status in a polar medium makes them appear as an electrostatic radical-ion pair rather than covalently bound molecules. Their stability is a function of the Lewis acid-base properties of both the radical and the leaving ion and is strongly influenced by the nature of the solvent.
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Affiliation(s)
- Annarita Cardinale
- Dipartimento di Chimica Fisica, Università di Padova, via Loredan 2, Italy
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Pause L, Robert M, Savéant JM. Stabilities of ion/radical adducts in the liquid phase as derived from the dependence of electrochemical cleavage reactivities upon solvent. J Am Chem Soc 2001; 123:11908-16. [PMID: 11724597 DOI: 10.1021/ja0117985] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The idea that significant ion/radical interactions should vary with solvent if they do exist in the liquid phase was pursued by an investigation of the dissociative electron-transfer reactivity of carbon tetrachloride and 4-cyanobenzyl chloride in four different solvents, 1,2-dichloroethane, N,N-dimethylformamide, ethanol, and formamide, by means of their cyclic voltammetric responses. Modification of the conventional dissociative electron transfer theory to take account of an interaction between fragments in the ion/radical pair resulting from the dissociative electron reaction allows a satisfactory fitting of the experimental data leading to the determination of the interaction energy. There is an approximate correlation between the interaction energies in the ion/radical pair and the solvation free energies of the leaving anion, Cl(-). The interaction is maximal in 1,2-dichloroethane, which is both the least polar and the least able to solvate Cl(-). The interaction is smaller in the polar solvents, albeit distinctly measurable. The two protic solvents, ethanol and formamide, which are the most able to solvate Cl(-), give rise to similar interaction energies. The interaction is definitely stronger in N,N-dimethylformamide, which has a lesser ability to solvate Cl(-) than the two other polar solvents. The existence of significant ion/radical interactions in polar media is thus confirmed and a route to their determination opened.
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Affiliation(s)
- L Pause
- Laboratoire d'Electrochimie Moléculaire, Unité Mixte de Recherche Université-CNRS No 7591, Université de Paris 7-Denis Diderot, 2 place Jussieu, 75251 Paris Cedex 05, France
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Nath S, Sapre AV. Photoinduced electron transfer from chloropromazine and promethazine to chloroalkanes accompanied by cleavage of C–Cl bond. Chem Phys Lett 2001. [DOI: 10.1016/s0009-2614(01)00685-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Pause L, Robert M, Savéant JM. Stepwise and concerted pathways in photoinduced and thermal electron-transfer/bond-breaking reactions. experimental illustration of similarities and contrasts. J Am Chem Soc 2001; 123:4886-95. [PMID: 11457315 DOI: 10.1021/ja004234u] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The electrochemical (cyclic voltammetry) and photoinduced (fluorescence quenching, quantum yields) reductive cleavages of four compounds, 4-cyano-alpha-trifluorotoluene (1), dimethylphenyl sulfonium (2), 4-cyanobenzylmethylphenyl sulfonium (3), and 4-cyanobenzyl chloride (4), are investigated and compared in terms of concerted vs stepwise mechanisms. Bearing in mind that an increase of the thermodynamic driving force shifts the mechanism from concerted to stepwise and that the driving force is larger under photochemical than under electrochemical conditions, 1 and 2 are typical examples where a stepwise mechanism is followed with compatible kinetic characteristics under both regimes. 4 undergoes a concerted electrochemical reductive cleavage, and the same mechanism is followed in the photoinduced reaction with consistent kinetic characteristics. The case of 3 is of particular interest, since a trend of passing from a concerted to a stepwise mechanism when going from the electrochemical to the photochemical conditions indeed appears upon analysis of the experimental results. The change of mechanism is, however, not complete since, in the photoinduced reaction, there is a balanced competition between the two pathways. In the same families of compounds, the unsubstituted benzylmethylphenyl sulfonium cations shows such a borderline behavior during the electrochemical reaction. In the photoinduced reaction, it is the 4-cyano derivative which behaves in a borderline manner, in line with the fact that it gives rise more readily to a concerted mechanism than the unsubstituted compound.
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Affiliation(s)
- L Pause
- Laboratoire d'Electrochimie Moléculaire, Unité Mixte de Recherche Université- CNRS No 7591, Université de Paris 7-Denis Diderot, 2 place Jussieu, 75251 Paris Cedex 05, France
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