Abstract
Cis-Cyclooctene, C8H14, undergoes an efficient electron-transfer (ET) catalyzed cycloaddition reaction in dichloromethane containing [NBu4][B(C6F5)4] as supporting electrolyte. The reactions were initiated by in-situ anodic generation of catalytic amounts of either [N(2,4-C6H3Br2)3]+ (1+, "magic green") or [ReCp(CO)3]+ (2+, Cp = (η5-C5H5)). The olefin radical chain reaction induced by ET mediation was complete in less than 10 min, some 100-1000 times faster than the optimum photochemically induced preparations of cyclobutane derivatives from cyclic olefins. Yields of up to 87% of mixtures of C16H28 isomers were obtained at an electro-synthetic level. Use of the weakly coordinating [B(C6F5)4]- anion, rather than a traditional small anion such as [PF6]- or [ClO4]-, was required to carry out the cyclization reactions. The more easily oxidized trans-cyclooctene, when anodized directly at an electrode, gave a similar isomeric mixture of cyclobutanes. Cycloheptene and cyclohexene underwent similar [2 + 2] coupling to give cyclobutane products. Cyclopentene gave a [2 + 2 + 2] cyclized trimer. The mechanism appears to involve a key radical-substrate propagation step in which an olefin radical cation reacts with a neutral olefin to give a cyclobutyl radical cation, which then accepts an electron, most likely from another olefin, to form the final neutral compound. Although the E1/2 potentials of the ET mediators are 660-900 mV lower than the estimated oxidation potentials of the olefins, the endergonic nature of the ET initiation step works to the advantage of the chain process by favoring the radical-substrate propagation step.
| Original language | English |
|---|---|
| Pages (from-to) | 68-77 |
| Number of pages | 10 |
| Journal | Journal of Electroanalytical Chemistry |
| Volume | 743 |
| DOIs | |
| Publication status | Published - Apr 15 2015 |
| Externally published | Yes |
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Keywords
- Cyclic olefins
- Cyclooctene
- Electrolyte anions
- Radical cation
- Radical-substrate reaction
- Tetrakis(perfluoroaryl)borate anion
ASJC Scopus subject areas
- Chemical Engineering(all)
- Analytical Chemistry
- Electrochemistry
Cite this
Electron-transfer catalyzed cycloaddition reactions of unactivated cyclic olefins in weakly coordinating anion electrolyte. / Stewart, Michael P.; Lam, Kevin; Chong, Daesung; Geiger, William E.
In: Journal of Electroanalytical Chemistry, Vol. 743, 15.04.2015, p. 68-77.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Electron-transfer catalyzed cycloaddition reactions of unactivated cyclic olefins in weakly coordinating anion electrolyte
AU - Stewart, Michael P.
AU - Lam, Kevin
AU - Chong, Daesung
AU - Geiger, William E.
PY - 2015/4/15
Y1 - 2015/4/15
N2 - Cis-Cyclooctene, C8H14, undergoes an efficient electron-transfer (ET) catalyzed cycloaddition reaction in dichloromethane containing [NBu4][B(C6F5)4] as supporting electrolyte. The reactions were initiated by in-situ anodic generation of catalytic amounts of either [N(2,4-C6H3Br2)3]+ (1+, "magic green") or [ReCp(CO)3]+ (2+, Cp = (η5-C5H5)). The olefin radical chain reaction induced by ET mediation was complete in less than 10 min, some 100-1000 times faster than the optimum photochemically induced preparations of cyclobutane derivatives from cyclic olefins. Yields of up to 87% of mixtures of C16H28 isomers were obtained at an electro-synthetic level. Use of the weakly coordinating [B(C6F5)4]- anion, rather than a traditional small anion such as [PF6]- or [ClO4]-, was required to carry out the cyclization reactions. The more easily oxidized trans-cyclooctene, when anodized directly at an electrode, gave a similar isomeric mixture of cyclobutanes. Cycloheptene and cyclohexene underwent similar [2 + 2] coupling to give cyclobutane products. Cyclopentene gave a [2 + 2 + 2] cyclized trimer. The mechanism appears to involve a key radical-substrate propagation step in which an olefin radical cation reacts with a neutral olefin to give a cyclobutyl radical cation, which then accepts an electron, most likely from another olefin, to form the final neutral compound. Although the E1/2 potentials of the ET mediators are 660-900 mV lower than the estimated oxidation potentials of the olefins, the endergonic nature of the ET initiation step works to the advantage of the chain process by favoring the radical-substrate propagation step.
AB - Cis-Cyclooctene, C8H14, undergoes an efficient electron-transfer (ET) catalyzed cycloaddition reaction in dichloromethane containing [NBu4][B(C6F5)4] as supporting electrolyte. The reactions were initiated by in-situ anodic generation of catalytic amounts of either [N(2,4-C6H3Br2)3]+ (1+, "magic green") or [ReCp(CO)3]+ (2+, Cp = (η5-C5H5)). The olefin radical chain reaction induced by ET mediation was complete in less than 10 min, some 100-1000 times faster than the optimum photochemically induced preparations of cyclobutane derivatives from cyclic olefins. Yields of up to 87% of mixtures of C16H28 isomers were obtained at an electro-synthetic level. Use of the weakly coordinating [B(C6F5)4]- anion, rather than a traditional small anion such as [PF6]- or [ClO4]-, was required to carry out the cyclization reactions. The more easily oxidized trans-cyclooctene, when anodized directly at an electrode, gave a similar isomeric mixture of cyclobutanes. Cycloheptene and cyclohexene underwent similar [2 + 2] coupling to give cyclobutane products. Cyclopentene gave a [2 + 2 + 2] cyclized trimer. The mechanism appears to involve a key radical-substrate propagation step in which an olefin radical cation reacts with a neutral olefin to give a cyclobutyl radical cation, which then accepts an electron, most likely from another olefin, to form the final neutral compound. Although the E1/2 potentials of the ET mediators are 660-900 mV lower than the estimated oxidation potentials of the olefins, the endergonic nature of the ET initiation step works to the advantage of the chain process by favoring the radical-substrate propagation step.
KW - Cyclic olefins
KW - Cyclooctene
KW - Electrolyte anions
KW - Radical cation
KW - Radical-substrate reaction
KW - Tetrakis(perfluoroaryl)borate anion
UR - http://www.scopus.com/inward/record.url?scp=84924058200&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84924058200&partnerID=8YFLogxK
U2 - 10.1016/j.jelechem.2015.02.001
DO - 10.1016/j.jelechem.2015.02.001
M3 - Article
VL - 743
SP - 68
EP - 77
JO - Journal of Electroanalytical Chemistry
JF - Journal of Electroanalytical Chemistry
SN - 1572-6657
ER -