Dynamics of α-CH deprotonation and α-desilylation reactions of tertiary amine cation radicals

Xiaoming Zhang, Syun-Ru Yeh, Seok Hong, Mauro Freccero, Angelo Albini, Daniel E. Falvey, Patrick S. Mariano

Research output: Contribution to journalArticle

157 Citations (Scopus)

Abstract

Time-resolved laser spectroscopy has been used to generate and characterize a series of tertiary amine cation radicals and to determine the rates of their α-CH deprotonation and α-desilylation reactions with bases and silophiles. Laser excitation (308 nm) of a 60:40 MeOH:MeCN solution of PhNMe2 (DMA) and 1,4-dicyanobenzene (DCB) promotes SET-induced formation of the DMA cation radical (460 nm) and DCB anion radical (340 nm), which undergo decay by back electron transfer at nearly equal rates and with respective second-order rate constants of 1.1 × 1010 and 1.3 × 1010 M-1 s-1 (25°C). The decay rate is lowered (ca. 4-fold) by the inclusion of salts (ca. 0.1 M) such as nBu4NClO4, LiClO4, HBu4NCl, nBu4NBF4, and nBu4NO3SCF3 in MeOH-MeCN and by changing the solvent from MeCN to MeOH and to EtOH. The cation radical of PhNMeCH2(TMS) (480 nm) and the simultaneously generated DCB anion radical undergo second order decay in MeCN with respective rate constants of 1.2 × 1010 and 9.9 × 109 M-1 s-1 (25°C). The silylamine cation radical decay rate was found to be governed by the concentration of silophiles (MeOH, H2O and nBu4NF) in MeCN solutions. The observations are consistent with a silophile-induced desilylation process with second-order rate constants of 8.9 × 105 (MeOH), 1.27 × 106 (H2O), and 3.1 × 109 M-1 s-1 (nBu4NF). The rate of DMA cation radical decay is a function of base concentration. Both nBu4NOAc and nBu4NO2CCF3 react with the DMA cation radical (in 60:40 MeOH:MeCN containing 0.1 M nBu4NClO4) with second-order rate constants for α-CH deprotonation of 3.1 × 105 and 8 × 104 M-1 s-1 (25°C), respectively. Measurements with PhN(CD3)2 and nBu4NOAc gave a kH/kD for α-CH deprotonation of 3.6 (60:40 MeOH:MeCN, 25°C). Para-substituents have a pronounced effect on the rate of α-CH deprotonation by nBu4NOAc; second-order rate constants of 2.3 × 104, 1.1 × 105, and 2.5 × 106 M-1 s-1 were determined for the P-OMeC6H4NMe2, p-MeC6H4NMe2 and p-CF3C6H4NMe2 cation radicals. Studies with Ph2NMe demonstrated that its cation radical (645 nm) can be generated by SET to DCB and that its decay through α-CH deprotonation by nBu4NOAc has a second-order rate constant of 9.5 × 105 M-1 s-1 and a kH/kD value of 2.8 (25:75 MeOH:MeCN, 25°C). Finally, the effects of α-substituents on the rates of nBu4-NOAc-induced α-CH deprotonation of tertiary amine cation radicals were evaluated by use of the amines Ph2NCHR1R2. The second-order rate constants (25°C, 25:75 MeOH:MeCN) are 2.3 × 105 (R1 = Me, R2 = H), 1.7 × 105 (R1 = R2 = Me), 3.2 × 106 (R1 = Ph, R2 = H), 2.6 × 106 (R1 = CH=CH2, R2 = H), and 7.0 × 107 M-1 s-1 (R1 = C≡CH, R2 = H).

Original languageEnglish (US)
Pages (from-to)4211-4220
Number of pages10
JournalJournal of the American Chemical Society
Volume116
Issue number10
StatePublished - May 18 1994
Externally publishedYes

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Deprotonation
Amines
Cations
Positive ions
Rate constants
Dynamic mechanical analysis
Anions
Lasers
Negative ions
Laser excitation
Laser spectroscopy
Spectrum Analysis
Salts
Electrons

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Zhang, X., Yeh, S-R., Hong, S., Freccero, M., Albini, A., Falvey, D. E., & Mariano, P. S. (1994). Dynamics of α-CH deprotonation and α-desilylation reactions of tertiary amine cation radicals. Journal of the American Chemical Society, 116(10), 4211-4220.

Dynamics of α-CH deprotonation and α-desilylation reactions of tertiary amine cation radicals. / Zhang, Xiaoming; Yeh, Syun-Ru; Hong, Seok; Freccero, Mauro; Albini, Angelo; Falvey, Daniel E.; Mariano, Patrick S.

In: Journal of the American Chemical Society, Vol. 116, No. 10, 18.05.1994, p. 4211-4220.

Research output: Contribution to journalArticle

Zhang, X, Yeh, S-R, Hong, S, Freccero, M, Albini, A, Falvey, DE & Mariano, PS 1994, 'Dynamics of α-CH deprotonation and α-desilylation reactions of tertiary amine cation radicals', Journal of the American Chemical Society, vol. 116, no. 10, pp. 4211-4220.
Zhang, Xiaoming ; Yeh, Syun-Ru ; Hong, Seok ; Freccero, Mauro ; Albini, Angelo ; Falvey, Daniel E. ; Mariano, Patrick S. / Dynamics of α-CH deprotonation and α-desilylation reactions of tertiary amine cation radicals. In: Journal of the American Chemical Society. 1994 ; Vol. 116, No. 10. pp. 4211-4220.
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abstract = "Time-resolved laser spectroscopy has been used to generate and characterize a series of tertiary amine cation radicals and to determine the rates of their α-CH deprotonation and α-desilylation reactions with bases and silophiles. Laser excitation (308 nm) of a 60:40 MeOH:MeCN solution of PhNMe2 (DMA) and 1,4-dicyanobenzene (DCB) promotes SET-induced formation of the DMA cation radical (460 nm) and DCB anion radical (340 nm), which undergo decay by back electron transfer at nearly equal rates and with respective second-order rate constants of 1.1 × 1010 and 1.3 × 1010 M-1 s-1 (25°C). The decay rate is lowered (ca. 4-fold) by the inclusion of salts (ca. 0.1 M) such as nBu4NClO4, LiClO4, HBu4NCl, nBu4NBF4, and nBu4NO3SCF3 in MeOH-MeCN and by changing the solvent from MeCN to MeOH and to EtOH. The cation radical of PhNMeCH2(TMS) (480 nm) and the simultaneously generated DCB anion radical undergo second order decay in MeCN with respective rate constants of 1.2 × 1010 and 9.9 × 109 M-1 s-1 (25°C). The silylamine cation radical decay rate was found to be governed by the concentration of silophiles (MeOH, H2O and nBu4NF) in MeCN solutions. The observations are consistent with a silophile-induced desilylation process with second-order rate constants of 8.9 × 105 (MeOH), 1.27 × 106 (H2O), and 3.1 × 109 M-1 s-1 (nBu4NF). The rate of DMA cation radical decay is a function of base concentration. Both nBu4NOAc and nBu4NO2CCF3 react with the DMA cation radical (in 60:40 MeOH:MeCN containing 0.1 M nBu4NClO4) with second-order rate constants for α-CH deprotonation of 3.1 × 105 and 8 × 104 M-1 s-1 (25°C), respectively. Measurements with PhN(CD3)2 and nBu4NOAc gave a kH/kD for α-CH deprotonation of 3.6 (60:40 MeOH:MeCN, 25°C). Para-substituents have a pronounced effect on the rate of α-CH deprotonation by nBu4NOAc; second-order rate constants of 2.3 × 104, 1.1 × 105, and 2.5 × 106 M-1 s-1 were determined for the P-OMeC6H4NMe2, p-MeC6H4NMe2 and p-CF3C6H4NMe2 cation radicals. Studies with Ph2NMe demonstrated that its cation radical (645 nm) can be generated by SET to DCB and that its decay through α-CH deprotonation by nBu4NOAc has a second-order rate constant of 9.5 × 105 M-1 s-1 and a kH/kD value of 2.8 (25:75 MeOH:MeCN, 25°C). Finally, the effects of α-substituents on the rates of nBu4-NOAc-induced α-CH deprotonation of tertiary amine cation radicals were evaluated by use of the amines Ph2NCHR1R2. The second-order rate constants (25°C, 25:75 MeOH:MeCN) are 2.3 × 105 (R1 = Me, R2 = H), 1.7 × 105 (R1 = R2 = Me), 3.2 × 106 (R1 = Ph, R2 = H), 2.6 × 106 (R1 = CH=CH2, R2 = H), and 7.0 × 107 M-1 s-1 (R1 = C≡CH, R2 = H).",
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T1 - Dynamics of α-CH deprotonation and α-desilylation reactions of tertiary amine cation radicals

AU - Zhang, Xiaoming

AU - Yeh, Syun-Ru

AU - Hong, Seok

AU - Freccero, Mauro

AU - Albini, Angelo

AU - Falvey, Daniel E.

AU - Mariano, Patrick S.

PY - 1994/5/18

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N2 - Time-resolved laser spectroscopy has been used to generate and characterize a series of tertiary amine cation radicals and to determine the rates of their α-CH deprotonation and α-desilylation reactions with bases and silophiles. Laser excitation (308 nm) of a 60:40 MeOH:MeCN solution of PhNMe2 (DMA) and 1,4-dicyanobenzene (DCB) promotes SET-induced formation of the DMA cation radical (460 nm) and DCB anion radical (340 nm), which undergo decay by back electron transfer at nearly equal rates and with respective second-order rate constants of 1.1 × 1010 and 1.3 × 1010 M-1 s-1 (25°C). The decay rate is lowered (ca. 4-fold) by the inclusion of salts (ca. 0.1 M) such as nBu4NClO4, LiClO4, HBu4NCl, nBu4NBF4, and nBu4NO3SCF3 in MeOH-MeCN and by changing the solvent from MeCN to MeOH and to EtOH. The cation radical of PhNMeCH2(TMS) (480 nm) and the simultaneously generated DCB anion radical undergo second order decay in MeCN with respective rate constants of 1.2 × 1010 and 9.9 × 109 M-1 s-1 (25°C). The silylamine cation radical decay rate was found to be governed by the concentration of silophiles (MeOH, H2O and nBu4NF) in MeCN solutions. The observations are consistent with a silophile-induced desilylation process with second-order rate constants of 8.9 × 105 (MeOH), 1.27 × 106 (H2O), and 3.1 × 109 M-1 s-1 (nBu4NF). The rate of DMA cation radical decay is a function of base concentration. Both nBu4NOAc and nBu4NO2CCF3 react with the DMA cation radical (in 60:40 MeOH:MeCN containing 0.1 M nBu4NClO4) with second-order rate constants for α-CH deprotonation of 3.1 × 105 and 8 × 104 M-1 s-1 (25°C), respectively. Measurements with PhN(CD3)2 and nBu4NOAc gave a kH/kD for α-CH deprotonation of 3.6 (60:40 MeOH:MeCN, 25°C). Para-substituents have a pronounced effect on the rate of α-CH deprotonation by nBu4NOAc; second-order rate constants of 2.3 × 104, 1.1 × 105, and 2.5 × 106 M-1 s-1 were determined for the P-OMeC6H4NMe2, p-MeC6H4NMe2 and p-CF3C6H4NMe2 cation radicals. Studies with Ph2NMe demonstrated that its cation radical (645 nm) can be generated by SET to DCB and that its decay through α-CH deprotonation by nBu4NOAc has a second-order rate constant of 9.5 × 105 M-1 s-1 and a kH/kD value of 2.8 (25:75 MeOH:MeCN, 25°C). Finally, the effects of α-substituents on the rates of nBu4-NOAc-induced α-CH deprotonation of tertiary amine cation radicals were evaluated by use of the amines Ph2NCHR1R2. The second-order rate constants (25°C, 25:75 MeOH:MeCN) are 2.3 × 105 (R1 = Me, R2 = H), 1.7 × 105 (R1 = R2 = Me), 3.2 × 106 (R1 = Ph, R2 = H), 2.6 × 106 (R1 = CH=CH2, R2 = H), and 7.0 × 107 M-1 s-1 (R1 = C≡CH, R2 = H).

AB - Time-resolved laser spectroscopy has been used to generate and characterize a series of tertiary amine cation radicals and to determine the rates of their α-CH deprotonation and α-desilylation reactions with bases and silophiles. Laser excitation (308 nm) of a 60:40 MeOH:MeCN solution of PhNMe2 (DMA) and 1,4-dicyanobenzene (DCB) promotes SET-induced formation of the DMA cation radical (460 nm) and DCB anion radical (340 nm), which undergo decay by back electron transfer at nearly equal rates and with respective second-order rate constants of 1.1 × 1010 and 1.3 × 1010 M-1 s-1 (25°C). The decay rate is lowered (ca. 4-fold) by the inclusion of salts (ca. 0.1 M) such as nBu4NClO4, LiClO4, HBu4NCl, nBu4NBF4, and nBu4NO3SCF3 in MeOH-MeCN and by changing the solvent from MeCN to MeOH and to EtOH. The cation radical of PhNMeCH2(TMS) (480 nm) and the simultaneously generated DCB anion radical undergo second order decay in MeCN with respective rate constants of 1.2 × 1010 and 9.9 × 109 M-1 s-1 (25°C). The silylamine cation radical decay rate was found to be governed by the concentration of silophiles (MeOH, H2O and nBu4NF) in MeCN solutions. The observations are consistent with a silophile-induced desilylation process with second-order rate constants of 8.9 × 105 (MeOH), 1.27 × 106 (H2O), and 3.1 × 109 M-1 s-1 (nBu4NF). The rate of DMA cation radical decay is a function of base concentration. Both nBu4NOAc and nBu4NO2CCF3 react with the DMA cation radical (in 60:40 MeOH:MeCN containing 0.1 M nBu4NClO4) with second-order rate constants for α-CH deprotonation of 3.1 × 105 and 8 × 104 M-1 s-1 (25°C), respectively. Measurements with PhN(CD3)2 and nBu4NOAc gave a kH/kD for α-CH deprotonation of 3.6 (60:40 MeOH:MeCN, 25°C). Para-substituents have a pronounced effect on the rate of α-CH deprotonation by nBu4NOAc; second-order rate constants of 2.3 × 104, 1.1 × 105, and 2.5 × 106 M-1 s-1 were determined for the P-OMeC6H4NMe2, p-MeC6H4NMe2 and p-CF3C6H4NMe2 cation radicals. Studies with Ph2NMe demonstrated that its cation radical (645 nm) can be generated by SET to DCB and that its decay through α-CH deprotonation by nBu4NOAc has a second-order rate constant of 9.5 × 105 M-1 s-1 and a kH/kD value of 2.8 (25:75 MeOH:MeCN, 25°C). Finally, the effects of α-substituents on the rates of nBu4-NOAc-induced α-CH deprotonation of tertiary amine cation radicals were evaluated by use of the amines Ph2NCHR1R2. The second-order rate constants (25°C, 25:75 MeOH:MeCN) are 2.3 × 105 (R1 = Me, R2 = H), 1.7 × 105 (R1 = R2 = Me), 3.2 × 106 (R1 = Ph, R2 = H), 2.6 × 106 (R1 = CH=CH2, R2 = H), and 7.0 × 107 M-1 s-1 (R1 = C≡CH, R2 = H).

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