Abstract
A combined experimental and theoretical study was conducted to investigate the isomerization of 2-methyl-3-butenenitrile (2M3BN) to 3-pentenenitrile (3PN) and to 2-methyl-2-butenenitrile (2M2BN) catalyzed by nickel diphosphine complexes. Ni(1,4-bis(diphenylphosphino)butane) (dppb) was identified as the most reactive catalyst among the complexes that we examined experimentally. Quantum mechanics (density functional theory) was then used to study the two isomerization mechanisms catalyzed by this complex. We find that for the 2M3BN → 3PN isomerization, the reaction is initiated with [Formula presented] bond cleavage, followed by an allyl direct rotation and [Formula presented] bond reformation. For the 2M3BN → 2M2BN isomerization, the most energetically favorable pathway begins with [Formula presented] bond activation, followed by a π-σ-σ-π allyl rearrangement and [Formula presented] bond reformation. Our proposed mechanism for the 2M3BN → 2M2BN isomerization is slightly different (yet energetically more favorable) than that described in previous studies, where it has been suggested that 2M2BN is obtained through a π-σ-σ allyl rearrangement rather than a π-σ-σ-π type rearrangement. Additionally, we investigated the effect of Lewis acids in the 2M3BN → 3PN isomerization, which has been shown in most experiments to attenuate the reaction. Notably, our calculations indicated that ZnCl2, which is used as a model Lewis acid, actually reduces the barriers for all elementary steps. However, the effective kinetic barrier for the isomerization increases from 23.7 (without ZnCl2) to 24.0 kcal/mol because of the formation of a very stable Ni(π-allyl) ([Formula presented]2) intermediate, causing a decrease in the reaction rate. This theoretical result was further confirmed by our own experiments.
| Original language | English |
|---|---|
| Pages (from-to) | 29-38 |
| Number of pages | 10 |
| Journal | Journal of Organometallic Chemistry |
| Volume | 822 |
| DOIs | |
| Publication status | Published - 2016 Jan 1 |
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All Science Journal Classification (ASJC) codes
- Biochemistry
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry
- Materials Chemistry
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Theoretical and experimental study of the nickel-catalyzed isomerization of 2-Methyl-3-butenenitrile and the effect of a Lewis acid. / Liu, Kun; Liu, Kai Kai; Cheng, Mu-Jeng; Han, Ming Han.
In: Journal of Organometallic Chemistry, Vol. 822, 01.01.2016, p. 29-38.Research output: Contribution to journal › Article
TY - JOUR
T1 - Theoretical and experimental study of the nickel-catalyzed isomerization of 2-Methyl-3-butenenitrile and the effect of a Lewis acid
AU - Liu, Kun
AU - Liu, Kai Kai
AU - Cheng, Mu-Jeng
AU - Han, Ming Han
PY - 2016/1/1
Y1 - 2016/1/1
N2 - A combined experimental and theoretical study was conducted to investigate the isomerization of 2-methyl-3-butenenitrile (2M3BN) to 3-pentenenitrile (3PN) and to 2-methyl-2-butenenitrile (2M2BN) catalyzed by nickel diphosphine complexes. Ni(1,4-bis(diphenylphosphino)butane) (dppb) was identified as the most reactive catalyst among the complexes that we examined experimentally. Quantum mechanics (density functional theory) was then used to study the two isomerization mechanisms catalyzed by this complex. We find that for the 2M3BN → 3PN isomerization, the reaction is initiated with [Formula presented] bond cleavage, followed by an allyl direct rotation and [Formula presented] bond reformation. For the 2M3BN → 2M2BN isomerization, the most energetically favorable pathway begins with [Formula presented] bond activation, followed by a π-σ-σ-π allyl rearrangement and [Formula presented] bond reformation. Our proposed mechanism for the 2M3BN → 2M2BN isomerization is slightly different (yet energetically more favorable) than that described in previous studies, where it has been suggested that 2M2BN is obtained through a π-σ-σ allyl rearrangement rather than a π-σ-σ-π type rearrangement. Additionally, we investigated the effect of Lewis acids in the 2M3BN → 3PN isomerization, which has been shown in most experiments to attenuate the reaction. Notably, our calculations indicated that ZnCl2, which is used as a model Lewis acid, actually reduces the barriers for all elementary steps. However, the effective kinetic barrier for the isomerization increases from 23.7 (without ZnCl2) to 24.0 kcal/mol because of the formation of a very stable Ni(π-allyl) ([Formula presented]2) intermediate, causing a decrease in the reaction rate. This theoretical result was further confirmed by our own experiments.
AB - A combined experimental and theoretical study was conducted to investigate the isomerization of 2-methyl-3-butenenitrile (2M3BN) to 3-pentenenitrile (3PN) and to 2-methyl-2-butenenitrile (2M2BN) catalyzed by nickel diphosphine complexes. Ni(1,4-bis(diphenylphosphino)butane) (dppb) was identified as the most reactive catalyst among the complexes that we examined experimentally. Quantum mechanics (density functional theory) was then used to study the two isomerization mechanisms catalyzed by this complex. We find that for the 2M3BN → 3PN isomerization, the reaction is initiated with [Formula presented] bond cleavage, followed by an allyl direct rotation and [Formula presented] bond reformation. For the 2M3BN → 2M2BN isomerization, the most energetically favorable pathway begins with [Formula presented] bond activation, followed by a π-σ-σ-π allyl rearrangement and [Formula presented] bond reformation. Our proposed mechanism for the 2M3BN → 2M2BN isomerization is slightly different (yet energetically more favorable) than that described in previous studies, where it has been suggested that 2M2BN is obtained through a π-σ-σ allyl rearrangement rather than a π-σ-σ-π type rearrangement. Additionally, we investigated the effect of Lewis acids in the 2M3BN → 3PN isomerization, which has been shown in most experiments to attenuate the reaction. Notably, our calculations indicated that ZnCl2, which is used as a model Lewis acid, actually reduces the barriers for all elementary steps. However, the effective kinetic barrier for the isomerization increases from 23.7 (without ZnCl2) to 24.0 kcal/mol because of the formation of a very stable Ni(π-allyl) ([Formula presented]2) intermediate, causing a decrease in the reaction rate. This theoretical result was further confirmed by our own experiments.
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U2 - 10.1016/j.jorganchem.2016.08.016
DO - 10.1016/j.jorganchem.2016.08.016
M3 - Article
VL - 822
SP - 29
EP - 38
JO - Journal of Organometallic Chemistry
JF - Journal of Organometallic Chemistry
SN - 0022-328X
ER -