TY - JOUR
T1 - DFT mechanistic study of RuII-catalyzed amide synthesis from alcohol and nitrile unveils a different mechanism for borrowing hydrogen
AU - Song, Chunyu
AU - Qu, Shuanglin
AU - Tao, Yuan
AU - Dang, Yanfeng
AU - Wang, Zhi Xiang
N1 - Publisher Copyright:
© 2014 American Chemical Society.
PY - 2014/9/5
Y1 - 2014/9/5
N2 - Using RuIIcomplex as a mediator, Hong and co-workers recently developed a redox-neutral synthetic strategy to produce amide from primary alcohol and nitrile with complete atom economy. Intrigued by the novel strategy, we performed DFT computations to unravel the catalytic mechanism of the system. The transformation is catalyzed by RuIIH2(CO)(PPh3)(IiPr) (IiPr = 1,2-diisopropylimidazol-2-ylidene) via four stages including nitrile reduction, alcohol dehydrogenation, C-N coupling, and amide production. Generally, alcohol dehydrogenation in dehydrogenative coupling (DHC) or borrowing hydrogen methodology (BHM) takes place separately, transferring the Hαand hydroxyl HOHatoms of alcohol to the catalyst to form the catalyst-H2hydride. Differently, the alcohol dehydrogenation in the present system couples with nitrile hydrogenation; alcohol plays a reductant role to aid nitrile reduction by transferring its HOHto nitrile N atom directly and Hαto the catalyst and meanwhile becomes partially oxidized. In our proposed preferred mechanism-B, the RuIIstate of the catalyst is retained in the whole catalytic cycle. Mechanism-A, postulated by experimentalists, involves RuII→ Ru0→ RuIIoxidation state alternation, and the Ru0intermediate is used to dehydrogenate alcohol separately via oxidative addition, followed by β-hydride elimination. As a result, mechanism-B is energetically more favorable than mechanism-A. In mechanism-B, the (N-)H atom of the amide bond exclusively originates from the hydroxyl HOHof alcohol. In comparison, the (N-)H atom in mechanism-A stems from either HOHor Hαof alcohol. The way of borrowing hydrogen that is used by nitrile is via participating in alcohol dehydrogenation, which is different from that in the conventional DHC/BHM reactions and may help expand the strategy and develop new routes for utilizing DHC and BHM strategies. (Chemical Equation Presented)
AB - Using RuIIcomplex as a mediator, Hong and co-workers recently developed a redox-neutral synthetic strategy to produce amide from primary alcohol and nitrile with complete atom economy. Intrigued by the novel strategy, we performed DFT computations to unravel the catalytic mechanism of the system. The transformation is catalyzed by RuIIH2(CO)(PPh3)(IiPr) (IiPr = 1,2-diisopropylimidazol-2-ylidene) via four stages including nitrile reduction, alcohol dehydrogenation, C-N coupling, and amide production. Generally, alcohol dehydrogenation in dehydrogenative coupling (DHC) or borrowing hydrogen methodology (BHM) takes place separately, transferring the Hαand hydroxyl HOHatoms of alcohol to the catalyst to form the catalyst-H2hydride. Differently, the alcohol dehydrogenation in the present system couples with nitrile hydrogenation; alcohol plays a reductant role to aid nitrile reduction by transferring its HOHto nitrile N atom directly and Hαto the catalyst and meanwhile becomes partially oxidized. In our proposed preferred mechanism-B, the RuIIstate of the catalyst is retained in the whole catalytic cycle. Mechanism-A, postulated by experimentalists, involves RuII→ Ru0→ RuIIoxidation state alternation, and the Ru0intermediate is used to dehydrogenate alcohol separately via oxidative addition, followed by β-hydride elimination. As a result, mechanism-B is energetically more favorable than mechanism-A. In mechanism-B, the (N-)H atom of the amide bond exclusively originates from the hydroxyl HOHof alcohol. In comparison, the (N-)H atom in mechanism-A stems from either HOHor Hαof alcohol. The way of borrowing hydrogen that is used by nitrile is via participating in alcohol dehydrogenation, which is different from that in the conventional DHC/BHM reactions and may help expand the strategy and develop new routes for utilizing DHC and BHM strategies. (Chemical Equation Presented)
KW - Acceptorless dehydrogenation
KW - Alcohol dehydrogenation
KW - Amide synthesis
KW - Borrowing hydrogen methodology
KW - DFT computations
KW - Dehydrogenative coupling
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U2 - 10.1021/cs5008156
DO - 10.1021/cs5008156
M3 - Article
AN - SCOPUS:84907683850
SN - 2155-5435
VL - 4
SP - 2854
EP - 2865
JO - ACS Catalysis
JF - ACS Catalysis
IS - 9
ER -