TY - JOUR
T1 - Optimal functionalization of a molecular electrocatalyst for hydride transfer
AU - Xu, Shenzhen
AU - Carter, Emily A.
N1 - Publisher Copyright:
© 2019 National Academy of Sciences. All rights reserved.
PY - 2019/11/12
Y1 - 2019/11/12
N2 - Optimization of hydride transfer (HT) catalysts to enhance rates and selectivities of (photo)electroreduction reactions could be a crucial component of a sustainable chemical industry. Here, we analyze how ring functionalization of the adsorbed transient intermediate 2-pyridinide (2-PyH−*)—predicted to form in situ from pyridine (Py) in acidified water at a cathode surface and to be the key to selective CO2 photoelectroreduction on p-GaP—may enhance catalytic activity. Earlier studies revealed that 2-PyH−*’s instability results from a protonation side reaction producing adsorbed dihydropyridine (DHP*), which is relatively HT-inactive. Reducing the electron density on 2-PyH−* could limit this protonation, with the trade-off that it may become less active for HT from 2-PyH−*–R to CO2. We explore here how Py functionalization affects the electron distribution and in turn tunes the catalytic performance of 2-PyH−*. We indeed find that electron-withdrawing groups could enhance the stability of 2-PyH−* by reducing its electron density on the ring. Furthermore, we find that the change in the number of electrons on the substituting group of the hydride donor is a good descriptor for both the stability against protonation and the magnitude of the HT barrier. We predict that –CH2–CH2F is the best candidate substituent, as it significantly improves the stability of 2-PyH−* with only a small increase in HT barrier. –CH=CH2 and –CH2F also could be promising, although they require further investigation due to a larger HT-barrier increase.
AB - Optimization of hydride transfer (HT) catalysts to enhance rates and selectivities of (photo)electroreduction reactions could be a crucial component of a sustainable chemical industry. Here, we analyze how ring functionalization of the adsorbed transient intermediate 2-pyridinide (2-PyH−*)—predicted to form in situ from pyridine (Py) in acidified water at a cathode surface and to be the key to selective CO2 photoelectroreduction on p-GaP—may enhance catalytic activity. Earlier studies revealed that 2-PyH−*’s instability results from a protonation side reaction producing adsorbed dihydropyridine (DHP*), which is relatively HT-inactive. Reducing the electron density on 2-PyH−* could limit this protonation, with the trade-off that it may become less active for HT from 2-PyH−*–R to CO2. We explore here how Py functionalization affects the electron distribution and in turn tunes the catalytic performance of 2-PyH−*. We indeed find that electron-withdrawing groups could enhance the stability of 2-PyH−* by reducing its electron density on the ring. Furthermore, we find that the change in the number of electrons on the substituting group of the hydride donor is a good descriptor for both the stability against protonation and the magnitude of the HT barrier. We predict that –CH2–CH2F is the best candidate substituent, as it significantly improves the stability of 2-PyH−* with only a small increase in HT barrier. –CH=CH2 and –CH2F also could be promising, although they require further investigation due to a larger HT-barrier increase.
KW - Carbon dioxide reduction
KW - Catalyst functionalization
KW - Hydride transfer
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U2 - 10.1073/pnas.1911948116
DO - 10.1073/pnas.1911948116
M3 - Article
C2 - 31659020
AN - SCOPUS:85074888658
SN - 0027-8424
VL - 116
SP - 22953
EP - 22958
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 46
ER -