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and SUNY Binghamton, respectively, for start-up support.
species (Figure S26). Notably, the electronic structure of two-
electron reduced 3-Ni is similar to that of iron porphyrin,
which is best formulated as an Fe(II) center supported by a
porphyrin diradical anion.16 In the case of 2-Ni + 2e–, singlet
and triplet states are degenerate in which the dx2-y2 orbital of
DOI: 10.1039/C8CC00266E
1
2
N. S. Lewis and D. G. Nocera, Proc. Natl. Acad. Sci. USA, 2006,
103, 15729.
J. R. Petit, J. Jouzel, D. Raynaud, N. I. Barkov, J.-M. Barnola, I.
Basile, M. Bender, J. Chappellaz, M. Davis, G. Delaygue, M.
Delmotte, V. M. Kotlyakov, M. Legrand, V. Y. Lipenkov, C.
Lorius, L. Pépin, C. Ritz, E. Saltzman and M. Stievenard,
Nature, 1999, 399, 429.
the nickel center couples antiferromagnetically (12'-Ni + 2e–
Figures S24, S27) or ferromagnetically (32-Ni + 2e–, Figures S25,
S27) with the * orbital of the bipyridine ligand. Importantly, a
closed-shell singlet ρNi = 0.00 was also
12-Ni 2e–
calculated to be within 1.0 kcal/mol of the unrestricted
singlet and triplet states (Table S6). This implies that 2-Ni + 2e–
is best represented by resonance form [NiII(L2•−)] [NiI(L•−)].
,
3
4
a) P. Kang, Z. Chen, M. Brookhart and T. J. Meyer, Top. Catal.,
2015, 58, 30; b) H. Takeda, C. Cometto, O. Ishitani and M.
(
+
,
)
~
Robert, ACS Catal., 2017,
a) I. Azcarate, C. Costentin, M. Robert and J.-M. Savéant, J.
Am. Chem. Soc., 2016, 138 16639; b) D. Behar, T.
7, 70.
,
↔
Dhanasekaran, P. Neta, C. M. Hosten, D. Ejeh, P. Hambright
and E. Fujita, J. Phys. Chem. A, 1998, 102, 2870; c) Z. Weng, J.
Jiang, Y. Wu, Z. Wu, X. Guo, K. L. Materna, W. Liu, V. S.
Batista, G. W. Brudvig and H. Wang, J. Am. Chem. Soc., 2016,
138, 8076; d) Y. Wu, J. Jiang, Z. Weng, M. Wang, D. L. J.
Broere, Y. Zhong, G. W. Brudvig, Z. Feng and H. Wang, ACS
At this point, we propose an explanation regarding the
observed product selectivities in which Faradaic efficiencies
(FE) for CO2-to-CO conversion of 5%, 56%, and 87% were
obtained for 1-Ni, 2-Ni, and 3-Ni, respectively. After two
reductions, a Ni(I) center is formed for 1-Ni while 3-Ni features
a Ni(II) center. In contrast, the closely-spaced electronic states
found following two reductions of 2-Ni give access to both a
Ni(I) center or Ni(II) center with the remaining electron(s)
localized on the ligand. In the case of 1-Ni, a metal hydride
species can be formed after one or two reductions while such
Cent. Sci., 2017, 3, 847.
5
a) M. Beley, J.-P. Collin, R. Ruppert and J.-P. Sauvage, J. Am.
Chem. Soc., 1986, 108, 7461; b) M. H. Schmidt, G. M.
Miskelly and N. S. Lewis, J. Am. Chem. Soc., 1990, 112, 3420;
c) J. Schneider, H. Jia, K. Kobiro, D. E. Cabelli, J. T.
Muckerman and E. Fujita, Energy Environ. Sci., 2012, 5, 9502;
d) G. Neri, J. J. Walsh, C. Wilson, A. Reynal, J. Y. C. Lim, X. Li, A.
J. P. White, N. J. Long, J. R. Durrant and A. J. Cowan, Phys.
Chem. Chem. Phys., 2015, 17, 1562.
an intermediate is not computationally accessible for 3-Ni
.
With 2-Ni, formation of a nickel-hydride intermediate is also
calculated to be accessible. It is widely established that
formation of a metal-hydride species is required to enter
catalytic cycles for the hydrogen evolution reaction.17 These
results are consistent with the observed FEs for H2 production
across the series. The full examination of these steps is beyond
the scope of this work and a comprehensive study is underway.
In summary, we have developed a series of well-defined
nickel complexes for electrocatalytic CO2 reduction. The nickel
complexes are competent, homogeneous electrocatalysts that
6
7
8
a) C. M. Lieber and N. S. Lewis, J. Am. Chem. Soc., 1984, 106,
5033; b) S. Kapusta and N. Hackerman, J. Electrochem. Soc.,
1984, 131, 1511.
a) B. Fisher and R. Eisenberg, J. Am. Chem. Soc., 1980, 102
7361; b) D. C. Lacy, C. C. L. McCrory and J. C. Peters, Inorg.
Chem., 2014, 53, 4980.
a) J. Grodkowski, P. Neta, E. Fujita, A. Mahammed, L.
Simkhovich and Z. Gross, J. Phys. Chem. A, 2002, 106, 4772;
b) S. Aoi, K. Mase, K. Ohkubo and S. Fukuzumi, Chem.
Commun., 2015, 51, 10226.
,
9
A. Chapovetsky, T. H. Do, R. Haiges, M. K. Takase and S. C.
Marinescu, J. Am. Chem. Soc., 2016, 138, 5765.
operate with
deactivation.
~
100% overall Faradaic efficiency with no sign of
structure-function relationship regarding
A
10 a) V. S. Thoi and C. J. Chang, Chem. Commun., 2011, 47, 6578;
b) V. S. Thoi, N. Kornienko, C. G. Margarit, P. Yang and C. J.
Chang, J. Am. Chem. Soc., 2013, 135, 14413; c) M. Sheng, N.
Jiang, S. Gustafson, B. You, D. H. Ess and Y. Sun, Dalton
Trans., 2015, 44, 16247.
11 X.-E. Wu, L. Ma, M.-X. Ding and L.-X. Gao, Chem. Lett., 2005,
34, 312.
12 A. J. Bard and L. R. Faulkner, Electrochemical Methods:
Fundamentals and Applications; 2nd Edition; John Wiley and
Sons: New York, 2001.
catalytic activity and selectivity has been elucidated for the
closely related 2,2'-bipyridine derivatized NHC ligands via
electrochemical experiments and DFT calculations. The results
show a clear macrocyclic effect on catalytic activity across the
series where increased rigidity of the redox-active macrocycle
leads to enhanced selectivity for CO2 reduction (CO2 + 2H+ +
2e–
(2H+ + 2e–
→
CO + H2O) over the competing proton reduction reaction
H2). These studies reveal a critical interplay
→
13 a) T. Soda, Y. Kitagawa, T. Onishi, Y. Takano, Y. Shigeta, H.
Nagao, Y. Yoshioka and K. Yamaguchi, Chem. Phys. Lett.,
2000, 319, 223; b) K. Yamaguchi, F. Jensen, A. Dorigo and K.
N. Houk, Chem. Phys. Lett., 1988, 149, 537.
between the metal and redox-active ligand that dictates the
reaction pathway and highlights the importance of electronic
structure considerations in managing redox inventories to
orchestrate multielectron chemistry. Further development of
this ligand family and its application to other first-row
transition metals are ongoing efforts in our laboratory.
14 a) J.-M. Savéant and E. Vianello, Electrochim. Acta, 1965, 10
,
905; b) E. S. Rountree, B. D. McCarthy, T. T. Eisenhart and J. L.
Dempsey, Inorg. Chem., 2014, 53, 9983.
15 (a) A. V. Marenich, J. Ho, M. L. Coote, C. J. Cramer and D. G.
Truhlar, Phys. Chem. Chem. Phys., 2014, 16, 15068; b) J. Ho,
Phys. Chem. Chem. Phys., 2015, 17, 2859; c) J. Ho and M. Z.
Ertem, J. Phys. Chem. B, 2016, 120, 1319.
Conflicts of interest
The authors declare no conflict of interest.
16 C. Römelt, J. Song, M. Tarrago, J. A. Rees, M. van Gastel, T.
Weyhermüller, S. DeBeer, E. Bill, F. Neese and S. Ye, Inorg.
Chem., 2017, 56, 4745.
Notes and references
17 a) M. Wang, L. Chen and L. Sun, Energy Environ. Sci., 2012, 5,
JWJ thanks the National Science Foundation (OIA-1539035) for
funding. JWJ and JAP are grateful to the University of Mississippi
6763; b) V. S. Thoi, Y. Sun, J. R. Long and C. J. Chang, Chem.
Soc. Rev., 2013, 42, 2388.
4 | J. Name., 2012, 00, 1-3
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