Inorganic Chemistry
Communication
(4) (a) Weiss, R.; Bulach, V.; Gold, A.; Terner, J.; Trautwein, A. X. J.
Biol. Inorg. Chem. 2001, 6, 831. (b) Evangelio, E.; Ruiz-Molina, D. Eur. J.
Inorg. Chem. 2005, 2005, 2957.
(5) Leeladee, P.; Baglia, R. A.; Prokop, K. A.; Latifi, R.; de Visser, S. P.;
Goldberg, D. P. J. Am. Chem. Soc. 2012, 134, 10397.
identity of the Lewis acid further influences the reaction rates,
with triarylborane being more reactive in both cases. In addition,
the much slower rate constants for the more sterically hindered
2,4,6-TTBP indicate a mechanism involving HAT. Support for
this mechanism was obtained by measuring a kinetic isotope
effect of 3.2 0.3 for 2,4,6-TTBP-OD (Figure S11 in the SI).10 It
was reported that the addition of Sc3+ to a nonheme MnIV(O)
complex caused a decrease in HAT rates, attributed to steric
hindrance from the Sc3+ ion.6b Our results appear to contrast
these findings, with Lewis acids strongly increasing the HAT
reactivity of a MnIV(O)(Cz•+) complex. However, this
comparison is complicated by the fact that the inherent HAT
reactivity of the valence tautomer with the electronic structure
MnIV(O)(Cz•+) is not known. The influence of the electronic
structure on the reactivity of high-valent metal−oxo complexes
remains an area of intense debate.11
In summary, we have demonstrated for the first time that a
nonmetal ion Lewis acid can induce reversible valence
tautomerism in a metalloporphyrinoid compound. We have
also shown that the HAT reactivity of a MnIV(O)-
(porphyrinoid•+) complex in the presence of Lewis acids is
strongly enhanced compared to its closed-shell MnV(O) valence
tautomer. This work provides new insight regarding how to
control valence tautomerism in porphyrinoid compounds, as well
as on how Lewis acids influence the reactivity of high-valent
metal−oxo species.
(6) (a) Tsui, E. Y.; Kanady, J. S.; Agapie, T. Inorg. Chem. 2013, 52,
13833. (b) Chen, J.; Lee, Y.-M.; Davis, K. M.; Wu, X.; Seo, M. S.; Cho,
K.-B.; Yoon, H.; Park, Y. J.; Fukuzumi, S.; Pushkar, Y. N.; Nam, W. J. Am.
Chem. Soc. 2013, 135, 6388. (c) Yoon, H.; Lee, Y.-M.; Wu, X.; Cho, K.-
B.; Sarangi, R.; Nam, W.; Fukuzumi, S. J. Am. Chem. Soc. 2013, 135,
9186. (d) Park, Y. J.; Ziller, J. W.; Borovik, A. S. J. Am. Chem. Soc. 2011,
133, 9258. (e) Lam, W. W. Y.; Yiu, S.-M.; Lee, J. M. N.; Yau, S. K. Y.;
Kwong, H.-K.; Lau, T.-C.; Liu, D.; Lin, Z. J. Am. Chem. Soc. 2006, 128,
2851. (f) Dong, L.; Wang, Y.; Lv, Y.; Chen, Z.; Mei, F.; Xiong, H.; Yin, G.
Inorg. Chem. 2013, 52, 5418. (g) Mukherjee, S.; Stull, J. A.; Yano, J.;
Stamatatos, T. C.; Pringouri, K.; Stich, T. A.; Abboud, K. A.; Britt, R. D.;
Yachandra, V. K.; Christou, G. Proc. Natl. Acad. Sci. U.S.A. 2012, 109,
2257−2262.
(7) Smeltz, J. L.; Lilly, C. P.; Boyle, P. D.; Ison, E. A. J. Am. Chem. Soc.
2013, 135, 9433.
(8) (a) Wade, C. R.; Broomsgrove, A. E. J.; Aldridge, S.; Gabbai, F. P.
Chem. Rev. 2010, 110, 3958. (b) Zhao, H.; Reibenspies, J. H.; Gabbai, F.
P. Dalton Trans. 2013, 42, 608.
(9) (a) Prokop, K. A.; de Visser, S. P.; Goldberg, D. P. Angew. Chem.,
Int. Ed. 2010, 49, 5091. (b) Fukuzumi, S.; Kotani, H.; Prokop, K. A.;
Goldberg, D. P. J. Am. Chem. Soc. 2011, 133, 1859. (c) Lansky, D. E.;
Goldberg, D. P. Inorg. Chem. 2006, 45, 5119.
(10) An electron transfer/proton transfer or proton transfer/electron
transfer mechanism cannot be definitively ruled out.
(11) (a) Saouma, C. T.; Mayer, J. M. Chem. Sci. 2014, 5, 21. (b) Sahu,
S.; Widger, L. R.; Quesne, M. G.; de Visser, S. P.; Matsumura, H.;
ASSOCIATED CONTENT
* Supporting Information
Experimental procedures, kinetic studies, and EPR and MS data.
This material is available free of charge via the Internet at http://
■
S
Moenne-Loccoz, P.; Siegler, M. A.; Goldberg, D. P. J. Am. Chem. Soc.
̈
2013, 135, 10590. (c) Usharani, D.; Janardanan, D.; Li, C.; Shaik, S. Acc.
Chem. Res. 2012, 46, 471.
AUTHOR INFORMATION
Corresponding Author
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the NIH (Grant GM101153 to D.P.G.) for financial
support. R.A.B. is grateful for an E2SHI Fellowship. I.I.-B. and
M.D. acknowledge support from the “Solar Technologies Go
Hybrid” initiative of the State of Bavaria.
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dx.doi.org/10.1021/ic500901y | Inorg. Chem. XXXX, XXX, XXX−XXX