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Visible Light Sensitized CO2 Activation by the Tetraaza [Co^(II)N_4H(MeCN)]^(2+) Complex Investigated by FT-IR Spectroscopy and DFT Calculations

Zhang, M. and El-Roz, M. and Frei, H. and Mendoza-Cortés, J. L. and Head-Gordon, M. and Lacy, David C. and Peters, Jonas C. (2015) Visible Light Sensitized CO2 Activation by the Tetraaza [Co^(II)N_4H(MeCN)]^(2+) Complex Investigated by FT-IR Spectroscopy and DFT Calculations. Journal of Physical Chemistry C, 119 (9). pp. 4645-4654. ISSN 1932-7447.

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In situ FT-IR measurements and electronic structure calculations are reported for the reduction of CO_2 catalyzed by the macrocyclic complex [Co^(II)N_4H]^(2+) (N_4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(17),2,11,13,15-pentaene). Beginning from the [Co^(II)N_4H]^(2+) resting state of the complex in wet acetonitrile solution, two different visible light sensitizers with substantially different reducing power are employed to access reduced states. Accessing reduced states of the complex with a [Ru(bpy)_3]^(2+) sensitizer yields an infrared band at 1670 cm^(–1) attributed to carboxylate, which is also observed for an authentic sample of the one-electron reduced complex [CoN_4H(MeCN)]^+ in CO_2 saturated acetonitrile solution. The results are interpreted based on calculations using the pure BP86 functional that correctly reproduces experimental geometries. Continuum solvation effects are also included. The calculations show that Co is reduced to Co^I in the first reduction, which is consistent with experimental d–d spectra of square Co(I) macrocycle complexes. The energy of the CO_2 adduct of the one-electron reduced catalyst complex is essentially the same as for [CoN_4H(MeCN)]^+, which implies that only a fraction of the latter forms an adduct with CO_2. By contrast, the calculations indicate a crucial role for redox noninnocence of the macrocyclic ligand in the doubly reduced state, [Co^I(N_4H) –•], and show that [Co^I(N_4H) –•] binds partially reduced CO_2 fairly strongly. Experimentally accessing [Co^I(N_4H) –•] with an Ir(bpy)_3 sensitizer with greater reducing power closes the catalytic cycle as FT-IR spectroscopy shows CO production. Use of isotopically substituted C^(18)O_2 also shows clear evidence for ^(18)O-substituted byproducts from CO_2 reduction to CO.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemSupporting Information
Head-Gordon, M.0000-0002-4309-6669
Peters, Jonas C.0000-0002-6610-4414
Additional Information:© 2015 American Chemical Society. Received: December 22, 2014. Revised: February 11, 2015. Publication Date (Web): February 12, 2015. This material is based on work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. M.E.-R. acknowledges the European Regional Development Fund Franco-British INTERREG IVA (Project E3C3, ref. 4274) for financial support, and Prof. Frederic Thibault-Starzyk for insightful discussions. D.C.L. would like to acknowledge the National Institute of Health (Award Number F32GM106726).
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0004993
European Regional Development Fund Franco-British INTERREG IVAProject E3C3, ref. 4274
Issue or Number:9
Record Number:CaltechAUTHORS:20150420-145653024
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Official Citation:Visible Light Sensitized CO2 Activation by the Tetraaza [CoIIN4H(MeCN)]2+ Complex Investigated by FT-IR Spectroscopy and DFT Calculations M. Zhang, M. El-Roz, H. Frei, J. L. Mendoza-Cortes, M. Head-Gordon, David C. Lacy, and Jonas C. Peters The Journal of Physical Chemistry C 2015 119 (9), 4645-4654 DOI: 10.1021/jp5127738
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56788
Deposited By: Ruth Sustaita
Deposited On:21 Apr 2015 14:58
Last Modified:09 Mar 2020 13:18

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