Kinzel NW, Demirbas D, Bill E, Weyhermüller T, Werlé C, Kaeffer N, Leitner W. Systematic Variation of 3d Metal Centers in a Redox-Innocent Ligand Environment: Structures, Electrochemical Properties, and Carbon Dioxide Activation.
Inorg Chem 2021;
60:19062-19078. [PMID:
34851088 PMCID:
PMC8693193 DOI:
10.1021/acs.inorgchem.1c02909]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Coordination compounds
of earth-abundant 3d transition metals are
among the most effective catalysts for the electrochemical reduction
of carbon dioxide (CO2). While the properties of the metal
center are crucial for the ability of the complexes to electrochemically
activate CO2, systematic variations of the metal within
an identical, redox-innocent ligand backbone remain insufficiently
investigated. Here, we report on the synthesis, structural and spectroscopic
characterization, and electrochemical investigation of a series of
3d transition-metal complexes [M = Mn(I), Fe(II), Co(II), Ni(II),
Cu(I), and Zn(II)] coordinated by a new redox-innocent PNP pincer
ligand system. Only the Fe, Co, and Ni complexes reveal distinct metal-centered
electrochemical reductions from M(II) down to M(0) and show indications
for interaction with CO2 in their reduced states. The Ni(0)
d10 species associates with CO2 to form a putative
Aresta-type Ni-η2-CO2 complex, where electron
transfer to CO2 through back-bonding is insufficient to
enable electrocatalytic activity. By contrast, the Co(0) d9 intermediate binding CO2 can undergo additional electron
uptake into a formal cobalt(I) metallacarboxylate complex able to
promote turnover. Our data, together with the few literature precedents,
single out that an unsaturated coordination sphere (coordination number
= 4 or 5) and a d7-to-d9 configuration in the
reduced low oxidation state (+I or 0) are characteristics that foster
electrochemical CO2 activation for complexes based on redox-innocent
ligands.
A series of 3d transition-metal complexes
(M = Mn, Fe, Co,
Ni, Cu, and Zn) coordinated by a new redox-innocent PNP pincer ligand
system were synthesized and structurally as well as electrochemically
analyzed to illuminate the role of the metal center in molecular electrochemical
carbon dioxide (CO2) activation.
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