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Phearman AS, Bullock RM. Synthesis and Reactivity of Fe(II) Complexes Containing Cis Ammonia Ligands. Inorg Chem 2024; 63:2024-2033. [PMID: 38230973 DOI: 10.1021/acs.inorgchem.3c03757] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2024]
Abstract
The development of earth-abundant transition-metal complexes for electrocatalytic ammonia oxidation is needed to facilitate a renewable energy economy. Important to this goal is a fundamental understanding of how ammonia binds to complexes as a function of ligand geometry and electronic effects. We report the synthesis and characterization of a series of Fe(II)-NH3 complexes supported by tetradentate, facially binding ligands with a combination of pyridine and N-heterocyclic carbene donors. Electronic modification of the supporting ligand led to significant shifts in the FeIII/II potential and variations in NH bond acidities. Finally, investigations of ammonia oxidation by cyclic voltammetry, controlled potential bulk electrolysis, and through addition of stoichiometric organic radicals, TEMPO and tBu3ArO• are reported. No catalytic oxidation of NH3 to N2 was observed, and 15N2 was detected only in reactions with tBu3ArO•.
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Affiliation(s)
- Alexander S Phearman
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - R Morris Bullock
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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Roithmeyer H, Sévery L, Moehl T, Spingler B, Blacque O, Fox T, Iannuzzi M, Tilley SD. Electrocatalytic Ammonia Oxidation with a Tailored Molecular Catalyst Heterogenized via Surface Host-Guest Complexation. J Am Chem Soc 2024; 146:430-436. [PMID: 38134360 DOI: 10.1021/jacs.3c09725] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2023]
Abstract
Macrocyclic host molecules bound to electrode surfaces enable the complexation of catalytically active guests for molecular heterogeneous catalysis. We present a surface-anchored host-guest complex with the ability to electrochemically oxidize ammonia in both organic and aqueous solutions. With an adamantyl motif as the binding group on the backbone of the molecular catalyst [Ru(bpy-NMe2)(tpada)(Cl)](PF6) (1) (where bpy-NMe2 is 4,4'-bis(dimethylamino)-2,2'-bipyridyl and tpada is 4'-(adamantan-1-yl)-2,2':6',2″-terpyridine), high binding constants with β-cyclodextrin were observed in solution (in DMSO-d6:D2O (7:3), K11 = 492 ± 21 M-1). The strong binding affinities were also transferred to a mesoporous ITO (mITO) surface functionalized with a phosphonated derivative of β-cyclodextrin. The newly designed catalyst (1) was compared to the previously reported naphthyl-substituted catalyst [Ru(bpy-NMe2)(tpnp)(Cl)](PF6) (2) (where tpnp is 4'-(naphthalene-2-yl)-2,2':6',2″-terpyridine) for its stability during catalysis. Despite the insulating nature of the adamantyl substituent serving as the binding group, the stronger binding of this unit to the host-functionalized electrode and the resulting shorter distance between the catalytic active center and the surface led to better performance and higher stability. Both guests are able to oxidize ammonia in both organic and aqueous solutions, and the host-anchored electrode can be refunctionalized multiple times (>3) following the loss of the catalytic activity, without a reduction in performance. Guest 1 exhibits significantly higher stability in comparison to guest 2 toward basic conditions, which often constitutes a challenge for anchored molecular systems. Ammonia oxidation in water led to the selective formation of NO3- with Faradaic efficiencies of up to 100%.
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Affiliation(s)
- Helena Roithmeyer
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich 8057, Switzerland
| | - Laurent Sévery
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich 8057, Switzerland
| | - Thomas Moehl
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich 8057, Switzerland
| | - Bernhard Spingler
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich 8057, Switzerland
| | - Olivier Blacque
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich 8057, Switzerland
| | - Thomas Fox
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich 8057, Switzerland
| | - Marcella Iannuzzi
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich 8057, Switzerland
| | - S David Tilley
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich 8057, Switzerland
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