A Stable Homoleptic Organometallic Iron(IV) Complex

Prakash, Om; Chábera, Pavel; Rosemann, Nils W.; Huang, Ping; Häggström, Lennart; Ericsson, Tore; Strand, Daniel; Persson, Petter; Bendix, Jesper; Lomoth, Reiner; Wärnmark, Kenneth

doi:10.1002/chem.202002158

Cited by 27 publications

(29 citation statements)

References 72 publications

(52 reference statements)

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“…63 Wärnmark and his collaborators as well as others have continued to pursue a deeper photophysical and photochemical understanding and explore the applications of these exciting LMCT-driven Fe complexes. [64][65][66][67][68][69][70] Prakash et al synthesized and characterized a high valent [Fe IV (phtmeimb)2] 2+ version of their original Fe III complex exhibiting a 3 LMCT absorption that appears to be shortlived (< 0.8 picoseconds) thus far. 69 Persson, Sundström, and co-workers also summarized the promising photophysical properties of the Fe carbene complexes for dye-sensitized solar cells and other solar energy conversion or photocatalytic functions.…”

Section: Ironmentioning

confidence: 99%

“…[64][65][66][67][68][69][70] Prakash et al synthesized and characterized a high valent [Fe IV (phtmeimb)2] 2+ version of their original Fe III complex exhibiting a 3 LMCT absorption that appears to be shortlived (< 0.8 picoseconds) thus far. 69 Persson, Sundström, and co-workers also summarized the promising photophysical properties of the Fe carbene complexes for dye-sensitized solar cells and other solar energy conversion or photocatalytic functions. 66,68 We anticipate that the deployment of Fe complexes that rely on LMCT photosensitization are still in embryonic stages and more valuable applications will be revealed in the near future.…”

Section: Ironmentioning

confidence: 99%

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Emergence of ligand-to-metal charge transfer in homogeneous photocatalysis and photosensitization

Kong

Tan

et al. 2022

Chemical Physics Reviews

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Light energy can be harnessed by photosensitizers or photocatalysts so that some chemical reactions can be carried out under milder conditions compared to the traditional heat-driven processes. To facilitate the photo-driven reactions, a large variety of chromophores that are operated via charge transfer excitations have been reported because of their typically longer excited-state lifetimes, which are the key to the downstream photochemical processes. Although both metal-to-ligand charge transfers and ligand-to-metal charge transfers are well-established light absorption pathways; the former has been widely adopted in photocatalysis, whereas the latter has recently taken on greater importance in photosensitization applications. In this article, we review the latest developments on ligand-to-metal charge transfer photosensitization by molecular complexes across the periodic table by focusing homogeneous photocatalysis and the use of photophysical measurements and computational calculations to understand the electronic structures, photochemical processes, structure–activity relationships, and reaction mechanisms. We also present our perspectives on the possible future developments in the field.

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Section: Ironmentioning

confidence: 99%

Section: Ironmentioning

confidence: 99%

Emergence of ligand-to-metal charge transfer in homogeneous photocatalysis and photosensitization

Kong

Tan

et al. 2022

Chemical Physics Reviews

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“…The scarcity of second- and third-row transition metals such as ruthenium, iridium, rhodium, or osmium, coupled with a global desire for sustainable chemistry, has led to the resurgence of research centered on Earth-abundant metal-based photosensitizers. − Several photosensitizers based on copper, , molybdenum, nickel, , tungsten, , zirconium, , chromium, − cobalt, , or iron − have recently been reported as promising candidates in cutting-edge research fields. In particular, luminescent complexes of iron are often considered a “holy grail” because of iron’s high abundance in the Earth’s crust, low toxicity, and low environmental impact.…”

Section: Introductionmentioning

confidence: 99%

Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light

et al. 2021

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Efficient excited-state electron transfer between an iron(III) photosensitizer and organic electron donors was realized with green light irradiation. This advance was enabled by the use of the previously reported iron photosensitizer, [Fe(phtmeimb)2]+ (phtmeimb = {phenyl[tris(3-methyl-imidazolin-2-ylidene)]borate}, that exhibited long-lived and luminescent ligand-to-metal charge-transfer (LMCT) excited states. A benchmark dehalogenation reaction was investigated with yields that exceed 90% and an enhanced stability relative to the prototypical photosensitizer [Ru(bpy)3]2+. The initial catalytic step is electron transfer from an amine to the photoexcited iron sensitizer, which is shown to occur with a large cage-escape yield. For LMCT excited states, this reductive electron transfer is vectorial and may be a general advantage of Fe(III) photosensitizers. In-depth time-resolved spectroscopic methods, including transient absorption characterization from the ultraviolet to the infrared regions, provided a quantitative description of the catalytic mechanism with associated rate constants and yields.

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“…Assuming CR to the ground state, the driving force for recombination is ∼1.4 eV, and if the internal reorganization is thought to be minimal, as suggested by negligible observed structural differences between [Fe III L 2 ] + and [Fe IV L 2 ] 2+ , 36 CR could take place in the inverted region, 37 resulting in an observable yield despite the spin allowed nature of the back-electron transfer. Regardless, the prognosis is positive for the design and optimization of such systems to improve performance.…”

mentioning

confidence: 99%

The Carbene Cannibal: Photoinduced Symmetry-Breaking Charge Separation in an Fe(III) N-Heterocyclic Carbene

Kaul

Lomoth

2021

J. Am. Chem. Soc.

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Photoinduced symmetry-breaking charge separation (SB-CS) processes offer the possibility of harvesting solar energy by electron transfer between identical molecules. Here, we present the first case of direct observation of bimolecular SB-CS in a transition metal complex, [Fe III L 2 ](PF 6 ) (L = [phenyl(tris(3-methylimidazol-1-ylidene))borate] − ). Photoexcitation of the complex in the visible region results in the formation of a doublet ligand-to-metal charge transfer ( 2 LMCT) excited state ( E 0–0 = 2.13 eV), which readily reacts with the doublet ground state to generate charge separated products, [Fe II L 2 ] and [Fe IV L 2 ] 2+ , with a measurable cage escape yield. Known spectral signatures allow for unambiguous identification of the products, whose formation and recombination are monitored with transient absorption spectroscopy. The unusual energetic landscape of [Fe III L 2 ] + , as reflected in its ground and excited state reduction potentials, results in SB-CS being intrinsically exergonic (Δ G CS ° ∼ −0.7 eV). This is in contrast to most systems investigated in the literature, where Δ G CS ° is close to zero, and the charge transfer driven primarily by solvation effects. The study is therefore illustrative for the utilization of the rich redox chemistry accessible in transition metal complexes for the realization of SB-CS.

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A Stable Homoleptic Organometallic Iron(IV) Complex

Cited by 27 publications

References 72 publications

Emergence of ligand-to-metal charge transfer in homogeneous photocatalysis and photosensitization

Emergence of ligand-to-metal charge transfer in homogeneous photocatalysis and photosensitization

Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light

The Carbene Cannibal: Photoinduced Symmetry-Breaking Charge Separation in an Fe(III) N-Heterocyclic Carbene

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