Reinterpreting the Fate of Iridium(III) Photocatalysts─Screening a Combinatorial Library to Explore Light-Driven Side-Reactions

Journal of the American Chemical Society, Journal Year: 2022, Volume and Issue: 144(25), P. 11189 - 11202

Published: June 15, 2022

Photoredox catalysts are primarily selected based on ground and excited state properties, but their activity is also intrinsically tied to the nature of reduced (or oxidized) intermediates. Catalyst reactivity often necessitates an inherent instability, thus these intermediates represent a mechanistic turning point that affords either product formation or side-reactions. In this work, we explore scope previously demonstrated side-reaction partially saturates one pyridine ring ancillary ligand in heteroleptic iridium(III) complexes. Using high-throughput synthesis screening under photochemical conditions, identified different chemical pathways, ultimately governed by composition. The was key factor determined stability. Following photoinitiated electron transfer from sacrificial tertiary amine, intermediate complexes containing 1,10-phenanthroline derivatives exhibited long-term contrast, 2,2′-bipyridines were highly susceptible hydrogen atom modification. Detailed characterization before after transformation showed differing effects reduction potentials dependent cyclometalating ligands states. implications catalyst stability model photoredox reaction.

Language: Английский

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Kinetics of a Ni/Ir-Photocatalyzed Coupling of ArBr with RBr: Intermediacy of ArNi^II(L)Br and Rate/Selectivity Factors

Journal of the American Chemical Society, Journal Year: 2022, Volume and Issue: 144(33), P. 15372 - 15382

Published: Aug. 15, 2022

The Ni/Ir-photocatalyzed coupling of an aryl bromide (ArBr) with alkyl (RBr) has been analyzed using in situ LED-19F NMR spectroscopy. Four components (light, [ArBr], [Ni], [Ir]) are found to control the rate ArBr consumption, but not product selectivity, while two ([(TMS)3SiH], [RBr]) independently rate. A major resting state nickel identified as ArNiII(L)Br, and 13C-isotopic entrainment is used show that complex undergoes Ir-photocatalyzed conversion products (Ar-R, Ar-H, Ar-solvent) competition release ArBr. range competing absorption quenching effects lead correlations between Ir Ni catalyst loadings reaction Differences Ir/Ni Beer-Lambert profiles allow be increased by use a shorter-wavelength light source without compromising selectivity. minimal kinetic model for process allows simulation provides insights optimization these processes laboratory.

Language: Английский

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Extending Photocatalyst Activity through Choice of Electron Donor

The Journal of Organic Chemistry, Journal Year: 2023, Volume and Issue: 88(10), P. 6445 - 6453

Published: Jan. 11, 2023

Sacrificial additives are commonly employed in photoredox catalysis as a convenient source of electrons, but what occurs after electron transfer is often overlooked. Tertiary alkylamines initially form radical cations following transfer, which readily deprotonate to strongly reducing, neutral α-amino radicals. Similarly, the oxalate anion (C2O4•-) rapidly decomposes CO2•- (E0 ≈ -2.2 V vs SCE). We show that not only these reactive intermediates formed under conditions, they can also impact desired photochemistry, both positively and negatively. Photoredox systems using an donor able engage substrates with greater energy demands, extending reactivity past limits single multiphoton transition metal catalysts. Furthermore, offers better chemoselectivity than triethylamine when reducing moderate requirements.

Language: Английский

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Metal–Organic Bichromophore Lowers the Upconversion Excitation Power Threshold and Promotes UV Photoreactions

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(20), P. 11402 - 11414

Published: May 15, 2023

Sensitized triplet–triplet annihilation upconversion is a promising strategy to use visible light for chemical reactions requiring the energy input of UV photons. This avoids unsafe ultraviolet sources and can mitigate photo-damage provide access reactions, which filter effects hamper direct excitation. Here, we report new approach make blue-to-UV more amenable photochemical applications. The tethering naphthalene unit cyclometalated iridium(III) complex yields bichromophore with high triplet (2.68 eV) naphthalene-based reservoir featuring lifetime 72.1 μs, roughly factor 20 longer than photoactive excited state parent complex. In combination three different annihilators, consistently lower thresholds crossover from quadratic into linear excitation power dependence regime were observed compared system composed 2,5-diphenyloxazole annihilator sufficiently robust under long-term blue irradiation continuously high-energy singlet-excited that drive normally light. Both photoredox transfer catalyses feasible using this concept, including reductive N–O bond cleavage Weinreb amides, C–C coupling reaction based on aryl debromination, two Paternò–Büchi [2 + 2] cycloaddition reactions. Our work seems relevant in context developing strategies driving energetically demanding photochemistry low-energy

Language: Английский

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Ion Pairing of Cationic and Anionic Ir(III) Photosensitizers for Photocatalytic CO₂ Reduction at Lipid–Membrane Surfaces

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(28), P. 15049 - 15053

Published: July 6, 2023

We synthesized an ion pair comprising cationic and anionic Ir(III) photosensitizers ([Ir1+][Ir2-]) for photocatalytic CO2 reduction showed that the component imparts stability, while cyclometalating ligands in ensure effective visible-light absorption. The triplet excited state of [Ir1+] is key photoredox species this system mainly generated through transfer excitation energy from moiety due to Coulombic interactions appropriate alignment between two ionic components. positive photosensitization effect pairing was demonstrated by cooperation with a Re(I) molecular catalyst incorporated into vesicle membrane.

Language: Английский

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Phosphonate-substituted porphyrins as efficient, cost-effective and reusable photocatalysts

Dalton Transactions, Journal Year: 2024, Volume and Issue: 53(17), P. 7498 - 7516

Published: Jan. 1, 2024

Incorporating phosphonate groups onto the phenyl substituents of meso -tetraphenylporphyrins proves advantageous for their utilization in photocatalysis.

Language: Английский

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Ruthenium(ii) complexes with phosphonate-substituted phenanthroline ligands: synthesis, characterization and use in organic photocatalysis

Dalton Transactions, Journal Year: 2022, Volume and Issue: 51(36), P. 13612 - 13630

Published: Jan. 1, 2022

Ru(II) complexes with polypyridyl ligands play a central role in the development of photocatalytic organic reactions. This work is aimed at structural modification such to increase their efficiency and adapt them for preparation reusable systems. Nine [Ru(phen)(bpy)2]2+-type (bpy = 2,2'-bipyridine, phen 1,10-phenanthroline) (Ru-Pcat) bearing P(O)(OEt)2 substituent attached core directly or through 1,4-phenylene linker were synthesized characterized by spectroscopic electrochemical techniques. The coordination mode was confirmed single crystal X-ray analysis. (spectro)electrochemical data show that first electron transfer Ru-Pcat takes place on ligand. emission maxima quantum yields are strongly affected substitution pattern, reaching far-red region (697 nm) Ru-3,8P2. singlet oxygen evaluated using chemical trapping method. Finally, performance oxidation sulfides molecular investigated. Both dialkyl alkyl aryl quantitatively transformed into sulfoxides under irradiation blue LED acetonitrile-water mixture (10 : 1) low loading 0.005-0.05 mol% photocatalysts. To rationalize effect phosphonate substituents efficiency, comparative kinetic studies (1) 4-nitrothioanisole proceeding predominantly via pathway (2) dibutyl sulfide wherein serves as an oxidant have been performed. It demonstrated positions 4 7 outperform benchmark photocatalyst Ru-(bpy)3 parent complex Ru-phen reactions (reductive quenching cycle). TON 4-methoxythioanisole found be high 1 000 is, our knowledge, highest among previously reported In contrast, upon separating group linker, significantly favors energy (the case). Thus, both series prepared this promising improvement known new transformations.

Language: Английский

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Photocatalytic Regeneration of a Nicotinamide Adenine Nucleotide Mimic with Water-Soluble Iridium(III) Complexes

Inorganic Chemistry, Journal Year: 2023, Volume and Issue: 62(20), P. 7636 - 7643

Published: Feb. 2, 2023

Nicotinamide adenine nucleotide (NADH) is involved in many biologically relevant redox reactions, and the photochemical regeneration of its oxidized form (NAD+) under physiological conditions interest for combined photo- biocatalysis. Here, we demonstrate that tri-anionic, water-soluble variants typically very lipophilic iridium(III) complexes can photo-catalyze reduction an NAD+ mimic a comparatively efficient manner. In combination with well-known rhodium co-catalyst to facilitate regioselective these photo-reductants outcompete commonly used [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) photosensitizer water by up 1 order magnitude turnover frequency. This improved reactivity attributable strong excited-state electron donor properties good chemical robustness tri-anionic sensitizers, their favorable Coulombic interaction di-cationic co-catalyst. Our findings seem greater context photobiocatalysis, which access strong, efficient, robust photoreductants solubility be essential.

Language: Английский

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Exploring the Photophysics and Photocatalytic Activity of Heteroleptic Rh(III) Transition-Metal Complexes Using High-Throughput Experimentation

Inorganic Chemistry, Journal Year: 2024, Volume and Issue: 63(31), P. 14267 - 14277

Published: July 20, 2024

High-throughput synthesis and screening (HTSS) methods were used to investigate the photophysical properties of 576 heteroleptic Rh(III) transition-metal complexes through measurement UV–visible absorption spectra, deaerated excited-state lifetime, phosphorescent emission spectra. While 4d photophysics are often highly influenced by deleterious metal-centered deactivation channels, HTSS structurally diverse cyclometalating ancillary ligands attached metal center facilitated discovery photoactive exhibiting long-lived charge-transfer phosphorescence (0.15–0.95 μs) spanning a substantial portion visible region (546–620 nm) at room temperature. Further electrochemical investigations then carried out on select with favorable understand underlying features controlling these superior properties. Heteroleptic Ir(III) identical ligand morphology also synthesized compare this family well understood chromophores. A number contained requisite for photocatalytic activity consequently tested as photocatalysts (PCs) in water reduction system using Pd cocatalyst. Under certain conditions, PC actually surpassed that PC, uncovering potential often-overlooked class transition metals both efficient chromophores PCs.

Language: Английский

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Factors Controlling Cage Escape Yields of Closed- and Open-Shell Metal Complexes in Bimolecular Photoinduced Electron Transfer

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(32), P. 22818 - 22828

Published: July 30, 2024

The cage escape yield, i.e., the separation of geminate radical pair formed immediately after bimolecular excited-state electron transfer, was studied in 11 solvents using six Fe(III), Ru(II), and Ir(III) photosensitizers tri-p-tolylamine as donor. Among all complexes, largest yields (0.67–1) were recorded for photosensitizer, showing highest potential a photocatalyst photoredox catalysis. These dropped to values around 0.65 both Ru(II) 0.38 Os(II) photosensitizer. Interestingly, open-shell Fe(III) small (<0.1) with dielectric constant greater than 20 but shown reach up 0.58 low constants. results presented herein on closed-shell suggest that rate triplet–singlet intersystem crossing within manifold states implies charge recombination toward ground state is spin-forbidden process, favoring large are not influenced by effects. Geminate metal such two herein, no longer process becomes highly sensitive solvent Altogether, this study provides general guidelines factors influencing reactivity prototypical also allows one foresee great development 2LMCT excited catalysis, providing constants used.

Language: Английский

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