Photocatalytic Oxidation of Bromide to Bromine

Tsai, Kelvin Yun-Da; Chang, I-Cheng

doi:10.1021/acs.inorgchem.6b01652

Cited by 19 publications

(31 citation statements)

References 26 publications

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“…Formation of I 2 during the reaction, confirmed by UV–vis spectroscopy (Figure S3), likely interfered with light absorption by PS. Light-driven formation of halogens from halides utilizing transition-metal chromophores has been previously reported …”

Section: Resultssupporting

confidence: 87%

“…Light-driven formation of halogens from halides utilizing transition-metal chromophores has been previously reported. 49 This catalytic system also exhibited functional group tolerance in the homocoupling of alkyl halides. Efficient dimerization was achieved with substrates containing methoxy (95%, reaction 6), methoxycarbonyl (98%, reaction 7), and tert-butoxycarbonyl protected amine (85%, reaction 8).…”

Section: ■ Introductionmentioning

confidence: 99%

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Photoredox-Assisted Reductive Cross-Coupling: Mechanistic Insight into Catalytic Aryl–Alkyl Cross-Couplings

2017

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Here, we describe a photoredox-assisted catalytic system for the direct reductive coupling of two carbon electrophiles. Recent advances have shown that nickel catalysts are active toward the coupling of sp-carbon electrophiles and that well-controlled, light-driven coupling systems are possible. Our system, composed of a nickel catalyst, an iridium photosensitizer, and an amine electron donor, is capable of coupling halocarbons with high yields. Spectroscopic studies support a mechanism where under visible light irradiation the Ir photosensitizer in conjunction with triethanolamine are capable of reducing a nickel catalyst and activating the catalyst toward cross-coupling of carbon electrophiles. The synthetic methodology developed here operates at low 1 mol % catalyst and photosensitizer loadings. The catalytic system also operates without reaction additives such as inorganic salts or bases. A general and effective sp-sp cross-coupling scheme has been achieved that exhibits tolerance to a wide array of functional groups.

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Section: Resultssupporting

confidence: 87%

Section: ■ Introductionmentioning

confidence: 99%

Photoredox-Assisted Reductive Cross-Coupling: Mechanistic Insight into Catalytic Aryl–Alkyl Cross-Couplings

2017

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“…Yun-Da Tsai et al have reported the photocatalytic oxidation of bromide by ruthenium polypyridyl species in acetonitrile solution. , In their early study, photooxidation of bromide was achieved with the [Ru(deeb) 2 (dmb)] 2+* excited state. However, the second-order rate constant for bromide oxidation k = 2 × 10 6 M –1 s –1 was small, resulting in inefficient excited-state quenching attributed to a small thermodynamic driving force.…”

Section: Halide Photoredox Chemistry With Metal-to-ligand Charge-tran...mentioning

confidence: 99%

Halide Photoredox Chemistry

et al. 2019

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Halide photoredox chemistry is of both practical and fundamental interest. Practical applications have largely focused on solar energy conversion with hydrogen gas, through HX splitting, and electrical power generation, in regenerative photoelectrochemical and photovoltaic cells. On a more fundamental level, halide photoredox chemistry provides a unique means to generate and characterize one electron transfer chemistry that is intimately coupled with X−X bond-breaking and -forming reactivity. This review aims to deliver a background on the solution chemistry of I, Br, and Cl that enables readers to understand and utilize the most recent advances in halide photoredox chemistry research. These include reactions initiated through outer-sphere, halide-to-metal, and metal-toligand charge-transfer excited states. Kosower's salt, 1-methylpyridinium iodide, provides an early outer-sphere charge-transfer excited state that reports on solvent polarity. A plethora of new inner-sphere complexes based on transition and main group metal halide complexes that show promise for HX splitting are described. Long-lived charge-transfer excited states that undergo redox reactions with one or more halogen species are detailed. The review concludes with some key goals for future research that promise to direct the field of halide photoredox chemistry to even greater heights. CONTENTS 1. Introduction, Background, and Motivation

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“…Excited state electron transfer reactions are central to molecular level approaches to solar energy conversion. − Recently hydrohalic acid splitting has re-emerged as a promising target. − Hydrobromic acid (HBr) is of particular interest in this regard, − eq , as the hydrogen and bromine products are solar fuels amenable to storage in flow batteries , and fuel cells. − Here we report bromide photo-oxidation sensitized to visible light with a Ru diimine complex. …”

Section: Introductionmentioning

confidence: 98%

Visible Light Driven Bromide Oxidation and Ligand Substitution Photochemistry of a Ru Diimine Complex

Brady

Meyer

2018

J. Am. Chem. Soc.

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The complex [Ru(deeb)(bpz)] (RuBPZ, deeb = 4,4'-diethylester-2,2'-bipyridine, bpz = 2,2'-bipyrazine) forms a single ion pair with bromide, [RuBPZ, Br], with K = 8400 ± 200 M in acetone. The RuBPZ displayed photoluminescence (PL) at room temperature with a lifetime of 1.75 μs. The addition of bromide to a RuBPZ acetone solution led to significant PL quenching and Stern-Volmer plots showed upward curvature. Time-resolved PL measurements identified two excited state quenching pathways, static and dynamic, which were operative toward [RuBPZ, Br] and free RuBPZ, respectively. The single ion-pair [RuBPZ, Br]* had a lifetime of 45 ± 5 ns, consistent with an electron transfer rate constant, k = (2.2 ± 0.3) × 10 s. In contrast, RuBPZ* was dynamically quenched by bromide with a quenching rate constant, k = (8.1 ± 0.1) × 10 M s. Nanosecond transient absorption revealed that both the static and dynamic pathways yielded RuBPZ and Br products that underwent recombination to regenerate the ground state with a second-order rate constant, k = (2.3 ± 0.5) × 10 M s. Kinetic analysis revealed that RuBPZ was a primary photoproduct, while Br was secondary product formed by the reaction of a Br with Br, k = (1.1 ± 0.2) × 10 M s. Marcus theory afforded an estimate of the formal reduction potential for E(Br) in acetone, 1.42 V vs NHE. A H NMR analysis indicated that the ion-paired bromide was preferentially situated close to the Ru center. Prolonged steady state photolysis of RuBPZ and bromide yielded two ligand-substituted photoproducts, cis- and trans-Ru(deeb)(bpz)Br. A photochemical intermediate, proposed to be [Ru(deeb)(bpz)(κ-bpz)(Br)], was found to absorb a second photon to yield cis- and trans-Ru(deeb)(bpz)Br photoproducts.

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Photocatalytic Oxidation of Bromide to Bromine

Cited by 19 publications

References 26 publications

Photoredox-Assisted Reductive Cross-Coupling: Mechanistic Insight into Catalytic Aryl–Alkyl Cross-Couplings

Photoredox-Assisted Reductive Cross-Coupling: Mechanistic Insight into Catalytic Aryl–Alkyl Cross-Couplings

Halide Photoredox Chemistry

Visible Light Driven Bromide Oxidation and Ligand Substitution Photochemistry of a Ru Diimine Complex

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