Ruthenium Dichloride Research Articles

Thiolato‐Bridged Arene–Ruthenium Complexes: Synthesis, Molecular Structure, Reactivity, and Anticancer Activity of the Dinuclear Complexes [(arene)2Ru2(SR)2Cl2

AbstractTreatment of an arene–ruthenium dichloride dimer with thiols RSH to lead to cationic trithiolato complexes of the type [(arene)2Ru2(SR)3]+ was shown to proceed through the neutral thiolato complexes [(arene)2Ru2(SR)2Cl2], which have been isolated and characterized for arene = p‐MeC6H4iPr and R = CH2Ph (1), CH2CH2Ph (2), CH2C6H4‐p‐tBu (3), and C6H11 (4). The single‐crystal X‐ray structure analysis of the p‐tert‐butylbenzyl derivative 3 reveals that the two ruthenium atoms are bridged by the two thiolato ligands without a metal–metal bond. The neutral dithiolato complexes[(arene)2Ru2(SR)2Cl2] (1–3) are intermediates in the formation of the cationic trithiolato complexes [(arene)2Ru2(SR)3]+ (5–7). Of the new [(arene)2Ru2(SR)2Cl2] complexes, derivative 2 is highly cytotoxic against human ovarian cancer cells, with IC50 values of 0.20 μM for the A2780 cell line and 0.31 for the cisplatin‐resistant cell line A2780cisR.

Submicrometer organic silica gel fiber for oxygen sensing

We introduce the electrospinning method into fabricating oxygen-sensitive submicrometer scale optical fiber. Uniform tris (4,7-diphenyl-1,10-phenathroline) ruthenium(II) dichloride ([Ru(dpp)(3)](2+)Cl(2))-doped fibers with a diameter of 900 nm are obtained by electrospinning the organic silicon sol solution derived from tetraethyl orthosilicate and n-Octyltriethoxysilane (C(14)H(32)O(3)Si). The experimental results show that the single gel fiber exhibits excellent optical and sensing properties. A laser with a wavelength of 452 nm can be efficiently launched into the fiber and guide along the fiber to excite the fluorescence. Then, we find that [Ru(dpp)(3)](2+)-gel fiber has favorable optical and sensing characteristics, and the Stern-Volmer plots are linear in the full concentration range of O(2) (0-100 vol. %). The ratio of I(0)/I(100), where I(0) and I(100) respectively represent the fluorescence intensities of the fiber exposed to 100% N(2) and 100% O(2), as the sensitivity of the fiber is 3.5. Simultaneously, the fiber can make a quick response within 100 ms. This method provides an effective and convenient way to fabricate highly uniform nanoscale or microscale optical waveguides for photonic devices.

Toward Brighter Hybrid Magnetic-Luminescent Nanoparticles: Luminosity Dependence on the Excited State Properties of Embedded Dyes

A series of hybrid, magnetic, and luminescent silica nanoparticles (SNP) have been synthesized and their photophysical properties characterized. The nanoparticles contain, on average, one iron oxide nanoparticle as a magnetic core. The embedded dyes include fluorescein, Alexa Fluor 546, tetramethylrhodamine (TMR), and 4,4-difluoro-5-(2-pyrrolyl)-4-bora-3a,4a-diaza-s-indacene (Bodipy), which are known to have a singlet excited state, and 5-(dimethylamino)naphthalene-1-sulfonyl (dansyl), 7-(diethylamino)coumarin-3-carboxy (coumarin), and tris(bipyridine)ruthenium(II) dichloride (Rubipy) derivatives, which have a charge transfer excited state. In general, the photophysical properties of the magnetic-core dye-doped silica nanoparticles, SNPdye, where dye is one of the seven dyes studied in this project, are dictated by homogeneous energy transfer between dye molecules and by dye aggregation. Molecules with a small Stokes shift and affinity for aggregation upon silica encapsulation (TMR and Bodipy derivatives) can be only sparsely loaded (<50–60 molecules per a 60 nm in diameter nanoparticle) into the nanoparticle matrix before strong fluorescence quenching takes effect. These dyes yield the least bright nanoparticles whose luminosity strongly decreases as the intraparticle dye concentration increases above the rather low maximum brightness loading. Other common fluorophores (Alexa Fluor 546 and fluorescein) can be loaded into the silica matrix with little to no fluorescence quenching until the intermolecular separation becomes less than ∼5 nm (∼100–200 fluorophores per a 60 nm in diameter nanoparticle). Finally, significantly more (∼1200–4600) dye molecules with a charge transfer lowest excited state and large Stokes shift (Rubipy, dansyl, coumarin) can be loaded into the 60 nm in dameter nanoparticle with no indication of luminescence quenching. The results of this study suggest that the luminosity of a hybrid nanoparticle is highest when the embedded dye has a large Stokes shift and is not susceptible to aggregation, which both guarantee no or little intrananoparticle luminescence quenching. No luminescence quenching by the iron oxide magnetic core has been observed for any SNPdye series.

Synthesis and ionic transport of sulfonated ring-opened polynorbornene based copolymers

The N-pentafluorophenyl-exo-endo-norbornene-5,6-dicarboximide (1a) and N-phenyl-exo-endo-norbornene-5,6-dicarboximide (1b) monomers were synthesized and copolymerized via ring opening metathesis polymerization (ROMP) using bis(tricyclohexylphosphine)benzylidene ruthenium(IV) dichloride (I) and tricyclohexylphosphine[1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene]ruthenium dichloride (II). Experiments, at distinct monomer molar ratios, were carried out using catalyst I in order to determine the copolymerization reactivity constants by applying the Mayo-Lewis and Fineman-Ross methods. Moreover, both catalysts were used to produce random and block high molecular weight copolymers of 1a with 1b and 1a with norbornene (NB) which were further hydrogenated using a Wilkinson’s catalyst. Then, the saturated copolymers underwent a nucleophilic aromatic substitution by reacting with sodium 4-hydroxybenzenesulfonate dihydrate to generate new polynorbornene ionomers bearing fluorinated pendant benzenesulfonate groups. A thorough study on the electrochemical characteristics involving electromotive forces of concentration cells and proton conductivity of cation-exchange membranes based on a block copolymer of norbornene dicarboximides containing structural units with phenyl and fluorinated pendant benzenesulfonate moieties is reported. The study of electromotive forces (emf) of concentration cells with the sulfonated membrane of copolymer 8 separating electrolyte solutions of different concentration indicate that the membranes exhibit high permselectivity to protons and sodium ions at moderately low concentrations. In principle, these results suggest that the membranes can be considered candidates for ionic separation applications.

Grubbs and Hoveyda-type ruthenium complexes bearing a cyclic bent-allene

Stable cyclic bent-allene 1 displaces the chelating ether linkage of the Hoveyda–Grubbs-type ruthenium complex 2 bearing triphenylphosphine. The resulting complex 3 features an unusual cis-arrangement of the phosphine and the cyclic bent-allene, while retaining a distorted square pyramidal geometry around the ruthenium center. Monitoring by 31P NMR spectroscopy the reaction of cyclic bent-allene 1 with the indenylidene bis(triphenylphosphine)ruthenium dichloride complex 4 allowed for the observation of dissociated triphenylphosphine, and the formation of a ruthenium complex featuring 1 and triphenylphosphine in the desired trans-configuration. However, continued reaction times saw the disappearance of this complex, and after workup complex 5 featuring a cis-arrangement was isolated.

Oxygen gas optrode based on microstructured polymer optical fiber segment

In this article, we first propose a novel type of oxygen gas optrode by forming fluorophore doped sensing film in the array microholes with the characteristics of microstructured optical fiber (MOF) segment. Comparing with the conventional O 2 detecting method, this slender shaped optrode shows potential in trace amount of O 2 sensing and online O 2 monitoring. Organical silicate gel or plastified cellulose acetate are chosen as sensing films and tris (4,7-diphenyl-1,10-phenathroline) ruthenium(II) dichloride ([Ru(dpp) 3]Cl 2) or meso-tetraphenylporphyin (TPP) as quenching fluorophores. From the experimental results, we find [Ru(dpp) 3] 2+–Gel–MOF optrode has favorable sensing characteristics, and the Stern–Volmer plots are linear in the full concentration range of O 2 (0–100% v/v). The ratio of I 0/I 100, where I 0 and I 100 respectively represents the fluorescence intensities of the optrode exposed to 100% N 2 and 100% O 2, as a sensitivity of the optrode is 10.8. Simultaneously, the optrode can make a quick response within 50 ms.

Vertically Integrated Human P450 and Oxygen Sensing Film for the Assays of P450 Metabolic Activities

An assaying method of cytochrome P450 (P450 or CYP) monooxygenase activities for toxicological evaluation of drugs and environmental pollutants was developed by immobilizing P450 on an oxygen sensoring layer. Membrane fractions from E. coli expressing human P450 were entrapped in agarose or silica-based gels and immobilized on 96-well microarrays having an oxygen sensing film at the bottom. The oxygen sensing film was made of an organically modified silica film (ORMOSIL) doped with Tris(4,7-diphenyl-1,10-phenanthroline) ruthenium dichloride (Ru(dpp)(3)Cl(2)). P450 activity toward the substrates was monitored through the fluorescence intensity enhancement due to the oxygen consumption by the metabolic reactions. For the metabolism of chlortoluron, a selective herbicide used to control grass weeds, CYP1A1 immobilized in agarose gel showed a higher activity and stability compared with those in silica gels and free suspensions. The luminescence changing rate evaluated by the dynamic transient method (DTM) could be correlated with the substrate concentration. We also compared the metabolic responses of human P450s (CYP1A1,CYP2C8, CYP2E1, CYP3A4) toward various substances. The use of immobilized P450 on an oxygen sensing layer provides a versatile assaying platform owing to the following features. First, the oxygen sensor can detect metabolic reactions of any P450 species, in contrast with assays using fluorogenic substrates. Second, vertical integration of the oxygen sensor and immobilized P450 enhanced the sensitivity because of the effective depletion of oxygen in the vicinity of the oxygen sensing layer. Third, immobilization enables repeated use of P450 by replacing the substrate solutions using a flow cell. Furthermore, the activity of immobilized P450 was retained at least for 3 weeks at 4 °C, suggesting its long-term stability, which is an additional attractive feature.

Fracture and fatigue response of a self-healing epoxy adhesive

A self-healing epoxy adhesive for bonding steel substrates is demonstrated using encapsulated dicyclopentadiene (DCPD) monomer and bis(tricyclohexylphosphine)benzylidine ruthenium (IV) dichloride (Grubbs’ first generation) catalyst particles dispersed in a thin epoxy matrix. Both quasi-static fracture and fatigue performance are evaluated using the width-tapered-double-cantilever-beam specimen geometry. Recovery of 56% of the original fracture toughness under quasi-static fracture conditions occurs after 24 h healing at room temperature conditions. Complete crack arrest is demonstrated for fatigue test conditions that render neat resin and control samples failed. Inspection of fracture surfaces by electron microscopy reveals evidence of polymerized DCPD after healing. These results are the first mechanical assessment of self-healing for thin (ca. 360 μm) films typical of adhesives applications.

Uptake and fate of surface modified silica nanoparticles in head and neck squamous cell carcinoma

BackgroundHead and neck squamous cell carcinoma (HNSCC) is currently the eighth leading cause of cancer death worldwide. The often severe side effects, functional impairments and unfavorable cosmetic outcome of conventional therapies for HNSCC have prompted the quest for novel treatment strategies, including the evaluation of nanotechnology to improve e.g. drug delivery and cancer imaging. Although silica nanoparticles hold great promise for biomedical applications, they have not yet been investigated in the context of HNSCC. In the present in-vitro study we thus analyzed the cytotoxicity, uptake and intracellular fate of 200-300 nm core-shell silica nanoparticles encapsulating fluorescent dye tris(bipyridine)ruthenium(II) dichloride with hydroxyl-, aminopropyl- or PEGylated surface modifications (Ru@SiO2-OH, Ru@SiO2-NH2, Ru@SiO2-PEG) in the human HNSCC cell line UMB-SCC 745.ResultsWe found that at concentrations of 0.125 mg/ml, none of the nanoparticles used had a statistically significant effect on proliferation rates of UMB-SCC 745. Confocal and transmission electron microscopy showed an intracellular appearance of Ru@SiO2-OH and Ru@SiO2-NH2 within 30 min. They were internalized both as single nanoparticles (presumably via clathrin-coated pits) or in clusters and always localized to cytoplasmic membrane-bounded vesicles. Immunocytochemical co-localization studies indicated that only a fraction of these nanoparticles were transferred to early endosomes, while the majority accumulated in large organelles. Ru@SiO2-OH and Ru@SiO2-NH2 nanoparticles had never been observed to traffic to the lysosomal compartment and were rather propagated at cell division. Intracellular persistence of Ru@SiO2-OH and Ru@SiO2-NH2 was thus traceable over 5 cell passages, but did not result in apparent changes in cell morphology and vitality. In contrast to Ru@SiO2-OH and Ru@SiO2-NH2 uptake of Ru@SiO2-PEG was minimal even after 24 h.ConclusionsOur study is the first to provide evidence that silica-based nanoparticles may serve as useful tools for the development of novel treatment options in HNSCC. Their long intracellular persistence could be of advantage for e.g. chronic therapeutic modalities. However, their complex endocytotic pathways require further investigations.

SiO2/polyester hybrid for immobilization of Ru(ii) complex as optical gas-phase oxygen sensor

Organic–inorganic hybrid materials produced from tetraethoxysilane, citric acid and ethylene glycol in different mole ratios and consisting of Si–O–Si and Si–O–C nets are prepared and their molecular structure (IR and NMR spectroscopy), morphology (fluorescent microscopy, SEM and AFM), thermochemical behavior and fluorescence properties (excitation and emission spectra) are studied. The optically active, oxygen sensitive complex of tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) dichloride is immobilized in the so prepared matrix and the applicability of the composite as an optical oxygen sensor (response to O2 in gaseous medium) is tested. The influence of the matrix composition on the linearity of the Stern–Volmer dependence and the films sensitivity to O2 is studied.

Visible-Light Photoredox Catalysis: Dehalogenation of Vicinal Dibromo-, α-Halo-, and α,α-Dibromocarbonyl Compounds

vic-Dibromo-, α-halo-, or α,α-dibromocarbonyl compounds can be efficiently dehalogenated using catalytic tris(2,2'-bipyridyl)ruthenium dichloride (Ru(bpy)(3)Cl(2)) in combination with 1,5-dimethoxynaphthalene (DMN) and ascorbate as sacrificial electron donor. For this process, a visible light promoted photocatalytic cycle is proposed that involves the reduction of carbon halogen bonds via free radical intermediates.

Location of anti-TB drugs and microstructural changes in organized surfactant media using optical properties

Microstructure elucidation is a critical step in the understanding of organized surfactant media such as microemulsions. In this work, a systematic approach for revelation of microstructure changes of Tween 80 microemulsion has been carried out using photophysical properties. Microemulsion structural changes have been monitored using pyrene and different solvatochromic probes for the presence of oil-rich, water-rich, and bicontinuous microstructures. The hydrophobic optical probe, Nile red (NR), has been used to report from the side of the oil–surfactant interface and to complement this, a hydrophilic optical probe tris(2,2′-bipyridine)ruthenium(II) dichloride (RC) from the side of the water–surfactant interface. The results show the partitioning of probes into different microenvironments within the system. NR occupies the interface toward the apolar side and RC toward the polar. The analysis also indicates conspicuous dependence of the emission/absorbance behavior of optical probes on the water:surfactant molar ratio ( ω). Quantitative estimates have been obtained for the polarities (ET(30)) of solubilization sites of the probes in different regions of microemulsions and are well correlated with a Stokes shift. Lastly, these probes of different solubilities have been used to locate the position of anti-tuberculosis drugs, i.e., rifampicin (hydrophobic), pyrazinamide, and isoniazid (hydrophilic) of variable solubilities loaded in Tween 80 systems.

Preparation of sulfonic-functionalized graphene oxide as ion-exchange material and its application into electrochemiluminescence analysis

Graphene oxide (GO) obtained from chemical oxidation of flake graphite was derivatized with sulfonic groups to form sulfonic-functionalized GO (GO–SO 3 −) through four sulfonation routes: through amide formation between the carboxylic group of GO and amine of sulfanilic acid (AA–GO–SO 3 −), aryl diazonium reaction of sulfanilic acid (AD–GO–SO 3 −), amide formation between the carboxylic group of GO and amine of cysteamine and oxidation by H 2O 2 (CA–GO–SO 3 −), and alkyl diazonium reaction of cysteamine and oxidation by H 2O 2 (CD–GO–SO 3 −). Results of Fourier transform infrared spectroscopy and X-ray photoelectrospectrocopy showed that –SO 3 − groups were attached onto GO. Thermo gravimetric analysis showed that derivatization with sulfonic groups improved thermo stability of GO. X-ray diffraction results indicated that GO–SO 3 − had more ordered π–π stacking structure than the original GO. GO–SO 3 − and cationic polyelectrote, poly (diallyldimethylammoniumchloride) (PDDA) were adsorbed at indium tin oxide (ITO) glass surface through layer-by-layer assembling to form (GO–SO 3 −/PDDA) n /ITO multilayers. After tris-(2,2′-bipyridyl) ruthenium (II) dichloride (Ru(bpy) 3 2+) was incorporated into the multilayers, the obtained Ru(bpy) 3 2+/(GO–SO 3 −/PDDA) n /ITO electrodes can be used as electrochemiluminescence sensors for detection of organic amine with high sensitivity (limit of detection of 1 nM) and stability.

One‐Pot Desilylation/Dimerization of Terminal Alkynes by Ruthenium and Acid‐Promoted (RAP) Catalysis

AbstractThe dimerization of terminal arylalkynes promoted by the (p‐cymene)ruthenium dichloride dimer/acetic acid system {[RuCl2(p‐cymene)]2/AcOH} can be performed starting from the trimethylsilylethynyl derivatives (12 substrates), deprotected in situ, to afford 1,4‐disubstituted 1‐en‐3‐ynes with high regio‐ and (E)‐stereoselectivity, at room temperature. The extension of this unprecedented two‐reaction sequence to a diyne substrate affords a fluorene‐based conjugated oligomer. The reaction mixture resulting from the desylilation‐dimerization process dimerizes additional aliquots of phenylacetylene. The one‐pot protocol results in shorter reaction times due to the presence of acetate salts which increase the concentration of active catalytic species, in which the acetate ligand acts as base toward the bound alkyne. The ruthenium source is transformed into a new trihapto‐hexa‐1,3‐dien‐5‐yn‐3‐yl complex, formed by metal‐assisted coupling of the enyne product and the terminal alkyne, and still maintaining catalytic activity. Selectivity, endurance, medium and functional group compatibility are the key features of the catalytic system obtained from the p‐cymene ruthenium dimer under the one‐pot conditions.

Glucose concentration determination based on silica sol–gel encapsulated glucose oxidase optical biosensor arrays

Optical biosensor arrays for rapidly determining the glucose concentrations in a large number of beverage and blood samples were developed by immobilizing glucose oxidase (GOD) on oxygen sensor layer. Glucose oxidase was first encapsulated in silica based gels through sol–gel approach and then immobilized on 96-well microarrays integrated with oxygen sensing film at the bottom. The oxygen sensing film was made of an organically modified silica film (ORMOSIL) doped with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium dichloride (Ru(dpp) 3Cl 2). The oxidation reaction of glucose by glucose oxidase could be monitored through fluorescence intensity enhancement due to the oxygen consumption in the reaction. The luminescence changing rate evaluated by the dynamic transient method (DTM) was correlated with the glucose concentration with the wide linear range from 0.1 to 5.0 mM ( Y = 13.28 X − 0.128, R = 0.9968) and low detection limit (0.06 mM). The effects of pH and coexisting ions were systemically studied. The results showed that the optical biosensor arrays worked under a wide range of pH value, and normal interfering species such as Na +, K +, Cl −, PO 4 3−, and ascorbic acid did not cause apparent interference on the measurement. The activity of glucose oxidase was mostly retained even after 2-month storage, indicating their long-term stability.

ChemInform Abstract: Ruthenium-Catalyzed Oxidation of Primary Alcohols with the New Oxidation System N-Methylmorpholine/Hydrogen Peroxide.

Abstract Long chain alcohols such as octanol, dodecanol and hexadecanols are oxidized to the corresponding aldehydes and carboxylic acids in the presence of the homogeneous catalyst tris(triphenylphosphine) ruthenium dichloride. The known oxidizing agent N-methylmorpholine N-oxide (MMO) has been compared with a new system involving N-methylmorpholine (MM) and hydrogen peroxide. With the system MM/H2O2 simple recycling of the ruthenium catalyst and of the oxygen transmitter MM is possible by a simple phase separation process. A mechanism is proposed in which the oxygen of the MMO formed in situ serves to convert a dihydrido-ruthenium complex into the catalytically active ruthenium species.

Ruthenium‐Catalyzed Alkyne Oxidation with Part‐Per‐Million Catalyst Loadings

AbstractUsing a catalytic system of the (cymene)ruthenium dichloride dimer, [Ru(cymene)Cl2]2, (0.001 mol%) and iodine (10 mol%), a variety of alkynes bearing different functional groups were oxidized with tert‐butyl hydroperoxide (TBHP; 70% solution in water) under mild conditions to give 1,2‐diketones in good to excellent yields. Two noteworthy features of the method are the extremely high catalyst productivity (TON up to 420,000) and scale‐up to 1 mol. Preliminary mechanism investigations showed that iodonium ion and water were involved in the transformation.

Polynorbornene with pentafluorophenyl imide side chain groups: Synthesis and sulfonation

AbstractThe mixtures of exo‐endo‐monomers and isomerically pure endo‐monomers of N‐pentafluorophenyl‐norbornene‐5,6‐dicarboximide (2a) and N‐phenyl‐norbornene‐5,6‐dicarboximide (2b) were synthesized and polymerized via ring opening metathesis polymerization using bis(tricyclohexylphosphine) benzylidene ruthenium (IV) dichloride (I) and tricyclohexylphosphine [1,3‐bis(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene][benzylidene] ruthenium dichloride (II). Ring opening metathesis polymerization of mixtures of exo‐endo‐monomers (2a) and (2b) and pure endo‐2b gave the corresponding high molecular weights poly(N‐pentafluorophenyl‐norbornene‐5,6‐dicarboximide) (3a) and poly(N‐phenyl‐norbornene‐5,6‐dicarboximide) (3b). The isomerically pure endo‐2a did not polymerize by I in these conditions, since I is the least active catalyst and endo‐2a is the least active monomer because of the intramolecular complex formation between the Ru active center and the fluorine atom of ring‐opened endo‐2a on the one hand and steric hindrances caused by the pentafluorinated ring on the other. The quantitative hydrogenation of the polymer 3a, at room temperature and 115 bar, was achieved by a Wilkinson's catalyst. The new polynorbornene bearing highly fluorinated sulfonic acid groups (5) was obtained by the reaction of the hydrogenated poly(N‐pentafluorophenyl‐norbornene‐5,6‐dicarboximide) (4) with sodium 4‐hydroxybenzenesulfonate dihydrate. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2925–2933, 2010

Ferrocenyl-Aryl Based trans-Chelating Diphosphine Ligands: Synthesis, Molecular Structure and Application in Enantioselective Hydrogenation

Potentially trans-chelating diphosphine ligands based on a ferrocenyl-aryl backbone were synthesised in a four-step sequence and the molecular structures in the solid state of two representatives were determined by X-ray diffraction. High throughput screening of these ligands in rhodium-, ruthenium- and iridium-mediated hydrogenations of a variety of alkenes and ketones revealed that these ligands can deliver high enantioselectivity for alkenes (up to 98% ee) but are less selective when ketones are used as the substrates. The coordination behaviour of one ligand in its square planar palladium and platinum dichloride complexes was studied by 31 P NMR and only trans-chelated complexes, together with oligomeric by-products, were observed. Reaction with the (p-cymene)ruthenium dichloride dimer, [RuCl 2 (p-cymene)] 2 , resulted in a mixture of diastereomeric complexes.

Electron Transfer Photoredox Catalysis: Intramolecular Radical Addition to Indoles and Pyrroles

The utilization of the photoredox catalyst, tris(2,2'-bipyridyl)ruthenium dichloride, and a household light bulb to effect radical cyclizations onto indoles and pyrroles at room temperature is reported. A reactive free radical intermediate is generated via the reduction of an activated C-Br bond by the single electron reductant, Ru(I), generated in a visible light induced photocatalytic cycle. This system represents an expansion of the application of photoredox catalysis in conventional free radical processes.