Organic Bases as the Organic Electron Donors (OED) Promoted Reductive Coupling of Diarylhalomethanes: Halogens Controlled Construction of Tetraarylethylenes and Tetraarylethanes

Using the organic base as the organic electron donors, the reductive coupling of diaryhalomethanes was smoothly achieved under transition-metal-free reaction conditions, giving a series of synthetically important tetraarylethylenes and tetraarylethanes in high yields. The mechanistic study revealed that the organic bases acting as the electron donor initiated the generation of a radical intermediate, realizing the construction of tetraarylethylene and tetraarylethane skeletons.

Photochemical pincer-catalyzed reductive cyclisation towards indolines and oxindoles

An organophotocatalytic method has been described towards the synthesis of indolines and oxindoles starting from unusual α-chloro amide and N-(2-chlorophenyl)-N-alkyl methacrylamide substrates. This marks a notable improvement since the earlier syntheses utilized iridium and gold catalysts, and involved C-I or C-Br bond cleavage as the initial step. Our photocatalyst is a pincer ligand that can be easily deprotonated to make a very strong reducing agent. The reductive cleavage of the carbon-chloride bond, and subsequent 5-exo-trig ring cyclization, followed by hydrogen atom abstraction, prepare the desired heterocycles under very mild reaction conditions. An atom economic use of KOtBu has been shown to demonstrate the unusual trifunctional role of the latter.

Moisture-resistant radical anions of quinoxalin-2(1H)-ones in aerial dioxygen activation

This study demonstrates the successful formation of a radical anion intermediate in a moist atmosphere, facilitating chemical reactions by activating aerial dioxygen through a single electron transfer (SET) mechanism. Derived from deprotonating quinoxaline-2(1H)-one with KOtBu, it shows potential in oxygenation chemistry. Validation comes from radical scavenging and EPR experiments.

Radical coupling of aryl halides to arenes facilitated by Ni(COD)(DQ) and other nickel sources

The air-stable complex Ni(COD)(DQ) (COD = 1,5-cyclooctadiene, DQ = duroquinone) promotes the coupling of aryl halides to arenes in the presence of KOtBu. This complex has recently been shown to perform coupling reactions based on organonickel intermediates, but in this case the coupling reactions proceed via aryl radicals as shown by our newly developed assay for aryl radicals. Coupling with this nickel source is more efficient than with Ni(COD)2, Ni(PPh3)4 and Ni(acac)2, all of which we also show to operate through aryl radical pathways.

An assay for aryl radicals using BHAS coupling

Aryl radicals are intermediates in many reactions, but determining their presence unambiguously is often challenging. As we recently reported, reaction of 2-iodo-1,3-dimethylbenzene (7) in benzene with KOtBu and a suitable organic additive, leads to a base-induced homolytic aromatic substitution (BHAS) coupling reaction giving 2,6-dimethylbiphenyl (12) and biphenyl (3) as coupled products, together with xylene (13). In this case, biphenyl arises from a radical translocation and is the major coupling product. This paper now quantitatively investigates that reaction, which shows a very similar ratio for 3 : 12 [ca. 4 : 1] when using different sources of radical initiation. Deuterium isotope studies provide detailed mechanistic support for the proposed mechanism; when carried out in C6D6vs. C6H6, the reaction is characterised by a strong isotope effect for formation of 3-d10vs. 3, but not for formation of 12-d5vs. 12. These distinctive properties mean that the transformation can act as an assay for aryl radicals. An advantage of such a BHAS process is its sensitivity, since it involves a chain reaction that can amplify radical activity.

A Hierarchy of Ligands Controls Formation and Reaction of Aryl Radicals in Pd-Catalyzed Ground-State Base-Promoted Coupling Reactions

Palladium salts and complexes were tested separately and in the presence of added ligands as potential sources of aryl radicals in ground-state coupling reactions of aryl halide with arenes under basic conditions (KOtBu). Our recently developed assay for aryl radicals was employed to test for aryl radicals. In this assay, aryl radicals derived from the test substrate, 1-iodo-2,6-dimethylbenzene 7, undergo base-promoted homolytic aromatic substitution (BHAS) with benzene to produce 2,6-dimethylbiphenyl 8 and biphenyl 9 in an approximately 1:4 ratio as well as m-xylene 10. The biphenyl arises from a diagnostic radical transfer reaction with the solvent benzene. Using substrate 7 with a range of Pd sources as potential initiators led to formation of 8, 9, and 10 in varying amounts. However, when any one of a range of diphosphinoferrocenes (e.g., dppf or dippf) or BINAP or the monophosphine, diphenylphosphinoferrocene, was added as a ligand to Pd(OAc)2, the ratio of [2,6-dimethylbiphenyl 8: biphenyl 9] moved decisively to that expected from the BHAS (radical) pathway. Further studies were conducted with dppf. When dppf was added to each of the other Pd sources, the ratio of coupled products was also diverted to that expected for radical BHAS chemistry. Deuterium isotope studies and radical trap experiments provide strong additional support for the involvement of aryl radicals. Accordingly, under these ground-state conditions, palladium sources, in the presence of defined ligands, convert aryl iodides to aryl radicals. A rationale is proposed for these observations.

Reductive Cleavage of C(sp2)-CF3 Bonds in Trifluoromethylpyridines

A reductive detrifluoromethylation protocol has been developed making use of an earth-abundant alkoxide base and silicon hydride species. A variety of pyridine and quinoline substrates bearing alkyl, aryl, and amino functional groups are reduced in moderate to high yields. The reaction is chemoselective for C(sp²)-CF₃ groups located at the 2-position on the pyridine ring, leaving trifluoromethyl groups located elsewhere on the molecule intact. Preliminary mechanistic studies demonstrate that the combination of silane and base generates a strongly reducing system that may transfer an electron to electron-deficient π systems.

KOtBu-promoted C3-homocoupling of quinoxalinones through single electron transfer from an sp2 carbanion intermediate

The C3-selective homodimerization of quinoxalinones is described. A C3-sp² carbanion species generated through deprotonation of quinoxalinone using potassium tert-butoxide (KO^tBu) transfers an electron (single electron transfer mechanism) to a second quinoxalinone, affording a radical-anion intermediate. The radical scavenging and electron paramagnetic resonance (EPR) experiments support the plausible radical reaction pathway. A mild reaction temperature and a short reaction time were attained under cost-effective conditions, which reveal the amenability of this protocol to pharmaceutical and chemical industries.

Phenalenyl Radical: Smallest Polycyclic Odd Alternant Hydrocarbon Present in the Graphene Sheet

Phenalenyl, a zigzag-edged odd alternant hydrocarbon unit can be found in the graphene nanosheet. Hückel molecular orbital calculations indicate the presence of a nonbonding molecular orbital (NBMO), which originates from the linear combination of atomic orbitals (LCAO) arising from 13 carbon atoms of the phenalenyl molecule. Three redox states (cationic, neutral radical, and anionic) of the phenalenyl-based molecules were attributed to the presence of this NBMO. The cationic state can undergo two consecutive reductions to result in neutral radical and anionic states, stepwise, respectively. The phenalenyl-based radicals were found as crucial building blocks and attracted the attention of various research fields such as organic synthesis, material science, computation, and device physics. From 2012 onward, a strategy was devised using the cationic state of phenalenyl-based molecules and in situ generated phenalenyl radicals, which created a new domain of catalysis. The in situ generated phenalenyl radicals were utilized for the single electron transfer (SET) process resulting in redox catalysis. This emerging range of applications rejuvenates the more than six decades-old phenalenyl chemistry. This review captures such developments ranging from fundamental understanding to multidirectional applications of phenalenyl-based radicals.

Rapid access to polycyclic N-heteroarenes from unactivated, simple azines via a base-promoted Minisci-type annulation

Conventional synthetic methods to yield polycyclic heteroarenes have largely relied on metal-mediated arylation reactions requiring pre-functionalised substrates. However, the functionalisation of unactivated azines has been restricted because of their intrinsic low reactivity. Herein, we report a transition-metal-free, radical relay π-extension approach to produce N-doped polycyclic aromatic compounds directly from simple azines and cyclic iodonium salts. Mechanistic and electron paramagnetic resonance studies provide evidence for the in situ generation of organic electron donors, while chemical trapping and electrochemical experiments implicate an iodanyl radical intermediate serving as a formal biaryl radical equivalent. This intermediate, formed by one-electron reduction of the cyclic iodonium salt, acts as the key intermediate driving the Minisci-type arylation reaction. The synthetic utility of this radical-based annulative π-extension method is highlighted by the preparation of an N-doped heptacyclic nanographene fragment through fourfold C–H arylation.

The functionalisation of unactivated azines has been restricted because of their intrinsic low reactivity. Here the authors show a transition-metal-free, radical relay π-extension approach to produce N-doped polycyclic aromatic compounds directly from simple azines and cyclic iodonium salts.

A Photoreactive Iron(II) Complex Luminophore

Controlling the order and lifetimes of electronically excited states is essential to effective light-to-potential energy conversion by molecular chromophores. This work reports a luminescent and photoreactive iron(II) complex, the first performant group homologue of prototypical sensitizers of ruthenium. Double cyclometalation of a phenylphenanthroline framework at iron(II) favors the population of a triplet metal-to-ligand charge transfer (³MLCT) state as the lowest energy excited state. Near-infrared (NIR) luminescence exhibits a monoexponential decay with τ = 2.4 ns in the solid state and 1 ns in liquid phase. Lifetimes of 14 ns at 77 K are in line with a narrowing of the NIR emission band at λ_em,max = 1170-1230 nm. Featuring a ³MLCT excited-state redox potential of -2 V vs the ferrocene/ferrocenium couple, the use of the Fe(II) chromophore as a sensitizer for light-driven synthesis is exemplified by the radical cross-coupling of 4-chlorobromobenzene and benzene.

Construction of quaternary carbon centers by KOtBu-catalyzed α-homoallylic alkylation of lactams with 1,3-dienes

We report a KOtBu-catalyzed α-homoallylic alkylation of lactams with 1,3-dienes.

Counterion Control of t-BuO-Mediated Single Electron Transfer to Nitrostilbenes to Construct N-Hydroxyindoles or Oxindoles

tert-Butoxide unlocks new reactivity patterns embedded in nitroarenes. Exposure of nitrostilbenes to sodium tert-butoxide was found to produce N-hydroxyindoles at room temperature without an additive. Changing the counterion to potassium changed the reaction outcome to yield solely oxindoles through an unprecedented dioxygen-transfer reaction followed by a 1,2-phenyl migration. Mechanistic experiments established that these reactions proceed via radical intermediates and suggest that counterion coordination controls whether an oxindole or N-hydroxyindole product is formed.

Electrochemical-induced hydroxylation of aryl halides in the presence of Et3N in water

A thorough study of mild and environmentally friendly electrochemical-induced hydroxylation of aryl halides without a catalyst is presented. The best protocol consists of hydroxylation of different aryl iodides and aryl bromides by water solution in the presence of Et3N under air, affording the target phenols in good isolated yields. Moreover, aryl chlorides were successfully employed as substrates. This methodology also provides a direct pathway for the formation of deoxyphomalone, which displayed a significant anti-proliferation effect.

Pyrenedione-Catalyzed α-Olefination of Nitriles under Visible-Light Photoredox Conditions

Herein, we report a combination of pyrenedione (PD) and KO^tBu to achieve facile alcohol dehydrogenation under visible-light excitation, where aerobic oxygen is utilized as the terminal oxidant. The resulting carbonyl compound can be easily converted to vinyl nitriles in a single-pot reaction, at 60 °C in 6-8 h. This environmentally benign, organocatalytic approach has distinct advantages over transition-metal-catalyzed α-olefination of nitriles, which often operate at a significantly higher temperature for an extended reaction time.

Modular Counter-Fischer-Indole Synthesis through Radical-Enolate Coupling

A single-electron transfer mediated modular indole formation reaction from a 2-iodoaniline derivative and a ketone has been developed. This transition-metal-free reaction shows a broad substrate scope and unconventional regioselectivity trends. Moreover, important functional groups for further transformation are tolerated under the reaction conditions. Density functional theory studies reveal that the reaction proceeds by metal coordination, which converts a disfavored 5-endo-trig cyclization to an accessible 7-endo-trig process.

Synthesis of quaternary centres by single electron reduction and alkylation of alkylsulfones

A new method for the generation of tertiary radicals through single electron reduction of alkylsulfones promoted by Zn and 1,10-phenanthroline has been developed. These radicals could be employed in the Giese reaction, affording structurally diverse quaternary products in good yields. With the high modularity and functional group compatibility of sulfones, the utility of this method was demonstrated by intramolecular and iterative reactions to give complex structures. The radical generation process was investigated by control experiments and theoretical calculations.

A new method for the generation of tertiary radicals through single electron reduction of alkylsulfones promoted by Zn and 1,10-phenanthroline has been developed.

The Chemistry of Acylgermanes: Triacylgermenolates Represent Valuable Building Blocks for the Synthesis of a Variety of Germanium-Based Photoinitiators

The formation of a stable triacylgermenolate 2 as a decisive intermediate was achieved by using three pathways. The first two methods involve the reaction of KOtBu or alternatively potassium with tetraacylgermane 1 yielding 2 via one electron transfer. The mechanism involves the formation of radical anions (shown by EPR). This reaction is highly efficient and selective. The third method is a classical salt metathesis reaction toward 2 in nearly quantitative yield. The formation of 2 was confirmed by NMR spectroscopy, UV–vis measurements, and X-ray crystallography. Germenolate 2 serves as a starting point for a wide variety of organo-germanium compounds. We demonstrate the potential of this intermediate by introducing new types of Ge-based photoinitiators 4b–4f. The UV–vis absorption spectra of 4b–4f show considerably increased band intensities due to the presence of eight or more chromophores. Moreover, compounds 4d–4f show absorption tailing up to 525 nm. The performance of these photoinitiators is demonstrated by spectroscopy (time-resolved EPR, laser flash photolysis (LFP), photobleaching (UV–vis)) and photopolymerization experiments (photo-DSC measurements).

Triacylgermenolate 2 was obtained by using KOtBu or alternatively potassium. The mechanism involves the formation of radical anions (shown by EPR). The one-pot synthetic protocol produces 2 in >95% yield, as confirmed by NMR spectroscopy and X-ray crystallography. Germenolate 2 serves as a starting point for a wide variety of organo-germanium compounds. This was demonstrated by introducing new types of Ge-based photoinitiators 4b−4f. Their performance was analyzed by sophisticated spectroscopic methods and photopolymerization experiments.

NaH-mediated direct C-H arylation in the presence of 1,10-phenanthroline

Transition-metal-free coupling of haloarenes with unactivated arenes has been developed in the presence of NaH and 1,10-phenanthroline. Various haloarenes bearing methyl, methoxy, halogen (fluoride, chloride, and bromide), cyano, trifluoromethyl, ester, and amide groups can be cross-coupled with unactivated arenes, or heteroarenes in this reaction.

Dehydrogenation of amines in aryl-amine functionalized pincer-like nitrogen-donor redox non-innocent ligands via ligand reduction on a Ni(ii) template

We have synthesized a series of new redox non-innocent azo aromatic pincer-like ligands: 2-(phenylazo)-6-(arylaminomethyl)pyridine (HLa-c: HLa = 2-(phenylazo)-6-(2,6-diisopropylphenylaminomethyl)pyridine, HLb = 2-(phenylazo)-6-(2,6-dimethylphenylaminomethyl)pyridine, and HLc = 2-(phenylazo)-6-(phenylaminomethyl)pyridine), in which one side arm is an arylaminomethyl moiety and the other arm is a 2-phenylazo moiety. Nickel(ii) complexes, 1-3, of these ligands HLa-c were synthesized in good yield (approximately 70%) by the reaction of ligands : (NiCl2·6H2O) in a 1 : 1 molar ratio in methanol. The amine donor in each of the ligands HLa-c binds to the Ni(ii) centre without deprotonation. In the solid state, complex 3 is a dimer; in solution it exists as monomer 3a. The reduction of acetonitrile solutions of each of the complexes 1, 2 and 3a, separately, with cobaltocene (1 equivalent), followed by exposure of the solution to air, resulted in the formation of new complexes 7, 8 and 9, respectively. Novel free ligands Lx and Ly have also been isolated, in addition to complexes 7 and 8, from the reaction of complexes 1 and 2, respectively. Complexes 7-9 and free ligands Lx and Ly have been formed via a dehydrogenation reaction of the arylaminomethyl side arm. The mechanism of the reaction was thoroughly investigated using a series of studies, including cyclic voltammetry, EPR, and UV-Vis spectral studies and density functional theory (DFT) calculations. The results of these studies suggest a mechanism initiated by ligand reduction followed by dioxygen activation. A Cl-/I- scrambling experiment revealed that the dissociation of the chloride ligand(s) was associated with the one-electron reduction of the ligand (azo moiety) in each of the complexes 1, 2 and 3a. The dissociated chloride ligand(s) were reassociated with the metal following the dehydrogenation reaction to yield the final products. All of the newly synthesized compounds were fully characterized using a variety of physicochemical techniques. Single-crystal X-ray structures of the representative compounds were determined to confirm the identities of the synthesized molecules.

Removal of copper and cadmium ions from alkaline solutions using chitosan-tannin functional paper materials as adsorbent

We successfully absorbed the copper ion (Cu²⁺) and cadmium ion (Cd²⁺) from alkaline aqueous solutions using the prepared chitosan-tannin (CTS/TA) functional paper as absorbent materials. The kinetics of the adsorption, the adsorption isotherms, and the influence of the solution flow rate and pH were investigated detailly. The adsorption data were described well by Langmuir isotherms, with maximum copper (Cu²⁺) and cadmium (Cd²⁺) adsorption capacities of 684.93 and 813.01 mg/m², respectively. The experimental results also showed that the adsorption of these heavy metals was selective in the order of Cu²⁺ > Cd²⁺, as Cu²⁺ competed with Cd²⁺ for bonding sites at solution concentrations greater than or equal to 200 mg/L. The results of this study illustrated that the chitosan-tannin functional paper materials mainly followed a complexation-adsorption model, and the best adsorption capacity was achieved at pH = 9. The desorption of heavy ions from this adsorbent and its reusability of functional paper was also involved. Therefore, this novel, environment-friendly functional paper can surely act as an effective adsorbent for the removal and recovery of heavy metals in alkaline aqueous solutions.

An organocatalytic method for constructing pyrroles via the cycloisomerisation of Z-1-iodo-4-N-methylbenzenesulfonyl-1,6-enynes

A new cycloisomerisation of Z-1-iodo-4-N-methylbenzenesulfonyl-1,6-enynes to functionalized pyrroles was realized in the presence of an organomolecule (4,4'-bis(1,1-dimethylethyl)-2,2'-bipyridine) and KOtBu. The transformations were performed efficiently to produce different kinds of functionalized pyrroles within 10 min. This is the first example of an organomolecule promoted methodology with vinyl iodides from a non-aromatic system to an aromatic system, which offers an excellent option toward establishing a new horizon for cross-coupling reactions of vinyl halides. Preliminary mechanistic studies were performed and a crude radical pathway was proposed.

Generation of Aryl Radicals from Aryl Halides: Rongalite-Promoted Transition-Metal-Free Arylation

A new and practical method for the generation of aryl radicals from aryl halides is reported. Rongalite as a novel precursor of super electron donors was used to initiate a series of electron-catalyzed reactions under mild conditions. These transition-metal-free radical chain reactions enable the efficient formation of C-C, C-S, and C-P bonds through homolytic aromatic substitution or S_RN1 reactions. Moreover, the synthesis of antipsychotic drug Quetiapine was performed on gram scale through the described method. This protocol demonstrated its potential as a promising arylation method in organic synthesis.

C-C Bond Formation of Benzyl Alcohols and Alkynes Using a Catalytic Amount of KOt Bu: Unusual Regioselectivity through a Radical Mechanism

We report a C-C bond-forming reaction between benzyl alcohols and alkynes in the presence of a catalytic amount of KO^t Bu to form α-alkylated ketones in which the C=O group is located on the side derived from the alcohol. The reaction proceeds under thermal conditions (125 °C) and produces no waste, making the reaction highly atom efficient, environmentally benign, and sustainable. Based on our mechanistic investigations, we propose that the reaction proceeds through radical pathways.

First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer Ligands

The use of 3d metals in de/hydrogenation catalysis has emerged as a competitive field with respect to "traditional" precious metal catalyzed transformations. The introduction of functional pincer ligands that can store protons and/or electrons as expressed by metal-ligand cooperativity and ligand redox-activity strongly stimulated this development as a conceptual starting point for rational catalyst design. This review aims at providing a comprehensive picture of the utilization of functional pincer ligands in first-row transition metal hydrogenation and dehydrogenation catalysis and related synthetic concepts relying on these such as the hydrogen borrowing methodology. Particular emphasis is put on the implementation and relevance of cooperating and redox-active pincer ligands within the mechanistic scenarios.

Electron Transfer Reactions: KO tBu (but not NaO tBu) Photoreduces Benzophenone under Activation by Visible Light

Long-standing controversial reports of electron transfer from KO tBu to benzophenone have been investigated and resolved. The mismatch in the oxidation potential of KO tBu (+0.10 V vs SCE in DMF) and the first reduction potential of benzophenone (of many values cited in the literature, the least negative value is -1.31 V vs SCE in DMF), preclude direct electron transfer. Experimental and computational results now establish that a complex is formed between the two reagents, with the potassium ion providing the linkage, which markedly shifts the absorption spectrum to provide a tail in the visible light region. Photoactivation at room temperature by irradiation at defined wavelength (365 or 400 nm), or even by winter daylight, leads to the development of the blue color of the potassium salt of benzophenone ketyl, whereas no reaction is observed when the reaction mixture is maintained in darkness. So, no electron transfer occurs in the ground state. However, when photoexcited, electron transfer occurs within a complex formed from benzophenone and KO tBu. TDDFT studies match experimental findings and also define the electronic transition within the complex as n → π*, originating on the butoxide oxygen. Computation and experiment also align in showing that this reaction is selective for KO tBu; no such effect occurs with NaO tBu, providing the first case where such alkali metal ion selectivity is rationalized in detail. Chemical evidence is provided for the photoactivated electron transfer from KO tBu to benzophenone: tert-butoxyl radicals are formed and undergo fragmentation to form (acetone and) methyl radicals, some of which are trapped by benzophenone. Likewise, when KOC(Et)₃ is used in place of KO tBu, then ethylation of benzophenone is seen. Further evidence of electron transfer was seen when the reaction was conducted in benzene, in the presence of p-iodotoluene; this triggered BHAS coupling to form 4-methylbiphenyl in 74% yield.

KOtBu as a Single Electron Donor? Revisiting the Halogenation of Alkanes with CBr₄ and CCl₄

The search for reactions where KO^tBu and other tert-alkoxides might behave as single electron donors led us to explore their reactions with tetrahalomethanes, CX₄, in the presence of adamantane. We recently reported the halogenation of adamantane under these conditions. These reactions appeared to mirror the analogous known reaction of NaOH with CBr₄ under phase-transfer conditions, where initiation features single electron transfer from a hydroxide ion to CBr₄. We now report evidence from experimental and computational studies that KO^tBu and other alkoxide reagents do not go through an analogous electron transfer. Rather, the alkoxides form hypohalites upon reacting with CBr₄ or CCl₄, and homolytic decomposition of appropriate hypohalites initiates the halogenation of adamantane.

Super electron donors derived from diboron

Single-electron transfer is an important process in organic chemistry, in which a single-electron reductant (electron donor) acts as a key component. Compared with metal-based electron donors, organic electron donors have some unique advantages, such as tunable reduction ability and mild reaction conditions. The development of novel organic electron donors with good reduction ability together with ease of preparation is in high demand. Based on the pyridine-catalyzed radical borylation reaction developed in our laboratory, we have discovered that, the reaction system consisting of a diboron(4) compound, methoxide and a pyridine derivative could smoothly produce super electron donors in situ. Two boryl-pyridine based species, the major one being a trans-2H,2'H-[2,2'-bipyridine]-1,1'-diide borate complex and the minor one being a pyridine radical anion-borate complex, were observed and carefully characterized. These complexes were found to be organic super electron donors unprecedented in literature, and their formation mechanisms were studied by DFT calculations. The diboron/methoxide/pyridine system enables the preparation of organic super electron donors from easily accessible starting materials under mild conditions, which has the potential to be a general and practical single-electron reducing agent in organic synthesis.

Accessing Heterobiaryls through Transition-Metal-Free C-H Functionalization

Herein we report a transition-metal-free synthetic protocol for heterobiaryls, one of the most important pharmacophores in the modern drug industry, employing a new multidonor phenalenyl (PLY)-based ligand. The current procedure offers a wide substrate scope (24 examples) with a low catalyst loading resulting in an excellent product yield (up to 95%). The reaction mechanism involves a single electron transfer (SET) from a phenalenyl-based radical to generate a reactive heteroaryl radical. To establish the mechanism, we have isolated the catalytically active SET initiator, characterizing by a magnetic study.