Outer-sphere Electron Transfer Research Articles

Fully Reduced and Mixed-Valent Multi-Copper Aggregates Supported by Tetradentate Diamino Bis(thiolate) Ligands.

Tetradentate diamino bis(thiolate) ligands (l-N2S2(2-)) with saturated linkages between heteroatoms support fully reduced [(Cu(l-N2S2))2Cu2] complexes that bear relevance as an entry point toward molecules featuring the Cu2ICu2II(μ4-S) core composition of nitrous oxide reductase (N2OR). Tetracopper [(Cu(l-N2(SMe2)2))2Cu2] (l-N2(SMe2H)2 = N1,N2-bis(2-methyl-2-mercaptopropane)-N1,N2-dimethylethane-1,2-diamine) does not support clean S atom oxidative addition but undergoes Cl atom transfer from PhICl2 or Ph3CCl to afford [(Cu(l-N2(SMe2)2))3(CuCl)5], 14. When introduced to Cu(I) sources, the l-N2(SArH)2 ligand (l-N2(SArH)2 = N1,N2-bis(2-mercaptophenyl)-N1,N2-dimethylethane-1,2-diamine), made by a newly devised route from N1,N2-bis(2-fluorophenyl)-N1,N2-dimethylethane-1,2-diamine, ultimately yields the mixed-valent pentacopper [(Cu(l-N2SAr2))3Cu2] (19), which has 3-fold rotational symmetry (D3) around a Cu2 axis. The single CuII ion of 19 is ensconced within an equatorial l-N2(SAr)2(2-) ligand, as shown by 14N coupling in its EPR spectrum. Formation of 19 proceeds from an initial, fully reduced product, [(Cu(l-N2SAr2))3Cu2(Cu(MeCN))] (17), which is C2 symmetric and exceedingly air-sensitive. While unreactive toward chalcogen donors, 19 supports reversible reduction to the all-cuprous state; generation of [19]1- and treatment with S atom donors only return 19 because structural adjustments necessary for oxidative addition are noncompetitive with outer-sphere electron transfer. Oxidation of 19 is marked by intense darkening, consistent with greater mixed valency, and by dimerization in the crystalline state to a decacopper species ([20]2+) of S4 symmetry.

Kinetic study of Ru(III) – catalyzed oxidation of L-phenylalanine by hexacyanoferrate(III) in an anionic surfactant medium

Abstract The kinetic investigation of Ru(III) promoted oxidation of L-phenylalanine (L-PheAla) by [Fe(CN)6]3− has been performed in anionic sodium dodecyl sulfate (SDS) micellar medium by recording the decrease in absorbance at 420 nm corresponding to [Fe(CN)6]3− using an UV–visible spectrophotometer. Using the pseudo-first-order condition, the course of the reaction was studied as a function of [Fe(CN)6 3−], ionic strength, [OH−], [SDS], [Ru3+], [L-PheAla] and temperature by changing one variable at a time. The results exhibit that [OH−], [SDS], and [L-PheAla] are the crucial parameters that have an appreciable influence on the reaction rate. The reaction exhibits first-order kinetics in concentration ranges of Ru(III), [Fe(CN)6]3− and at low [L-PheAla] and [OH−] concentrations. The incremental trend observed in the reaction rate with electrolyte concentration shows a positive salt effect. The reaction rate is almost 10 times faster in SDS micellar medium than in aqueous medium. [Fe(CN)6]3− has no appreciable effect on the CMC of SDS, since the polar head of SDS and [Fe(CN)6]3− are both negatively charged. The K+ obtained from K3[Fe(CN)6] and KNO3 decreases the repulsion between the negatively charged heads of the surfactant molecules, which decreases the CMC of SDS. The activation parameters also support the outer-sphere electron transfer mechanism.

Features of electrochemical behavior of graphene films on metal foams

ABSTRACT Electrochemical behaviour of 4.8 ± 0.2 nm graphene films on nickel and copper foams was investigated by cyclic voltammetry (CV). The graphene films were prepared by chemical vapor deposition and characterized by electron energy loss spectroscopy, elastic peak electron spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The CV of the [Ru(NH3)6]+2/+3 redox reaction was performed using these substrates. The obtained results demonstrated a high continuity of the deposited graphene film and independence of the electron transfer rate on them from the metal substrate used. The rate of outer-sphere electron transfer on the graphene surface appeared to be substantially less than that on the polished glassy carbon. Partial splitting of graphene layers due to wedged action of 2D adsorption layers, formed by camphor solution, led to the increase in double-layer capacitance.

Theory for Heterogeneous Electron Transfer Kinetics on Nanocorrugated Atomic Stepped Metal Electrodes

We develop a novel mean-field theoretical approach for the outer-sphere heterogeneous electron transfer (OS-HET) rate constant at an atomically stepped nanocorrugated metal surface. Theory accounts for the contributions from the nature of the metal, local curvature of the nanocorrugated atomic step, the density of atomic steps and kinks, dipolar solvents, and the frontier molecular orbital of electroactive molecules. Our theoretical approach develops a novel model for the free energy of activation obtained using the alignment of the Fermi energy level in the metal with one of the frontier molecular orbitals of the electroactive species. The activation free energy is obtained as a product of a modified work function (WF) and the fractional electronic charge of activation for the alignment of levels. Metal surface local curvatures at atomic steps are modeled as a hyperbolic tangent functional with a random nanocorrugated step edge. The influence of step density and edge fluctuations (or kinks) on the activation free energy is included through the surface average mean curvature and the mean-square gradient dependent modified WF. The theoretical results highlight the step density-dependent nonmonotonic variation in WF, fractional electronic charge, and activation free energy. The increase in step density shifts the Fermi energy level toward LUMO and away from HOMO energy levels. This causes the reduced (for the LUMO) and enhanced (for the HOMO) activation free energy for ET kinetics compared to the basal plane. The dichotomy in the OS-HET kinetics at the atomically stepped metal results in anomalous enhancement and suppression for the LUMO and HOMO, respectively. The strong influence of kinks along the step edge on the HET rate constant is predicted up to 6 decades (compared to the basal surface of Pt metal). Finally, theory shows agreement with the reported experimental data of WF and exchange current density for single crystal Pt electrodes.

Redox Reactions of Ag(I)/Ag and Ferrocenium/Ferrocene in 1-Butyl-1-methylpyrrolidinium Bis(fluorosulfonyl)amide Ionic Liquid

The electrode reactions of Ag(I)/Ag and ferrocenium/ferrocene (Fc+/Fc) were investigated in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA). The potential of Ag(I)/Ag depended on the logarithm of the concentration of Ag(I), as predicted by the Nernst equation, indicating the Ag(I)/Ag can be used as a reference electrode reaction in BMPFSA. The reversible electrode reaction of Fc+/Fc was observed in BMPFSA by cyclic voltammetry. The donor number of BMPFSA was estimated to be 13 from the difference in the formal potentials of Ag(I)/Ag and Fc+/Fc, indicating the coordination ability of FSA– was slightly stronger than that of bis(trifluoromethylsulfonyl)amide (TFSA–). The diffusion coefficients (D) of Fc and Fc+ were (5.7 ± 0.7) and (3.3 ± 0.2) × 10–7 cm2 s–1, respectively. The ratio of D of Fc+ against that of Fc was smaller than those in TFSA–-type ionic liquids, reflecting the higher charge density of FSA–. The standard rate constant (k 0) of Fc+/Fc was estimated to be (5.4 ± 1.1) × 10–3 cm s–1. The apparent activation energy for k 0 was close to the activation energy for D, suggesting the electrode reaction of Fc+/Fc can be regarded as the outer sphere electron transfer reaction with a very small reorganization energy.

Electrocatalytic Aldehyde Oxidation by a Tungsten Dependent Aldehyde Oxidoreductase from Aromatoleum Aromaticum.

In contrast to their molybdenum dependent relatives, tungsten enzymes operate at significantly lower redox potentials, and in some cases they can carry out reversible redox transformations of their substrates and products. Still, the electrochemical properties of W enzymes have received much less attention than their Mo relatives. Herein we analyse the tungsten enzyme aldehyde oxidoreductase (AOR) from the mesophilic bacterium Aromatoleum aromaticum which has been immobilised on a glassy carbon working electrode. This generates a functional system that electrochemically oxidises a wide variety of aromatic and aliphatic aldehydes in the presence of the electron transfer mediators benzyl viologen, methylene blue or dichlorophenol indophenol. Simulation of the cyclic voltammetry has enabled a thorough kinetic analysis of the system, which reveals that methylene blue acts as a two-electron acceptor. In contrast, the other two mediators act as single electron oxidants. The different electrochemical driving forces imparted by these mediators also lead to significantly different outer sphere electron transfer rates with AOR. This work shows that electrocatalytic aldehyde oxidation can be achieved at a low applied electrochemical potential leading to an extremely energy efficient catalytic process.

Effects of support material and electrolyte on a triphenylamine substituted cobalt porphyrin catalytic oxygen reduction reaction

The interfacial charge transfer conditions are crucial for understanding the catalytic mechanism and thus developing high performing electrocatalysts. To justify the effects of support material and electrolyte on metalloporphyrin catalytic oxygen reduction reaction (ORR), we synthesize a symmetric triphenylamine (TPA) substituted cobalt porphyrin, nominated as s-TPA-CoP, and select carbon black and multi-walled carbon nanotubes as the supports to fabricate composite catalysts. The ORR performances are measured in both acidic and alkaline solutions. While the support material affects negligibly on reduction potentials, the stronger π-π stacking in s-TPA-CoP/CNT, as revealed by X-ray photoelectron spectroscopy measurements, leads to greater limiting current densities and larger electron transfer numbers as compared to s-TPA-CoP/XC in either electrolyte. Both composites perform better ORR activity but poorer 4-electron selectivity in base than in acid, whose origins are discussed from the aspects of interfacial charge states and inner- / outer-sphere electron transfer mechanisms. Strikingly, s-TPA-CoP/CNT exhibits an electron transfer number of 3.8 in acid, demonstrating the privilege of TPA as the substitution on monometallic cobalt porphyrins in chasing 4-electron transfer oxygen reduction.

QM Calculations Revealed that Outer-Sphere Electron Transfer Boosted O-O Bond Cleavage in the Multiheme-Dependent Cytochrome bd Oxygen Reductase.

The cytochrome bd oxygen reductase catalyzes the four-electron reduction of dioxygen to two water molecules. The structure of this enzyme reveals three heme molecules in the active site, which differs from that of heme-copper cytochrome c oxidase. The quantum chemical cluster approach was used to uncover the reaction mechanism of this intriguing metalloenzyme. The calculations suggested that a proton-coupled electron transfer reduction occurs first to generate a ferrous heme b595. This is followed by the dioxygen binding at the heme d center coupled with an outer-sphere electron transfer from the ferrous heme b595 to the dioxygen moiety, affording a ferric ion superoxide intermediate. A second proton-coupled electron transfer produces a heme d ferric hydroperoxide, which undergoes efficient O-O bond cleavage facilitated by an outer-sphere electron transfer from the ferrous heme b595 to the O-O σ* orbital and an inner-sphere proton transfer from the heme d hydroxyl group to the leaving hydroxide. The synergistic benefits of the two types of hemes rationalize the highly efficient oxygen reduction repertoire for the multi-heme-dependent cytochrome bd oxygen reductase family.

Theoretical Insight into Oxidation of Anilines to Azobenzenes Catalyzed by Hexamolybdate: Outer-Sphere Electron and Proton Transfer

Recently, the catalytic activity of Lindqvist-type hexamolybdate [Mo6O19]2– in the oxidation of an aniline derivative (LPhNH2, L = substituent) was demonstrated by Wei and co-workers (Angew. Chem. Int. Ed. 2021, 60, 6382–6385). Herein, taking phenylamine (PhNH2) oxidation to azobenzene (PhNNPh) as a model reaction, we report the density functional theory investigation of the catalytic mechanism of [Mo6O19]2– and illustrate the critical experimental phenomena. During the catalytic reaction, once the preassociation of [Mo6O19]2– and PhNH2 takes place, electron transfer and proton transfer immediately proceed to form an N radical intermediate. The higher the highest occupied molecular orbital energy of the substrate, the easier the formation of the N radical intermediate. The N–N bond formation proceeds via the second PhNH2 nucleophilic attack on the N radical intermediate. The substituent position and the N reaction site of the substrate have a significant effect on the second PhNH2 nucleophilic attack process. In the reaction process, the six MoVI of [Mo6O19]2– are still hexacoordinated, which is defined as the outer-sphere pathway. One of the factors determining the product selectivity is the electrostatic repulsion between LPhNH2 and the N radical intermediate. The experiment reveals that the product yield is increased by the addition of Na2S2O3, while the catalytic reaction is completely deactivated with Na2CO3 or K3PO4. Based on the proposed mechanism, the experimental observation was rationalized. The S2O32– part of Na2S2O3 has a similar function as the electron-withdrawing substituent due to its low lowest unoccupied molecular orbital (LUMO) energy, which reduces the LUMO energy of the N radical intermediate and thus facilitates PhNH2 nucleophilic attack, while the CO32– part of Na2CO3 or PO43– part of K3PO4 has an undesirable effect on the electrophilicity of the N radical intermediate, resulting in the interruption of the catalytic reaction. This work would provide a detailed understanding of the catalytic reaction.

An energy decomposition and extrapolation scheme for evaluating electron transfer rate constants: a case study on electron self-exchange reactions of transition metal complexes.

A simple approach to the analysis of electron transfer (ET) reactions based on energy decomposition and extrapolation schemes is proposed. The present energy decomposition and extrapolation-based electron localization (EDEEL) method represents the diabatic energies for the initial and final states using the adiabatic energies of the donor and acceptor species and their complex. A scheme for the efficient estimation of ET rate constants is also proposed. EDEEL is semi-quantitative by directly evaluating the seam-of-crossing region of two diabatic potentials. In a numerical test, EDEEL successfully provided ET rate constants for electron self-exchange reactions of thirteen transition metal complexes with reasonable accuracy. In addition, its energy decomposition and extrapolation schemes provide all the energy values required for activation-strain model (ASM) analysis. The ASM analysis using EDEEL provided rational interpretations of the variation of the ET rate constants as a function of the transition metal complexes. These results suggest that EDEEL is useful for efficiently evaluating ET rate constants and obtaining a rational understanding of their magnitudes.

Long-Range Charge Transport via Redox Ligands in Quantum Dot Assemblies

We present a strategy to actively engineer long-range charge transport in colloidal quantum dot assemblies by using ligand functionalities that introduce electronic states and provide a path for carrier transfer. This is a shift away from the use of inactive spacers to modulate charge transport through the lowering of the tunneling barrier for interparticle carrier transfer. This is accomplished with the use of electronically coupled redox ligands by which a self-exchange chain reaction takes place and long-range charge transport is enabled across the film. We identified the different modes of charge transport in these quantum dot/redox ligand assemblies, their energetic position and kinetics, and explain how to rationally manipulate them through modulation of the Fermi level and redox ligand coverage.

Nanogap-Resolved Adsorption-Coupled Electron Transfer by Scanning Electrochemical Microscopy: Implications for Electrocatalysis.

Here, we demonstrate for the first time that the mechanism of adsorption-coupled electron-transfer (ACET) reactions can be identified experimentally. The electron transfer (ET) and specific adsorption of redox-active molecules are coupled in many electrode reactions with practical importance and fundamental interest. ACET reactions are often represented by a concerted mechanism. In reductive adsorption, an oxidant is simultaneously reduced and adsorbed as a reductant on the electrode surface through the ACET step. Alternatively, the non-concerted mechanism mediates outer-sphere reduction and adsorption separately when the reductant adsorption is reversible. In electrocatalysis, reversibly adsorbed reductants are ubiquitous and crucial intermediates. Moreover, electrocatalysis is complicated by the mixed mechanism based on simultaneous ACET and outer-sphere ET steps. In this work, we reveal the non-concerted mechanism for ferrocene derivatives adsorbed at highly oriented pyrolytic graphite as simple models. We enable the transient voltammetric mode of nanoscale scanning electrochemical microscopy (SECM) to kinetically control the adsorption step, which is required for the discrimination of non-concerted, concerted, and mixed mechanisms. Experimental voltammograms are compared with each mechanism by employing finite element simulation. The non-concerted mechanism is supported to indicate that the ACET step is intrinsically slower than its outer-sphere counterpart by at least four orders of magnitude. This finding implies that an ACET step is facilitated thermodynamically but may not be necessarily accelerated or catalyzed by the adsorption of the reductant. SECM-based transient voltammetry will become a powerful tool to resolve and understand electrocatalytic ACET reactions at the elementary level.

States of Aggregation and Phase Transformation Behavior of Metallosurfactant Complexes by Hexacyanoferrate(II): Thermodynamic and Kinetic Investigation of ETR in Ionic Liquids and Liposome Vesicles.

Electronic absorption spectroscopy was used to study the ETR of surfactant-cobalt(III) complexes containing imidazo[4,5-f][1,10]phenanthroline, dipyrido[3,2-d:2'-3'-f]quinoxaline and dipyrido[3,2-a:2',4'-c](6,7,8,9-tetrahydro)phenazine ligands by using ferrocyanide ions in unilamellar vesicles of dipalmitoylphosphotidylcholine (DPPC) and 1-butyl-3-methylimidazolium bromide ((BMIM)Br), at different temperatures under pseudo-first-order conditions using an excess of the reductant. The reactions were found to be second-order and the electron transfer is postulated as occurring in the outer sphere. The rate constant for the electron transfer reactions was found to increase with increasing concentrations of ionic liquids. Besides these, the effects of surfactant complex ions on liposome vesicles in these same reactions have also been studied on the basis of hydrophobicity. We observed that, below the phase transition temperature, there is an increasing amount of surfactant-cobalt(III) complexes expelled from the interior of the vesicle membrane through hydrophobic effects, while above the phase transition temperature, the surfactant-cobalt(III) complexes are expelled from the interior to the exterior surface of the vesicle. Kinetic data and activation parameters are interpreted in respect of an outer-sphere electron transfer mechanism. By assuming the existence of an outer-sphere mechanism, the results have been clarified based on the presence of hydrophobicity, and the size of the ligand increases from an ip to dpqc ligand and the reactants become oppositely charged. In all these media, the ΔS# values are recognized as negative in their direction in all the concentrations of complexes employed, indicative of a more ordered structure of the transition state. This is compatible with a model in which these complexes and [Fe(CN)6]4- ions bind to the DPPC in the transition state. Thus, the results have been interpreted based on the self-aggregation, hydrophobicity, charge densities of the co-ligand and the reactants with opposite charges.

Merging the Interfaces of Different Shape-Shifting Polymers Using Hybrid Exchange Reactions.

Sophisticated shape-shifting structures and integration of advanced functions often call for different-chemistry-based polymers (such as epoxy and polyurethane) in a unified system. However, permanent cross-links pose crucial obstacles to be seamless. Here, merging interfaces via hybrid exchange reactions among different dynamic covalent bonds (including ester, urethane, thiourethane, boronic-ester, and oxime-ester linkages) is proposed, breaking the long-lasting restriction that these widely used bonds only undergo self-exchange reactions. Model compound studies are conducted to verify that hybrid exchange reactions occur. As demonstrations, different liquid crystal elastomers are tenaciously joined into coherent assemblies, with the desired biomimetic structures (e.g., flying fish containing stiff and flexible parts) and rare deformation modes (e.g., flower blooming upon both heating and cooling). Besides connecting polymers, hybrid exchange reactions also facilitate the creation of new materials through cross-fusion of different polymers. In addition to the polymers used in this work, hybrid exchange reactions can be adapted to other polymers based on similar mechanisms and beyond. Besides shape-shifting-related areas (e.g., soft robots, flexible electronics, and biomedical devices), it may also foster innovation in other fields involving general polymers, as well as promote deeper understanding of dynamic covalent chemistry.

Aliphatic and Aromatic C–H Bond Oxidation by High-Valent Manganese(IV)-Hydroxo Species

The strong C-H bond activation of hydrocarbons is a difficult reaction in environmental and biological chemistry. Herein, a high-valent manganese(IV)-hydroxo complex, [MnIV(CHDAP-O)(OH)]2+ (2), was synthesized and characterized by various physicochemical measurements, such as ultraviolet-visible (UV-vis), electrospray ionization-mass spectrometry (ESI-MS), electron paramagnetic resonance (EPR), and helium-tagging infrared photodissociation (IRPD) methods. The one-electron reduction potential (Ered) of 2 was determined to be 0.93 V vs SCE by redox titration. 2 is formed via a transient green species assigned to a manganese(IV)-bis(hydroxo) complex, [MnIV(CHDAP)(OH)2]2+ (2'), which performs intramolecular aliphatic C-H bond activation. The kinetic isotope effect (KIE) value of 4.8 in the intramolecular oxidation was observed, which indicates that the C-H bond activation occurs via rate-determining hydrogen atom abstraction. Further, complex 2 can activate the C-H bonds of aromatic compounds, anthracene and its derivatives, under mild conditions. The KIE value of 1.0 was obtained in the oxidation of anthracene. The rate constant (ket) of electron transfer (ET) from N,N'-dimethylaniline derivatives to 2 is fitted by Marcus theory of electron transfer to afford the reorganization energy of ET (λ = 1.59 eV). The driving force dependence of log ket for oxidation of anthracene derivatives by 2 is well evaluated by Marcus theory of electron transfer. Detailed kinetic studies, including the KIE value and Marcus theory of outer-sphere electron transfer, imply that the mechanism of aromatic C-H bond hydroxylation by 2 proceeds via the rate-determining electron-transfer pathway.

Effect of the number of graphene layers on the electron transfer kinetics at metal/graphene heterostructures

We theoretically investigated the kinetics of outer-sphere electron transfer (ET) at graphene with different number of layers in the presence and absence of metal substrates using density functional theory (DFT) calculations. It is shown that the experimental data on the electrocatalytic activity of the metal substrate for few-layer graphene can be explained under the assumption of the nonadiabatic electron transfer. However, the electron transfer at the metal-supported single-layer graphene is likely adiabatic. The enhanced electron transfer in the presence of the metal substrate is explained by the hybridization of the metal and graphene electronic states, which provides more efficient interaction of the metal substrate with the reactant near the graphene surface.

Photoinduced Ion-Pair Inner-Sphere Electron Transfer-Reversible Addition-Fragmentation Chain Transfer Polymerization.

Photoredox-mediated reversible deactivation radical polymerization (RDRP) is a promising method of precise synthesis of polymers with diverse structures and properties. However, its mechanism mainly based on the outer-sphere electron transfer (OSET) leads to stringent requirements for an efficient photocatalyst. In this paper, the zwitterionic organoboranes [L2B]+X- are prepared and applied in reversible addition-fragmentation chain transfer (RAFT) polymerization with the photoinduced ion-pair inner-sphere electron transfer (IP-ISET) mechanism. The ion-pair electron transfer mechanism and the formation of the radical [L2B]• are supported by electron paramagnetic resonance (EPR) radical capture experiments, 1H/11B NMR spectroscopy, spectroelectrochemical spectroscopy, transient absorption spectroscopy, theoretical calculation, and photoluminescence quenching experiments. Photoluminescence quenching experiments show that when [CTA]/[[L2B]+] ≥ 0.6, it is static quenching because of the in situ formation of [L2B]+[ZCS2]-, the real catalytic species. [L2B]+[C3H7SCS2]- is synthesized, and its photoluminescence lifetime is the same as the lifetime in the static quenching experiment, indicating the formation of [L2B]+[ZCS2]- in polymerization and the IP-ISET mechanism. The matrix-assisted laser desorption ionization time-of-flight mass (MALDI-TOF MS) spectra show that the structure of [C3H7SCS2] was incorporated into the polymer, indicating that ion-pair electron transfer occurs in catalytic species. The polymerization shows high catalytic activity at ppb catalyst loading, a wide range of monomers, excellent tolerance in the presence of 5 mol % phenolic inhibitors, and the synthesis of ultrahigh-molecular-weight polymers. This protocol with the IP-ISET mechanism exhibits a value in the development of new organic transformations and polymerization methods.

Substrate-Rhodium Cooperativity in Photoinduced ortho-Alkynylation of Arenes.

In the realm of metallaphotocatalytic C-H activation strategy, the direct excitation of the transition metal which plays the dual role of light energy harnessing alongside performing the bond breaking and forming is a rare phenomenon. In this context we have developed the first photo-induced Rh-catalyzed ortho-alkynylation under ambient conditions without the requirement of silver salt, photocatalyst (PC) or any engineered substrate or catalyst. The transformation functions by the specific cooperative effect of a six-membered rhodacycle which is the photo-responsive species. The catalytic system allows the conjugation of arenes with sp3 -rich pharmacophoric fragments. The control experiments as well as the computational studies resolve the mechanistic intricacies for this transformation. An outer sphere electron transfer process from Rh to alkynyl radical is operative for the present photo-induced transformation over the more common oxidative addition or 1,2-migratory insertion pathways.

Substrate‐Rhodium Cooperativity in Photoinduced ortho‐Alkynylation of Arenes

AbstractIn the realm of metallaphotocatalytic C−H activation strategy, the direct excitation of the transition metal which plays the dual role of light energy harnessing alongside performing the bond breaking and forming is a rare phenomenon. In this context we have developed the first photo‐induced Rh‐catalyzed ortho‐alkynylation under ambient conditions without the requirement of silver salt, photocatalyst (PC) or any engineered substrate or catalyst. The transformation functions by the specific cooperative effect of a six‐membered rhodacycle which is the photo‐responsive species. The catalytic system allows the conjugation of arenes with sp3‐rich pharmacophoric fragments. The control experiments as well as the computational studies resolve the mechanistic intricacies for this transformation. An outer sphere electron transfer process from Rh to alkynyl radical is operative for the present photo‐induced transformation over the more common oxidative addition or 1,2‐migratory insertion pathways.

Outer-Sphere Electron-Transfer Process of Molecular Donor–Acceptor Organic Dye in the Dye-Sensitized Photocatalytic System for CO2 Reduction

Outer-Sphere Electron-Transfer Process of Molecular Donor–Acceptor Organic Dye in the Dye-Sensitized Photocatalytic System for CO₂ Reduction