Iodonium Salts Research Articles

Efficacy analysis of new copper complex for visible light (455, 530 nm) radical/cationic photopolymerization: The synergic effects and catalytic cycle.

The kinetics and the conversion features of two 3-component systems (A/B/N), based on the proposed new kinetic schemes of Mokbel and Mau et al, in which a visible LED is used to excite a copper complex to its excited triplet state (G*). The coupling of G* with iodonium salt and ethyl 4-(dimethylamino)benzoate (EDB) produces both free radical polymerization (FRP) of acrylates and the free radical promoted cationic polymerization (CP) of epoxides using various new copper complex as the initiator. Higher FRP and CP conversion can be achieved by co-additive of [B] and N, via the dual function of (i) regeneration [A], and (ii) generation of extra radicals. The interpenetrated polymer network (IPN) capable of initiating both FRP and CP in a blend of TMPTA and EPOX. The synergic effects due to CP include: (i) CP can increase viscosity limiting the diffusional oxygen replenishment; (ii) the cation also acts as a diluting agent for the IPN network, and (iii) the exothermic property of the CP. The catalytic cycle, synergic effects, and the oxygen inhibition are theoretically confirmed to support the experimental hypothesis. The measured results of Mokbel and Mau et al are well analyzed and matching the predicted features of our modeling.

Diastereo-selective synthesis of CF3-substituted epoxide viain situ generated trifluoroethylideneiodonium ylide

The first example for the generation of 2,2,2-trifluoroethylidene ylide from corresponding iodonium salt is reported, which has been successfully applied in the epoxidation of aldehydes, achieving the corresponding trifluoromethylated epoxides in high yields and diastereo-selectivities.

Organocatalytic Synthesis of Phenols from Diaryliodonium Salts with Water under Metal-Free Conditions.

The metal-free synthesis of phenols from diaryliodonium salts with water was developed by using N-benzylpyridin-2-one as an organocatalyst. In this process, sterically congested, functionalized, and heterocycle-containing iodonium salts were smoothly converted to the desired products, and the clofibrate and mecloqualone derivatives were also synthesized in high yields. In addition, the gram-scale experiment was successfully carried out with 10 mmol of a sterically congested substrate.

Base‐Promoted Reaction of Phenols with Spirocylic λ3‐Iodanes: Access to Both 2‐Iodovinyl Aryl Ethers and Diaryl Ethers

AbstractHerein, an efficient method for vinyl or aryl C(sp2)−O bond forming to construct both the (Z)‐2‐iodovinyl aryl ethers and diaryl ethers under metal‐, photocatalyst‐ and light‐free condition in one‐step, has been developed. To generate the two desired products, we proposed a SNAr2 reaction of phenol with vinyl aryl iodonium salts intermediates that subsequently lead to the phenyl‐I bond cleavage and phenyl‐O bond formation. We firstly found that the vinyl aryl iodonium salts was formed in situ from the spiro‐cis‐β‐phenol‐VBXs, which was generated between electrophilic spiro‐EBXs and nucleophilic arylols. Trisubstituted alkenes and functionalized diaryl ethers can be afforded from the two desired products.

Rapid Synthesis of Polycyclic Aromatic Compounds by Iodocyclization of Ynamides

AbstractYnamides are recognized as electron‐rich π‐components and show high reactivity toward electrophiles such as iodonium salts. Here we report the iodocyclization of ene‐ynamides and arene‐ynamides leading to naphthalenes and phenanthrenes. We found these reactions were completed within 3 seconds by using I(coll)2PF6 as an iodonium reagent, and cyclized products were obtained in good to high yields. To the best of our knowledge, this method is the most rapid synthesis known to date of polycyclic aromatic compounds.

Redox Non‐Innocence of ortho ‐Benzoquinone Dioximate Dianion in Ligand Exchange on Ruthenium

An o-benzoquinone dioximato ruthenium complex 1 was synthesized. Treatment of 1 with an iodonium salt resulted in oxidation of the dioximato ligand along with ligand substitution to afford 2 bearing an aromatic o-dinitrosobenzene ligand. Complex 2 reacted with benzensulfohydroxamic acid as an NO− source to regenerate 1. The two ligands are compared by NMR, X-ray analysis, and DFT calculations.

Metal‐Free C−H Functionalization via Diaryliodonium Salts with a Chemically Robust Dummy Ligand

AbstractA two‐step strategy for the transition‐metal‐free C−H functionalization of arenes using unsymmetrical iodonium salts as versatile synthetic linchpins is presented. The key to the success of this strategy is the identification of the 3,5‐dimethyl‐4‐isoxazolyl (DMIX) group as a superior dummy ligand, which enables not only site‐selective C−H functionalization to afford unsymmetrical iodonium salts, but also highly selective aryl transfer during the subsequent metal‐free coupling reaction. Both electron‐rich and moderately electron‐deficient arenes can be converted into the iodonium salts through C−H functionalization, allowing for diverse structural elaboration by metal‐free C−N, C−C, C−S, and C−O coupling.

Metal-Free C-H Functionalization via Diaryliodonium Salts with a Chemically Robust Dummy Ligand.

A two-step strategy for the transition-metal-free C-H functionalization of arenes using unsymmetrical iodonium salts as versatile synthetic linchpins is presented. The key to the success of this strategy is the identification of the 3,5-dimethyl-4-isoxazolyl (DMIX) group as a superior dummy ligand, which enables not only site-selective C-H functionalization to afford unsymmetrical iodonium salts, but also highly selective aryl transfer during the subsequent metal-free coupling reaction. Both electron-rich and moderately electron-deficient arenes can be converted into the iodonium salts through C-H functionalization, allowing for diverse structural elaboration by metal-free C-N, C-C, C-S, and C-O coupling.

Novel Copper Complexes as Visible Light Photoinitiators for the Synthesis of Interpenetrating Polymer Networks (IPNs).

This work is devoted to the study of two copper complexes (Cu) bearing pyridine ligands, which were synthesized, evaluated and tested as new visible light photoinitiators for the free radical photopolymerization (FRP) of acrylates functional groups in thick and thin samples upon light-emitting diodes (LED) at 405 and 455 nm irradiation. These latter wavelengths are considered to be safe to produce polymer materials. The photoinitiation abilities of these organometallic compounds were evaluated in combination with an iodonium (Iod) salt and/or amine (e.g., N-phenylglycine—NPG). Interestingly, high final conversions and high polymerization rates were obtained for both compounds using two and three-component photoinitiating systems (Cu1 (or Cu2)/Iodonium salt (Iod) (0.1%/1% w/w) and Cu1 (or Cu2)/Iod/amine (0.1%/1%/1% w/w/w)). The new proposed copper complexes were also used for direct laser write experiments involving a laser diode at 405 nm, and for the photocomposite synthesis with glass fibers using a UV-conveyor at 395 nm. To explain the obtained polymerization results, different methods and characterization techniques were used: steady-state photolysis, real-time Fourier transform infrared spectroscopy (RT-FTIR), emission spectroscopy and cyclic voltammetry.

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.

Influence of different concentrations of an iodonium salt on properties of amine-free resins

Objectivesto evaluate the effect of different concentrations of an iodonium salt on the degree of conversion, polymerisation rate, flexural strength and modulus of an amine-free photopolymerizable resin system. MethodsTwo series of UDMA/TEGDMA resin mixtures (1:1 mass ratio) containing 0, 0.5, 1.0 or 2.0 mol% of bis(4-methyl phenyl)iodonium hexafluorophosphate(BPI): and 1 mol% camphorquinone (CQ) were evaluated. One of the series contained 2 mol% of the amine (2-(dimethylamino)ethyl methacrylate-DMAEMA), while the other series had only CQ and BPI as photoinitiators. Polymerisation kinetics and degree of conversion (DC) were evaluated by Fourier transform near-infrared spectroscopy (n = 3). Flexural strength (FS) and modulus (E) were evaluated by a three-point bending method (n = 12). Data were analysed by two-way ANOVA and Tukey’s test. ResultsThe system containing CQ + DMAEMA + BPI provided the highest DC and FS. Amine-free resins had similar E regardless of the presence of BPI. The resins containing CQ+DMAEMA with 1 and 2 mol% of BPI presented higher E compared with others. SignificanceAmine-containing resins reached statistically higher DC, rate of polymerisation and FS than amine-free systems. The use of higher BPI concentrations did not improve the properties of amine-free resins.

Catalytic and non-catalytic selective aryl transfer from (mesityl)iodonium(III) salts to diarylsulfide compounds

Catalytic and non-catalytic selective aryl transfer from (mesityl)iodonium(III) salts to diarylsulfide compounds

The covalent functionalization of few-layered MoTe2 thin films with iodonium salts

Covalent functionalization of 2D materials provides a tailored approach towards tuning of their chemical, optical, and electronic properties making the search for new ways to graft small molecules important. Herein, the reaction with (3,5-bis(trifluoromethyl)phenyl)iodonium salt is revealed as an effective strategy for functionalization of MoTe2 thin films. Upon decomposition of the salt, the generated radicals graft covalently as aryl-(CF3)2 groups at the surface of both metallic (1T’) and semiconducting (2H) polymorphs of MoTe2. Remarkably, the reactivity of the salt is governed by the electronic structure of the given polymorph. While the functionalization of the metallic MoTe2 occurs spontaneously, the semiconducting MoTe2 requires activation by light. The reaction proceeds with the elimination of oxide from the original films yielding the functionalized products that remain protected in ambient conditions, presenting a viable solution to the ageing of MoTe2 in air.

Phenothiazine-based charge-transfer complexes as visible-light photoinitiating systems for acrylate and thiol-ene photopolymerization

Owing to their unique photodynamics, phenothiazine (PTZ) can be used to form charge-transfer complexes (CTCs), which serve as effective visible-light photoinitiating systems (PIS) for acrylate and thiol-based click polymerization. In this study, seven PTZ structures and their corresponding CTCs with iodonium salt (Iod) were evaluated by calculated spectra and polymerization kinetics. The effectiveness of the initiator decreased in the order of N-substituted polycyclic aromatic hydrocarbons > electron-donating aromatics > electron-withdrawing aromatics ≈ aliphatic alkanes. Substituted dimethylaminophenyl derivatives exhibited a lower energy gap and higher photoinitiation efficiency in CTCs. Moreover, PTZ-based CTCs as PIS rendered increased thermal stability to the photosensitive resin systems due to the mild free-radical quenching of PTZ. Such characteristic demonstrates potential versatility in the 3D printing of high-performance and high-precision materials.

Charge transfer complexes as dual thermal/photo initiators for free‐radical frontal polymerization

AbstractFrontal polymerization is a process in which a localized reaction zone propagates from the coupling of thermal transport and the Arrhenius rate dependence of an exothermic polymerization; monomer is converted into polymer as the front passes through an unstirred medium. Herein we report the first study of charge transfer complexes (CTCs) as photo/thermal initiators for free‐radical frontal polymerization. Front velocity was studied as a function of mole ratio between an aromatic amine, such as dimethyl‐p‐toluidine or dimethylaniline, and an iodonium salt. It was found that the front velocity reached a maximum at a certain mole ratio of amine to iodonium salt. The velocity remained constant upon increasing the ratio of amine to iodonium salt past this critical ratio. Fronts were also studied using N‐phenyl glycine as an electron donor, but its utility was limited by low solubility. Lastly, the steric and electronic effects of the iodonium salt and counter anion were explored. It was found that CTCs using iodonium salts with less nucleophilic anions gave higher front velocities. In terms of intrinsic reactivity, the CTC composed of N,N‐dimethyl‐p‐toluidine and bis[4‐(tert‐butyl)phenyl]iodonium tetra(nonafluoro‐tert‐butoxy)aluminate gave the highest front velocity per molal of iodonium salt.

Front Cover Picture: Chiral Binaphthyl‐Based Iodonium Salt (Hypervalent Iodine(III)) as Hydrogen‐ and Halogen‐Bonding Bifunctional Catalyst: Insight into Abnormal Counteranion Effect and Asymmetric Synthesis of N,S‐Acetals (Adv. Synth. Catal. 6/2022)

The front cover picture, prepared by Dr Y. Yoshida, illustrates the asymmetric syntheses of N,S-acetals catalysed by their originally-designed chiral iodonium salts. The 1,2-addition reaction of bulky thiols to isatin-derived ketimines were catalysed by the chiral iodonium salts in excellent yields and enantioselectivities under neutral conditions. The reaction mechanism was studied using NMR experiments and DFT calculations of a plausible intermediate, which revealed that the imine substrate was activated by the catalyst in a hydrogen- and halogen-bonding bidentate activation manner. Details can be found in the Research Article by Yoshida and co-workers. (Y. Yoshida, T. Fujimura, T. Mino, M. Sakamoto, Adv. Synth. Catal. 2022, 364, 1091-1097; DOI: 10.1002/adsc.202101380)

Oxygen-Demanding Photocontrolled RAFT Polymerization Under Ambient Conditions.

A photocontrolled reversible addition-fragmentation chain transfer (RAFT) process is developed by initiating polymerization through a 1,3-diaminopropane-triethylborane (DAPTB)-diphenyl iodonium salt (Ph2 I+ ) complex (DAPTB/Ph2 I+ ) under ambient temperature and atmospheric conditions. Upon demand, this air-stable DAPTB/Ph2 I+ complex is photolyzed to liberate a reactive triethylborane that consumes atmospheric oxygen and generates ethyl radicals, which initiate and mediate RAFT polymerization. Controlled RAFT polymerization is thus achieved without any prior deoxygenation using a novel RAFT chain transfer agent, BP-FSBC, which contains both benzophenone and sulfonyl fluoride moieties. Furthermore, the kinetics of polymerization reveal that the reaction process is rapid, and well-defined polymers are produced by a 61% conversion of 2-hydroxyethyl acrylate (HEA) within 7 min and 77% conversion of N,N-dimethylacrylamide (DMA) within 10.5 min. The temporal and spatial control of this photopolymerization is also demonstrated by an "on/off" switch of UV irradiation and a painting-on-a-surface approach, respectively. In addition, active chain ends are demonstrated by preparing block copolymers by chain extension and click sulfur(VI)-fluoride exchange postreaction using RAFT-derived macrochain transfer agents.

Diarylation of N- and O-nucleophiles through a metal-free cascade reaction

Diarylation of N- and O-nucleophiles through a metal-free cascade reaction

Synthesis of azulenolactones through sequential C(2)‐bromoarylation and intramolecular CO bond formation from azulene‐1‐carboxylic acids and di(2‐bromoaryl)iodonium salts in one pot

AbstractSequential C(2)‐bromoarylation reaction and intramolecular CO bond formation from azulene‐1‐carboxylic acids and di(2‐bromoaryl)iodonium salts produced azulenolactones in one pot. The sequential reaction proceeded smoothly through the copper(I)‐mediated cyclization of 2‐(2‐bromoaryl)azulene‐1‐carboxylic acids derived from the regioselective iridium(III)‐catalyzed C(2)‐bromoarylation reaction without decarboxylation.

Silyl Glyoximides: Toward a New Class of Visible Light Photoinitiators

AbstractMany academic and industrial works are carried out for the search of new classes of visible light photoinitiators. In the last decade, new Type I photoinitiator generating silyl, germyl, or stannyl radicals is elegantly reported; the chemical mechanisms being often associated with the cleavage of the C(═O)Si, C(═O)Ge, or C(═O)Sn bonds. In this context, silyl glyoxylates are also reported as dual Type I and Type II photoinitiators. Silyl glyoximides are proposed here as new near‐UV and blue light sensitive photoinitiators. The synthesis of such compounds as well as their light absorption properties is discussed. Their photochemical properties are studied through steady state photolysis experiments and molecular modeling data (i.e., through the calculations of the frontier orbitals, CC bond dissociation energies and triplet state energy levels). To finish, their photoinitiating ability upon near‐UV or blue light emitting diode light is examined in a benchmark methacrylate monomer blend (BisGMA/TEGDMA). Markedly, a Type I photoinitiator behavior is highlighted but better initiating properties are found in multicomponent systems in combination with iodonium salt and amine.