Photogeneration of Chlorine Radical from a Self-Assembled Fluorous 4CzIPN•Chloride Complex: Application in C-H Bond Functionalization.

The chlorine radical is a strong HAT (Hydrogen Atom Transfer) agent that is very useful for the functionalization of C(sp)-H bonds. Albeit highly attractive, its generation from the poorly oxidizable chloride ion mediated by an excited photoredox catalyst is a difficult task. We now report that 8R-4CzIPN, an electron-deficient fluorous derivative of the benchmark 4CzIPN photoredox catalyst belonging to the donor-acceptor carbazole-cyanoarene family, is not only a better photooxidant than 4CzIPN, but also becomes an excellent host for the chloride ion.

Dual Photoredox Ni/Benzophenone Catalysis: A Study of the Ni Precatalyst Photoreduction Step.

The combination of NiX salts with a bipyridine-type ligand and aromatic carbonyl-based chromophores has emerged as a benchmark precatalytic system to efficiently conduct cross-couplings mediated by light. Mechanistic studies have led to two scenarios in which Ni is proposed as the catalytic species. Nonetheless, in none of these studies has a Ni to Ni photoreduction been evidenced.

Alkylation of the α-amino C-H bonds of anilines photocatalyzed by a DMEDA-Cu-benzophenone complex: reaction scope and mechanistic studies.

The Cu(ii) complex 1 incorporating a BP chromophore is a highly active and chemoselective photocatalyst for the alkylation of α-amino C-H bonds of anilines. The reaction was shown to proceed with a broad substrate scope in the absence of additives. Extensive mechanistic studies were performed, in particular using transient absorption spectroscopy, and spectroscopic signatures of key intermediates were identified in the conditions of catalysis.

A Bis-Acridinium Macrocycle as Multi-Responsive Receptor and Selective Phase-Transfer Agent of Perylene.

A bis-acridinium cyclophane incorporating switchable acridinium moieties linked by a 3,5-dipyridylanisole spacer was studied as a multi-responsive host for polycyclic aromatic hydrocarbon guests. Complexation of perylene was shown to be the most effective and was characterized in particular by a charge-transfer band as signal output. Effective catch and release of the guest was triggered by both chemical (proton/hydroxide) and redox stimuli.

A fluorous sodium l-prolinate derivative as low molecular weight gelator for perfluorocarbons.

We report the first study dealing with the self-assembly of an α-amino acid derivative in perfluorocarbons. Rheology, microscopy, and spectroscopy studies reveal that the fluorous sodium l-prolinate derivative 1 self-assembles in perfluorocarbons to form a three-dimensional network of left-handed nano-helices resulting in solvent gelation. Singlet oxygen lifetime measured in a gel of perfluorodecalin is about 1000 times longer than in pure water.

Dual Benzophenone/Copper-Photocatalyzed Giese-Type Alkylation of C(sp )-H Bonds.

Photocatalyzed Giese-type alkylations of C(sp )-H bonds are very attractive reactions in the context of atom-economy in C-C bond formation. The main limitation of such reactions is that when using highly polymerizable olefin acceptors, such as unsubstituted acrylates, acrylonitrile, or methyl vinyl ketone, radical polymerization often becomes the dominant or exclusive reaction pathway. Herein, we report that the polymerization of such olefins is strongly limited or suppressed when combining the photocatalytic activity of benzophenone (BP) with a catalytic amount of Cu(OAc) .

Light-mediated iodoperfluoroalkylation of alkenes/alkynes catalyzed by chloride ions: role of halogen bonding.

An innovative procedure for the iodoperfluoroalkylation of alkenes/alkynes is described. These reactions, including iodotrifluoromethylations of alkenes, proceed very efficiently under low intensity UVA irradiation in deoxygenated methanol solutions containing catalytic amounts of NaCl or Bu4NCl. Preliminary mechanistic studies indicate that the light-promoted homolytic cleavage of the Rf-I bond that initiates the reaction is facilitated by the halogen bonding interaction between RfI and chloride ions.

Light-promoted metal-free cross dehydrogenative couplings on ethers mediated by NFSI: reactivity and mechanistic studies.

Cross dehydrogenative couplings on ethers occur very effectively using N-fluorobis(phenyl)sulfonimide (NFSI) as oxidizing agent under UVA irradiation in the presence of 2 mol% benzophenone. The reaction was shown to proceed first by fast radical fluorination of the α-C-H bond of ethers, followed by HF elimination to yield the highly electrophilic oxocarbenium ion as a key intermediate.

2D and 3D surface photopatterning via laser-promoted homopolymerization of a perfluorophenyl azide-substituted BODIPY.

An innovative photopatterning process is described that allows, in a single laser-promoted operation, the covalent attachment of a molecule on a surface (2D patterning - xy dimensions) and its photopolymerization to grow micro-/nanostructures with spatial control in a third z-dimension. The surface patterning process, based on nitrene reactivity, was harnessed using the highly fluorescent azide-substituted boron difluoride dipyrromethene (BODIPY) 1 that was prepared in a single synthetic step from the parent pentafluorophenyl BODIPY on reacting with NaN. Using the laser of a fluorescence microscope (375 nm or 532 nm) 1 could be grafted on adapted surfaces and then homopolymerised.

Metal-free and light-promoted radical iodotrifluoromethylation of alkenes with Togni reagent as the source of CF and iodine.

A light-promoted methodology for the iodotrifluoromethylation of alkenes was developed. For the first time a Togni reagent was exploited as the source of both the CF group and iodine atom. Preliminary mechanistic studies suggest that both CFI and 2-iodobenzoic acid are direct sources of the iodine atom that is transferred to the products.

Effective ascorbate-free and photolatent click reactions in water using a photoreducible copper(II)-ethylenediamine precatalyst.

The search for copper catalysts able to perform effectively click reactions in water in the absence of sodium ascorbate is an active area of current research with strong potential for applications in bioconjugation. The water-soluble and photoreducible copper(II)-EDA (EDA = ethylenediamine) complex 1, which has two 4-benzoylbenzoates acting as both counterion and photosensitizer, has been synthesized and characterized by different techniques including single crystal X-ray diffraction. Highly efficient photoreduction was demonstrated when solutions of 1 in hydrogen atom donating solvents, such as THF or MeOH, were exposed to UVA radiation (350-400 nm) provided by a low pressure mercury lamp (type TLC = thin-layer chromatography, 365 nm), or by a 23 W fluorescent bulb, or by ambient/sunlight.

A fluorosurfactant and photoreducible Cu(II)-tren click catalyst: surfactant and catalytic properties at liquid/liquid interfaces.

The fluorous copper(ii) complex [Cu(II)(trenRf6)3-benzoylbenzoate]3-benzoylbenzoate 2, composed of a highly fluorophilic tris(2-aminoethyl)amine ligand and two 3-benzoylbenzoates as counterions and photosensitizers, was synthesized from the dinuclear complex [Cu(3-benzoylbenzoate)4(H2O)2] 1 which was characterized by X-ray analysis. Complex 2, which is highly soluble in perfluorocarbons, moderately soluble in organic solvents while insoluble in water, was found to be a very effective fluorosurfactant. At the air/water interface it formed a Langmuir film, which upon compression slowly collapsed at about 28 mN m(-1), which corresponds to a surface area of about 220 Å(2) per molecule.

Sunlight-driven copper-catalyst activation applied to photolatent click chemistry.

The synthesis, full characterization, photoreduction properties, and catalytic activity for the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction of a copper(II)-DMEDA (N,N'-dimethylethylendiamine) complex is reported. Spectroscopic studies (UV/Vis, EPR) demonstrated that under daylight illumination highly effective copper(II) to copper(I) reduction occurs in this complex. These findings are in agreement with a high photoreduction quantum yield value of 0.

Organocatalyzed step-growth polymerization through desymmetrization of cyclic anhydrides: synthesis of chiral polyesters.

The polymerization of prochiral bis-anhydrides with diols catalyzed by a cinchona alkaloid was shown to provide chiral polyesters in good yields and with high levels of stereocontrol. The structures of the polyesters were determined by (1) H and (13) C NMR analyses, whereas their size was estimated by both size-exclusion chromatography (SEC) and MALDI-TOF mass spectrometry, which indicated that moderate degrees of polymerization were attained through this step-growth polymerization. The enantioselectivity of the process was evaluated by using chiral HPLC analysis of the bis-lactones resulting from a controlled chemoselective degradation of the polyesters.

A photoreducible copper(II)-tren complex of practical value: generation of a highly reactive click catalyst.

A detailed study on the photoreduction of the copper(II) precatalyst 1 to generate a highly reactive cuprous species for the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click reaction is presented. For the photoactive catalyst described herein, the activation is driven by a photoinduced electron transfer (PET) process harnessing a benzophenone-like ketoprofenate chromophore as a photosensitizer, which is equally the counterion. The solvent is shown to play a major role in the Cu(II) to Cu(I) reduction process as the final electron source, and the influence of the solvent nature on the photoreduction efficiency has been studied.

Organocatalyzed aldol reaction between pyridine-2-carbaldehydes and α-ketoacids: a straightforward route towards indolizidines and isotetronic acids.

Enantioselective aldol reactions between substituted pyridine carbaldehydes and α-ketoacids were shown to provide isotetronic acids or their corresponding pyridinium salts, depending on the nature of the substituents on the pyridine ring. The pyridinium salts were generated through nucleophilic attack of the pyridine nitrogen atom onto the reactive keto functional group. Moderate-to-good yields of both compounds were typically obtained and high levels of enantioselectivity were observed by using benzimidazole pyrrolidine I as a catalyst.

Recent advances of fluorous chemistry in material sciences.

In recent years, there has been an increasing interest in exploiting fluorous derivatives/moieties for applications that are not only related to reaction mixture purification issues and catalyst recycling, but to confer unique/improved properties to materials. Herein we will focus on the recent advances of fluorous chemistry in material sciences, with special emphasis on applications in organic electronics, crystals/metal-organic frameworks (MOFs) engineering and surface modification chemistry, in particular SiO(2) surfaces. By selecting major contributions in these areas, we wish to highlight the benefits imparted by the introduction of fluorous tags within/onto materials, such as favouring the self-organisation of charge-carrier compounds in bulk heterojunctions, improving the hydrophobicity and/or stability of coordination polymer networks, facilitating solid-state structural rearrangement of large magnitude within crystals or the modification of surfaces through adsorption processes.

Copper catalyst activation driven by photoinduced electron transfer: a prototype photolatent click catalyst.

PET cat. While the copper(II) tren ketoprofenate precatalyst 1 (see picture) is inactive at room temperature in methanol, it is quantitatively and rapidly reduced to its cuprous state upon light irradiation to provide a highly reactive click catalyst. By simply introducing air into the reaction medium the catalysis can be switched off and then switched on again by bubbling argon followed by irradiation.

Fluorous catalysis: from the origin to recent advances.

Among the various strategies developed in the last two decades to recycle catalysts, fluorous catalysis has emerged as one of the most powerful approaches as it combines the advantages of homogeneous catalysis for reactivity (molecular catalysts, most often reactions conducted in one-phase homogeneous conditions) and heterogeneous catalysis for catalyst recovery (liquid/liquid- or solid/liquid-phase separation protocols). Of particular interest is the general character of this approach and the variety and efficiency of separation protocols available to recover catalysts.

Reversible hydrocarbon/perfluorocarbon phase-switching of [Ru(bipy)3]2+ driven by supramolecular heteromeric fluorous carboxylate-carboxylic acid H-bond interactions.

The Ru(bipy)(3) dication is efficiently and reversibly transferred into perfluorocarbons due to the formation of a highly fluorophillic hydrogen-bonded fluorous carboxylate-carboxylic acid counter-anion, whilst retaining key luminescence and photosensitizer characteristics, for example in singlet oxygen production.

Self-adaptive hydrophilic and coordinating Teflon surfaces through a straightforward physisorption process.

Teflon surfaces exhibiting self-adaptive behaviour with both highly hydrophilic character and strong coordinating properties are prepared in a straightforward manner by physisorption of the fluorophilic copper(II)-carboxylate complex 2.

Chemisorption of fluorous copper(II)-carboxylate complexes on SiO2 surfaces: versatile binding layers applied to the preparation of porphyrin monolayers.

The fluorous copper(II)-carboxylate complexes 1 and 2 are readily chemisorbed on SiO(2) surfaces affording super-hydrophilic binding layers for subsequent versatile functionalization by coordination chemistry.

A triblock fluorous surfactant as a specific gelator for perfluorocarbons.

The fluorinated double-tailed triblock surfactant 1-Na represents a new type of gelator for perfluorocarbons which can gelate at low concentration (1.5 wt%) both bromoperfluorooctane and perfluorodecalin, two of the most appealing perfluorinated fluids for pharmaceutical applications.

Dramatic solid-state humidity-induced modification of the magnetic coupling in a dimeric fluorous copper(II)-carboxylate complex.

The very fast and efficient water vapor absorption of the dimeric fluorous copper(II)-carboxylate complex [Cu(2)(C(8)F(17)CO(2))(4)(acetone)(2)] (1) leads, in the solid state, to a dramatic decrease of the exchange magnetic coupling between the copper(II) ions and to a drastic change of its powder EPR spectrum.

A highly active and reusable copper(I)-tren catalyst for the "click" 1,3-dipolar cycloaddition of azides and alkynes.

The copper(I) complex [Cu(C18(6)tren)]Br 1 (C18(6)tren = tris(2-dioctadecylaminoethyl)amine) which exhibits a good stability towards aerobic conditions is a versatile, highly reactive and recyclable catalyst for the Huisgen cycloaddition of azides with terminal or internal alkynes and is a useful catalyst for the preparation of "click" dendrimers.