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Bis-NHC adducts of the type (NHC)2·B2(OR)4 are sources of boryl radicals of the type NHC–BR2˙, which are formed by homolytic B–B bond cleavage.

International audience; The emulsion photopolymerization under visible light of acrylate and methacrylate monomers is reported. We previously introduced an NHC-borane-based system that was efficient for the emulsion photopolymerization of styrene [acridine orange (AO)/disulfide/NHC-borane]. This system relies on the disulfide photoreduction from the excited AO, followed by H-atom abstraction from the NHC-borane by the thiyl radical generated from the disulfide, eventually forming initiating NHC-boryl radicals. For the photopolymerization of (meth)acrylates, the boron-based photoinitiating system was simplified; as under LED illumination, the water-soluble disulfide alone is able to generate thiyl radicals that could initiate the polymerizations. With this disulfide/blue light system, MMA efficiently polymerized in emulsion, with solid contents up to 40%. The simplified system led to smaller particles than the full photoinitiating boron-based system, but the latter gave slightly better particle size distributions. Compared to styrene, the particle sizes attained for MMA were generally smaller. The disulfide photoinitiator gives access to a wide range of poly(meth)acrylic latexes, but it does not initiate the photopolymerization of styrene. We suggest that the propagation rate prevails on monomer solubility in the case of (meth)acrylates, which explains the efficiency of the photopolymerization with a much weaker initiating system. The method can also lead to the production of random copolymer latexes, such as P(MMA-co-St) and the film-forming P(MMA-co-BA). The fact that the disulfide is able to lead to the former further supports the predominant role of the propagation rate on the polymerization. Finally, the polymerization allows for temporal control. It proceeds under light and stops in the dark.

International audience; Polyazanes (that is, higher nuclearity homologues of hydrazines) with increasing numbers of bound nitrogen atoms (from 3 to 5) were prepared via additions of lower order polyazanes to diazo reagents, including the first pentazane ever described. A structure was obtained. It was shown that the polynitrogen chains adopt a helical conformation. DFT modeling shows that the arrangement subsists in solution. While the polyazanes are all reducing agents, they become less so with the increasing number of nitrogens.

Several urea-inserted organo-polyoxometalates (POMs) derived from polyoxotungstovanadate [P2 V3 W15 O61 ]9- were prepared. The insertion of the carbonyl into the polyoxometallic framework activates the urea toward Hydrogen-bond catalysis. This was shown on the Friedel-Crafts arylation of trans-β-nitrostyrene. Modelling shows that the most stable form of the organo-POMs features a cis-trans arrangement of the two N-H bonds, but that the likely catalytically active trans-trans form is accessible at room temperature. Finally, it is possible that the oxo substituents next to the vanadium atoms may help the approach of the nucleophile via H-bonding.

1,3-Dimethylimidazol-2-ylidene difluoroborane (NHC-BF2 H) was prepared in a one-pot, two-step reaction from the parent ligated borane (NHC-BH3 ). The derived difluoroboryl radical (NHC-BF2. ) was generated by laser flash photolysis experiments and characterized by UV spectroscopy and rate-constant measurements. It is transient and reacts quickly with O2 . Unusually, it also reacts more rapidly with ethyl vinyl ether than with methyl acrylate. By this measure, it is the first electrophilic ligated boryl radical. Both NHC-BH3 and NHC-BF2 H serve as co-initiators in bulk photopolymerizations, converting both electron-poor and electron-rich monomers at roughly similar rates. However, the difluorinated coinitiator provides polymers with dramatically increased chain lengths from both monomers.

Functionalized hydrazines and bishydrazines are interesting straightforward precursors for accessing higher nitrogenated compounds. They offer structural diversity and promising energetic properties as well, namely for propulsion applications. A novel and scalable synthesis has been developed for a new family of bishydrazines, starting from monomethylhydrazine (MMH). This solvent-free route represents a suitable alternative to the one described in the literature. It was extended to design a new family of unsymmetrical hydrazines bearing various functional groups. A selected series of promising compounds, densified with nitrogenated groups (amino, hydrazino or azido functions), was identified as a class of plausible candidates for liquid propulsion. Indeed, the energetic interest of such hydrazines was demonstrated by computing their heats of formation and specific impulse values in bipropellant systems. This led to theoretical energetic performances comparable to that of the MMH/N2 O4 system already in use today.

Dedicated to Philippe Renaud on the occasion of his 60th birthday.; International audience; The synthesis and reactivity of mono and bis-S-xanthyl NHC-boranes is reported. The new NHC-boranes are prepared via nucleophilic exchange at boron from either mono or bis-triflyl NHC–boranes, themselves obtained by protolysis of the NHC–BH3 starting compounds. The B–H bond of the S-xanthyl NHCboranes can be cleaved both homolytically and heterolytically, albeit the latter is more synthetically useful. The S-xanthyl NHC-boranes can reduce both aldehydes and imines. The B–S bond can also be cleaved homolytically. Under UV irradiation, the S-xanthyl NHC-boranes generate NHC–boryl radicals that can initiate radical polymerizations of acrylates.

The multistep synthesis of a polyethylene-supported iridium(III)-(N-heterocyclic carbene) hydrogen/deuterium exchange catalyst was performed starting from an iodo-polyethylene obtained via catalyzed polyethylene chain growth (CCG) on magnesium. Unique thermomorphic polyethylene properties give the possibility to perform catalytic hydrogen/deuterium exchange reactions at 100 °C in the homogeneous phase with simple catalyst separation as a precipitate at room temperature. The catalytic activity of the polymer-supported catalyst was compared with that of its monomeric analogue. The catalytic studies showed that the supported catalyst exhibits similar profiles and turnover numbers as homogeneous counterparts without deactivation.

The Dawson tungstovanadate [P2 W15 V3 O62 ](9-) can be grafted to secondary diolamides. The electron-withdrawing character of the polyanion increases the acidity of the amide proton, leading to an organo-polyoxometalate, which can be used as a Bronsted organocatalyst. High-field NMR and DFT modeling indicate that the amide proton stays on the nitrogen and that the exalted acidity derives from the interaction between the organic and inorganic parts of the organo-polyoxometalate. The amide-inserted vanadotungstates thus form a new family of (hybrid) heteropolyacids, offering new perspectives for the application of POM-based catalysis in organic synthesis.

International audience; Several N-Heterocyclic Carbene (NHC)-boryl sulfides with B-substituents were prepared. The added steric hindrance leads to much improved selectivities as only the NHC-boryl mono-sulfides were obtained. The B-substituted NHC-boranes are also conducive to more selective S to N NHC-boryl shift, provided that the NHC used is not too sterically demanding.

International audience; The photopolymerization of styrene in emulsion is achieved in a conventional double-wall reactor equipped with a LED ribbon coiled around the external glass wall. Styrene mixed to acridine orange is added to the water phase containing sodium dodecyl sulfate, a water-soluble N-heterocyclic carbene–borane and disulfide, and irradiated. Highly stable latexes are obtained, with particles up to a diameter of 300 nm. The ability to reach such large particle sizes via a photochemical process in a dispersed medium is due to the use of visible light: the photons in the visible range are less scattered by larger objects and thus penetrate and initiate better the polymerizations. They are also greener and cheaper to produce via LEDs, and much safer than UVs. The method presented does not require any specific glassware; it works at lower temperature and delivers larger particles compared to thermal processes at similar solids contents and surfactant concentrations.

International audience; An Ir(NHC) supported catalyst is used in the selective hydrogenation of terpinen-4-ol to cis p-menthan-4-ol. Its activity, selectivity and stability are compared to those of a homogeneous homologue [IrCl(COD)MesImPr] and to a commercial Pd/C. The solid Ir catalyst is much more selective than the Pd catalyst (92 vs. 42% at 80°C) but also more active, more selective and more stable than the iridium complex in solution. For the first time, a supported catalyst shows an enhanced activity with respect to a complex in a diastereoselective hydrogenation reaction.

The conformation of a family of α1 and α2 polyglycine-containing organo-polyoxometalates was determined through a mixed experimental/molecular dynamics approach. The flexible peptide arm folds around the metal oxide surface in a rigid arrangement in low to average polarity solvents. The topology of the hybrid is the main factor that determines which oxos from the metal-oxide surface accept a H-bond from the closest amino acid. The rest of the peptide follows in a zipper mechanism that establishes a H-bond network that locks the system. The covalent constraint leads to a new type of H-bond where two consecutive amino acids clamp down terminal oxo ligands.

1,1,4,4-Tetramethyl-2-tetrazene (TMTZ) is considered as a prospective replacement for toxic hydrazines used in liquid rocket propulsion. The heat of formation of TMTZ was computed and measured, giving values well above those of the hydrazines commonly used in propulsion. This led to a predicted maximum Isp of 337 s for TMTZ/N2 O4 mixtures, which is a value comparable to that of monomethylhydrazine. We found that TMTZ has a vapor pressure well below that of liquid hydrazines, and it is far less toxic. Finally, an improved synthesis is proposed, which is compatible with existing industrial production facilities after minor changes. TMTZ is thus an attractive liquid propellant candidate, with a performance comparable to hydrazines but a lower vapor pressure and toxicity.

The first C3-symmetric 44-core-valence-electron triangular palladium clusters, [{(SAr′)(PAr3)Pd}3]+, have been synthesized by activation of the CS bond of isothioureas. Owing to delocalized metal–metal bonding, these stable complexes are the first noble-metal analogues of the π-aromatic cyclopropenyl cation [C3H3]+, with their all-metal aromaticity involving d-type atomic orbitals.

International audience; An organotin-substituted Dawson-type phosphotungstate was covalently linked to a trithiocarbonate group by postfunctionalization methods. This organopolyoxometalate led to a series of polyoxometalate (POM)–poly(N,N-diethylacrylamide) hybrids in a controlled way through reversible addition–fragmentation chain transfer (RAFT) polymerization. Detailed comparison with and without the presence of POMs revealed that they do not profoundly disturb the RAFT mechanism, despite their oxidative power. The molar masses of the polymers were in the range of 10 to 100 kg mol−1 and molar mass dispersities of the composites were low (Mw/Mn

International audience; Two natural quinazolinones and two analogues can be prepared from the cascade cyclizations of alkyl-substituted N-acylcyanamide radicals, including 5-exo-dig or 6-exo-dig cyclizations onto the cyano group, followed by radical arylations of the resulting amidyl radicals. The fact that one can carry out the cascades from alkyl radicals in addition to aryl, vinyl and aminyl ones, shows the versatility of the method to rapidly access nitrogen-containing polycyclic structures.

International audience; Reactions of 1,3-dimethylimidazol-2-ylidene-borane (diMe-Imd-BH3) and related NHC-boranes with diaryl and diheteroaryl disulfides provide diverse NHC-boryl monosulfides (diMe-Imd-BH2SAr) and NHC-boryl disulfides (diMe-Imd-BH(SAr)2). Heating in the dark with 1 equiv of disulfide favors monosulfide formation, while irradiation with 2 equiv disulfide favors disulfide formation. With heteroaryl disulfides, the NHC-borane in the primary NHC-boryl sulfide product migrates from sulfur to nitrogen to give new products with a thioamide substructure. Most substitution reactions are thought to proceed through radical chains in which homolytic substitution of a disulfide by an NHC-boryl radical is a key step. However, with electrophilic disulfides under dark conditions, a competing ionic path may also be possible.

We thank Vincent Joly and Xavier Dagany for the development of data acquisition for fluorescence and Laure Cohendet and Mathilde Ghafar (MSc student) for their contribution to this work. Jacques Maurelli and Christian Clavier are acknowledged for their invaluable technical assistance.; International audience; Nanoparticle-based temperature imaging is an emerging field of advanced applications. Herein, the sensitivity of the fluorescence of rhodamine B-doped latex nanoparticles toward temperature is described. Submicrometer size latex particles were prepared by a surfactant-free emulsion polymerization method that allowed a simple and inexpensive way to incorporate rhodamine B into the nanoparticles. Also, rhodamine B-coated latex nanoparticles dispersed in water were prepared in order to address the effect of the dye location in the nanoparticles on their temperature dependence. A better linearity of the temperature dependence emission of the rhodamine B-embedded latex particles, as compared to that of free rhodamine B dyes or rhodamine B-coated latex particles, is observed. Temperature-dependent fluorescence measurements by fluorescent confocal microscopy on individual rhodamine B-embedded latex particles were found similar to those obtained for fluorescent latex nanoparticles in solution, indicating that these nanoparticles could be good candidates to probe thermal processes as nanothermometers.

Thermal 1,3-dipolar cycloaddition reactions of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene dihydridoboron azide occur smoothly with alkynes, nitriles, and alkenes bearing electron-withdrawing groups. New, stable NHC-boryl-substituted triazoles, tetrazoles, and triazolidines are formed in good to excellent yields.

To protect and serve: The efficiency of TypeI radical photoinitiators for acrylate polymerization is greatly increased by the presence of NHC-boranes. Conversion of the initially photogenerated radicals, R . (see scheme), into strongly nucleophilic NHC-boryl radicals, through hydrogen-atom transfer, gives a better matched radical for subsequent reaction with monomer, ensuring better initiation. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The cyanamide moiety provides many opportunities as a building block for the synthesis of nitrogen-containing heterocycles. This review discusses the reported methods for the preparation of alkyl- and N-acylcyanamides and illustrates their reactivity vis-a-vis nucleophilic additions, cycloadditions, radical chemistry and coordination chemistry. 1 Introduction 2 Biological Relevance of the Cyanamide Moiety 3 Access to Cyanamides 3.1 Cyanation of Amines 3.2 Palladium Catalysis 3.3 Deoxygenation of Isocyanates 3.4 Desulfurization of Thioureas 4 Reactivity of Cyanamides 4.1 Nucleophilic Additions 4.2 Cycloadditions 4.3 Additions to Carbonyl Groups 4.4 Chlorinations and Oxidations with tert-Butyl-N-chloro­cyanamide 4.5 Cyanamides as Radical Partners 5 Coordination Chemistry of Cyanamides 6 Conclusion

Otherwise sluggish or completely ineffective radical reductions of alkyl and aryl halides by N-heterocyclic carbene boranes (NHC-boranes) are catalyzed by thiols. Reductions and reductive cyclizations with readily available 1,3-dimethylimidazol-2-ylidene borane and a water-soluble triazole relative are catalyzed by thiophenol and tert-dodecanethiol [C(9)H(19)C(CH(3))(2)SH]. Rate constants for reaction of the phenylthiyl (PhS•) radical with two NHC-boranes have been measured to be ~10(8) M(-1) s(-1) by laser flash photolysis experiments. An analysis of the available evidence suggests the operation of polarity reversal catalysis.

International audience; The nucleophilicity parameters (N) of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene borane and 1,3-dimethylimidazol-2-ylidene borane are 9.55 and 11.88. This places N-heterocyclic carbene boranes (NHC-boranes) among the most nucleophilic classes of neutral hydride donors. Reductions of highly electron-poor C═N and C═C bonds provide hydrogenation products along with new, stable borylated products. The results suggest that NHC-boranes have considerable untapped potential as neutral organic reductants.

The [ε-PMo(V)(8)Mo(VI)(4)O(36)(OH)(4){Ln(III)(H(2)O)}(4)](5+) (Ln=La, Ce, Nd, Sm) polyoxocations, called εLn(4), have been synthesized at room temperature as chloride salts soluble in water, MeOH, EtOH, and DMF. Rare-earth metals can be exchanged, and (31)P NMR spectroscopic studies have allowed a comparison of the affinity of the reduced {ε-PMo(12)} core, thus showing that the La(III) ions have the highest affinity and that rare earths heavier than Eu(III) do not react with the ε-Keggin polyoxometalate. DFT calculations provide a deeper insight into the geometries of the systems studied, thereby giving more accurate information on those compounds that suffer from disorder in crystalline form. It has also been confirmed by the hypothetical La→Gd substitution reaction energy that Ln ions beyond Eu cannot compete with La in coordinating the surface of the ε-Keggin molybdate. Two of these clusters (Ln=La, Ce) have been tested to evidence that such systems are representative of a new efficient Lewis acid catalyst family. This is the first time that the catalytic activity of polyoxocations has been evaluated.

Borane sind weit verbreitete Lewis-Sauren, und N-heterocyclische Carbene (NHCs) sind beliebte Lewis-Basen. Dennoch war bis in die jungste Zeit erstaunlich wenig uber Komplexe dieser beiden Verbindungsklassen miteinander bekannt. NHC-Borane sind leicht herzustellen, und teilweise sind sie so stabil, dass sie weniger als Komplex, sondern vielmehr als eigenstandige organische Verbindung betrachtet werden konnen. Sie verhalten sich nicht wie klassische Borane, und sie konnen ein breites Spektrum an funktionellen Gruppen enthalten. Als vielseitige Reaktionspartner, Reagentien und Katalysatoren verfugen NHC-Borane uber ein immenses Potenzial fur die organische Synthese und die Polymerchemie. Viele Reaktionen von NHC-Boranen laufen uber neue reaktive Intermediate wie Boreniumkationen, Borylradikale und sogar Borylanionen ab. Hier geben wir eine umfassende Ubersicht uber die Synthese, Charakterisierung und Reaktionen von NHC-Boranen.

This paper is a choral personal account on a longstanding and fruitful collaboration of organic and inorganic chemists to develop new hybrid polyoxometallic systems. .We explain our motivation and the context of our work that led to polyoxometalates with highly functional and reactive organic groups. Our approach yielded catalytically, biologically, and photochemically active systems.

Eight N-heterocyclic carbene-boranes (NHC-boranes) are proposed as new efficient co-initiators for acrylate photopolymerization reactions. They are particularly interesting in aerated conditions, where they help overcome the classical oxygen inhibition. The carbene boryl radicals that are the initiating species have been characterized by their transient absorption spectra obtained in laser flash photolysis (LFP) experiments. Rate constants for the generation of the carbene boryl radicals by hydrogen abstraction with t-butoxyl radical and triplet benzophenone as well as the reactions with oxygen, electron rich and electron poor alkenes, two alkyl halides (CHCl3 and iodopropane) and diphenyliodonium hexafluorophosphate have been measured. The reactivity of N-heterocyclic carbene borane radicals is clearly affected by the NHC substituent.

A method for the synthesis of phenanthridines from benzylamines and aryl iodides which uses a dual palladium-catalyzed process is developed. The domino sequence ends via an intramolecular amination and an oxidative dehydrogenation. No protecting group or prefunctionalization of the amine is required, and the process uses dioxygen as the terminal oxidant.

Boryl halide, carboxylate and sulfonate complexes of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (dipp-Imd-BH(2)X, X = halide or sulfonate) have been prepared from the parent borane dipp-Imd-BH(3) by (1) substitution reactions with R-X (X = halide or sulfonate), (2) reactions with electrophiles (like I(2) or NIS), or (3) acid/base reactions with HX (provided that HX has a pK(a) of about 2 or less). Dipp-Imd-BH(2)I is most conveniently prepared by reaction with diiodine while dipp-Imd-BH(2)OTf is best prepared by reaction with triflic acid. These and other less reactive complexes behave as electrophiles and can be substituted by a wide range of heteroatom nucleophiles including halides, thiolates and other sulfur-based nucleophiles, isocyanate, azide, nitrite, and cyanide. The resulting products are remarkably stable, and many have been characterized by X-ray crystallography. Several are members of very rare classes of functionalized boron compounds (boron azide, nitro compound, nitrous ester, etc.).

α-Alkoxy allenes are smoothly converted into α′-alkoxy enones by oxidation with m-chloroperbenzoic acid.

Rate constants for hydrogen abstraction by a nonyl radical from 20 complexes of N-heterocyclic carbenes and boranes (NHC-boranes) have been determined by the pyridine-2-thioneoxycarbonyl (PTOC) competition kinetic method at a single concentration point. The rate constants range from1 x 10(4) to 8 x 10(4) M(-1) s(-1). They show little dependence on the electronic properties of the carbene core, but there is a trend for increasing rate constants with decreasing size of the carbene N-substituents. Two promising new reagents with small N-substituents (R = Me) have been identified.

Newly discovered N-heterocyclic carbene-boryl radicals (NHC-BH2•) derived from readily available N-heterocyclic carbene−boranes are found to be efficient initiators for acrylate photopolymerization. Laser flash photolysis (LFP) experiments were used to generate three carbene-boryl radicals, which were characterized by their transient absorption spectra with the aid of DFT calculations. Rate constants were measured for the generation of the carbene-boryl radicals by hydrogen abstraction with tert-butoxyl radical, a ketophosphonyl radical, and triplet benzophenone. Rate constants were also measured for the reactions of the carbene-boryl radicals with oxygen, three alkenes, two alkyl chlorides, and diphenyliodonium hexafluorophosphate. The observed trends were interpreted with the aid of measured oxidation potentials of the carbene−boranes and calculated ionization potentials of the carbene-boryls. N-Heterocyclic carbene−boranes show excellent potential as both photopolymerization co-initiators and mediators...

Complexes of triaryl- and trialkylboranes with N-heterocyclic carbenes (NHCs) participate in Suzuki-Miyaura cross-coupling reactions and provide coupled products in good yields under base-free conditions. The reaction can be applied to Csp(2)-Csp(2) and Csp(2)-Csp(3) carbon-carbon bond formation with triflates, iodides, bromides, and chlorides. These results enrich the utility of NHC-borane complexes, which can be added to the toolkit of Suzuki-Miyaura cross-couplings, along with boronic acids and organotrifluoroborates.

POM alert: The incorporation of an amide oxygen atom into the framework of the Dawson-type polyoxometalate (POM) cluster [P(2)V(3)W(15)O(62)](9-) (see picture) allows the communication of electronic effects between the organic and the inorganic parts of the molecule, including fine-tuning of the redox properties of the entire hybrid POM by the organic components, and transmission of the POM's electron-attracting properties to the organic moiety.