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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.

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.

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.

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

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 [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.

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

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.

An α1-Dawson polyanion bearing a lateral side chain with a 4-aminopyridine end group is synthesized.

Reaction of sulfonamides with iodosobenzene leads to phenyliodinanes. A new catalysis reaction of the decomposition of these products in the presence of sulfoxides that allows the smooth synthesis of sulfoximines has been evidenced and studied: copper(II) salts were used to prepare compounds 4 a-j and 5 b, d, f, j, k from the corresponding, easily prepared, sulfoxides. The reactions proceed with retention of configuration at the sulfur center, and copper(II) triflate is the best candidate for the catalyst for the imination. Switching from sulfonamides to sulfinamides in the preparation of the starting iodinanes completely alters the reaction pathway: iodinanes are no longer accessible, and sulfonimidates 7 a-j are obtained instead. This behavior can be rationalized by the increase in pK(a) brought about by the removal of one oxygen atom from the sulfur center. Sulfonimidates are interesting molecules with varied applications. Optimization of their one-pot synthesis has been achieved by carrying out the reaction in acetonitrile. The stereochemical study has shown that the transformation proceeds with global retention of the configuration at the sulfur center, albeit with erosion of the enantiomeric purity. A model accounting for this outcome is proposed. In addition, the presence of oxidized sulfonamide by-products has been explained, and this latter pathway becomes the sole one when alcohol is replaced by water. Good yields of the oxidized products are obtained.

An unprecedented radical β-elimination of vinyl sulfoxides has opened a new route to functionalized allenes. The radical precursors were obtained in two steps from a carbonyl derivative and a vinyl sulfoxide. The radical translocation stratagem could also be used to trigger the β-elimination of the sulfinyl radical. Variation of the nature of the sulfur group on a common precursor gave no allene with the thio, sulfonyl, and iminosulfinyl moieties, in contrast to the analogous vinyl sulfoxide and vinylsulfimide precursors. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Resolution of gram quantities of a subtly chiral polyoxometalate (POM; the chirality originates from substitution of one metal in the nanosized framework) is possible by reaction with small peptides. Functionalizable acyl polyoxotungstate (TBA)(6)[alpha(1)-P(2)W(17)O(61){SnCH(2)CH(2)C(=O)}] (see picture) can be resolved by kinetic resolution. This approach paves the way for applications of chiral POMs ranging from asymmetric catalysis to their bioactivity.

Photochemical reaction of diaryl disulfides with N-acyl cyanamides and iPr2NEt proceeds with 1,3-migration of the acyl group and provides a new approach to isothioureas.

This method is particularly useful for the cycloisomerization of allenols, which are sensitive to dehydration, e.

Based on electrochemical investigations this reaction is proposed to proceed via electron-transfer activation of the halide mediated by an in situ generated anionic hydrido iron(I) species.

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

The reduction of ketones, esters and the imine (XXIV) under mild conditions is achieved with diphenylsilane in the presence of TAC.

N,N′-Dialkyl and N,N′-diaryl imidazol-2-ylidene-boranes and trifluoroboranes are rapidly lithiated at C4 of the imidazole ring, and the resulting intermediates have been quenched with an assortment of electrophiles to provide ring-functionalized imidazol-2-ylidene-boranes. Further deprotonation and functionalization of C5 have been demonstrated. Deboronation of the products by treatment with triflic acid or iodine and then methanol opens a route to C4/C5 functionalized imidazolium salts and imidazol-2-ylidenes.

Boranes are widely used Lewis acids and N-heterocyclic carbenes (NHCs) are popular Lewis bases, so it is remarkable how little was known about their derived complexes until recently. NHC-boranes are typically readily accessible and many are so stable that they can be treated like organic compounds rather than complexes. They do not exhibit “borane chemistry”, but instead are proving to have a rich chemistry of their own as reactants, as reagents, as initiators, and as catalysts. They have significant potential for use in organic synthesis and in polymer chemistry. They can be used to easily make unusual complexes with a broad spectrum of functional groups not usually seen in organoboron chemistry. Many of their reactions occur through new classes of reactive intermediates including borenium cations, boryl radicals, and even boryl anions. This Review provides comprehensive coverage of the synthesis, characterization, and reactions of NHC-boranes.

The carbene derived from triazolium salt TRC catalyzes the title reactions to give the corresponding saturated alcohols or (E)-alkenols, correspondingly, after quenching of the resulting siloxanes with Bu4NF.

Epoxides substituted by an aryl ketone are efficiently reduced using different visible-light photoredox catalysts under irradiation with a 14 W fluorescent light bulb.

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.

A microwave-assisted protocol is developed for the reaction of the substrates with aryl iodides in a short time.

Reduction of boryl iodide (I) with LDBB and subsequent trapping of the resulting N-heterocyclic carbene boryl anion with various electrophiles yields derivatives that would be difficult to access with existing methods.

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

New organosoluble polyoxometalates are shown to catalyze a series of Mannich [ (III), (V), (VII)], aza-Diels—Alder [ (IX), (XI)], Mukaiyama-type aldol [ (XIV)], aminal [ (XVI)], and three-component Mannich reactions [ (XVIII)].

Vinyl radicals generated from bromomethyldimethylsilyl propargyl ethers have been efficiently engaged in cascades of radical cyclizations. Through the enchainment of 5- exo-dig -5-(π- endo)-exo-trig -6- endo-trig or 5- exo-dig -5-(π- endo)-exo-trig -6- exo-trig radical processes, hydrindene and a steroid skeleton could be assembled. Appending on the alkyne a suitable chain bearing a dioxolane for 1,5-radical translocations proved also very rewarding since a very diastereoselective access to cyclopentanone derivatives could be devised.

Two C—C and one C—N bonds are formed by an unprecedented radical cascade reaction involving the migration of ortho-hydrogen or an ortho-alkyl group at the phenyl ring of N-benzoyl cyanamides to give pyrrolo- or pyrido-fused quinazolinones.

Simple treatment of tributyltin halide-containing reaction mixtures with Me3Al or aq. 1M NaOH leads after filtration through silica gel to complete removal of tin residues. The Me3Al method is particularly convenient for polar products and the NaOH method for non-polar products.

New prospects for synthetic applications are offered by the 1,2-acyloxy shift of β-(acyloxy)alkyl radicals, which proceeds with high yields under Lewis acidic conditions [Eq. (1)]. With the exception of cyclizations, this is the first Lewis acid mediated acceleration of a radical rearrangement.

Alkylidene-substituted cyclopentane derivatives are formed in high enantiomeric purity by the reaction shown below. A highly diastereoselective radical cyclization is followed by elimination of a β-sulfinyl radical. Interestingly, the addition of the Lewis acid methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD) totally reverses the stereochemical outcome of the reaction. E=CO2 Me.