Polarity reversal, or "umpolung", is a widely acknowledged strategy to allow organic functional groups amenable to react in alternative ways to the usual preference set by their electronic features. In this article, we demonstrate that cyclohexyne umpolung, realized through complexation to zirconocene, makes the small strained cycloalkyne amenable to C-F bond functionalisation. Such strong bond activation chemistry is unprecedented in "free" aryne and strained alkyne chemistry. Our study also reveals that the reactivity of the Zr-cyclohexyne complex is highly sensitive to the degree of fluorination of the heteroarene. In addition, parasitic reactions of the ancillary ligand PMe3 were observed when pentafluoropyridine was the substrate.

The development of advanced photocatalysts for air pollution removal is essential to improve indoor air quality. TiO2/mesoporous silica SBA-15 nanocomposites were synthesized using an organometallic decoration method, which leverages the high reactivity of Ti precursors to be hydrolyzed on the surface water groups of silica supports. Both lab-made Ti(III) amidinate and commercial Ti(IV) amino precursors were utilized to react with water-rich SBA-15, obtained through a hydration process. The hydrated SBA-15 and the TiO2/SBA-15 nanocomposites were characterized using TGA, FTIR, 1H and 29Si NMR, TEM, SEM, N2 physisorption, XRD, and WAXS. This one-step TiO2 decoration method achieved a loading of up to 51.5 wt.% of approximately 9 nm anatase particles on the SBA-15 surface. This structuring provided excellent accessibility of TiO2 particles for photocatalytic applications under pollutant gas and UV-A light exposure. The combination with the high specific surface area of SBA-15 resulted in the efficient degradation of 400 ppb of NO pollutant gas. Due to synergistic effects, the best nanocomposite in this study demonstrated a NO abatement performance of 4.0% per used mg of TiO2, which is 40% more efficient than the reference photocatalytic material TiO2 P-25.

Delivering metallomimetic reactivity from simple p-block compounds is highly desirable in the search to replace expensive, scarce precious-metals by cheap and abundant elements in catalysis. This contribution demonstrates that metallomimetic catalysis, involving facile redox cycling between the P(III) and P(V) oxidation states, is possible using only simple, cheap and readily available trialkylphosphines with no need for complex ligand architectures or external oxidising/reducing agents. Hydrodefluorination and aminodefluorination of a range of fluoroarenes was realised with good to very good yields under mild conditions. Experimental and computational mechanistic studies show that the phosphines undergo oxidative addition of the fluoroaromatic substrate, via a Meisenheimer-like transition state, to form a fluorophosphorane. This undergoes a pseudo-transmetallation step with a silane, via initial fluoride transfer from P to Si, to give experimentally observed phosphonium ions. Hydride transfer from a hydridosilicate counterion then leads to a hydridophosphorane, which undergoes reductive elimination of the product to re-form the phosphine catalyst. This behaviour is analogous to many classical transition-metal catalysed reactions and so is a rare example of both functional and mechanistically metallomimetic behaviour in catalysis by a main-group element system. Crucially, the reagents used are cheap, readily available commercially and easy to handle, making these reactions a realistic prospect in a wide range of academic and industrial settings.

We present here an efficient method for hydroelementation reactions such as hydroamination, hydrothiolation, and hydrophosphorylation of the heterocumulenes carbodiimides, aryl isocyanates, and isothiocyanates with anilines or thiophenols using a p-tolylsulfonylimide-supported dinuclear titanium complex. All the reactions were achieved in excellent yield under mild conditions and within a short reaction time. The products were isolated and fully characterized by spectroscopic techniques. We also propose a mechanism involving the proton abstraction (of the E-H of anilines or thiophenols) in the first step. In the reaction mechanism, the amido groups of the binuclear Ti-IV complex act as the leaving group whereas the sulfonylimide linkage remains unaffected.

alpha,omega-Dienes are an important class of monomers due to their utility in the synthesis of cyclopolyolefins and reactive polyolefin intermediates. In this contribution, the terpolymerization of two alpha,omega-dienes (i.e., 1,5-hexadiene and 1,7-octadiene) with ethylene and various cyclic olefins [i.e., norbornene (NB), 5-ethylidene-2-norbornene (ENB), and dicyclopentadiene (DCPD)] catalyzed by a chelated imido vanadium complex has been examined. The ENB and DCPD diene termonomers provide additional sites for post-polymerization functionalization. Vanadium-catalyzed terpolymerization of the investigated alpha,omega-dienes yields polyolefins with a high molecular weight (M-w up to 200 X 10(3) g mol(-1)), unimodal and narrow molecular weight distribution, subambient glass transition temperatures (-30 < T-g degrees C < -3), and a proper content of C=C bonds. Comprehensive NMR investigation of the obtained polymers revealed that subtle changes in the alpha,omega-diene size have important effects on the numerous combinations of insertion paths (ring closure vs ring opening), from which different repeating units with a C=C bond in the side or main polymer chain and cyclic units are installed. Finally, the polyethylene-ter-1,5-hexadiene-ter-NB) was subjected to thiol-ene addition using thioglycolic acid, methyl thioglycolate, and N-acetyl-L-cysteine to access polar-functionalized polyolefins with a degree of functionalization and properties dependent on the thiol substitution.

Thermoplastic elastomers (TPEs) are materials combining the processability of thermoplastics and the elasticity of rubbers. The global value and demand of TPEs are expected to grow in the coming years, and advancement in synthetic chemistry is the key driving force. This contribution provides a simple synthesis of high-ethylene EPDMs with high molecular weight, narrow molecular weight distribution (1.9 < M-w/M-n < 2.3), and properties which can be adjusted from soft thermoplastic to elastomer. EPDMs are prepared through the terpolymerization of ethylene with propylene and 5-ethylidene-2-norbornene (ENB), where ethylene is continuously supplied to the reaction bath, while propylene and ENB are added only at the beginning. Polymerizations are catalyzed by three known imido vanadium(IV) complexes, differing in the imido substituent and coligand, in combination with Et2AlCl and Cl3CCO2Et. The obtained EPDMs are a mixture of macromolecules, each of them featuring a nonrandom comonomer distribution and nonuniform composition. Each chain likely contains multiblocks where the comonomers are segmented, i.e., blocks with high ethylene content that may crystallize and blocks with high propylene and ENB content that may not crystallize. This broad chemical composition distribution is due to time drift that occurs during the polymerization, which in turn depends on the experimental conditions and ligand set. Composition drift causes variation in the instantaneous feed comonomer ratio and hence in the chemical composition of the terpolymer over the period of conversion. In proper experimental conditions, EPDMs behave as TPEs without the need of vulcanization, polymer blending, and reinforcement through the addition of fillers. They exhibit high elongation at break, strain hardening at large deformation, remarkable shape retention properties (up to 76% recovery after 10 cycles at 300% and about 90% at 410% strain), and remelting processability with no fall in properties for recycle and reuse.

We have synthesized and characterized a series of (imido)V(iv) complexes bearing different imido groups and coligands, to be used, in combination with an aluminum alkyl, as catalysts for the (co)polymerization of ethylene with propylene.

The synthesis and the characterization of a series of phosphine adducts of (imido)vanadium(IV) dichloride complexes of the type V(=NR)Cl-2(PMe2Ph)(2) [R = 2,6-Cl-2-Ph (1), 2,6-Pr-i(2)-Ph (2), and Bu-t (3)] and V(= NtBu)Cl-2(PMe3)(2) (3') are reported. The solid-state structures of 1 and 3' were determined by X-ray crystallography. The complexes present a geometry around the metal center between a distorted trigonal-bipyramid and a square pyramid, with an almost linear N V C bond. Complexes 1-3 were evaluated as catalyst precursors for the polymerization of ethylene and ethylene copolymerization with various cyclic olefins (i.e., norbornene, dicyclopentadiene, 5-ethylidene-2-norbornene, and 5-vinyl-2-norbornene). with Et(2)A1C1 (500 equiv to V) and Cl3CCO2Et (ETA, 10 equiv to V), 1-3 are versatile and promising catalysts for the synthesis of high molecular weight linear poly(ethylene)s and alternating copolymers with efficient comonomer incorporation, unimodal molecular weight distributions, and uniform composition under mild conditions. Differences in the homo- and copolymerization of ethylene regarding the activity, stability over temperature, reactivity toward the target comonomers, and (co)polymer chain growth were investigated to probe the effects of imido ligand substitution. The introduction of more electron -donating groups led to an increase in polymers molecular weight and provided increased stability over temperature to the catalysts, particularly for 3. Both of these effects are likely because the tert-butyl imido moiety in 3 strengthens the V N bond, thus improving the stability of the active intermediate. The steric shielding of the tert-butyl group may also contribute to inhibit the associative chain transfer. Control over the molecular weight of the resultant copolymers proved to be possible also by varying the ETA loading. ETA acts as a reoxidant, restarting the catalytic cycle, but it behaves also like a chain transfer agent and to a different extent strongly depending on the type of imido ligand.

Vanadium complexes are attractive potential alternatives to platinum-based anticancer drugs. Two vanadium(V) complexes, based on a common chelating tetradentate diaminobis(phenolato) ligand featuring a branched connectivity but differing in their labile ligands, were synthesized and characterized. Whereas the isopropoxido complex was obtained as a mixture of cis and trans isomers with regard to the orientation of the labile group vs. the amine sidearm, the salicylato-containing complex was obtained as a single trans isomer. X-ray structures of the complexes featured octahedral geometry for both. The two complexes exhibited high cytotoxic activity toward different cancer cells, often higher than that of cisplatin, including toward cisplatin-resistant ovarian cancer cells. These complexes demonstrated rapid hydrolysis, releasing the labile ligand within several minutes, with no indications of release of free chelating ligand after water exposure, suggesting that polynuclear hydrolysis products are involved in the cellular activity.

AbstractReview: syntheses, structures, reactivity, and applications; 142 refs.

A series of vanadium complexes bearing dianionic tetradentate amine-bisphenolate [ONNO] ligands, V([double bond, length as m-dash]O)X[ONNO(Me)] (X = Cl (1); O(i)Pr (2)), VCl2[ONNO(Me)] (3) and V(O(i)Pr)2[ONNO(R)] (R = Me (4), (t)Bu (5), Cl (6)), displaying various electronic and steric properties have been prepared. The molecular structures of two of these complexes, namely V[ONNO(R)](O(i)Pr)2 with R = (t)Bu (5) or Cl (6), are reported. Activated with dialkylmagnesium, all complexes lead to modest isoprene homo-polymerization activities at 50 °C. Quantitative polymerizations were observed using 4 and 6 as pre-catalysts combined with Al(i)Bu3. The resulting polyisoprene microstructure was composed of ca. 70% 3,4 enchainments, the remaining 30% 1,4 enchainments being a mixture of cis and trans stereoisomers. 6 leads to a more active catalyst than 4. β-Hydride abstraction occurs during the reaction.

This review surveys the organometallic chemistry of vanadium during the period 1993–2014. It is an updated version of the ‘Vanadium’ chapter in COMC-III (2007) that originally covered the period 1993–2004. The synthesis, characterization, reactivity, and applications of organovanadium complexes are described.

The lipid peroxidation of fatty acids leads to secondary products, among which several carbonyl compounds are of concern in food toxicology. The detection of these reactive aldehydes for identification and evaluation is required. Derivatization is necessary to improve their stability and detection in liquid chromatography/high-resolution mass spectrometry (LC/HRMS) trace analyses. Therefore, a brominated O-benzylhydroxylamine, namely 1-((ammoniooxy)methyl)-2-bromobenzene chloride, was selected as a new probe for the mild and selective derivatization of carbonyl compounds. New oxime ethers were thus synthesized under mild reaction and workup conditions, with full analytical characterization. The relevance of the chemical reaction was assessed with nine aldehydes, especially conjugated and deuterium-labeled aldehydes, and two ketones. Virtually, the reaction should be applicable to a large set of carbonyl compounds for derivatization in complex biological samples and selective detection of the in situ–synthesized brominated oxime ethers by LC/HRMS methodology.

This review summarizes the syntheses, structures, reactivity, and applications of titanium- and vanadium-complexes bearing a bridging imide group reported until September 2014. The incorporation of this functional group has evolved from 'fortuitous approaches' to designed syntheses of molecules of higher diversity and greater complexity. The review begins with an introduction and a general and brief description of the bridging imido motifs, followed by a discussion of the more common synthetic approaches used to generate such Ti and V compounds. The main focus of the review is the survey of the imido-bridged complexes of Ti and V with an emphasis on their synthesis and reactivity, and with a particular attention to the recent research conducted in the author's group at the Laboratoire de Chimie de Coordination (LCC), as this review is part of a thematic issue "Perspective in coordination chemistry on the occasion of the 40th anniversary of the LCC-CNRS". (C) 2015 Elsevier B.V. All rights reserved.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Treating the imidotitanium dimer [Ti(μ-NAr)(NMe2)2]2 (Ar = 2,6-(i)Pr2C6H3) with excess Me3SiCl affords the hexanuclear complex [{Ti(═NAr)Cl2}6(Cl)](-)[Q](+). The self-assembled hexameric cage arrangement encapsulates a chloride ion guest that provides evidence of new host-guest chemistry in this area, while the cationic part is composed of mixtures of the Q(+) cations Me2NHSiMe3(+) and Me2N(SiMe3)2(+).

New imido bis(borohydride) complexes [(RN=)M(PMe3)2(2-BH4)2] [R = Ar, M = Ti (3); R = Ar, M = V (5); R = Ar, M = Mo (6); R = Ar, M = Mo (7); Ar = 2,6-iPr2C6H3, Ar = 2,6-Me2C6H3] were prepared by the reaction of dichlorides [(RN=)MCl2(PMe3)n] (M = Ti, n = 2; M = V, n = 2, M = Mo, n = 3) with LiBH4 (2 equiv) in THF. Compounds 3, 5, 6 and 7 were studied by IR spectroscopy and X-ray diffraction, and an EPR spectroscopy study was performed for paramagnetic compound 5. In 3, the two borohydride units are orthogonal to each other as a result of the overlap of an antiphase combination of BH orbitals with the empty dxy orbital of Ti. In contrast, the dxy orbital of the metal atom is singly occupied in 5 and fully occupied in 6 and 7, and both borohydride ligands are oriented in the same way, with the B(-H2)M moieties orthogonal to the PMP vector.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.