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Ruthenium(ii) η6-arene complexes with easily-available dioxime ligands are efficient catalytic precursors for the selective reduction/N-methylation of aromatic nitrocompounds with methanol.

The [Rh(μ-Cl)(IPr)(η2-coe)]2/pyridine system efficiently catalyzes the polyhydrothiolation of a series of dialkynes with dithiols, producing sulfur-rich poly(vinylidene sulfide)s with a typical Mw in the range 20.000–124.000 and vinylidene content of 75–87%. A combination of flexible aliphatic dithiols, including 1,6-hexanedithiol and 2,2′-(ethylendioxy)diethanethiol, and the rigid aromatic dithiol 4,4′-thiobisbenzenethiol, with rigid aromatic dialkynes, 1,3-diethynylbenzene and 1,4-diethynylbenzene, and flexible dialkynes, including propargyl ether and 1,7-octadiyne, have been used to prepare poly(vinylidene sulfide)s. The copolymerization of flexible dithiols with rigid aromatic dialkynes or vice versa results in high molecular weight polymers, Mw up to 259.000, with low polydispersities. However, polyhidrothiolation of flexible dialkynes with flexible dithiols is much less efficient and usually results in the formation of oligomers. The interplay of the IPr and pyridine ligands on the RhCl(IPr)(py)(η2-coe) catalyst, which controls the regioselectivity of the alkyne insertion step towards the branched vinyl sulfide, is key in the preparation of these poly(vinylidene sulfide)s.

The controlled functionalization of a single fluorine in a CF

The controlled functionalization of a single fluorine in a CF3 group is difficult and rare. Photochemical C–F bond functionalization is achieved using catalysts made from a range of earth-abundant lanthanides by using a ligand that enables M–L cooperativity.

The preparation of three novel active and stable magnetic nanocatalysts for the selective liquid-phase oxidation of several olefins, has been reported. The heterogeneous systems are based on the coordination of cis-MoO2 moiety onto three different SCMNP@Si-(L1-L3) magnetically active supports, functionalized with silylated acylpyrazolonate ligands L1, L2 and L3. Nanocatalysts thoroughly characterized by ATR-IR spectroscopy, TGA and ICP-MS analyses, showed excellent catalytic performances in the oxidation of conjugated or unconjugated olefins either in organic or in aqueous solvents. The good magnetic properties of these catalytic systems allow their easy recyclability, from the reaction mixture, and reuse over five runs without significant decrease in the activity, either in organic or water solvent, demonstrating their versatility and robustness.

This article also appears in: RSEQ-GEQO Prize Winners., A series of neutral and cationic rhodium complexes bearing IPr {IPr=1,3-bis-(2,6-diisopropylphenyl)imidazolin-2-carbene} and π-acceptor ligands are reported. Cationic species [Rh(η4-cod)(IPr)(NCCH3)]+ and [Rh(CO)(IPr)(L)2]+ (L=pyridine, CH3CN) were obtained by chlorido abstraction in suitable complexes, whereas the cod-CO derivative [Rh(η4-cod)(IPr)(CO)]+ was formed by the carbonylation of [Rh(η4-cod)(IPr)(NCCH3)]+. Alternatively, neutral derivatives of type RhCl(IPr)(L)2 {L=tBuNC or P(OMe)3} can be accessed from [Rh(μ-Cl)(η2-coe)(IPr)]2. In addition, the mononuclear species Rh(CN)(η4-cod)(IPr) was prepared by cyanide-chlorido anion exchange, which after carbonylation afforded the unusual trinuclear compound [Rh{1κC,2κN-(CN)}(CO)(IPr)]3. Divergent catalytic outcomes in the phenylacetylene-methanol transformations have been observed. Thus, enol ethers, arisen from hydroalkoxylation of the alkyne, were obtained with neutral Rh−CO catalyst precursors whereas dienol ethers were formed with cationic catalysts. Variable amounts of alkyne dimerization, cyclotrimerization or polymerization products were obtained in the absence of a strong π-acceptor ligand on the catalyst., Financial support from the Spanish Ministerio de Ciencia e Innovación (MICINN/FEDER) under the Project PID2019-103965GB−I00 and the Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón (group E42 20R) are gratefully acknowledged. A.D.G. thanks the Spanish Ministerio de Economía y Competitividad (MINECO) for the postdoctoral grant Juan de la Cierva - Incorporación2015 (IJCI-2015-27029).

The mononuclear square-planar Rh{κ2-X,N-(Xpy)}(η2-coe)(IPr) (X = O, NH, NMe, S) complexes have been synthesized from the dinuclear precursor [Rh(μ-Cl)(IPr)(η2-coe)]2 and the corresponding 2-heteroatom-pyridinate salts. The Rh-NHC-pyridinato derivatives are highly efficient catalysts for gem-specific alkyne dimerization. Particularly, the chelating N,O-pyridonato complex displays turnover frequency levels of up 17 000 h–1 at room temperature. Mechanistic investigations and density functional theory calculations suggest a pyridonato-based metal–ligand cooperative proton transfer as responsible for the enhancement of catalytic activity. The initial deprotonation of a Rh-π-alkyne complex by the oxo-functionality of a κ1-N-pyridonato moiety has been established to be the rate-limiting step, whereas the preferential protonation of the terminal position of a π-coordinated alkyne accounts for the exclusive observation of head-to-tail enynes. The catalytic cycle is closed by a very fast alkenyl–alkynyl reductive elimination., Financial support from the Spanish Ministerio de Ciencia e Innovación (MICINN/FEDER) under the Projects PID2019-103965GB-I00 and PGC2018-099383-B-I00, and the Diputación General de Aragón (FEDER 2014-2020 “Building Europe from Aragón”, group E42_20R) are gratefully acknowledged. A.D.G. thanks the Spanish Ministerio de Economía y Competitividad (MINECO) for the postdoctoral grant Juan de la Cierva - Incorporación 2015 (IJCI-2015-27029). A.U. thankfully acknowledges the Spanish MECD for a FPU fellowship (FPU 2017/05417). The authors would like to acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza and the computational resources provided by the Institute for Biocomputation and the Physics of Complex Systems (BIFI)–Universidad de Zaragoza.

A series of Rh(κ2‐BHetA)(η2‐coe)(IPr) complexes bearing 1,3‐bis‐hetereoatomic acidato ligands (BHetA) including carboxylato (O,O), thioacetato (O,S), amidato (O,N), thioamidato (N,S), and amidinato (N,N), have been prepared by reaction of the dinuclear precursor [Rh(μ‐Cl)(IPr)(η2‐coe)]2 with the corresponding anionic BHetA species. The RhI‐NHC‐BHetA compounds catalyze the dimerization of aryl alkynes, showing excellent selectivity for the head‐to‐tail enynes. Among them, the acetanilidato‐based catalyst has shown an outstanding catalytic performance reaching unprecedented TOF levels of 2500 h−1 with complete selectivity for the gem‐isomer. Investigation of the reaction mechanism supports a non‐oxidative pathway in which the BHetA ligand behaves as proton shuttle through intermediate κ1‐HBHetA species. However, in the presence of pyridine as additive, the identification of the common RhIIIH(C≡CPh)2(IPr)(py)2 intermediate gives support for an alternative oxidative route., Financial support from the Spanish Ministerio de Economía y Competitividad (MINECO/FEDER) under the Project CTQ2016‐75884‐P, the CSIC under the Project Proyectos Intramurales Especiales (201680I011), and the Diputación General de Aragón (DGA/FSE‐E42‐17R) are gratefully acknowledged. A.D.G. thanks the Spanish Ministerio de Economía y Competitividad (MINECO) for the postdoctoral grant Juan de la Cierva–Incorporación 2015 (IJCI‐2015‐27029).

550 years after the death of Giorgio Castriota Scanderbeg (1405-1468) the fresco fragments in the plinth of the Church of St. Anthony in Kepi i Rodonit (Albania) are analyzed ; the fresco, illustrates a bicephalous eagle, a horse rider, and a siege of herons. After a typological review of the iconographic themes, a stylistic and chronological evaluation of the paintings in connection with the commission of the great military leader of the Albanian resistance is proposed ; Scanderbeg’s banner presented the heraldic symbol of the double-headed eagle. A comparison is made of the testimonies in Italy and the Balkan area between XII and XV centuries., 550 vjetë pas vdekjes së Gjergj Kastriotit Skënderbeut (1405-1468) merren në shqyrtim fragmentet e afreskut të xokolit absidal të kishës së Shën Antonit në Kepin e Rodonit në Shqipëri. Ata paraqesin një shqiponjë dykrenore, një kalorës me kalë dhe një grup lejlekësh. Mbas një rishikimi tipologjik të temave ikonografike, propozohet një vlerësim stilistik dhe kronologjik i pikturimeve në lidhje me veprimtarinë e prijësit të madh të rezistencës shqiptare, në flamurin e së cilës figuronte simboli heraldik i shqiponjës dykrenore. Ky interpretim bëhet duke hequr paralele me dëshmi dukurish të tilla në rajonin në mes Italisë dhe arealit ballkanik në harkun kohor mes shekujve XII dhe XV., di Giuseppe Andrea. Velaria picta albanica: un velario con aquila bicefala, cavaliere, aironi Shën Andoni, Kepi i Rodonit (Sant’Antonio a Capo Rodone, Albania) / Velaria picta albanica: një velarium me shqiponjë dykrenore, kalorës dhe lejlekë. Kisha e Shën Antonit në Kepin e Rodonit / Velaria picta albanica: a velarium of an twoheaded eagle, knights, herons in the Church of St.Anthony, Cape of Rodon (Albania). In: Iliria, vol. 41, 2017. pp. 367-415.

Dinuclear rhodium–NHC complexes of formula [Rh(μ-Cl)(NHC)(η2-coe)]2 react with 2-vinylpyridine to yield the chelate compounds RhCl(NHC)(κ-N,η2-CH2═CHC5H4N) {NHC = IPr, 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-carbene; IMes, 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-carbene}. The strained metallacycle can be opened by substitution of the pyridine ring by the small electron-rich PEt3 to give RhCl(IPr){η2-CH2═CH(C5H4N)}(PEt3), whereas π ligands such as olefins or alkynes undergo C–C coupling to yield 2-(butenyl)pyridine or 2-(butadienyl)pyridine RhCl(NHC){κ-N,η2-CH(R)═CH(C5H4N)} complexes by formal hydroalkenylation of the unsaturated bond by vinylpyridine. Reaction of the dinuclear precursors with 2-vinylpyrazine in the presence of pyridine affords the η2 derivative RhCl(IPr){η2-CH2═CH(C4H3N2)}(py). Compound RhCl(IMes)(κ-N,η2-CH2═CHC5H4N) is an efficient catalyst for the hydroalkenylation of a range of alkenes and alkynes with 2-vinylpyridine and 2-vinylpyrazine. The butadienyl-heterocycle derivatives resulting from coupling of 2-vinylazines with alkynes undergo a thermal 6π-electrocyclization to yield 4H-quinolizines or 6H-pyrido[1,2-a]pyrazines depending on the nature and position of the substituent of the butadienyl fragment. DFT calculations reveal that fused N-bridgehead heterocycles are more stable than opened butadienylazine derivatives, in spite of the dearomatization of the azine moiety., Financial support from the Spanish Ministerio de Economía y Competitividad (MINECO/FEDER) under the Projects CTQ2013-42532-P and CTQ2016-75884-P, the CSIC under the Project Proyectos Intramurales Especiales (201680I011), and the Diputación General de Aragón (DGA/FSE-E07) are gratefully acknowledged. A.D.G. thanks the Spanish Ministerio de Economía y Competitividad (MINECO) for the postdoctoral grant Juan de la Cierva - Incorporación 2015 (IJCI-2015-27029).

Complex RhCl(IPr)(pyridine)(η2-coe) (IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene) efficiently catalyzes the polyhydrothiolation of aromatic diynes with aliphatic dithiols to give vinylidene-based polymers (vinylidene content of 80%) with high molecular weights (Mw up to 199 000). These polymers have been shown to be chemically modifiable through hydrogenation and chemical oxidation processes., This research was supported by the Ministerio de Economía y Competitividad (MINECO/FEDER) under the Project CTQ2016-75884-P and the Diputación General de Aragón (DGA/FSE-E07). A. D. G. also thanks MINECO for the postdoctoral grant Juan de la Cierva-Incorporación 2015 (IJCI-2015-27029).

New RhI-IPr (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-carbene) complexes bearing an N,O-pyridine-2-methanolato (N-O) bidentate ligand have been prepared. The carbonyl complex Rh(N-O)(IPr)(CO) efficiently catalyzes the hydrothiolation of a range of alkynes with high selectivity to α-vinyl sulfides. Reactivity studies and DFT calculations have revealed a new nonoxidative catalytic pathway, passing through RhI catalytic intermediates, which is driven by the interplay between the pyridine-2-methanolato and carbonyl ligands. The basic alkoxo ligand promotes the deprotonation of the thiol to generate the RhI active species, whereas the π-acceptor character of the carbonyl ligand hinders the oxidative addition process. In addition, the stereochemistry of the key thiolate-π-alkyne intermediate, which is determined by the electronic preference of the carbonyl ligand to coordinate cis to IPr, facilitates the rate-limiting alkyne thiometalation step., Financial support from the Spanish Ministerio de Economía y Competitividad (MINECO/FEDER) under the Projects CTQ2013-42532-P and CTQ2016-75884-P, the Diputación General de Aragón (E07) and CONSOLIDER INGENIO-2010, under the Project MULTICAT (CSD2009-00050) are gratefully acknowledged. A.D.G. thanks the Spanish Ministerio de Economia y Competitividad (MINECO) for the post- doctoral grant Juan de la Cierva - Incorporacion 2015 (IJCI-2015-27029).

The regioselective double hydrophosphination of alkynes mediated by rhodium catalysts is presented. The distinctive stereoelectronic properties of the NHC ligand prevent the catalyst deactivation by diphosphine coordination thereby allowing for the closing of a productive catalytic cycle., Financial support from the Spanish Ministerio de Economía y Competitividad (MEC/FEDER) under the Project (CTQ2013-­42532‐P), the Diputación General de Aragón (DGA/FSE‐E07) and Fondo Social Europeo, the CONSOLIDER INGENIO-2010 under the Project MULTICAT (CSD2009-00050) and the Campus Iberus are gratefully acknowledged. The authors also thank the support of King Fahd University of Petroleum & Minerals (KFUPM) under the KFUPM-­University of Zaragoza research agreement. ADG thanks the “Subprograma de Formación Posdoctoral” from the Spanish Ministerio de Economía y Competitividad.

Die Hydrothiolierung ungesattigter Kohlenstoff-Kohlenstoff-Bindungen ist eine praktische und atomokonomische Methode zum Einbau von Schwefel in organische Grundgeruste. In den letzten Jahren haben wir die Entwicklung einiger Ubergangsmetallkatalysatoren zur Kontrolle von Regio- und Stereoselektivitat beobachtet. In diesem Kurzaufsatz beleuchten wir den mechanistischen Hintergrund dieser Transformation, um die Planung spezifischerer und aktiverer metallorganischer Hydrothiolierungskatalysatoren zu erleichtern.

A computational study based on standard Density Functional Theory and polarized continuum model has been carried out for investigating the essential mechanistic features occurring in the catalytic oxidation of two model substrates, namely ethylene and 1,3-butadiene, promoted by vanadyl acetylacetonate [VO(acac)2] in the presence of hydrogen peroxide. Results, showing in general a qualitative agreement with experimental data carried out on more complex systems, provide quite different scenarios depending on the conditions employed for the reaction. In particular, under thermodynamic control, no selectivity is observed between the two competitive routes, either epoxidation or double bond oxidative cleavage, in both the substrates. On the other hand, under kinetic control, in both systems the double bond oxidative cleavage is always the favored path, although in the case of 1,3-butadiene the difference with the epoxidation route is enhanced, this confirming that the selectivity is sensitive to the nature of the substituent in the vinyl position.

Rh-N-heterocyclic carbene compounds [Rh(μ-Cl)(IPr)(ν 2- olefin)] 2 and RhCl(IPr)(py)(ν 2-olefin) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-carbene, py = pyridine, olefin = cyclooctene or ethylene) are highly active catalysts for alkyne hydrothiolation under mild conditions. A regioselectivity switch from linear to 1-substituted vinyl sulfides was observed when mononuclear RhCl(IPr)(py)(ν 2- olefin) catalysts were used instead of dinuclear precursors. A complex interplay between electronic and steric effects exerted by IPr, pyridine, and hydride ligands accounts for the observed regioselectivity. Both IPr and pyridine ligands stabilize formation of square-pyramidal thiolate-hydride active species in which the encumbered and powerful electron-donor IPr ligand directs coordination of pyridine trans to it, consequently blocking access of the incoming alkyne in this position. Simultaneously, the higher trans director hydride ligand paves the way to a cis thiolate-alkyne disposition, favoring formation of 2,2-disubstituted metal-alkenyl species and subsequently the Markovnikov vinyl sulfides via alkenyl-hydride reductive elimination. DFT calculations support a plausible reaction pathway where migratory insertion of the alkyne into the rhodium-thiolate bond is the rate-determining step. © 2012 American Chemical Society., Financial support from the Ministerio de Ciencia e Innovación (MICINN/FEDER) of Spain (Project CTQ2010-15221), the Diputación General de Aragón (E07), the ARAID Foundation under the program “Jóvenes Investigadores”, and CONSOLIDER INGENIO-2010, Projects MULTICAT (CSD2009-00050) and Factoría de Cristalización (CSD2006-0015) are gratefully acknowledged. R.C. thanks the CSIC and the European Social Fund for his Research Contract in the framework of the “Ramón y Cajal” Program.

Pacman bites selectively! Stable rhodium(III)-N-heterocyclic carbene-hydride complexes (Pacman-like catalysts) are highly active and selective catalysts for H/D exchange at the β position of aromatic α-olefins (see picture). The interplay between bulky N-heterocyclic carbene and quinolinate ligands determines the size of the steric window responsible for this selectivity., Financial support from the MICINN of Spain (project numbers CTQ2009-08089 and CTQ2010-15221), the ARAID Foundation under the program “jóvenes investigadores”, and CONSOLIDER INGENIO-2010 program, under the projects MULTICAT (CSD2009-00050) and Factoría de Cristalización (CSD2006-0015) is gratefully acknowledged. R.C. thanks the CSIC and the European Social Fund for his Research Contract in the framework of the “Ramón y Cajal” program.

Novel complexes between methyltrioxorhenium (MTO) and natural polysaccharides like chitin and chitosan, or modified chitosan-bearing N-substituted acyl or alkyl pyridine moieties, were synthesized and used for the oxidation of alkenes, including acid-sensitive styrene derivatives, with urea hydrogen peroxide adduct (UHP) as primary oxidant. High conversions and yields of the corresponding epoxides were obtained. Silica-chitosan hybrid composites with increased surface area and mechanical properties were also prepared and used as MTO supports. A correlation on the role played by the different MTO-coordinating ligand sites of supports, on the experimental outcome of olefin catalytic oxidations, is discussed. L'articolo è disponibile sul sito dell'editore: http://www.sciencedirect.com

Reaction of VOSO4·5H2O with a methanol solution of the HQ proligand (HQ = 1-R1-4-R2(C O)pyrazol-5-one in general, in detail: HQnPe, R1 = phenyl, R2 = neopentyl; HQMe,Me, R1 = R2 = methyl; HQMe,naph, R1 = methyl, R2 = naphthalen-1-yl; HQnaph, R1 = phenyl, R2 = naphthalen-1-yl; HQPh, R1 = R2 = phenyl; HQCF3, R1 = phenyl, R2 = trifluoromethyl; HQpy,CF3, R1 = pyridin-2-yl, R2 = trifluoromethyl) gave seven novel VO(Q)2(H2O) complexes which have been characterized by elemental analyses, IR, ESI-MS, electronic spectroscopy and magnetic susceptibility measurements and, in the case of derivative VO(QCF3)2, also by EPR spectroscopy. The X-ray diffraction study, carried out on derivative VO(QnPe)2(H2O), evidenced a distorted octahedral environment with the two pyrazolonates in anti configuration and the vanadium atom 0.2914(7) A away from the least-squares plane defined by the four equatorial oxygen atoms. The catalytic activity of these new oxovanadium(IV) complexes has been exhaustively tested for the oxidation of styrene, α-methylstyrene and cis-β-methylstyrene, in the presence of H2O2 as primary oxidant. The effects of oxidant to substrate molar ratio, catalyst amount, solvent and temperature have been studied. Overall, the vanadium complexes showed high activity and high to moderate selectivity toward the benzaldehyde (acetophenone) formation, depending from both the type of starting substrate and experimental reaction times.

Sulfur-containing molecules are commonly found in chemical biology, organic synthesis, and materials chemistry. The preparation of these compounds through traditional methods usually required harsh reaction conditions. The use of transition-metal-based catalysts has allowed the development of more efficient and sustainable synthetic processes. Rhodium-catalyzed C–S bond formation through the reaction between sulfur sources such as S8, thiols, or disulfides with organic substrates such as alkynes, allenes, and aryl/alkyl halides is one of the most important methods in the synthesis of thioethers. Here, we summarize recent efforts in the reactions of cross coupling, C–H activation, metathesis, thiolation, carbothiolation, and hydrothiolation for the C–S bond formation catalyzed by rhodium complexes, particularly highlighting the synthetic and mechanistic aspects.

RhI–NHC–olefin complexes bearing a N,O-quinolinolate bidentate ligand have been prepared from [Rh(μ-OH)(NHC)(η2-olefin)]2 precursors (olefin = cyclooctene, ethylene). The disposition of the chelate ligand with regard to the carbene in the square planar derivatives is strongly influenced by the steric hindrance exerted by the coordinated olefin. These complexes efficiently catalyzed the addition of thiophenol to phenylacetylene with good selectivity to α-vinyl sulfides, which can be increased up to 97% by addition of pyridine. Several key intermediates have been detected including the η1-alkenyl species resulting from alkyne insertion into a Rh–H bond. DFT calculations on the mechanism support a hydrometallation pathway that entails the oxidative addition of thiol, 2,1-insertion of the alkyne into the Rh–H bond, and reductive elimination as the rate-determining step. Remarkably, coordination of pyridine to the β-alkenyl intermediate but not to the α-alkenyl, which results in a net stabilization, is the key for the Markovnikov selectivity., Financial support from the Ministerio de Economía y Competitividad (MEC/FEDER) of Spain (Project CTQ2013-42532-P), the Diputación General de Aragón (E07) and CONSOLIDER INGENIO-2010, under the Project MULTICAT (CSD2009-00050) is gratefully acknowledged. The support under the KFUPM–University of Zaragoza research agreement is also highly appreciated. ADG thanks the “Subprograma de Formación Posdoctoral” from the Ministerio de Economia y Competitividad.

The purpose of this review is to analyze the different reaction mechanisms of the H/D exchange on organic substrates catalyzed by transition metal complexes in homogeneous phase. The metal-catalyzed H/D exchange is a multifaceted reaction whose mechanism depends strongly on the reaction conditions and on the metal complex used as a catalyst. It is possible to group the different mechanisms into three main families depending on the “role” and behavior of the catalyst: (i) Lewis acid–base catalysis; (ii) C H activation (iii) insertion/β-elimination. For each macro-group, several representative examples are discussed and critically evaluated in order to provide the reader with keys to the understanding of how the different catalytic systems act and how their modification may affect their performance in terms of activity and selectivity. This knowledge is fundamental for designing improved organometallic H/D catalysts for labeling organic products in greener conditions with more cost-effective processes.

Experimental and theoretical studies on the factors that control the coordination chemistry of N-donor ligands in square-planar complexes of the type RhCl(NHC)L1L2 (NHC = N-heterocyclic carbene) are presented. The dinuclear complexes [Rh(μ-Cl)(IPr)(η2-olefin)]2 {IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-carbene} have been reacted with different combinations of ligands including pyridine, acetonitrile, 2-pyridylacetonitrile, triphenylphosphine, tricyclohexylphosphine, carbon monoxide or molecular oxygen. In addition, the reactivity of RhCl(IPr)(PPh3)2 has also been studied. Pyridine preferentially coordinates trans to the carbene ligand whereas π-acceptor ligands (olefin, CO or PPh3) are prone to bind cis to IPr and trans to chlorido, unless steric bulk hinders the coordination of the ligand (PCy3). In contrast, acetonitrile is more labile than pyridine but is able to form complexes coordinated cis-to-IPr. Molecular dioxygen also displaces the labile cyclooctene ligand in RhCl(IPr)(η2-coe)(py) to give a square-planar dioxygen adduct which can be transformed into a peroxo derivative by additional coordination of pyridine. Charge decomposition analysis (CDA) shows that σ-donation values are similar for coordination at cis- or trans-IPr positions, whereas efficient π-backbonding is significantly observed at cis position being the favoured coordination site for π-acceptor ligands. The Rh-IPr rotational barrier in a series of square-planar complexes has been analysed. It has been found that the main contribution is the steric hindrance of the ancillary ligand. The presence of a π-donor ligand such as chlorido slows down the dynamic process., Financial support from the spanish Ministerio de Economía y Competitividad (MINECO/FEDER) (CTQ2013-42532-P and CONSOLIDER INGENIO CSD2009-0050 projects), the Diputación General de Aragón (DGA/FSE-E07), the ARAID Foundation under the program “Jóvenes Investigadores”, and the Campus Iberus, are gratefully acknowledged. ADG thanks the 35 “subprograma de Formación Postdoctoral” from the Spanish MINECO.

The purpose of this review is to analyze the different reaction mechanisms of the H/D exchange on organic substrates catalyzed by transition metal complexes in homogeneous phase. The metal-catalyzed H/D exchange is a multifaceted reaction whose mechanism depends strongly on the reaction conditions and on the metal complex used as a catalyst. It is possible to group the different mechanisms into three main families depending on the “role” and behavior of the catalyst: (i) Lewis acid–base catalysis; (ii) CH activation (iii) insertion/β-elimination. For each macro-group, several representative examples are discussed and critically evaluated in order to provide the reader with keys to the understanding of how the different catalytic systems act and how their modification may affect their performance in terms of activity and selectivity. This knowledge is fundamental for designing improved organometallic H/D catalysts for labeling organic products in greener conditions with more cost-effective processes., Financial support from the Spanish “Ministerio de Economía y Competitividad” (MEC/FEDER) under Project CTQ2013-42532-P, the “Diputación General de Aragón” (DGA/FSE-E07), and the “Fondo Social Europeo”, the CONSOLIDER INGENIO-2010 under the Project MULTICAT (CSD2009-00050) and the campus Iberus are gratefully acknowledged. The authors also thank the support of King Fahd University of Petroleum & Minerals (KFUPM) under the KFUPM – University of Zaragoza research agreement. ADG thanks the “Subprograma de Formación Posdoctoral” from the Spanish “Ministerio de Economía y Competitividad”.

The complex [Rh(μ-Cl)(IPr)(η2-coe)]2 {IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-carbene, coe = cis-cyclooctene} efficiently catalyzes the coupling of alkynes and N-vinylpyrazole via C–H activation, leading to Markovnikov-selective butadienylpyrazole derivatives under mild conditions. A straightforward approach to cross-conjugated acyclic trienes is also operative through a one-pot alkyne dimerization-hydrovinylation tandem reaction. The proposed mechanism involves C–H activation of vinylpyrazole directed by nitrogen coordination to the metallic center. Subsequent alkyne coordination, insertion, and reductive elimination steps lead to the coupling products. Several key intermediates participating in the catalytic cycle have been detected and characterized, including a κ-N, η2-C═C coordinated vinylpyrazole complex and a RhIII-hydride-alkenyl species resulting from the C–H activation of the vinylpyrazole., Financial support from the Spanish Ministerio de Economía y Competitividad (MEC/FEDER) of Spain Projects (CTQ2010-15221), the Diputación General de Aragón (E07), the ARAID Foundation, and CONSOLIDER INGENIO-2010, under the Project MULTICAT (CSD2009-00050) are gratefully acknowledged. L. R.-P. thanks CONACyT (Mexico, 186898 and 204033) for a postdoctoral fellowship.

A series of neutral and cationic RhIII-hydride and Rh III-ethyl complexes bearing a NHC ligand has been synthesized and evaluated as catalyst precursors for H/D exchange of styrene using CD 3OD as a deuterium source. Various ligands have been examined in order to understand how the stereoelectronic properties can modulate the catalytic activity. Most of these complexes proved to be very active and selective in the vinylic H/D exchange, without deuteration at the aromatic positions, displaying very high selectivity toward the positions. In particular, the cationic complex [RhClH(CH3CN)3(IPr)]CF 3SO3 showed excellent catalytic activity, reaching the maximum attainable degree of vinylic deuteration in only 20 min. By modulation of the catalyst structure, we obtained improved α/β selectivity. Thus, the catalyst [RhClH(κ2-O,N-C9H 6NO)(SIPr)], bearing an 8-quinolinolate ligand and a bulky and strongly electron-donating SIPr as the NHC, showed total selectivity for the β-vinylic positions. This systematic study has shown that increased electron density and steric demand at the metal center can improve both the catalytic activity and selectivity. Complexes bearing ligands with very high steric hindrance, however, proved to be inactive. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., Financial support from the Spanish Ministerio de Economía y Competitividad (MEC/FEDER) under the Project CTQ2010–15221, the Diputación General de Aragón (E07) and Fondo Social Europeo, the ARAID Foundation, and the CONSOLIDER INGENIO-2010 under the Project MULTICAT (CSD2009–00050) is gratefully acknowledged.

The hydrothiolation of unsaturated carbon-carbon bonds is a practical and atom-economical approach for the incorporation of sulfur into organic frameworks. In recent years, we have witnessed the development of a range of transition-metal-based catalytic systems for the control of the regio- and stereoselectivity. In this Minireview we highlight the mechanistic background behind this transformation so as to help the design of more specific and active organometallic hydrothiolation catalysts.

The hydrothiolation of unsaturated carbon-carbon bonds is a practical and atom-economical approach for the incorporation of sulfur into organic frameworks. In recent years, we have witnessed the development of a range of transition-metal-based catalytic systems for the control of the regio- and stereoselectivity. In this Minireview we highlight the mechanistic background behind this transformation so as to help the design of more specific and active organometallic hydrothiolation catalysts. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim., Financial support from the MICINN of Spain Project CTQ2010-15221), the Diputación General de Aragón (E07), the ARAID Foundation under the program “Jóvenes Investigadores”, and CONSOLIDER INGENIO-2010, under the Project MULTICAT (CSD2009-00050) are gratefully acknowledged.

The neutral square-planar complexes Rh(acac)(IPr)(η2-olefin) have been prepared from [Rh(μ-Cl)(IPr)(η2-olefin)]2 (IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-carbene; olefin = cyclooctene, ethylene) and sodium acetylacetonate (acac). Protonation of the acetylacetonato complexes with triflic acid opens the way to the formation of the putative bare [Rh-IPr]+ fragment that has been stabilized at low temperature by labile ligands such as triflate, cyclooctene, and acetonitrile to generate Rh(OTf)(IPr)(η2-coe), [Rh(IPr)(η2-coe)(NCCH3)2]OTf, and [Rh(IPr)(NCCH3)3]OTf complexes. The derivative [Rh(IPr)(η2-coe)(NCCH3)2]OTf was further characterized by an X-ray diffraction analysis., Financial support from the Spanish Ministerio de Economía y Competitividad (MEC/FEDER) Project (CTQ2010-15221), the Diputación General de Aragón (E07), the ARAID Foundation under the program “Jóvenes Investigadores”, the CONSOLIDER INGENIO 2010 program, under the projects MULTICAT (CSD2009-00050) and “Factorıá de Cristalización” (CSD2006-0015), and the Campus Iberus are gratefully acknowledged.

Forging the lock that autolocks! Rh-NHC catalysts promote a new access to 4 H-quinolizine species from 2-vinylpyridine and terminal and internal alkynes through C-H activation and C-C coupling reactions (see figure). N-Bridgehead heterocycle formation is favored for internal- over terminal-substituted butadienylpyridine derivatives in a thermal 6π-electrocyclization process. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., Financial support from the Ministerio de Economía y Competitividad of Spain Project CTQ2010–15221), the Diputación General de Aragón (E07), the ARAID Foundation under the program “Jóvenes Investigadores”, and CONSOLIDER INGENIO-2010, under the Project MULTICAT (CSD2009–00050) are gratefully acknowledged.

The first rhodium alkylidene square-planar complex stabilized by an N-heterocyclic carbene ligand, RhCl(=CHPh)(IPr)PPh3 (2; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-carbene), has been prepared by reaction of RhCl(IPr)(PPh3)2 (1) with phenyldiazomethane and its dynamic behavior in solution studied. Treatment of 2 with alkenes results in the formation of the η2-olefin complexes RhCl(η2- CH2=CHR)(IPr)PPh3 (3, R = H; 4, R = Ph; 5, R = OEt) and new olefins arising from the coupling of the alkylidene with the alkenes, likely via a metallacyclobutane intermediate. © 2011 American Chemical Society., Financial support from the Ministerio de Ciencia e Innovación (MICINN/FEDER) of Spain (Project CTQ2010-15221), the Diputación General de Aragón (E07), the ARAID Foundation under the program “Jóvenes Investigadores”, and CONSOLIDER INGENIO-2010, Projects MULTICAT (CSD2009-00050) and Factoría de Crystalización (CSD2006-0015), are gratefully acknowledged. R.C. thanks the CSIC and the European Social Fund for his Research Contract in the framework of the “Ramón y Cajal” Program.

The oxidation of benzothiophene (BTs) and dibenzothiophene (DBTs) derivatives, of model fuel (MF) and authentic diesel fuel (ADF) with homogeneous and heterogeneous rhenium catalysts and H2O2 has been studied to design an alternative environmentally benign oxidative desulfurization process (ODS), for oil industry. The quantitative conversion of both BTs and DBTs derivatives was obtained in several of the cases investigated, to afford the corresponding sulfones as the only recovered products in very high yield. Excellent results in terms of both conversion of substrates and yields of sulfones were also obtained during oxidation of MF and ADF. Heterogeneous rhenium catalysts were stable systems to be used for several runs without any appreciable reduction of reactivity and selectivity.

This paper describes the development of a system for measuring surface coordinates (commonly known as "shape measurements") which is able to give the temporal evolution of the position of the tire sidewall in transient conditions (such as during braking, when there are potholes or when the road surface is uneven) which may or may not be reproducible. The system is based on the well-known technique of projecting and observing structured light using a digital camera with an optical axis which is slanted with respect to the axis of the projector. The transient nature of the phenomenon has led to the development of specific innovative solutions as regards image processing algorithms. This paper briefly describes the components which make up the measuring system and presents the results of the measurements carried out on the drum bench. It then analyses the performance of the measuring system and the sources of uncertainty which led to the development of the system for a specific dynamic application: impact with an obstacle (cleat test). The measuring system guaranteed a measurement uncertainty of 0.28 mm along the Z axis (the axial direction of the tire) with a measurement range of 250(X) x 80(Y) x 25(Z) mm(3), with the tire rolling at a speed of up to 30 km/h.

Using a post-synthetic grafting method, mesoporous SBA-15 was functionalized first with aminopropyl silane reagents such as (3-aminopropyl)trimethoxysilane (APTMS) or bis[3-(trimethoxysilyl)propyl]amine (BTMSPA) and then with chlorinated ligands such as 4-(2-chloroacetyl)-3-methyl- 1-phenyl-1H-pyrazol-5(4H)-one (H-AP) or 5-chloromethyl-8-quinolinol hydrochloride (H-HQ). Vanadyl cations [(VO)2+] were then immobilized over functionalized silica samples in order to prepare new oxovanadium(iv) based >quasi-homogeneous> catalysts, namely Ia (Ia′), Ib (Ib′), and IIa. Alternatively, a preformed oxovanadium(iv) complex such as [VO(AP)2(H2O)] has been immobilized over a previously functionalized SBA-15-NH2 silica support, affording catalyst Ic. Elemental analysis (C, H, N), N2 adsorption-desorption isotherms, FT-IR, 29Si and 13C CP-MAS NMR, XPS, ICP-AES, SEM-EDX and TG-DTG techniques have been used for the full characterization of these materials. Their catalytic properties in the H2O2 promoted oxidation of conjugated olefins like styrene, α-methyl and β-methylstyrene were investigated, in terms of activity, selectivity and recyclability, and compared with that shown by more simple systems prepared by the direct grafting of the vanadyl cation onto SBA-15 (catalyst A) or SBA-15-NH2 (catalyst B). Generally, high activity, selectivity and recyclability (over the first three runs) were shown by all anchored catalysts, with the only exception of A and B systems. A full account of the obtained results, along with insights into the effects due to the different strategies employed for the functionalization of SBA-15 on the properties of final anchored catalysts, are reported. This journal is © 2013 The Royal Society of Chemistry.