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A Co(iii) complex featuring a novel benzotriazole-based P–N ligand acts as an efficient catalyst for nucleophilic fluorination reactions in organic carbonates.

Copper(I) [Cu2(μ-Br)2(tBuImCH2pyCH2L)]n (L = OMe, NEt2, NHtBu) compounds supported by flexible functionalized NHC-based polydentate ligands have been prepared in a one-pot procedure by reacting the corresponding imidazolium salt with an excess of copper powder and Ag2O. An X-ray diffraction analysis has revealed that [Cu2(μ-Br)2(tBuImCH2pyCH2NEt2)]n is a linear coordination polymer formed by bimetallic [Cu(μ-Br)]2 units linked by the lutidine-based NHC-py-NEt2 ligand, which acts as a heteroditopic ligand with a 1κC-2κ2N,N′ coordination mode. We propose that the polymeric compounds break down in the solution into more compact tetranuclear [Cu2(μ-Br)2(tBuImCH2pyCH2L)]2 compounds with a coordination mode identical to the functionalized NHC ligands. These compounds have been found to exhibit high catalytic activity in the Cu-catalyzed azide–alkyne cycloaddition (CuAAC) reaction. In particular, [Cu2(μ-Br)2(tBuImCH2pyCH2NEt2)]2 efficiently catalyzes the click reaction of a range of azides and alkynes, under an inert atmosphere at room temperature in neat conditions at a very low catalyst loading, to quantitatively afford the corresponding 1,4-disubstituted 1,2,3-triazole derivatives in a few minutes. The cycloaddition reaction of benzyl azide to phenylacetylene can be performed at 25–50 ppm catalyst loading by increasing the reaction time and/or temperature. Reactivity studies have shown that the activation of the polynuclear catalyst precursor involves the alkyne deprotonation by the NHC moiety of the polydentate ligand to afford a copper(I)-alkynyl species bearing a functionalized imidazolium ligand. DFT calculations support the participation of the dinuclear species [(CuBr)2(μ-tBuImCH2pyCH2NEt2)], resulting from the fragmentation of the tetranuclear compound, as the catalytically active species. The proposed reaction pathway proceeds through zwitterionic dinuclear intermediates and entails the active participation of both copper atoms, as well as the NHC moiety as an internal base, which activates the reacting alkyne via deprotonation., The authors express their appreciation for the financial support from the Spanish Ministerio de Ciencia e Innovación (MICINN/FEDER) under Projects PID2019-103965GB-I00/AEI/10.13039/501100011033 and PGC2018-095953-B-I00 (MCIU/AEI/FEDER, UE), as well as the ″Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón″ (group E42_20R) and ″Fundación para el Fomento en Asturias de la Investigación Científica Aplicada y Tecnológica″ (grant IDI-2021-000054). M.G.-L. thanks the Spanish Ministerio de Economía y Competitividad (MINECO) for a predoctoral fellowship (BES-2014-069624). M.G. thankfully acknowledges the Spanish Ministerio de Ciencia, Innovación y Universidades (MICIU) for a predoctoral FPU fellowship (FPU19/02903).

A set of neutral [IrBr(L2)(κC-tBuImCH2PyCH2OMe)] and cationic [Ir(L2)(κ2C,N-tBuImCH2PyCH2OMe)]PF6 (L2 = cod, (CO)2) Ir(I) compounds featuring a flexible lutidine-derived polydentate ligand having NHC and −OMe as donor functions have been evaluated as catalyst precursors for the N-methylation of aniline using methanol both as a reducing agent and a C1 source. The carbonyl complexes are somewhat more active than the related diene compounds with the neutral compound [IrBr(CO)2(κC-tBuImCH2PyCH2OMe)] being the more active. A range of aromatic primary amines, including heterocyclic amines, have been selectively transformed into the corresponding N-methylamino derivatives using this catalyst at a low catalyst loading (0.1 mol %) and substoichiometric amounts of Cs2CO3 (half equiv) as a base, in methanol at 423 K. For aliphatic primary amines, selective N,N-dimethylation was achieved under the same catalytic conditions. The unselective deprotonation of the methylene linkers in [IrBr(CO)2(κC-tBuImCH2PyCH2OMe)] affords two isomeric neutral complexes featuring a coordinated dearomatized pyridine core, which were converted into [Ir(OMe)(CO)2(κC-tBuImCH2PyCH2OMe)] upon addition of methanol. This compound undergoes thermal activation of a C–H bond of the tert-butyl group to give the cyclometalated iridium(I) complex [Ir(CO)2{κ2C,C-(-CH2Me2C-ImCH2PyCH2OMe)}] featuring a bidentate C,C-coordinated NHC ligand. Mechanistic investigations support a borrowing hydrogen mechanism proceeding through iridium(I) intermediates with the methoxo complex as the catalytic active species and the cyclometalated complex as the catalyst resting state. Deuterium labeling experiments have demonstrated that both species are in equilibrium under catalytic conditions, which is consistent with the exhibited catalytic activity of the cyclometalated complex., The authors express their appreciation for the financial support from the Spanish Ministerio de Ciencia e Innovación, MCIN/AEI/10.13039/501100011033, under the project PID2019-103965GB-I00, and the “Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón” (group E42_20R).

Monodentate aminophosphanes HNP [NH(4-tolyl)PPh2] and SiMe3NP [SiMe3N(4-tolyl)PPh2] react with [Ir(μ-Cl)(cod)]2 affording tetra- or pentacoordinate complexes of formula [IrCl(L)n(cod)] (L = HNP, n = 1, 2; L = SiMe3NP, n = 1). The reaction of [IrCl(SiMe3NP)(cod)] with carbon monoxide smoothly renders [Ir(CO)3(SiMe3NP)2][IrCl2(CO)2]. The reaction of HNP or SiMe3NP with [Ir(CH3CN)2(cod)][PF6] yields the cyclometalated iridium(III)-hydride derivatives [IrH{κ2C,P-NR(4-C6H3CH3)PPh2}(cod)(CH3CN)][PF6] (R = H, SiMe3) as a result of the intramolecular oxidative addition of the tolyl C2–H bond to iridium. The straighforward formation of [IrH{κ2C,P-SiMe3N(4-C6H3CH3)PPh2}(cod)(CH3CN)]+ was observed when the reaction was monitored by NMR spectroscopy at 233 K, whereas a more complex reaction sequence was observed in the formation of [IrH{κ2C,P-NH(4-C6H3CH3)PPh2}(cod)(CH3CN)]+, including the formation of [IrH{κ2C,P-NH(4-C6H3CH3)PPh2}(HNP)(cod)]+ and [Ir(cod)(HNP)2]+. The “mixed” complex [IrH{κ2C,P-SiMe3N(4-C6H3CH3)PPh2}(HNP)(cod)]+ was obtained upon reaction of [IrH{κ2C,P-NH(4-C6H3CH3)PPh2}(cod)(CH3CN)][PF6] with SiMe3NP at 233 K. Finally, the reaction of [Ir(CH3CN)2(coe)2][PF6] with SiMe3NP or HNP resulted in the formation of [Ir(CH3CN)2(SiMe3NP)2][PF6] and [IrH{κ2C,P-NH(4-C6H3CH3)PPh2}(HNP)2(CH3CN)][PF6], respectively. Both the OC-6-35 and the OC-6-52 isomers of [IrH{κ2C,P-NH(4-C6H3CH3)PPh2}(HNP)2(CH3CN)]+ – featuring facial and meridional dispositions of the phosphorus atoms, respectively – were isolated depending on the reaction solvent. Several compounds described herein catalyse the dehydrogenation of formic acid in DMF, [IrCl(HNP)2(cod)] being the most active, with TOF1 min of about 2300 h−1 (5 mol% catalyst, 50 mol% sodium formate, DMF, 80 °C)., Financial support from the Spanish Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/501100011033, under the project PID2019-103965GB-I00, and the Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón (group E42_20R) is gratefully acknowledged.

Reaction of the dimers [(Cp*MCl)

The iridium(III) hydride compound [IrH{κ3C,P,P′-(SiNP–H)}(CNtBu)2][PF6] (1PF6) was obtained by reaction of [Ir(SiNP)(cod)][PF6] with CNtBu as the result of the intramolecular oxidative addition of the SiCH2–H bond to iridium(I) [SiNP = Si(CH3)2{N(4-tolyl)PPh2}2, SiNP–H = CH2Si(CH3){N(4-tolyl)PPh2}2]. The mechanism of the reaction was investigated by NMR spectroscopy and DFT calculations showing that the pentacoordinated intermediate [Ir(SiNP)(cod)(CNtBu)][PF6] (2PF6) forms in the first place and that further reacts with CNtBu, affording the square planar intermediate [Ir(SiNP)(CNtBu)2][PF6] (3PF6) that finally undergoes the intramolecular oxidative addition of the SiCH2–H bond. The reactivity of 1PF6 was investigated. On one hand, the reaction of 1PF6 with N-chlorosuccinimide or N-bromosuccinimide provides the haloderivatives [IrX{κ3C,P,P′-(SiNP–H)}(CNtBu)2][PF6] (X = Cl, 4PF6; Br, 5PF6), and the reaction of 5PF6 with AgPF6 in the presence of acetonitrile affords the solvato species [Ir{κ3C,P,P′-(SiNP–H)}(CH3CN)(CNtBu)2]2+ (62+) isolated as the hexafluorophosphate salt. On the other hand, the reaction of 1PF6 with HBF4 gives the iridium(III) compound [IrH(CH2SiF2CH3)(HNP)2(CNtBu)2][BF4] (7BF4) as the result of the formal addition of hydrogen fluoride to the Si–N bonds of 1+ [HNP = HN(4-tolyl)PPh2]. A similar outcome was observed in the reaction of 1PF6 with CF3COOH rendering 7PO2F2. In this case the intermediate [IrH{κ2C,P-CH2SiMeFN(4-tolyl)PPh2}(HNP)(CNtBu)2]+ (8+) was observed and characterised in situ by NMR spectroscopy. DFT calculations suggests that the reaction goes through the sequential protonation of the nitrogen atom of the Si–N–P moiety followed by the formal addition of fluoride ion to silicon. Also, the crystal structures of SiNP, 1PF6, 4PF6 and 7BF4 have been determined by X-ray diffraction measurements., Financial support from the Spanish Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/501100011033, under the Project PID2019-103965GB-I00, and the Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón (group E42_20R) is gratefully acknowledged.

The dinuclear complex [Rh(μ-Cl)(η2-coe)(IPr)]2 is an efficient catalyst for the O-selective Markovnikov-type addition of 2-pyridones to terminal alkynes. DFT calculations support a hydride-free pathway entailing intramolecular oxidative protonation of a π-alkyne by a κ1N-hydroxypyridine ligand. Subsequent O-nucleophilic attack on a metallacyclopropene species affords an O-alkenyl-2-oxypyridine chelate rhodium intermediate as the catalyst resting state. The release of the alkenyl ether is calculated as the rate-determining step., Financial support from the Spanish Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/501100011033, under the Projects PID2019-103965GB-I00 and PGC2018-099383-B-I00, and the Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón (group E42_20R) is gratefully acknowledged.

We report a high-yield heterogeneous solid/liquid phase synthetic method to a series of

Compound [IrBr(CO)2(κC-tBuImCH2PyCH2OMe)] featuring a flexible pyridine/OMe functionalized NHC ligand κ1C coordinated efficiently catalyzes the selective N-monomethylation of nitroarenes using methanol as both the reducing agent and the C1 source. A range of functionalized nitroarenes including heterocyclic or sterically hindered derivatives have been efficiently converted to the corresponding N-monomethyl amines in good yields at low catalyst loadings using sub-stoichiometric amounts of Cs2CO3 as a base. Mechanistic investigations support a borrowing-hydrogen mechanism in which methanol acts as the hydrogen source and methylating agent. Further, the hydrogen transfer reduction of nitrobenzene to aniline under optimized reaction conditions should proceed through a direct mechanism involving nitrosobenzene and N-phenylhydroxylamine intermediates., Financial support from the Ministerio de Ciencia e Innovación (MICINN/FEDER) under the Project CTQ2016-75884-P and the Regional Government of Aragón/FEDER 2014-2020 “Building Europe from Aragón” (group E42_17R) is gratefully acknowledged. M. G.-L. thanks MINECO for a predoctoral fellowship (BES-2014-069624).

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).

Resumen del póster presentado a la XXXVIII Reunión Bienal de la Real Sociedad Española de Química, celebrada en el Palacio de Congresos de Granada, del 27 de junio al 30 de junio de 2022., Formic acid is a promising hydrogen carrier, as independently described by Beller and Laurenczy in their seminal work. The homogeneously catalysed dehydrogenation of HCOOH allows the generation of an equimolar H2/CO2 mixture virtually free of CO, which is crucial for the optimal performance of hydrogen fuel cells. In this work, the activity of two iridium complexes based on PCNHCP and PCNHCO ligands, [Ir(COD)(κ3-P,C,P'-PCNHCP)]BF4 (1) and [Ir(COD)(κ2-P,C-PCNHCO)]BF4 (2), was studied in the dehydrogenation of formic acid under different conditions (Figure 1). In this context, the use of dimethylcarbonate as co-solvent (1:1 (v/v)) was observed to drastically increase the catalytic activity in the case of complex 2, from a TOF1h of 61 to 988 h-1, while complex 1 was hardly affected. The study of the reaction mechanism was carried out by stoichiometric tests, KIE measurements and DFT calculations. These data, both theoretical and experimental, suggest that the use of organic carbonates as co-solvents prevents the deactivation of the catalyst, which occurs after the formation of dinuclear species.

A set of iridium(I) complexes of formula IrCl(κC,η2-IRCouR′)(cod) or IrCl(κC, η2-BzIRCouR′)(cod) (cod = 1,5-cyclooctadiene; Cou = coumarin; I = imidazolin-2-carbene; BzI = benzimidazolin-2-carbene) have beeen prepared from the corresponding azolium salt and [Ir(μ-OMe)(cod)]2 in THF at room temperature. The crystalline structures of 4b and 5b show a distorted trigonal bipyramidal configuration in the solid state with a coordinated coumarin moiety. In contrast, an equilibrium between this pentacoordinated structure and the related square planar isomer is observed in solution as a consequence of the hemilability of the pyrone ring. Characterization of both species by NMR was achieved at the low and high temperature limits, respectively. In addition, the thermodynamic parameters of the equilibrium, ΔHR and ΔSR, were obtained by VT 1H NMR spectroscopy and fall in the range 22–33 kJ mol−1 and 72–113 J mol−1 K−1, respectively. Carbonylation of IrCl(κC,η2-BzITolCou7,8-Me2)(cod) resulted in the formation of a bis-CO derivative showing no hemilabile behaviour. The newly synthesised complexes efficiently catalyze the hydrosilylation of alkynes at room temperature with a preference for the β-(Z) vinylsilane isomer.

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.

Iridium(I) N-heterocyclic carbene complexes of formula Ir(κ2O,O’-BHetA)(IPr)(η2-coe) [BHetA=bis-heteroatomic acidato, acetylacetonate or acetate; IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-carbene; coe=cyclooctene] have been prepared by treating Ir(κ2O,O’-BHetA)(η2-coe)2 complexes with IPr. These complexes react with 2-vinylpyridine to afford the hydrido-iridium(III)-alkenyl cyclometalated derivatives IrH(κ2O,O’-BHetA)(κ2N,C-C7H6N)(IPr) through the iridium(I) intermediate Ir(κ2O,O’-BHetA)(IPr)(η2-C7H7N). The cyclometalated IrH(κ2O,O’-acac)(κ2N,C–C7H6N)(IPr) complex efficiently catalyzes the hydroalkenylation of aromatic and aliphatic terminal alkynes and enynes with 2-vinylpyridine to afford 2-(4R-butadienyl)pyridines with Z,E configuration as the major reaction products (yield up to 89 %). In addition, unprecedented (Z)-2-butadienyl-5R-pyridine derivatives have been obtained as minor reaction products (yield up to 21 %) from the elusive 1Z,3gem-butadienyl hydroalkenylation products. These compounds undergo a thermal 6π-electrocyclization to afford bicyclic 4H-quinolizine derivatives that, under catalytic reaction conditions, tautomerize to 6H-quinolizine to afford the (Z)-2-(butadienyl)-5R-pyridine by a retro-electrocyclization reaction., Financial support from the Spanish Ministerio de Ciencia e Innovación (MICINN/FEDER) under Project PID2019-103965GB-I00, and the Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón (group E42_20R) is gratefully acknowledged. I.G. thanks the Humboldt Foundation for a research fellowship.

This review focuses on the contributions of the last 5 years to the application of iridium complexes as homogeneous catalysts in transfer hydrogenation (TH) reactions. The reduction of carbonyls, imines, alkenes and alkynes is considered. The TH of unsaturated alkene-carbonyl substrates and heterocycles is particularly studied. Recent results on the reduction of CO2 are also included. Special attention is paid to THs performed in aqueous medium as well as to the development of TH in biological media. The employ of biomass-derived products as reagents or solvents in TH transformations is also reviewed. Finally, the proposed mechanisms for TH reactions are revised.

We report a high-yield heterogeneous solid/liquid phase synthetic method to a series of nido-6-metalladecaboranes. The hydridoirida– and hydridorhoda–decaboranes, [6,6,6-H(PPh3)2-nido-6-MB9H13] [M = Ir (1), Rh (2)] are isolatable in 98% yields from the reaction of the square-planar M(I) complexes, [MCl(PPh3)3] (M = Rh, Ir), with K[B9H14]. The same synthetic procedure, but using [MCl(CO)H(PPh3)3] (M = Ru, Os) as metal starting reagents produces the CO-ligated clusters, [6,6,6-(CO)(PPh3)2-nido-6-MB9H13] [M = Ru (3), Os (4)], in yields of 83% and 95%, respectively. These highly convenient syntheses permit the investigation of the reaction chemistry of the new nido-6-metalladecaboranes. Thus, the CO-ligated compounds, 3 and 4, react with the square-planar platinum(II) complex, [PtCl2(PMe2Ph)2], in the presence of potassium triethylborohydride, to give the bimetallic clusters, [1,1,1-(CO)H(PPh3)-isocloso-1-RuB9H8-μ-(1,2)-{Pt(PMe2Ph)2}] (5) and [7,7-(PMe2Ph)2-9,9,9-(CO)(PPh3)2-nido-7,9-PtOsB9H11] (6), and the monometallic nido-5-osamadecaborane, [5,5,5-(PPh3)2(CO)-nido-5-OsB9H13] (7). This reactivity illustrates the potential of polyhedral boron-based clusters as molecular scaffolds (“B-frames”) for the construction of multimetallic species. Single-crystal X-ray diffraction analyses have revealed the molecular structures of 3, 5, 6 and 7; the compounds are also studied by multielement NMR spectroscopy, mass spectrometry, IR spectroscopy, and in some cases computationally. Futhermore, the rotation of the {M(X)(PR3)2} moiety (X = H, CO), as PH3-ligated models, is studied by means of DFT-calculated relaxed potential energy surface scans, giving some insight into the lability of the metal-to-borane fragment interaction and of the exo-polyhedral ligands.

The cyclometalated Rh(III)–NHC compounds [Cp*RhI(C,C′)-Triaz] (Triaz = 1,4-diphenyl-3-methyl-1,2,3-triazol-5-ylidene) and [Cp*RhI(C,C′)-Im] (Im = 1-phenyl-3-methyl-imidazol-2-ylidene) are efficient catalysts for the hydrosilylation of terminal alkynes with complete regio- and stereoselectivity toward the thermodynamically less stable β-(Z)-vinylsilane isomer at room temperature in chloroform or acetone. Catalyst [Cp*RhI(C,C′)-Triaz] shows a superior catalytic performance in terms of activity and has been applied to the hydrosilylation of a range of linear 1-alkynes and phenylacetylene derivatives with diverse hydrosilanes, including HSiMePh2, HSiMe2Ph, HSiEt3, and the bulkier heptamethylhydrotrisiloxane (HMTS), to afford the corresponding β-(Z)-vinylsilanes in quantitative yields. The graphene-based hybrid material TRGO-Triaz-Rh(III), featuring cyclometalated [Cp*RhI(C,C′)-Triaz] (Triaz = 1,4-diphenyl-3-methyl-1,2,3-triazol-5-ylidene) rhodium(III) complexes covalently immobilized through the triazolylidene linker, has been prepared by metalation of the trimethylsilyl-protected 3-methyl-4-phenyl-1,2,3-triazolium iodide functionalized graphene oxide material, TRGO-Triaz, with [Cp*RhCl2]2 using sodium tert-butoxide as base. The coordination sphere of the supported rhodium(III) complexes has been determined by means of XPS and extended X-ray absorption fine structure (EXAFS) spectroscopy, showing the replacement of the iodido ligand by O-functionalities on the carbon wall. In sharp contrast with the homogeneous catalyst, the heterogeneous hybrid catalyst TRGO-Triaz-Rh(III) is not active at room temperature although it shows an excellent catalytic performance at 60 °C. In addition, the hybrid catalyst TRGO-Triaz-Rh(III) has shown an excellent recyclability, allowing at least six catalytic runs in the hydrosilylation of oct-1-yne with HSiMePh2 in acetone with complete selectivity to the β-(Z)-vinylsilane product. The reaction mechanism for the molecular catalyst [Cp*RhI(C,C′)-Triaz] has been explored by means of DFT calculations, pointing to a metal–ligand bifunctional mechanism involving reversible cyclometalation that is competitive with a noncooperative pathway. The proposed mechanism entails the Rh–CAr assisted hydrosilane activation to afford a reactive Rh–silyl intermediate that leads to a (E)-silylvinylene intermediate after alkyne insertion and a metallacyclopropene-driven isomerization. The release of the β-(Z)-vinylsilane product can occur by a reversible cyclometalation mechanism involving σ-CAM with the CAr–H bond or, alternatively, the Si–H bond of an external hydrosilane. The energy barrier for the latter is 1.2 kcal·mol–1 lower than that of the CAr–H bond, which results in a small energy span difference that makes both pathways competitive under catalytic conditions., The authors express their appreciation for the financial support from MICINN/FEDER, projects PID2019-103965GB-100, CTQ2016-75884-P and RTI2018-098537-B-C22, DGA/FEDER 2014-2020 “Building Europe from Aragón” (groups E42_20R and E12_20R), and Principado de Asturias/FEDER (IDI/2018/000121).

A sturdy iridium complex that features a PCP ligand based on an N-heterocyclic olefin shows remarkable activity for the solventless dehydrogenation of formic acid. Reactivity studies highlight the importance of NHO in the activity of the catalyst. A plausible intermediate has been isolated and the mechanism was substantiated by DFT calculations., This work was supported by the Spanish Ministry of Education, Culture and Sports (MECD) (project CTQ2016-75884-P, “Ramón y Cajal” program RYC2016-20864 (M. I.) and FPU14/06003 (J. M.)) and the DGA/E42_17R.

[Cp*Rh(κN,N′,P-L)][SbF] (Cp*=CMe), bearing a guanidine-derived phosphano ligand L, behaves as a “dormant” frustrated Lewis pair and activates H and HO in a reversible manner. When DO is employed, a facile H/D exchange at the Cp* ring takes place through sequential C(sp)−H bond activation., We thank the Ministerio de Economía y Competitividad of Spain (CTQ2015‐66079‐P) and Gobierno de Aragón (Grupo Consolidado E05‐17R: Catálisis Homogénea Enantioselectiva) for financial support. M.C. acknowledges Diputación General de Aragón, CSIC and European Social Fund for a grant. R.R. acknowledges the Ministerio de Economía y Competitividad of Spain for a Ramón y Cajal (RYC‐2013‐13800) grant. P.G.‐O. acknowledges CSIC, European Social Fund and Ministerio de Economía y Competitividad of Spain for a PTA contract.

The mono- and dinuclear rhodium(I) complexes featuring 2-(diphenylphosphino)pyridine ligands, [Rh(cod)(Ph2PPy)]+ and [Rh(nbd)(μ-Ph2PPy)]22+ (cod = 1,5-cyclooctadiene, nbd = 2,5-norbornadiene), have been prepared in order to be evaluated as phenylacetylene (PA) polymerization catalysts. In contrast with compound [Rh(nbd){Ph2P(CH2)2Py}]+, featuring a 2-(2-(diphenylphosphino)ethyl)pyridine ligand, that showed a moderate catalytic activity, both [Rh(diene)(Ph2PPy)]nn+ (n = 1, cod; n = 2, nbd) complexes showed no catalytic activity due to the formation of unusual dinuclear species [Rh2(diene)2(μ-Ph2PPy)(μ-C≡C-R)]+, supported by a Ph2PPy bridging ligand and an alkynyl ligand coordinated in a μ-η1:η2 fashion, which are inactive in PA polymerization. However, compounds [Rh(diene)(Ph2PPy)]nn+ efficiently polymerize PA in the presence of a cocatalyst as iPrNH2 affording highly stereoregular poly(phenylacetylene) (PPA) of Mw = 3.42 × 105 (cod) and 2.02 × 105 (nbd) with polydispersities of 1.39 and initiation efficiencies of 4–7%. NMR studies on the polymerization reaction have allowed identification of the alkynyl species [Rh(C≡CPh)(cod)(Ph2PPy)] as the likely initiating species involved in the generation of the rhodium-vinyl species responsible for the propagation step. The iPrNH2 cocatalyst is possibly involved in the efficient proton transfer from the coordinated PA to iPrNH2 that allows for a significant concentration of the key initiating species [Rh(C≡CPh)(cod)(Ph2PPy)]. The distinct behavior of compounds [Rh(diene)(Ph2PPy)]nn+ as PA polymerization catalysts is a consequence of the binucleating ability of the Ph2PPy ligand in combination with the low basicity of the pyridine fragment which allows for the stabilization of the inactive alkynyl-bridge dinuclear species., Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER) under the Project CTQ2016-75884-P and the Diputación General de Aragón (DGA/FSE-E07) is gratefully acknowledged.

The newly synthesized mer-trans-[RuCl2(OH2)(PTA)3] (1) is the first compound isolated in solid state containing the Ru(PTA)3-fragment (PTA = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane). Dissolution of 1 in aqueous HCl leads to mer-[RuCl3(HPTA)3]Cl2 (2) which is stable in the dark but is transformed into fac-[RuCl3(HPTA)3]Cl2 (3) under visible light. Irradiation with visible light of an aqueous solution of 1 at room temperature or refluxing of the same solution in the dark leads to the formation of [{Ru(PTA)3}2(μ-Cl)3]Cl (4). The dinuclear complex 4 was also formed upon irradiation of solutions of PTA and various Ru(II)-complexes ([RuCl2(DMSO)4], [{RuCl2(η6-p-cymene)}2]) or cis-cis-trans-[RuCl2(DMSO)2(PTA)2]). All complexes were characterized by elemental analysis and NMR spectroscopy, furthermore solid state structures of 2·1.25H2O, 3·HCl·2H2O and 4·9H2O were also determined by single crystal X-ray diffraction. We have investigated the influence of the above photochemical processes on reduction of benzaldehyde and cinnamaldehyde with trans-[RuCl2(PTA)4] and cis-cis-trans-[RuCl2(DMSO)2L2] (L = PTA, (PTA-Me)CF3SO3, (PTA-Bn)Cl; Me = methyl, Bn = benzyl) complexes as catalysts. The effect of visible light on benzonitrile hydration with various Ru(II)-PTA catalysts is also reported.

The metallathiaboranes [8,8‐(dppe)‐nido‐8,7‐NiSB9H11] [1, dppe = bis(diphenylphosphanyl)ethane], [7‐Et‐8,8‐(dppe)‐nido‐8,7‐NiSB9H10] (2), [9‐Et‐8,8‐(dppe)‐nido‐8,7‐NiSB9H10] (3) and [2,2‐(dppe)‐closo‐2,1‐NiSB8H8] (4) are isolated from the reactions between Cs[arachno‐SB9H12], Li[BHEt3] and [NiCl2(dppe)] at low temperature in yields of 30, 1, 0.1 and, We acknowledge the Spanish Ministry of Science and Innovation (CTQ2012-32095, CTQ2009-10132) for the support of this work.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Nano Materials, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsanm.9b02398, Thermally partially reduced graphene oxide has been covalently modified with 3-methyl-4-phenyl-1,2,3-triazolium salts making use of the epoxy functionalities on the carbon nanomaterial. Characterization of the functionalized materials through adequate solid characterization techniques, particularly X-ray photoelectron spectroscopy (XPS), allows one to follow the stepwise building up of the triazolium fragments on the graphene oxide attached to the wall via covalent C–N linkage. The hydroxyl-triazolium-functionalized materials have been used to prepare rhodium hybrid materials containing either alkoxo or triazolylidene molecular rhodium(I) complexes depending on the protection of the hydroxyl groups present in the material. Characterization of the heterogeneous systems, especially by means of XPS and extended X-ray absorption fine structure (EXAFS) spectroscopy, has evidenced the coordination sphere of the supported rhodium(I) complexes in both rhodium hybrid materials. The graphene-oxide-supported rhodium–triazolylidene hybrid catalysts show excellent activity, comparable to that of the homogeneous [RhI(cod)(Triaz)] (Triaz = 1,4-diphenyl-3-methyl-1,2,3-triazol-5-ylidene) catalyst, for the hydrosilylation of terminal and internal alkynes. In addition, these catalysts have shown good selectivity to the β-(Z) vinylsilane isomers (for the not hindered terminal substrates) or syn-additions (for the internal substrates). In contrast to the rhodium(I)–alkoxo-based hybrid material, the silyl-protected rhodium(I)–triazolylidene-based hybrid catalyst can be reused in consecutive cycles without loss of activity maintaining the selectivity. The lack of leaching of active rhodium species demonstrates the strength of the C–N covalent bond of the triazolylidene linker to the graphitic wall., The authors express their appreciation for the financial support from MICINN/FEDER projects CTQ2016-75884-P and RTI2018-098537-B-C22, and the Regional Governments of Aragón/FEDER 2014-2020 “Building Europe from Aragón” (groups E42_17R and E12_17R) and Principado de Asturias (FEDER: IDI/2018/000121) are gratefully acknowledged. The authors also acknowledge ALBA synchrotron for granting beamtime and the collaboration of the CLAESS beamline staff.

The discovery of systems that interact with small molecules plays a vital facilitating role in the development of devices that show sensitivity to their surroundings and an ability to quickly relay chemical and physical information. Herein, we report on the reaction of [NiCl2(dppe)] with decaborane that produces in usable yield a new 11-vertex nickelaborane, [7,7-(dppe)-nido-7-NiB10H12] (1), which shows interesting reactivity and functionality toward carbon monoxide and ethylisonitrile. This contribution describes the synthesis and full structural characterization of 1 and its small-molecule EtNC and CO adducts, 2 and 3, and delineates the dynamic molecular behavior of all of these species in solution. This information sets a foundation from which more advanced work on this and related metallaborane systems can be conceived and provides a more general reference to how NMR spectroscopy, combined with DFT calculations, can be used to analyze the precise locomotion of labile ligands around a metal center held within a borane cluster, The authors gratefully acknowledge the support of the Spanish Ministerio de Ciencia, Innovación y Universidades under reference no. PGC2018-099383-B-I00. We acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza. J.B. and M.G.S.L. also acknowledge support from the Czech Science Foundation and project no. 18-20286S.

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).

The bis-imidazolium salt, 1,1-bis(N-methylimidazolium) acetate bromide, is a convenient precursor for the synthesis of zwitterionic iridium(I) [Ir(cod){(MeIm)2CHCOO}] and cationic iridium(III) [IrH(cod){(MeIm)2CHCOO}]+ compounds (MeIm = 3-methylimidazol-2-yliden-1-yl) having a carboxylate-functionalized bis(NHC) ligand. The [Ir(cod){(MeIm)2CHCOO}] compound catalyzes the hydrogenation of CO2 to formate in water using NEt3 as base, reaching turnover numbers of approximately 1500. Reactivity studies have shown that activation of the catalyst precursor involves the reaction with H2 in a multistep process that under catalytic conditions results in the formation of a dihydrido iridium(III) octahedral [IrH2(H2O){(MeIm)2CHCOO}] species stabilized by the κ3-C,C′,O coordination of the ligand. DFT studies on the mechanism were carried out to elucidate two possible roles of the base. In the first one, NEt3 neutralizes only the produced formic acid, whereas in the second it assists the proton transfer in heterolytic cleavage of the H2 molecule. Although this base-involved mechanism is more favorable in that it exhibits a lower energy span for the overall reaction, the energy barrier obtained from kinetic experiments suggests that both mechanisms could be operative under the experimental reaction conditions., Financial support from the Ministerio de Economía y Competitividad (MINECO/FEDER) of Spain (Projects CTQ2013-42532-P and CTQ2016-75884-P) and Diputación General de Aragón (DGA/FSE E07) is gratefully acknowl-edged. R. P-O. acknowledges her fellowship from MINECO (BES-2011-045364, EEBB-I-14-08939 and EEBB-I-15-10125). Additional support from the DFG (Cluster of Excellence “Tailor-made Fuels from Biomass”, which is funded by the Excellence initiative by the German Federal and State Governments to promote science and research at German universities) is gratefully acknowledged.

Dedicated to Prof. Ekkehardt Hahn on the occasion of his 65th birthday with our most sincere congratulations for his leadership and his many diverse and creative contributions to the field of Organometallic Chemistry, and best wishes., The use of protic ligands to generate metal-ligand bifunctional catalysts has proved an excellent strategy to enhance the catalytic activity in formic acid dehydrogenation. We present here synthetic routes for complexes of general formula [Ir(H)2(IPr)(PR3)(CH3CN)2]BF4 (1a-c), [Ir (8-AQ)(H)2(IPr)(PR3)]BF4 (2a-c and 3), and [Ir(IPr)(C-N)(8-AQ)H]BF4 (5a-c) (8-AQ = 8-aminoquinoline; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; C-N = 1-phenylpiridine-1H, 1-phenylpirazol-1H or 2-(p-tolyl-1H)pyridine-1H). Complexes 2a-c, 3, 5a and c were evaluated as catalysts for the dehydrogenation of formic acid in water. The nature of the phosphane in complexes 2a-c and 3 affects drastically the catalytic activity, with more basic and less encumbered phosphanes bringing about better performances. DFT calculations suggest that the coordinated NH2 moiety of the 8-AQ ligand plays a crucial role throughout the catalytic cycle. Two key steps are the protonation of the hydride ligand directed by the NH2 moiety (H2 formation), and the hydride abstraction to regenerate the dihydride active species (CO2 formation). Complexes 5a and 5c do not improve the results obtained with 2a-c and 3, probably due to the fact that a preactivation step is required. This may be attributable to an isomerization step that places the NH2, initially trans to the hydride ligand, in cis position., This work was supported by the “Ramón y Cajal” program (RYC2016-20864) (FSE/Agencia Estatal de Investigación) (M. I.); the Spanish Ministry of Science, Innovation and Universities (RTI2018-099136-A-I00); “Centro Universitario de la Defensa” (UZCUD2018-CIE-01) and the DGA (DGA/E42_17R). J

Chiral-at-metal rhodium(III) complexes of the formula [Rh(κ4C,N,N′,P-L)A(Solv)][SbF6]n (Solv = A = MeCN, n = 2 (1); Solv = H2O, A = MeCN, n = 2 (2); Solv = MeCN, A = Cl, n = 1 (3); Solv = H2O, A = Cl, n = 1 (4)) catalyze the Friedel–Crafts reaction of trans-β-nitrostyrene and N-methyl-2-methylindole. Complex 4 reacts with trans-β-nitrostyrene, affording [RhCl(κ4C,N,N′,P-L)(trans-β-nitrostyrene)]+ (5). In the presence of N-methyl-2-methylindole, complex 5 reversibly gives a mixture of aci-nitro complexes 6 in high diastereoselectivity which, in turn, evolve to the FC adducts through 1,3-prototropy mediated by a water molecule. On the basis of experimental NMR studies and DFT calculations, a detailed mechanistic pathway for the alkylation reaction is proposed, including an explanation of the origin of the measured enantiomeric ratio., We thank the Ministerio de Economía y Competitividad of Spain (Project CTQ2015-66079-P) and Gobierno de Aragón (Grupo Consolidado: Catalizadores Organometálicos Enantioselectivos) for financial support. R.R. acknowledges the Ministerio de Economía y Competitividad of Spain for a Ramón y Cajal (RYC-2013-13800) grant. M.C. acknowledges Diputación General de Aragón, CSIC, and the European Social Fund for a grant.

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).

A series of water-soluble zwitterionic complexes featuring a carboxylate bridge-functionalized bis-N-heterocyclic carbene ligand of formula [Cp MCl{(MeIm)CHCOO}] and [M(diene){(MeIm)CHCOO}] (Cp∗ = 1,2,3,4,5-pentamethylcyclopentadienyl; M = Rh, Ir; MeIm = 3-methylimidazol-2-yliden-1-yl; diene = 1,5-cyclooctadiene (cod), norbornadiene (nbd)) were prepared from the salt [(MeImH)CHCOO]Br and suitable metal precursor. The solid-state structure of both types of complexes shows a boat-shaped six-membered metallacycle derived of the κC,C′ coordination mode of the bis-NHC ligand. The uncoordinated carboxylate fragment is found at the bowsprit position in the Cp M complexes, whereas in the M(diene) complexes it is at the flagpole position of the metallacycle. The complexes [Rh(diene){(MeIm)CHCOO}] (diene = cod, nbd) exist as two conformational isomers in dichloromethane, bowsprit and flagpole, that interconvert through the boat-to-boat inversion of the metallacycle. An inversion barrier of ∼17 kcal·mol was determined by two-dimensional exchange spectroscopy NMR measurements for [Rh(cod){(MeIm)CHCOO}]. Reaction of zwitterionic Cp M complexes with methyl triflate or tetrafluoroboric acid affords the cationic complexes [Cp MCl{(MeIm)CHCOOMe}] or [Cp MCl{(MeIm)CHCOOH}] (M = Rh, Ir) featuring carboxy and methoxycarbonyl functionalized methylene-bridged bis-NHC ligands, respectively. Similarly, complexes [M(diene){(MeIm)CHCOOMe}] (M = Rh, Ir) were prepared by alkylation of the corresponding zwitterionic M(diene) complexes with methyl triflate. In contrast, reaction of [Ir(cod){(MeIm)CHCOO}] with HBF·EtO (Et = ethyl), CHOTf, CHI, or I gives cationic iridium(III) octahedral complexes [IrX(cod){(MeIm)CHCOO}] (X = H, Me, or I) featuring a tripodal coordination mode of the carboxylate bridge-functionalized bis-NHC ligand. The switch from κC,C′ to κC,C′,O coordination of the bis-NHC ligand accompanying the oxidative addition prevents the coordination of the anions eventually formed in the process that remain as counterions., Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER) under the Project CTQ2016-75884-P and the Diputación General de Aragón (DGA/FSE-E07) is gratefully acknowledged. R.P.-O. also thanks MINECO for a predoctoral fellowship (BES-2011-045364).

Chiral bis-amido phosphites L1 and L2 containing a diaminobiphenyl unit and a chiral alkoxy group derived from either (−)-menthol or 3-acetoxy deoxycholic methyl ester have been synthesised. Both L1 and L2 react with PdCl2(NCPh)2 affording di- or mononuclear derivatives with formula trans-[Pd(μ-Cl)Cl(L)]2 (1a, L = L1; 1b, L = L2) or trans-PdCl2(L)2 (2a, L = L1; 2b, L = L2) depending on the Pd : L molar ratio. The crystal structure of (M,P)-1a confirms the trans arrangement of the ligand L1 and shows an unusual puckering of the Pd2(μ-Cl)2 core (θ 46°). Both the ligands L1 and L2 and their complexes (1 and 2) are fluxional in solution as a consequence of the tropo-inversion of the diaminobiphenyl unit. For L1, L2, 1a and 2a a combined study including variable temperature 31P{1H} NMR spectroscopy and line shape analysis, Eyring plots and DFT calculations have shed light on the mechanism of the tropo-inversion., Financial support from the Ministerio de Economía y Competitividad (MINECO/FEDER) of Spain (Projects CTQ2013-42532-P and CTQ2016-75884-P), Diputación General de Aragón (DGA/FSE E07) and the University of Pisa is gratefully acknowledged. A. P. acknowledges financial support from the ERASMUS+ programme.

The reaction of [Ir(SiNP)(cod)][PF] ([1][PF]) and of IrCl(SiNP)(cod) (5) (SiNP = SiMe{N(4-CHCH)PPh}) with trimethyl phosphite affords the iridium(iii) derivatives of the formula [IrHCl(SiNP-H){P(OMe)}] (x = 0, 3; x = 1, 6) containing the κC,P,P′-coordinated SiNP-H ligand (SiNP-H = Si(CH)(CH){N(4-CHCH)PPh}). The thermally unstable pentacoordinated cation [Ir(SiNP){P(OMe)}(cod)] (2) has been detected as an intermediate of the reaction and has been fully characterised in solution. Also, the mechanism of the C-H oxidative addition has been elucidated by DFT calculations showing that the square planar iridium(i) complexes of the formula [IrCl(SiNP){P(OMe)}] (x = 0, 4; x = 1, 7) should be firstly obtained from 2 and finally should undergo the C-H oxidative addition to iridium(i) via a concerted intramolecular mechanism. The influence of the counterion of 2 on the outcome of the C-H oxidative addition reaction has also been investigated., Financial support from Spanish “Ministerio de Economía y Competitividad” (CTQ2013–42532–P), “Diputación General de Aragón” (Group E07) and University of Zaragoza (UZCUD2014–CIE–13) is gratefully acknowledged.

It has been demonstrated that the reaction of [2,2,2-(H)(PPh)-closo-2,1-RhSBH] (1) with PPh affords the boron substituted rhodathiaborane-PPh adduct, [6,6-(PPh)-9-(PPh)-arachno-6,5-RhSBH] (2). Building upon this reaction, we report herein that the 10-vertex hydridorhodathiaborane 1 reacts with the Lewis bases, PCy, py, 2-Mepy, 2-Etpy, 3-Mepy and 4-Mepy to form the rhodathiaborane-ligand adducts, [6,6-(PPh)-9-(L)-arachno-6,5-RhSBH], where L = PCy (3), 2-Mepy (4), 2-Etpy (5), py (6a), 3-Mepy (7a) or 4-Mepy (8a), and [8,9-μ-(H)-9-(PPh)-8-(L)-arachno-9,6-RhSBH], where L = py (6b), 3-Mepy (7b) or 4-Mepy (8b). The selectivity of the reactions depended on the nature of the entering Lewis bases, affording the 6,5-isomers, 2, 3, 4 and 5 as single products for PPh, PCy, 2-Mepy and 2-Etpy; and mixtures of the 6,5-/9,6-regioisomers, 6a/6b, 7a/7b and 8a/8b for py, 3-Mepy and 4-Mepy, respectively. The molecular structures of both regioisomers were characterized by X-ray diffraction analysis for the 6,5-isomers, 3 and 4, and for the 9,6-isomers, 7b and 8b. Variable temperature NMR studies of the reaction between 1 and PPh or 2-Mepy demonstrated that at low temperatures there is formation of the 9,6-species that subsequently isomerizes to the 6,5-regioisomer, indicating that for the more sterically hindered Lewis bases, PPh, 2-Mepy and PCy, the latter isomer is more stable and accessible through an intramolecular {Rh(PPh)} vertex flip. The formation of both isomers with py, 3-Mepy and 4-Mepy indicates that the kinetic and thermodynamic energies of the 6,5 and 9,6 rhodathiaborane-ligand adducts are similar for these Lewis bases. Lewis base bonding to exo-polyhedral boron vertices results in a change of the metal coordination from pseudo-octahedral Rh(iii) in 1 to pseudo-square planar Rh(i) in the adducts. The chemistry described here highlights the remarkable structural flexibility of these polyhedral boron-containing compounds, their modular architecture and their easy postsynthetic modification., We acknowledge the Spanish Ministry of Science and Innovation (CTQ2012-32095, CTQ2009-10132, CONSOLIDER INGENIO, CSD2009-00050, MULTICAT and CSD2006-0015, Crystallization Factory) for support of this work. S. L. thanks the Spanish Ministry of Science and Innovation for a predoctoral scholarship.

Acetonitrile suspensions of the dichlorido complexes [MCl

Acetonitrile suspensions of the dichlorido complexes [MCl2(κ4C,N,N′,P−L)] [M=Rh (1), Ir (2)] react with AgSbF6 in a 1:2 molar ratio affording the bis‐acetonitrile complexes [M(κ4C,N,N′,P−L)(NCMe)2][SbF6]2 (3 and 4). The reaction takes place in a sequential manner and the intermediates can be isolated varying the M:Ag molar ratio. In a 2:1 molar ratio, it affords the dimetallic monochlorido‐bridged compounds [{MCl(κ4C,N,N′,P−L)}2(μ‐Cl)][SbF6] (5 and 6). In a 1:1 molar ratio, the monosubstituted solvato‐complexes [MCl(κ4C,N,N′,P−L)(Solv)][SbF6] (Solv=H2O, MeCN, 7–10) were obtained. Finally, in a 2:3 molar ratio, it gives complexes 11 and 12 of formula [{M(κ4C,N,N′,P−L)(NCMe)(μ‐Cl)}2Ag][SbF6]3 in which a silver cation joints two cationic monosubstituted acetonitrile‐complexes [MCl(κ4C,N,N′,P−L)(NCMe)]+ through the remaining chlorido ligands and two Ag⋅⋅⋅C interactions with one of the phenyl rings of each PPh2 group. In all the complexes, the aminic nitrogen and the central metal atom are stereogenic centers. In the trimetallic complexes 11 and 12, the silver atom is also a stereogenic center. The formation of the cation of the dimetallic complexes 5 and 6, as well as that of the trimetallic complexes 11 and 12, takes place with chiral molecular self‐recognition. Experimental data and DFT calculations provide plausible explanations for the observed molecular recognition. The new complexes have been characterized by analytical, spectroscopic means and by X‐ray diffraction methods., We thank the Ministerio de Economía y Competitividad of Spain (CTQ2015‐66079‐P) and Gobierno de Aragón (Grupo Consolidado E‐63: Catalizadores Organometálicos Enantioselectivos) for financial support. M.C. acknowledges Diputación General de Aragón, CSIC and European Social Fund for a grant. R.R. acknowledges the Ministerio de Economía y Competitividad of Spain for a Ramón y Cajal (RYC‐2013‐13800) grant. P.G.‐O. acknowledges CSIC, European Social Fund and Ministerio de Economía y Competitividad of Spain for a PTA contract. V.P. thanks the resources of the supercomputer “Memento” and the technical expertise and assistance provided by the Institute for Biocomputation and Physics of Complex Systems (BIFI), Universidad de Zaragoza. We acknowledge Universidad de Zaragoza‐Centro Universitario de la Defensa for financial support (UZCUD 20/6‐CIE‐05).

Chiral binaphthyl diamidophosphites derived from deoxycholic acid were synthesized and used as ligands for the preparation of mononuclear Pd(II) complexes, which were employed as catalysts in the asymmetric Suzuki-Miyaura cross-coupling of arylboronic acids with aryl bromides. Among the different reaction parameters, the substrate concentration emerged as being crucial for the outcome of the reaction: the reaction was faster in a concentrated reaction mixture, and could be performed at 0 °C, where the reaction promoted by the Pd-complexes was more enantioselective affording cross-coupling products with ee up to 70%., This work was supported by University of Pisa. Financial support from the Ministerio de Economía y Competitividad (MINECO/FEDER) of Spain (Projects CTQ2013-42532-P and CTQ2016-75884-P) and Diputación General de Aragón (DGA/FSE E07) is gratefully acknowledged.

Ligands LH1–LH3 have been prepared by two successive condensation/reduction steps. These ligands react with MCl3 (M = Rh, Ir) rendering the trichlorido complexes [MCl3(κ3N,N’,P-LH)] (M = Rh, LH = LH1 (1), LH2 (2), LH3 (3); M = Ir, LH = LH1, (4)) as racemic mixtures of fac and mer isomers. Only one of the two possible fac isomers was detected. The mer isomer of the rhodium compounds 1–3 quantitatively isomerizes to the more stable fac isomer, whereas the mer isomer of the iridium complex 4 does not. DFT calculations indicate a dissociative pathway for this isomerization. In the presence of acetate or trifluoroacetate, complexes 1–3 or 4, respectively, undergo cyclometallation of their free benzylic arm affording the corresponding dichlorido compounds [MCl2(κ4C,N,N’,P-L)] (M = Rh, L = L1 (5), L2 (6), L3 (7); M = Ir, L = L1 (8)). Only one of the three possible enantiomeric pairs of coordination isomers was detected. The configuration at the stereogenic centres, namely the metal and the iminic nitrogen atom is stereospecifically predetermined. DFT calculations reveal that the cyclometallation follows an acetateassisted mechanism and indicate that the isolated isomers are the most stable. Complexes 1–8 have been characterized by analytical and spectroscopic means and by the determination of the crystal structures of the complexes 1, 3 and 5–8 by X-ray diffractometry., We thank the Ministerio de Economía y Competitividad of Spain (CTQ2015-66079-P) and Gobierno de Aragón (Grupo Consolidado E-63: Catalizadores Organometálicos Enantioselectivos) for financial support. M. C. acknowledges Diputación General de Aragón, CSIC and European Social Fund for a grant. R. R. acknowledges the Ministerio de Economía y Competitividad of Spain for a Ramón y Cajal (RYC-2013-13800) grant. P. G.-O. acknowledges CSIC, European Social Fund and Ministerio de Economía y Competitividad of Spain for a PTA contract.

This article is part of the themed collection: Celebrating our 2018 prize and award winners., A well-defined NHC-Ir(iii) catalyst, [Ir(H)(IPr)(py)][BF] (IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene), that provides access to a wide range of aryl- and heteroaryl-silanes by intermolecular dehydrogenative C-H bond silylation has been prepared and fully characterized. The directed and non-directed functionalisation of C-H bonds has been accomplished successfully using an arene as the limiting reagent and a variety of hydrosilanes in excess, including EtSiH, PhMeSiH, PhMeSiH, PhSiH and (EtO)SiH. Examples that show unexpected selectivity patterns that stem from the presence of aromatic substituents in hydrosilanes are also presented. The selective bisarylation of bis(hydrosilane)s by directed or non-directed silylation of C-H bonds is also reported herein. Theoretical calculations at the DFT level shed light on the intermediate species in the catalytic cycle and the role played by the ligand system on the Ir(iii)/Ir(i) mechanism., This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER) (CONSOLIDER INGENIO CSD-2009-00050, CTQ-2015-67366-P and CTQ-2013-42532-P projects) and the DGA/FSE-E07. The support from the KFUPM-University of Zaragoza research agreement and the Centre of Research Excellence in Petroleum Refining & KFUPM is gratefully acknowledged. V. P. thankfully acknowledges the resources from the supercomputer “Memento”, technical expertise and assistance provided by BIFI-ZCAM (Universidad de Zaragoza). L. R. -P. thanks CONACyT for a postdoctoral fellowship (204033). J. M. acknowledges financial support from the Ministry of Education Culture and Sports (FPU14/06003).

A relatively small number of freshwater dinoflagellates are involved in symbiotic association with cryptophytes. The chloroplasts of the cryptophytes are retained by the dinoflagellate and give it the characteristic phycobilin pigmentation, either phycoerythrin or phycocyanin. The pigment characterization of the retained chloroplasts can give precise and accurate information about the type of cryptophyte preyed upon by the dinoflagellate. For this purpose, we performed microspectrophotometric evaluation of the pigments of Gymnodinium acidotum Nygaard and three different cryptophytes present in samples collected from a tributary of the river Arno, in Tuscany (Italy). The comparison of the different spectroscopic data allowed us to discriminate effectively among the cryptophytes preyed upon by the dinoflagellate.

The coordination abilities of the novel N,N'-diphosphino-silanediamine ligand of formula SiMe(2)(NtolPPh(2))(2) (SiNP, 1) have been investigated toward rhodium, and the derivatives [RhCl(SiNP)](2) (2), [Rh(SiNP)(COD)][BF(4)] (3), and Rh(acac)(SiNP) (4) have been synthesized. The stability of the dinuclear frame of [RhCl(SiNP)](2) (2) toward incoming nucleophiles has been shown to be dependent on their π-acceptor ability. Indeed, the mononuclear complexes RhCl(SiNP)(L) (L = CO, 5; CN(t)Bu, 6) have been isolated purely and quantitatively upon reaction of 2 with CO and CN(t)Bu, respectively. Otherwise, PPh(3) and RhCl(SiNP) equilibrate with Rh(Cl)(SiNP)(PPh(3)) (7). Carbon electrophiles such as MeI and 3-chloro-1-proprene afforded the oxidation of rhodium(I) to rhodium(III) and the formation of RhCl(2)(η(3)-C(3)H(5))(SiNP) (8) and Rh(Me)(I)(SiNP)(acac) (10), respectively. The methyl derivative 10 is thermally stable and does not react either with CO or with CN(t)Bu even in excess. Otherwise, RhCl(2)(η(3)-C(3)H(5))(SiNP) (8) is thermally stable but reacts with CO, affording 3-chloro-1-proprene and RhCl(SiNP)(CO) (5). Finally, upon reaction of Rh(acac)(SiNP) (4) and 3-chloro-1-proprene, RhCl(acac)(η(1)-C(3)H(5))(SiNP) (9a) and [Rh(acac)(η(3)-C(3)H(5))(SiNP)]Cl (9b) could be detected at 233 K. At higher temperatures, 9a and 9b smoothly decompose, affording the dinuclear derivative [RhCl(SiNP)](2) (2) and the CC coupling product 3-allylpentane-2,4-dione.

The synthesis of the new 4-(4-acetyl-5- substituted -4, 5-dihydro-1,3,4-oxodiazol-2-yl)methoxy)-2H-chromen-2-ones derivatives 5 was accomplished by the use of 4-hydroxycoumarine as a starting material. The structures of the compounds were confirmed by analytical UV, IR, 1H, 13C-NMR, NOESY and HMBC NMR spectra to elucidate the different positions of protons and carbons. All the compounds exhibited one quasireversible redox process. The UV absorption spectra of the obtained compounds showed strong absorption bands between 264 and 291 nm assigned to π-π * transitions of the oxadiazole group. All the newly synthesized compounds were screened for their antibacterial and antioxidant activities. Antimicrobial studies revealed that compounds 5a and 5b showed significant antibacterial activity against Escherichia coli and Pseudomonas Aeruginosa 27853. Furthermore these compounds showed antioxidant activities of different extents with respect to individual compounds as well as to the antioxidant methods. The compounds 5a-d was found to be the most active antioxidant in the series then Trolox, which makes the investigated complexes promising a new class of antibacterial compounds.

A relatively small number of freshwater dinoflagellates are involved in symbiotic association with cryptophytes. The chloroplasts of the cryptophytes are retained by the dinoflagellate and give it the characteristic phycobilin pigmentation, either phycoerythrin or phycocyanin. The pigment characterization of the retained chloroplasts can give precise and accurate information about the type of cryptophyte preyed upon by the dinoflagellate. For this purpose, we performed microspectrophotometric evaluation of the pigments of Gymnodinium acidotum Nygaard and three different cryptophytes present in samples collected from a tributary of the river Arno, in Tuscany (Italy). The comparison of the different spectroscopic data allowed us to discriminate effectively among the cryptophytes preyed upon by the dinoflagellate.

The preparation of a number of new 9-substituted octafluorofluorene derivatives, solution NMR studies, and the first examples of solid state structures of octafluorofluorenes [1,2,3,4,5,6,7,8-octafluorofluorene, C13H2F8, 1; 1,2,3,4,5,6,7,8-octafluoro-9-(pentafluoro)phenylfluorene, C19HF13, 8; 1,1′,2,2′,3,3′,4,4′,5,5′,6,6′,7,7′,8,8′-hexadecafluoro-9,9′-bifluorenyl, C26H2F16, 11] are reported. Variable temperature 19F NMR investigations have been performed on the 9-aryl substituted compounds 1,2,3,4,5,6,7,8-octafluoro-9-(pentafluoro)phenyl-9-hydroxyfluorene, C19HF13O, 4, 1,2,3,4,5,6,7,8-octafluoro-9-(nonafluoro-4′-biphenylyl)-9-hydroxyfluorene, C25HF17O, 5, and 8, and the energetic barriers to rotation of the aryl have been determined. A lower rotational barrier is observed for compound 4 with respect to compound 8, while 5 does not show fluxional behaviour below 338 K. The results of the variable temperature experiments performed on 8 have been rationalized by 2D NMR studies, and compared to the solid state data resulting from the X-ray structural analysis.

Euglena gracilis possesses a simple but sophisticated light detecting system, consisting of an eyespot formed by carotenoids globules and a photoreceptor. The photoreceptor of Euglena is characterized by optical bistability, with two stable states. In order to provide important and discriminating information on the series of structural changes that Euglena photoreceptive protein(s) undergoes inside the photoreceptor in response to light, we measured the in vivo absorption spectra of the two stable states A and B of photoreceptor photocycle. Data were collected using two different devices, i.e. a microspectrophotometer and a digital microscope. Our results show that the photocycle and the absorption spectra of the photoreceptor possess strong spectroscopic similarities with a rhodopsin-like protein. Moreover, the analysis of the absorption spectra of the two stable states of the photoreceptor and the absorption spectrum of the eyespot suggests an intriguing hypothesis for the orientation of microalgae toward light.