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New titanocene pyridinethiolate compounds [(RCp)2Ti(4-Spy)2] (R = H (1), Me (2); Cp = cyclopentadienyl; 4-Spy = pyridine-4-thiolate) and [Cp2Ti(2-Spy)2] (3; 2-Spy = pyridine-2-thiolate) have been prepared by reaction of the corresponding Li(Spy) salt with the appropriate compound [(RCp)2TiCl2]. Compounds 1 and 2 have been used as metalloligands in self-assembly reactions with the acceptor late-transition-metal compounds [M(H2O)2(dppp)](OTf)2 (M = Pd (a) Pt (b); dppp = 1,3-bis(diphenylphosphino)propane), and the series of early-late tetranuclear metallamacrocycles [{(RCp)2Ti(4-Spy)2}{M(dppp)}]2(OTf)4 (R = H, M = Pd (12a2); R = H, M = Pt (12b2); R = Me, M = Pd (22a2); R = Me, M = Pt (22b2)) arising from the anti isomer of the titanocene metalloligands have been obtained. Only ligand transfer reactions from Ti to either Pd or Pt atoms have been observed when the pyridine-2-thiolate derivative 3 has been assayed in self-assembly processes. The obtained species have been characterized by NMR spectroscopy and ESI(+) mass spectrometry. The supramolecular assemblies have shown to be nonrigid in solution, and their fluxional behavior has been studied by VT 1H NMR spectroscopy. A DFT study including ab initio molecular dynamics in order to elucidate the structures and the relative stability of the isomers has been performed. [ABSTRACT FROM AUTHOR]

A proper design of heterogeneous molecular catalysts supported on carbon materials requires a systematic study of “metal–carbon support interactions” and their influence on catalytic activity. In this study, hybrid materials containing covalently anchored iridium N-heterocyclic carbene (NHC) organometallic complexes have been successfully prepared from oxidized and partially reduced carbon nanotubes (CNTs). The preparation method for these supported materials relies on the selective functionalization of the superficial hydroxylic groups using the imidazolium salt, 1-(3-hydroxypropyl)-3-methyl-1 H -imidazol-3-ium chloride. The hydrogen transfer catalysis activity of these nanotube-based hybrid catalysts was tested by the reduction of cyclohexanone to cyclohexanol with 2-propanol, and the results of the tests were compared with those obtained using similar hybrid graphene-based catalysts. While EXAFS analysis revealed a common first coordination shell of the iridium atom for all the hybrid materials examined, independently of whether they were either supported on carbon nanotubes or graphene materials, catalytic activity in all the reduced materials was significantly superior. Moreover, catalytic systems based on reduced CNTs exhibited a better performance than those based on reduced graphene materials. Both these facts suggest there is a positive correlation between hydrogen transfer catalytic activity, reconstruction of the aromatic carbon structure and the smaller amount of oxygen functional groups. [ABSTRACT FROM AUTHOR]

The effect of the structural properties of graphene materials on the local structure of –OH anchored Ir(I)–NHC complexes is herein investigated. For that, two partially reduced graphene oxides exhibiting different sheet properties due to an adequate selection of the crystalline characteristics of their parent graphite were used. The main differences among them were the size of Csp2 domains within their graphenic layers and the distribution of functional groups at the basal planes and edges. Anchoring of N-methylimidazolium moieties through the graphene –OH functional groups and subsequent formation of the Ir(I)–NHC complexes resulted in graphene-based hybrid materials. The structural differences of the support have an influence in the interaction of the supported iridium compounds with the graphene sheet. The oxygenated functional groups in the material with a smaller graphene sheet are closer leaving larger Csp2 domains in the graphene layer, favoring their interaction with the supported iridium atoms therefore displacing the chlorido ligand from the first coordination shell. In contrast, the hybrid material in which the distribution of the oxygenated functional groups within the basal planes of the graphenic layer is more homogeneous shows partial chlorido displacement. This fact has an influence on the electrocatalytic performance of the iridium-based hybrid materials as water oxidation catalysts (WOCs), exhibiting improved catalytic activity the catalyst having coordinated chlorido ligands. Image 1 • Hybrid materials comprised of graphene modified with Ir-NHC complexes are suitable electrocatalysts for water oxidation. • EXAFS analysis evidences that the parent graphite influences the iridium local structure in the hybrid materials. • The iridium local structure determines the electrocatalytic behavior in water oxidation. [ABSTRACT FROM AUTHOR]

The iridium(I)-aminophosphane complex [Ir{κ 3 C , P , P '-(SiNP-H)}(cod)] has been prepared by reaction of [IrCl(cod)(SiNP)] with KCH 3 COO. DFT calculations show that this reaction takes place through an unexpected outer sphere mechanism (SiNP = SiMe 2 {N(4-C 6 H 4 Me)PPh 2 } 2 ; SiNP-H = CH 2 SiMe{N(4-C 6 H 4 Me)PPh 2 } 2 ). The reaction of [IrCl(cod)(SiNP)] or [Ir{κ 3 C , P , P '-(SiNP-H)}(cod)] with diverse oxidants has been explored, yielding a range of iridium(III) derivatives. On one hand, [IrCl(cod)(SiNP)] reacts with allyl chloride rendering the octahedral iridium(III) derivative [IrCl 2 (η 3 -C 3 H 5 )(SiNP)], which, in turn, reacts with tert -butyl isocyanide yielding the substitution product [IrCl(η 3 -C 3 H 5 )(CN t Bu)(SiNP)]Cl via the observed intermediate [IrCl 2 (η 1 -C 3 H 5 )(CN t Bu)(SiNP)]. On the other hand, the reaction of [Ir{κ 3 C , P , P '-(SiNP-H)}(cod)] with [FeCp 2 ]X (X = PF 6 , CF 3 SO 3 ), I 2 or CF 3 SO 3 CH 3 results in the metal-centered two-electron oxidation rendering a varied assortment of iridium(III) compounds. [Ir{κ 3 C , P , P '-(SiNP-H)}(cod)] reacts with [FeCp 2 ] + (1 : 2) in acetonitrile affording [Ir{κ 3 C , P , P '-(SiNP-H)}(CH 3 CN) 3 ] 2+ isolated as both the triflato and the hexafluorophosphato derivatives. Also, the reaction of [Ir{κ 3 C , P , P '-(SiNP-H)}(cod)] with I 2 (1 : 1) yields a mixture of iridium(III) derivatives, namely the mononuclear compound [IrI(κ 2 P , P '-SiNP)(η 2 ,η 3 -C 8 H 11 )]I, containing the η 2 ,η 3 -cycloocta-2,6-dien-1-yl ligand, and two isomers of the dinuclear derivative [Ir 2 {κ 3 C , P , P '-(SiNP-H)} 2 (μ-I) 3 ]I, the first species being isolated in low yield. DFT calculations indicate that [IrI(κ 2 P , P '-SiNP)(η 2 ,η 3 -C 8 H 11 )]I forms as the result of a bielectronic oxidation of iridium(I) followed by the deprotonation of the cod ligand by iodide and the protonation of the methylene moiety of the [Ir{κ 3 C , P , P '-(SiNP-H)}] platform by the newly formed HI. Finally, the oxidation of [Ir{κ 3 C , P , P '-(SiNP-H)}(cod)] by methyl triflate proceeds via a hydride abstraction from the cod ligand, with the elimination of methane and the formation of the η 2 ,η 3 -cycloocta-2,6-dien-1-yl ligand with the concomitant two-electron oxidation of the iridium centre. The crystal structures of selected compounds have been determined.

Monodentate aminophosphanes HNP [NH(4-tolyl)PPh 2 ] and SiMe 3 NP [SiMe 3 N(4-tolyl)PPh 2 ] react with [Ir(μ-Cl)(cod)] 2 affording tetra- or pentacoordinate complexes of formula [IrCl(L) n (cod)] (L = HNP, n = 1, 2; L = SiMe 3 NP, n = 1). The reaction of [IrCl(SiMe 3 NP)(cod)] with carbon monoxide smoothly renders [Ir(CO) 3 (SiMe 3 NP) 2 ][IrCl 2 (CO) 2 ]. The reaction of HNP or SiMe 3 NP with [Ir(CH 3 CN) 2 (cod)][PF 6 ] yields the cyclometalated iridium(III)-hydride derivatives [IrH{κ 2 C , P -NR(4-C 6 H 3 CH 3 )PPh 2 }(cod)(CH 3 CN)][PF 6 ] (R = H, SiMe 3 ) as a result of the intramolecular oxidative addition of the tolyl C 2 -H bond to iridium. The straighforward formation of [IrH{κ 2 C , P -SiMe 3 N(4-C 6 H 3 CH 3 )PPh 2 }(cod)(CH 3 CN)] + 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{κ 2 C , P -NH(4-C 6 H 3 CH 3 )PPh 2 }(cod)(CH 3 CN)] + , including the formation of [IrH{κ 2 C , P -NH(4-C 6 H 3 CH 3 )PPh 2 }(HNP)(cod)] + and [Ir(cod)(HNP) 2 ] + . The "mixed" complex [IrH{κ 2 C , P -SiMe 3 N(4-C 6 H 3 CH 3 )PPh 2 }(HNP)(cod)] + was obtained upon reaction of [IrH{κ 2 C , P -NH(4-C 6 H 3 CH 3 )PPh 2 }(cod)(CH 3 CN)][PF 6 ] with SiMe 3 NP at 233 K. Finally, the reaction of [Ir(CH 3 CN) 2 (coe) 2 ][PF 6 ] with SiMe 3 NP or HNP resulted in the formation of [Ir(CH 3 CN) 2 (SiMe 3 NP) 2 ][PF 6 ] and [IrH{κ 2 C , P -NH(4-C 6 H 3 CH 3 )PPh 2 }(HNP) 2 (CH 3 CN)][PF 6 ], respectively. Both the OC -6-35 and the OC -6-52 isomers of [IrH{κ 2 C , P -NH(4-C 6 H 3 CH 3 )PPh 2 }(HNP) 2 (CH 3 CN)] + - 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 TOF 1 min of about 2300 h -1 (5 mol% catalyst, 50 mol% sodium formate, DMF, 80 °C).

Copper(I) [Cu 2 (μ-Br) 2 ( t BuImCH 2 pyCH 2 L)] n (L = OMe, NEt 2 , NH t Bu) 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 Ag 2 O. An X-ray diffraction analysis has revealed that [Cu 2 (μ-Br) 2 ( t BuImCH 2 pyCH 2 NEt 2 )] n is a linear coordination polymer formed by bimetallic [Cu(μ-Br)] 2 units linked by the lutidine-based NHC-py-NEt 2 ligand, which acts as a heteroditopic ligand with a 1κ C -2κ 2 N,N' coordination mode. We propose that the polymeric compounds break down in the solution into more compact tetranuclear [Cu 2 (μ-Br) 2 ( t BuImCH 2 pyCH 2 L)] 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, [Cu 2 (μ-Br) 2 ( t BuImCH 2 pyCH 2 NEt 2 )] 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- t BuImCH 2 pyCH 2 NEt 2 )], 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., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

The iridium(III) hydride compound [IrH{κ 3 C , P , P '-(SiNP-H)}(CN t Bu) 2 ][PF 6 ] (1PF 6 ) was obtained by reaction of [Ir(SiNP)(cod)][PF 6 ] with CN t Bu as the result of the intramolecular oxidative addition of the SiCH 2 -H bond to iridium(I) [SiNP = Si(CH 3 ) 2 {N(4-tolyl)PPh 2 } 2 , SiNP-H = CH 2 Si(CH 3 ){N(4-tolyl)PPh 2 } 2 ]. The mechanism of the reaction was investigated by NMR spectroscopy and DFT calculations showing that the pentacoordinated intermediate [Ir(SiNP)(cod)(CN t Bu)][PF 6 ] (2PF 6 ) forms in the first place and that further reacts with CN t Bu, affording the square planar intermediate [Ir(SiNP)(CN t Bu) 2 ][PF 6 ] (3PF 6 ) that finally undergoes the intramolecular oxidative addition of the SiCH 2 -H bond. The reactivity of 1PF 6 was investigated. On one hand, the reaction of 1PF 6 with N -chlorosuccinimide or N -bromosuccinimide provides the haloderivatives [IrX{κ 3 C , P , P '-(SiNP-H)}(CN t Bu) 2 ][PF 6 ] (X = Cl, 4PF 6 ; Br, 5PF 6 ), and the reaction of 5PF 6 with AgPF 6 in the presence of acetonitrile affords the solvato species [Ir{κ 3 C , P , P '-(SiNP-H)}(CH 3 CN)(CN t Bu) 2 ] 2+ (6 2+ ) isolated as the hexafluorophosphate salt. On the other hand, the reaction of 1PF 6 with HBF 4 gives the iridium(III) compound [IrH(CH 2 SiF 2 CH 3 )(HNP) 2 (CN t Bu) 2 ][BF 4 ] (7BF 4 ) as the result of the formal addition of hydrogen fluoride to the Si-N bonds of 1 + [HNP = HN(4-tolyl)PPh 2 ]. A similar outcome was observed in the reaction of 1PF 6 with CF 3 COOH rendering 7PO 2 F 2 . In this case the intermediate [IrH{κ 2 C , P -CH 2 SiMeFN(4-tolyl)PPh 2 }(HNP)(CN t Bu) 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, 1PF 6 , 4PF 6 and 7BF 4 have been determined by X-ray diffraction measurements.

This frontiers article highlights recent developments on the application of transition metal-based zwitterionic complexes in catalysis. Recent applications of selected zwitterionic catalysts in polymerization reactions, including the carbonylative polymerization of cyclic ethers, carbon-carbon coupling reactions, the asymmetric hydrogenation of unfunctionalized olefins, and the hydrofunctionalization of alkenes are reviewed. In addition, advances in the field of hydrogenation/dehydrogenation reactions related to energy applications, including the hydrogenation of CO 2 and the dehydrogenation of formic acid and N-heterocycles, the functionalization of CO 2 with amines and hydrosilanes, and the valorization of polyfunctional bio-based feedstocks, such as the dehygrogenation of glycerol to lactic acid or the reduction of levulinic acid into γ-valerolactone, are also described.

Reaction of [Ir(μ-Cl)(COE)2]2 (COE = cis-cyclooctene) with tris(3,5-dimethylpyrazol-1-yl)methane (MeTpm) affords [IrCl(κ1-N-MeTpm)(COD)] (1) (COD = 1,5-cyclooctadiene). The formation of 1 implies the transfer dehydrogenation of a COE ligand to give COD and COA (cyclooctane). A mechanistic proposal based on DFT calculations that explains this iridium promoted process has been disclosed. Additionally, reactivity studies have allowed the preparation and characterization, including determination of the molecular structures of a number of iridium complexes with the MeTpm ligand in κ1, κ2 or κ3-N coordination modes. Moreover, the first example of an Ir-cyclooctyl complex featuring hydride and carbonyl ligands, whose solid state structure has been determined by X-ray diffraction methods, is reported.

A series of water-soluble zwitterionic complexes featuring a carboxylate bridge-functionalized bis-N-heterocyclic carbene ligand of formula [Cp*M III Cl{(MeIm) 2 CHCOO}] and [M I (diene){(MeIm) 2 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) 2 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 κ 2 C,C' coordination mode of the bis-NHC ligand. The uncoordinated carboxylate fragment is found at the bowsprit position in the Cp*M III complexes, whereas in the M I (diene) complexes it is at the flagpole position of the metallacycle. The complexes [Rh I (diene){(MeIm) 2 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 -1 was determined by two-dimensional exchange spectroscopy NMR measurements for [Rh I (cod){(MeIm) 2 CHCOO}]. Reaction of zwitterionic Cp*M III complexes with methyl triflate or tetrafluoroboric acid affords the cationic complexes [Cp*M III Cl{(MeIm) 2 CHCOOMe}] + or [Cp*M III Cl{(MeIm) 2 CHCOOH}] + (M = Rh, Ir) featuring carboxy and methoxycarbonyl functionalized methylene-bridged bis-NHC ligands, respectively. Similarly, complexes [M I (diene){(MeIm) 2 CHCOOMe}] + (M = Rh, Ir) were prepared by alkylation of the corresponding zwitterionic M I (diene) complexes with methyl triflate. In contrast, reaction of [Ir I (cod){(MeIm) 2 CHCOO}] with HBF 4 ·Et 2 O (Et = ethyl), CH 3 OTf, CH 3 I, or I 2 gives cationic iridium(III) octahedral complexes [Ir III X(cod){(MeIm) 2 CHCOO}] + (X = H, Me, or I) featuring a tripodal coordination mode of the carboxylate bridge-functionalized bis-NHC ligand. The switch from κ 2 C,C' to κ 3 C,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.

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 PdCl 2 (NCPh) 2 affording di- or mononuclear derivatives with formula trans-[Pd(μ-Cl)Cl(L)] 2 (1a, L = L1; 1b, L = L2) or trans-PdCl 2 (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 Pd 2 (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 31 P{ 1 H} NMR spectroscopy and line shape analysis, Eyring plots and DFT calculations have shed light on the mechanism of the tropo-inversion.

A well-defined NHC-Ir(iii) catalyst, [Ir(H) 2 (IPr)(py) 3 ][BF 4 ] (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 Et 3 SiH, Ph 2 MeSiH, PhMe 2 SiH, Ph 3 SiH and (EtO) 3 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.

The synthesis of a wide variety of carbamates from amines, alcohols and carbon monoxide has been achieved by means of a Rh-catalysed oxidative carbonylation reaction that uses Oxone as a stoichiometric oxidant. In-depth studies on the reaction mechanism shed light on the intimate role of Oxone in the catalytic cycle.

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.

Pentacoordinated iridium(i) complexes of formula IrCl(SiNP)(tfbb) (1) and IrCl(HNP)2(tfbb) (2) (SiNP = SiMe2{N(4-C6H4CH3)PPh2}2; HNP = NH(4-C6H4CH3)PPh2) have been prepared and fully characterised. Both feature a distorted square pyramidal coordination polyhedron at the metal centre in the solid state and are fluxional in solution. Their reaction with trimethyl phosphite yields the derivatives [Ir(SiNP){P(OMe)3}(tfbb)]Cl ([3]Cl) and Ir{PO(OMe)2}(HNP)2(tfbb) (4). The course of the reaction between IrCl(HNP)2(tfbb) (2) and trimethyl phosphite was elucidated by NMR spectroscopy and DFT calculations, showing that the intermediate [Ir(HNP)2{P(OMe)3}(tfbb)](+) ((5+)) forms and further reacts with the chloride anion yielding the phosphonato derivative 4 and methyl chloride. The decisive role of the N-H group in the formation of the phosphonato ligand has been established by IR and NMR spectroscopic measurements and by DFT calculations.

The β-Z selectivity in the hydrosilylation of terminal alkynes has been hitherto explained by introduction of isomerisation steps in classical mechanisms. DFT calculations and experimental observations on the system [M(I)2{κ-C,C,O,O-(bis-NHC)}]BF4 (M=Ir (3a), Rh (3b); bis-NHC=methylenebis(N-2-methoxyethyl)imidazole-2-ylidene) support a new mechanism, alternative to classical postulations, based on an outer-sphere model. Heterolytic splitting of the silane molecule by the metal centre and acetone (solvent) affords a metal hydride and the oxocarbenium ion [R3Si-O(CH3)2](+), which reacts with the corresponding alkyne in solution to give the silylation product [R3Si-CH=C-R](+). Thus, acetone acts as a silane shuttle by transferring the silyl moiety from the silane to the alkyne. Finally, nucleophilic attack of the hydrido ligand over [R3Si-CH=C-R](+) affords selectively the β-(Z)-vinylsilane. The β-Z selectivity is explained on the grounds of the steric interaction between the silyl moiety and the ligand system resulting from the geometry of the approach that leads to β-(E)-vinylsilanes., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A general regioselective rhodium-catalyzed head-to-tail dimerization of terminal alkynes is presented. The presence of a pyridine ligand (py) in a Rh-N-heterocyclic-carbene (NHC) catalytic system not only dramatically switches the chemoselectivity from alkyne cyclotrimerization to dimerization but also enhances the catalytic activity. Several intermediates have been detected in the catalytic process, including the π-alkyne-coordinated Rh(I) species [RhCl(NHC)(η(2)-HC≡CCH2Ph)(py)] (3) and [RhCl(NHC){η(2)-C(tBu)≡C(E)CH=CHtBu}(py)] (4) and the Rh(III)-hydride-alkynyl species [RhClH{-C≡CSi(Me)3}(IPr)(py)2] (5). Computational DFT studies reveal an operational mechanism consisting of sequential alkyne C-H oxidative addition, alkyne insertion, and reductive elimination. A 2,1-hydrometalation of the alkyne is the more favorable pathway in accordance with a head-to-tail selectivity., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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.)

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., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Unsaturated σ,π-cyclooctenyl and hydrido Ir(III) complexes bearing an unusual tridentate dianionic ONO pincer-type ligand have been straightforwardly obtained from 2,6-pyridinedicarboxylic acid and standard Ir(I) starting materials. These complexes efficiently catalyzed the arene C-H borylation under thermal conditions., (This journal is © The Royal Society of Chemistry 2011)

The treatment of [{Rh(μ-SH){P(OPh)(3)}(2)}(2)] with [{M(μ-Cl)(diolef)}(2)] (diolef=diolefin) in the presence of NEt(3) affords the hydrido-sulfido clusters [Rh(3)(μ-H)(μ(3)-S)(2)(diolef){P(OPh)(3)}(4)] (diolef=1,5-cyclooctadiene (cod) for 1, 2,5-norbornadiene (nbd) for 2, and tetrafluorobenzo[5,6]bicyclo[2.2.2]octa-2,5,7-triene (tfb) for 3) and [Rh(2)Ir(μ-H)(μ(3)-S)(2)(cod){P(OPh)(3)}(4)] (4). Cluster 1 can be also obtained by treating [{Rh(μ-SH){P(OPh)(3)}(2)}(2)] with [{Rh(μ-OMe)(cod)}(2)], although the main product of the reaction with [{Ir(μ-OMe)(cod)}(2)] was [RhIr(2)(μ-H)(μ(3)-S)(2)(cod)(2){P(OPh)(3)}(2)] (5). The molecular structures of clusters 1 and 4 have been determined by X-ray diffraction methods. The deprotonation of a hydrosulfido ligand in [{Rh(μ-SH)(CO)(PPh(3))}(2)] by [M(acac)(diolef)] (acac=acetylacetonate) results in the formation of hydrido-sulfido clusters [Rh(3)(μ-H)(μ(3)-S)(2)(CO)(2) (diolef)(PPh(3))(2)] (diolef=cod for 6, nbd for 7) and [Rh(2)Ir(μ-H)(μ(3)-S)(2)(CO)(2)(cod)(PPh(3))(2)] (8). Clusters 1-3 and 5 exist in solution as two interconverting isomers with the bridging hydride ligand at different edges. Cluster 8 exists as three isomers that arise from the disposition of the PPh(3) ligands in the cluster (cis and trans) and the location of the hydride ligand. The dynamic behaviour of clusters with bulky triphenylphosphite ligands, which involves hydrogen migration from rhodium to sulfur with a switch from hydride to proton character, is significant to understand hydrogen diffusion on the surface of metal sulfide hydrotreating catalysts., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Several bis(hydrosulfido)-bridged dinuclear rhodium(I) compounds, [{Rh(mu-SH)(L)(2)}(2)], have been prepared from rhodium(I) acetylacetonato complexes, [Rh(acac)(L)(2)], and H(2)S(g). Reaction of [Rh(acac){P(OPh)(3)}(2)] with H(2)S(g) affords the dinuclear bis(hydrosulfido)-bridged compound [{Rh(mu-SH){P(OPh)(3)}(2)}(2)] (1). However, reaction of complexes [Rh(acac)(CO)(PR(3))] with H(2)S(g) gives the dinuclear compound [{Rh(mu-SH)(CO)(PR(3))}(2)] (R=Cy, 2; R=Ph, 4) and the trinuclear cluster [Rh(3)(mu-H)(mu(3)-S)(2)(CO)(3)(PR(3))(3)] (R=Cy, 3; R=Ph, 5). The selective synthesis of both type of compounds has been carried out by control of the H(2)S(g) concentration in the reaction media. The trinuclear hydrido-sulfido cluster [Rh(3)(mu-H)(mu(3)-S)(2)(CO)(3)(PPh(3))(3)] (5) has been also obtained by reaction of [{Rh(mu-SH)(CO)(PPh(3))}(2)] (4) with [Rh(acac)(CO)(PPh(3))], proceeding through the trinuclear hydrosulfido-sulfido intermediate [Rh(3)(mu(3)-SH)(mu(3)-S)(CO)(3)(PPh(3))(3)]. The molecular structures of complexes 1 and 3 have been determined by X-ray diffraction methods. Compound 1 is stable in solution, but complexes 2 and 4 slowly transform in solution into the trinuclear hydrido-sulfido clusters 3 and 5, respectively, with the release of H(2)S(g) in a reversible way. (1)H NMR kinetic experiments for the transformation of 4 into 5 have revealed that this transformation follows second-order-type kinetic. The following activation parameters, DeltaH( not equal)=24+/-3 kJ mol(-1) and of DeltaS( not equal)=-223+/-8 J K(-1) mol(-1), have been calculated from the determination of the second-order rate constants in the temperature range 30-45 degrees C. The large negative value of the activation entropy is consistent with an associative character of the rate-determining step. A plausible multistep mechanism based on the chemical behaviour of hydrosulfido-metal complexes and compatible with the kinetic behaviour has been proposed.