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The influence of phosphane “arm-on, arm-off” association/dissociation in rhodium catalysed alkene hydrogenation using [Rh(COD)(κ³-triphos)]PF₆ {1, COD = cyclooctadiene, triphos = 1,1,1-tris(diphenylphosphanylmethyl)ethane} has been investigated by comparison of the activity of 1 to mixtures of the related diphosphane complex, [Rh(COD)(κ²-dppp)]PF₆ {2, dppp = 1,3-bis(diphenylphosphanyl)propane} and triphenylphosphane (THF, 50 °C, 1 bar H₂). These investigations are supplemented by a demonstration of the κ²–κ³ fluxionally of the triphos coordination in 1 by reversible reaction with [RuCl₂(p-cymene)]₂ at room temperature in CH₂Cl₂. The product of this reaction, the bimetallic complex [(p-cymene)Cl₂Ru{(PPh₂CH₂)CMe(CH₂PPh₂)₂}Rh(COD)]PF₆, was isolated and fully characterized, including determination of the solid-state structure by X-ray diffraction analysis. Despite this evidence for facile arm-off dissociation of the triphos ligand in 1, complex 2, with or without triphenylphosphane, was found to be more efficient for the hydrogenation of styrene and cyclohexene. Notably, use of triphenylphosphane together with 2 was found to have beneficial effects – increasing the rate of styrene hydrogenation (in some cases) and helping to stabilise the metal center during cyclohexene hydrogenation. These observations are supported by mercury poisoning experiments and reactivity experiments with 2 in medium pressure sapphire NMR tubes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The triple-chlorido-bridged heterodimetallic dinuclear complex [(dibenzo-18-crown-6)K(μ-Cl)₃Ru(η⁶-p-cymene)] containing an (η⁶-arene)Ru^II fragment and a Group 1 metal crown ether fragment was synthesized and characterized by spectroscopy and X-ray crystallography. The solid-state structure clearly reveals the presence of the triple-chlorido-bridged dinuclear complex, whereas NMR investigations in different deuteriated solvents reveal the presence of an essentially 1:1 mixture of 1 and starting materials, indicating the presence of a dynamic equilibrium. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The reaction of chloromethyl thiocyanate with 1-methylimidazole affords the imidazolium salt, 1-thiocyanomethyl-3-methylimidazolium chloride, [C₁SCNmim]Cl (1a). Exchange of the chloride anion in 1a by [PF₆]^–, [BF₄]^–, [Tf₂N]^– or [AuCl₄]^– affords salts 1b, 1c, 1d and 1e, respectively. Salts [C₁SCNmim][BF₄] (1c) and [C₁SCNmim][Tf₂N] (1d) melt below 100 °C and can therefore be classified as ionic liquids. The reaction of 1a with PdCl₂ affords [C₁SCNmim]₂[PdCl₄] (2a), whereas 1c reacts with PdCl₂ to form the complex [PdCl₂{C₁SCNmim}₂][BF₄]₂ (2c). In the presence of HNO₃ both 1a and 1c react with PdCl₂ with the loss of HCN to form a sulfide-bridged palladium dimer [PdCl₂{C₁Smim}]₂ (3). The structures of 1a, 1e, 2a and 3 have been determined in the solid state by single-crystal X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The effect of pressure on the Diels–Alder reaction was examined in room temperature ionic liquids, followed by high-pressure FT-IR spectroscopy using pressures up to 150 MPa. Pressure enhances the kinetic sensitivity of the reaction. The kinetic effect of fluorophobic interactions was examined using ionic liquids with fluorous cations. Ionic liquids in combination with ZnI₂ as a Lewis acid catalyst were also studied under high pressure. Copyright © 2007 John Wiley & Sons, Ltd.

Task-specific ionic liquids bearing nitrile functional groups attached to the cation and nitrogen-donor-containing anions strongly affect the efficiency of the Stille cross-coupling, influencing the nature of the catalyst and its stability. The relative strengths of the coordinating power of the cations and anions are varied and compared, and under certain conditions nanoparticles are observed.

The cover picture shows an organoruthenium antimetastasis compound, superimposed over a Sudoku puzzle, representing the challenge of discovering new anticancer drugs and elucidating their mechanisms of action. One needs to uncover pieces of information which are interrelated, and eventually, the complete ‘picture’ is revealed. In this review, we describe the extent to which the picture has been revealed for ruthenium-based drugs, which are currently growing in interest as a result of recent successes in clinical trials. The emphasis is directed towards classifying the vast array of ruthenium compounds already evaluated in vitro and in vivo against primary and secondary cancers within the context of their probable target. It is hoped that on the basis of the picture presented here more of this intriguing puzzle will be revealed soon. Details are presented in the Microreview by W. H. Ang and P. J. Dyson on p. 4003 ff.

Ruthenium-based anticancer chemotherapies are making significant advances in clinical trials. Until recently, the focus has been on coordination complexes, and mechanisms such as “activation by reduction” and “transferrin-targeted delivery” have been proposed to account for the excellent cytotoxicity and low general toxicity of these complexes. More recently organoruthenium compounds, which to some extent appear not to follow the established rules, have started to be investigated. Despite such differences, similar activities between certain coordination and organometallic compounds suggest similar modes of action are present. DNA, the classic target, is believed to be the dominant mechanism for cytotoxicity with certain ruthenium drugs, while with others, non-classical targets are thought to be more important. In this article we describe these features and show how both ruthenium coordination complexes and organoruthenium compounds represent an ideal scaffold for further drug design and optimisation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A series of imidazolium dicarboxylic acids have been prepared from the reaction of the 1,3-bis(carboxymethyl)imidazolium zwitterion with the Brønsted acids HX (X=F, Br, Cl, ClO₄). The structures of these acids have been established in the solid state by single-crystal X-ray diffraction, which revealed that the cations and anions form strong hydrogen bonds through OH⋅⋅⋅X interactions, leading to the formation of dimeric and polymeric networks. These acids react with elemental zinc and cobalt to form stable polymeric coordination complexes, some of which have also been characterised by X-ray diffraction.

Some of the recent developments concerning the synthesis, properties and applications of functionalised ionic liquids are highlighted. Various strategies are presented, including functionalisation of the cation, anion or both cation and anion in the same ionic liquid, leading to what has been termed dual-functionalised ionic liquids. Particular attention is given to the application of functionalised ionic liquids as reaction media, to stabilise nanoparticles/modify surfaces and to generate porous materials.

The Diels–Alder reaction between cyclopentadiene and methyl acrylate in ionic liquids has been studied in detail. The effect of contamination of the ionic liquids by common impurities, viz. sodium and chloride ions, and water, on the selectivity has been investigated. The presence of high concentrations of chloride was found to decrease the selectivity. Anion and, in particular, cation effects have been investigated using an extensive series of air-stable room temperature ionic liquids, and kinetic parameters have been determined. It has been found that strongly interacting groups, particularly electrophilic moieties on the cation, accelerate the formation of the endo products. Substrate solubility intimately connected to the selectivity was found to be mainly anion dependent. An NMR-based solvent parameter scale and semi-empirical models are used to analyse the results and provide a tool for the prediction of selectivities in ionic liquids.

Two nitrile-functionalized alkyltriflouroborate anion based complexes [(Ph₃P)₂N][CH₃CH(BF₃)CH₂CN] and [K(18-crown-6)][CH₃CH(BF₃)CH₂CN] were synthesized and characterized by spectroscopic methods and single X-ray diffraction analysis. In the former complex no direct cation-anion (FN or FP) interactions are observed although F···H–C hydrogen bonds are present. In the later complex all three fluorine atoms interact with the potassium cation and C–H···F hydrogen bonds are also present. The ESI-MS spectra in methanol solution of the potassium complex show similar anion-cation aggregation to that observed for ionic liquids, and comparisons between the two complexes and ionic liquid systems are made. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The reaction of [(η⁶-p-cymene)RuCl₂]₂ with some bis(phosphane) ligands (dppm, dppe, dppv, dppa, dpp14b, dppf) has been investigated. In general mixtures of products were obtained, although the pendant phosphane complexes [(η⁶-p-cymene)RuCl₂(η¹-dppv)] and [(η⁶-p-cymene)RuCl₂(η¹-dppa)] were isolated and characterized in the solid state by X-ray diffraction. The later complex was obtained in lower yield and undergoes an equilibration reaction resulting in the formation of a dimeric species, where the dppa bridges two ruthenium centres, and uncoordinated phosphane; the bridging species was also structurally characterised in the solid state. In contrast, the reaction of [(η⁶-p-cymene)RuCl₂(PPh₃)] with dppa in the presence of [NH₄]PF₆ results in the formation of [(η⁶-p-cymene)RuCl(PPh₃)(η¹-dppa)]PF₆, which is stable in solution. A series of linked ruthenium–borane complexes, viz. [(η⁶-p-cymene)RuCl₂(η¹-phosphane-BH₃)] (phosphane = dppm, dppe, dppv, dppa, dpp14b, dppf) and [(η⁶-p-cymene)RuCl(PPh₃)(η¹-dppa-BH₃)]PF₆ have been prepared from isolated pendant phosphane complexes, those generated in situ, or from a preformed phosphane–borane adduct. The solid-state structures of [(η⁶-p-cymene)RuCl₂(η¹-dppm-BH₃)], [(η⁶-p-cymene)RuCl₂(η¹-dppe-BH₃)] and [(η⁶-p-cymene)RuCl₂(η¹-dppv-BH₃)] have been determined by X-ray diffraction analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

This paper is aimed at introducing the organometallic chemist to the fascinating area of organometallic pharmaceuticals. It commences by identifying the properties of organometallic (transition metal) compounds that lend themselves to medical applications. Next, the specialized techniques and methods that are used to assess the medicinal properties of compounds are summarized, and although these techniques are not restricted to organometallic compounds, all examples are concerned with organometallic compounds. The design and evaluation of organometallic compounds for medicinal applications are described in context with the diseases they have been evaluated against, and areas are identified that may have most potential for organometallic pharmaceuticals. Some new results, including the first example of an organo-osmium compound that might exhibit effective anticancer properties, are also described. Copyright © 2005 John Wiley & Sons, Ltd.

The two known Me- and allyl-substituted 1H-imidazol-3-ium bromides 1 and 2, respectively, were converted to the corresponding BF and BPh salts 3–6 (Scheme 1). Compounds 3 and 4 were liquids at ambient temperature. Reaction of 1 or 2 with [PdCl₂] afforded the corresponding 2 : 1 imidazolium/metal complexes 7 and 8. The latter complex, melting at 58°, can be regarded as a ‘true’ ionic liquid. Attempts to polymerise 7 by radical promotion (AIBN) were unsuccessful, but resulted in the centrosymmetric 2 : 1 complex 9. The allyl group of 1 could be arylated (giving rise to 10) or hydrogenated (at 100 bar H₂ pressure). The solid-state structures of compounds 5–7 and 9 were solved by means of single-crystal X-ray analyses (Figs. 1–4).

Lange ersehnt und dann gleich als Doppelpack: Nur kurze Zeit nach einem oktaedrischen Spätübergangsmetallcluster mit 12 Hydridliganden, der 10 Elektronen weniger enthält als erwartet, wurde ein ebenso bemerkenswerter elektronenarmer Fünfkerncluster mit trigonal-bipyramidalem Triplatindirhenium-Kern entdeckt, der drei Äquivalente H₂ oxidativ addiert (siehe Schema).

Nano-Klempner: Ein zwitterionisches, helicales, nanodimensioniertes Rohr, das eine zweidimensionale Wasserkette enthält (siehe Bild; Br gelb, C grau, N blau, O rot, H_Wasser weiß, H_Imidazolium weggelassen), entsteht bei der Reaktion von Zinkmetall mit N,N′-Diessigsäure-imidazoliumbromid. Die Dynamik der eingeschlossenen Wassermoleküle wurde mithilfe der Festkörper-NMR-Spektroskopie genau untersucht.

Nanoscale plumbing: A zwitterionic, helical pipe of nanodimensions that contains a two-dimensional water chain (see picture; Br yellow, C gray, N blue, O red, H_water white, H_imidazolium omitted) assembles from the reaction between zinc metal and N,N′-diacetic acid imidazolium bromide. A detailed study on the dynamics of the incorporated water molecules has been conducted by solid-state NMR spectroscopy.

After a very long wait two arrive together: Following the recent highlight of a late-transition-metal octahedral cluster with 12 hydride ligands and 10 too few electrons, an equally remarkable highly electron-deficient pentanuclear cluster based on a triplatinum–dirhenium trigonal-bipyramidal core has been discovered which undergoes oxidative addition with three equivalents of H₂ (see scheme)

A combination of mass spectrometry, UV/Vis spectroscopy and molecular modelling techniques have been used to characterise the interaction of cisplatin with human serum transferrin (Tf). Mass spectrometry indicates that cisplatin binds to the hydroxy functional group of threonine 457, which is located in the iron(III)-binding site on the C-terminal lobe of the protein. UV/Vis spectroscopy confirms the stoichiometry of binding and shows that cisplatin and iron(III) binding are competitive. The binding of cisplatin has been modelled by using molecular dynamic simulations and the results suggest that cisplatin can occupy part of both the iron(III)- and carbonate-binding sites in the C-terminal lobe of the protein. Combined, the studies suggest that cisplatin binding sterically restricts iron(III) binding to the C-terminal lobe binding site, whereas the N-terminal lobe binding site appears to be unaffected by the cisplatin interaction, possibly allowing the iron(III)-induced conformational change necessary for binding to a Tf receptor.

Reaction of the diphosphanylamine 2,6-{(Ph₂P)₂N}₂C₅H₃N with four equivalents of Au(tht)Cl (tht = tetrahydrothiophene) affords the tetragold complex 2,6-{(ClAuPh₂P)₂N}₂C₅H₃N in high yield. Decomposition of the tetragold compound results in the formation of the digold complex 2,6-{(ClAuPh₂P)HN}₂C₅H₃N and colloidal gold. A trigold intermediate, which contains a Au−Au interaction [2.9886(5) Å] has been isolated, and while ultimately unstable, it is thought to be partially stabilised by virtue of the aurophilic nature of gold. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The reactivity of the iminodiphosphane C₆H₄(o-CN)N=PPh₂−PPh₂, which contains an N=P−P unit, has been investigated. Reaction with small molecules, [viz. H₂O/O₂, H₂O₂, CH₃OH, C₆H₄(o-CN)NH₂] and elemental sulfur result in cleavage of the P−P bond to give aminophosphane-derivatised compounds. The products from these reactions have been characterized spectroscopically, including two by single-crystal X-ray diffraction. The reactivity of the iminodiphosphane towards the transition metal complexes [M(cod)Cl₂] (M = Pd or Pt) has also been investigated. In the reactions, the iminodiphosphane rearranges to form the more common diphosphonylamine (P−N−P) unit which chelates to the metal centres. Three different compounds were isolated from these reactions and they have all been fully characterised by spectroscopy and single-crystal X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Six of one and half a dozen of the other: A late-transition-metal octahedral cluster [Rh₆(PiPr₃)₆(μ-H)₁₂]²⁺ (1) with six phosphine ligands has been reported with a structure and electron count akin to that of early-transition-metal halide clusters, and provides a unique link between the two classes of cluster (see scheme). Cluster 1 is also decorated with 12 hydride ligands.

Zwischen den Welten: Der oktaedrische Cluster [Rh₆(PiPr₃)₆(μ-H)₁₂]²⁺ (1) eines späten Übergangsmetalls mit sechs Phosphanliganden ähnelt in Struktur und Elektronenzahl den Halogenidclustern früher Übergangsmetalle und ist somit ein einzigartiges Bindeglied zwischen diesen Clusterfamilien (siehe Schema). Der Cluster trägt außerdem zwölf Hydridliganden.

Imidazolium chlorides with one or two carboxylic acid substituent groups, 1-methyl-3-alkylcarboxylic acid imidazolium chloride, [Me{(CH₂)_nCOOH}im]Cl (n=1, 3), and 1,3-dialkylcarboxylic acid imidazolium chloride, [{(CH₂)_nCOOH}₂im]Cl (n=1, 3), have been synthesized via their corresponding acid esters. Deprotonation of the carboxylic acid functionalized imidazolium chlorides with triethylamine affords the corresponding zwitterions [Me{(CH₂)_nCOO}im] (n=1, 3) and [{(CH₂)_nCOOH}{(CH₂)_nCOO}im] (n=1, 3). Subsequent reaction of the zwitterions with strong acids gives the new imidazolium salts [Me{(CH₂)_nCOOH}im]X (n=1, 3; X=BF₄, CF₃SO₃) and [{(CH₂)_nCOOH}₂im]X (n=1, 3; X=BF₄, CF₃SO₃), which exhibit melting points as low as −61 °C. The solid-state structures of two of the carboxylic acid functionalized imidazolium salts have been determined by single-crystal X-ray diffraction analysis. Extensive hydrogen bonding is present between the chloride and the imidazolium, with eight Cl⋅⋅⋅H interactions below 3 Å. The pK_a values of all the salts, determined by potentiometric titration, lie between 1.33 and 4.59 at 25 °C.

The hydrogenation of benzene and other arenes under aqueous-organic biphasic conditions is evaluated using the ruthenium complexes Ru(η⁶-C₁₀H₁₄)(pta)Cl₂ (pta=1,3,5-triaza-7-phosphaadamantane), Ru(η⁶-C₁₀H₁₄)(tppts)Cl₂ (tppts=tris-3-sulfonatophenylphosphine trisodium salt) and [Ru(η⁶-C₁₀H₁₄)(pta)₂Cl]⁺. The active catalysts formed during the hydrogenations correspond to a trinuclear cluster, a colloid and a mononuclear complex, respectively.

The hydrogenation of benzene and other arene substrates under biphasic conditions is evaluated using the catalyst precursor Ru(η⁶-C₁₀H₁₄)(pta)Cl₂ (pta=1,3,5-triaza-7-phosphaadamantane) immobilised in water and 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids. The effect that contamination of the 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids with chloride has on the hydrogenation reaction has also been examined. Of the immobilisation solvents tested the optimum solvent was found to be chloride-free 1-butyl-3-methylimidazolium tetrafluoroborate. Catalytic turnovers in this solvent are highest, and in general, turnovers for the hydrogenation reactions follow the trend: chloride-free 1-butyl-3-methylimidazolium tetrafluoroborate > water > chloride-contaminated 1-butyl-3-methylimidazolium tetrafluoroborate.

A range of coordination and organometallic compounds have been analysed by quadrupole ion-trap mass spectrometry using various photoionisation methods. Atmospheric-pressure photo ionisation (APPI), which combines atmospheric-pressure chemical ionisation (APCI) with a photolysis lamp, was compared with the new technique photo-assisted electrospray ionisation (PAESI). Additionally, the atmospheric-pressure matrix-assisted laser desorption ionisation (AP-MALDI) was also evaluated and compared to MALDI quadrupole ion-trap time-of-flight (MALDI-QIT-TOF) mass spectrometry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The reaction of the aminophosphane C₆H₄(o-CN)NHPPh₂ with elemental potassium in the presence of 18-crown-6 affords the phosphinoamide-containing complex [C₆H₄(o-CN)N-PPh₂(THF)(18-Crown-6)K] which has been fully characterised in solution and the solid state. The potassium cation interacts with the nitrile substituent group and crown, but does not interact with the P−N bond. The anion appears to be considerably more reactive than related anions in which the cation interacts with the P-N unit, as demonstrated by the reaction with O₂/H₂O which affords [Ph₂P(:O)OK(18-Crown-6)] and C₆H₄(o-CN)NH₂. A co-crystal containing these two products was obtained and the structure has been elucidated by single-crystal X-ray diffraction analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The polydentate phosphinoamines 1,3-{(Ph₂P)₂N}₂C₆H₄ and 2,6-{(Ph₂P)₂N}₂C₅H₃N have been prepared in a single step from the reaction of the amines 1,3-(NH₂)₂C₆H₄ or 2,6-(NH₂)₂C₅H₃N with Ph₂PCl in presence of Et₃N (1 : 4 : 4 molar ratio) in CH₂Cl₂. Reaction of 1,3-{(Ph₂P)₂N}₂C₆H₄ or 2,6-{(Ph₂P)₂N}₂C₅H₃N with elemental sulfur or selenium in CH₂Cl₂ affords the corresponding tetrasulfide or tetraselenide, respectively, in good yield. The complexes [1,3-{Mo(CO)₄(Ph₂P)₂N}₂(C₆H₄)] and [2,6-{Mo(CO)₄(Ph₂P)₂N}₂(C₅H₃N)] were prepared from the reaction of these phosphinoamines with [Mo(CO)₄(nbd)] (nbd=norbornadiene) in toluene, and the structure of the latter complex has been determined by single-crystal X-ray diffraction analysis.

The reactivity of the cluster family [Ru₃(CO)_12−x(L)_x] (in which L=PMe₃, PMe₂Ph, PPh₃ and PCy₃, x=1–3) towards hydrogen is described. When x=2, three isomers of [Ru₃(H)(μ-H)(CO)₉(L)₂] are formed, which differ in the arrangement of their equatorial phosphines. Kinetic studies reveal the presence of intra- and inter-isomer exchange processes with activation parameters and solvent effects indicating the involvement of ruthenium-ruthenium bond heterolysis and CO loss, respectively. When x=3, reaction with H₂ proceeds to form identical products to those found with x=2, while when x=1 a single isomer of [Ru₃(H)(μ-H)(CO)₁₀(L)] is formed. Species [Ru₃(H)(μ-H)(CO)₉(L)₂] have been shown to play a kinetically significant role in the hydrogenation of an alkyne substrate through initial CO loss, with rates of H₂ transfer being explicitly determined for each isomer. A less significant secondary reaction involving loss of L yields a detectable product that contains both a pendant vinyl unit and a bridging hydride ligand. Competing pathways that involve fragmentation to form [Ru(H)₂(CO)₂(L)(alkyne)] are also observed and shown to be favoured by nonpolar solvents. Kinetic data reveal that catalysis based on [Ru₃(CO)₁₀(PPh₃)₂] is the most efficient although [Ru₃(H)(μ-H)(CO)₉(PMe₃)₂] corresponds to the most active of the detected intermediates.