Tricarbonyl Species Research Articles

In Vitro Biological Activity of α-Diimine Rhenium Dicarbonyl Complexes and Their Reactivity with Different Functional Groups

Cancer remains one of the leading causes of death worldwide. The interest in organometallic complexes as anticancer drug candidates continues to be pivotal for many researchers. Initially underestimated for their therapeutic potentials, rhenium complexes are now slowly gaining momentum. While tricarbonyl complexes of rhenium are widely investigated, dicarbonyl derivatives of the cis-[Re(CO)2]+ core remain largely unexplored. In this study, we tested in vitro a variety of rhenium dicarbonyl complexes for their activity towards three cancer cell lines (A549, MCF-7 and HCT116) and one healthy cell line (HEK293). The most lipophilic compounds showed, like the tricarbonyl species, good activity against specific cancer lines (IC50 = 1.5–2.5 µM); however, the same were also toxic towards healthy cells. In order to understand these differences, we performed a reactivity study of cis-[Re(CO)2(NN)]+ species (where NN = diimine) with biologically relevant functional groups (-COOH, -NH2, -SH and aromatic nitrogen-based ligands) and compared the chemistry to what is known for the fac-[Re(CO)3]+ core. Overall, we found that the rhenium dicarbonyl complexes only show good reactivity with aromatic nitrogen-based ligands. The reaction of cis-[Re(CO)2(NN)]+ species with common bio-functional groups leads, rather, to the formation of bis-diimine dicarbonyl complexes (cis-[Re(CO)2(NN)2]+) as the major by-product.

Antimicrobial Activity of Rhenium Di- and Tricarbonyl Diimine Complexes: Insights on Membrane-Bound S. aureus Protein Binding.

Antimicrobial resistance is one of the major human health threats, with significant impacts on the global economy. Antibiotics are becoming increasingly ineffective as drug-resistance spreads, imposing an urgent need for new and innovative antimicrobial agents. Metal complexes are an untapped source of antimicrobial potential. Rhenium complexes, amongst others, are particularly attractive due to their low in vivo toxicity and high antimicrobial activity, but little is known about their targets and mechanism of action. In this study, a series of rhenium di- and tricarbonyl diimine complexes were prepared and evaluated for their antimicrobial potential against eight different microorganisms comprising Gram-negative and -positive bacteria. Our data showed that none of the Re dicarbonyl or neutral tricarbonyl species have either bactericidal or bacteriostatic potential. In order to identify possible targets of the molecules, and thus possibly understand the observed differences in the antimicrobial efficacy of the molecules, we computationally evaluated the binding affinity of active and inactive complexes against structurally characterized membrane-bound S. aureus proteins. The computational analysis indicates two possible major targets for this class of compounds, namely lipoteichoic acids flippase (LtaA) and lipoprotein signal peptidase II (LspA). Our results, consistent with the published in vitro studies, will be useful for the future design of rhenium tricarbonyl diimine-based antibiotics.

Cyclopentadienone Iron Complex-Catalyzed Hydrogenation of Ketones: An Operando Spectrometric Study Using Pressurized Sample Infusion-Electrospray Ionization-Mass Spectrometry

The sulfonate charge-tagged cyclopentadienone iron complexes [FeR(MeCN)(CO)2-SO3]Na (R = TMS, tBu) were prepared and used for mechanistic investigations using pressurized sample infusion-electrospray ionization-mass spectrometry in the hydrogenation of acetophenone. Reactions were conducted in a mixed aqueous/alcoholic solvent. Based on kinetic and mass spectrometric experiments, information about the operating reaction mechanism was obtained. Furthermore, analysis of the kinetic profiles and mass spectra indicated catalyst decomposition. By analysis of the mass spectrometric results, the decomposition cascade was found to start by solvolysis of the trimethylsilyl (TMS) groups flanking the carbonyl group in the cyclopentadienone ligand of the catalyst. Subsequent dimerization, comproportionation to form Fe(I) radical species, and formation of catalytically inactive iron tricarbonyl species were observed, limiting the catalyst lifetime. Replacement of the TMS groups by non-hydrolyzable tert-butyl groups leads to a significant increase in the observed turnover frequency and catalyst longevity. The turnover number, determined to be approximately 65 under standardized reaction conditions, could be increased to >1000 by the mechanism-guided structural change in the catalyst. No compounds corresponding to Fe(I) species or dimerization products could be identified in this case. The present study suggests that for hydrogenations with cyclopentadienone iron complexes, the use of alkyl groups flanking the C═O double bond in the ligand is beneficial over the use of silyl groups when conducted in aqueous media.

Review on Bioorganometallic Chemistry and New Outcomes in the Synthesis and Substitution of Tetracarbonyl(pyrrolylimine) Complexes of Rhenium with Organophosphorus Ligands.

: After a short review dealing with bioorganometallic chemistry, the synthesis of tetracarbonyl (pyrrolylimine) complexes of rhenium bearing chirality on the pyrrolyl ligands was reported.The reactivity of these compounds towards the substitution of one carbonyl ligand with triphenyl phosphine, tricyclohexyl phosphine and trimethyl phosphite was studied. The rhenium becoming a stereogenic center in that transformation, the resulting tricarbonyl species were obtained as mixtures of diastereomers, with diastereomeric excesses varying from 8 to 84%, according to the reaction conditions and the relative steric hindrances of the pyrrolylimine and the organophosphorus ligands. These bioorganometallics are potential CO releasing molecules that could be used in the field of medicinal chemistry.

Mn-carbonyl molecular catalysts containing a redox-active phenanthroline-5,6-dione for selective electro- and photoreduction of CO2 to CO or HCOOH

One advantage of using homogenous molecular catalysts versus their heterogeneous counterparts for CO2 reduction is the greater degree of control one usually retains over the selectivity of the catalyst. In this context, a pair of new manganese(I) tricarbonyl species, based on the N,N’-coordinated 1,10-phenanthroline-​5,​6-​dione (phen-dione) ligand, have been synthesized and characterized by spectroscopic methods and X-ray diffraction. They exhibit excellent selectivity for homogeneous catalytic CO2 reduction to CO or HCOOH through electrochemical or photochemical activation, respectively. Under the latter particularly, switching the solvent from dimethylformamide to acetonitrile remarkably enhances the selectivity of the reduction reaction towards formic acid. To obtain deeper mechanistic insight, the evolution of the catalysts and products in solution during the catalytic processes was investigated by combined electrochemical, chromatographic and spectroscopic methods It has been shown that the presence of the π-accepting, redox-active phen-dione ligand leads to different reduced intermediates compared with standard 2,2′-bipyridine and 1,10-phenanthroline complexes, with the two first redox processes remaining localized on the ligand.

Understanding the Scope of Feist–Bénary Furan Synthesis: Chemoselectivity and Diastereoselectivity of the Reaction Between α‐Halo Ketones and β‐Dicarbonyl Compounds

Feist–Bénary furan synthesis, the reaction between α‐halocarbonyl and β‐dicarbonyl compounds, has been known as an efficient method for generating many different types of furans containing a carbonyl group at C‐3. However, it has also been reported that, under similar reaction conditions, intermediate tricarbonyl species could be further converted to alternative furan isomers through the application of a Paal–Knorr synthesis. In this manuscript, we investigate the chemoselectivity and diastereoselectivity of furan synthesis from α‐halo ketones and β‐dicarbonyl compounds, by carrying out the separation and characterization of the intermediates involved in the reaction. Additionally, a one‐pot Feist–Bénary furan synthesis from α‐halo ketones and β‐dicarbonyl compounds without any base or solvent has also been developed.

Design of a Catalytic Active Site for Electrochemical CO2 Reduction with Mn(I)-Tricarbonyl Species.

The design, synthesis, and assessment of a new manganese-centered catalyst for the electrochemical reduction of CO2 is described. The reported species, MnBr(6-(2-hydroxyphenol)-2,2'-bipyridine)(CO)3, includes a ligand framework with a phenolic proton in close proximity to the CO2 binding site, which allows for facile proton-assisted C-O bond cleavage. As a result of this modification, seven times the electrocatalytic current enhancement is observed compared to MnBr(2,2'-bipyridine)(CO)3. Moreover, reduction is possible at only 440 mV of overpotential. Theoretical computations suggest that the entropic contribution to the activation free energy is partially responsible for the increased catalytic activity. Experimental work, including voltammetry and product quantification from controlled potential electrolysis, suggests a key mechanistic role for the phenolic proton in the conversion of CO2 to CO.

Ligand-Induced Structural, Photophysical, and Electrochemical Variations in Tricarbonyl Rhenium(I) Tetrazolato Complexes

Treatment of [Re(CO)5X] (X = Cl, Br) with 2-(2-tert-butyltetrazol-5-yl)pyridine yielded neutral mononuclear complexes by exchange of two CO ligands for the chelating tetrazolato ligand. Treatment of [Re(CO)5Br] with phenyltetrazolate resulted in the assembly of an anionic dinuclear rhenium tricarbonyl species bridged by three tetrazole rings. The reaction of [Re(CO)5Br] with (2-tert-butyltetrazol-5-yl)benzene formed an analogous neutral dinuclear complex bridged by a tetrazole ring as well as two bromide ligands; however this complex was found to be rather unstable in solution and was only structurally characterized via X-ray diffraction. The first three complexes were investigated for their photophysical properties, highlighting phosphorescent emission from their triplet metal-to-ligand charge transfer excited states, although in the case of the dinuclear species the quantum yield was found to be extremely low. The complexes are also characterized for their electrochemical behavior, and while the neutral...

Coordination of Two N2 Molecules to One Ni+ Site in Ni–ZSM-5: An FTIR Spectroscopy Study

Ni+ cations were produced in a Ni–ZSM-5 zeolite by partial reduction with CO, and the ability of the Ni+ and Ni2+ sites to coordinate 14N2, 15N2, and/or CO molecules was studied by FTIR spectroscopy. With Ni+ cations, CO produces mono-, di-, and tricarbonyl species while only mono- and dicarbonyls are formed with Ni2+. Adsorption of 14N2 at 100 K results in formation of Ni2+–14N2 adducts (band at 2343 cm–1) and geminal Ni+(14N2)2 complexes (νs at 2287 and νas at 2270 cm–1). The Ni+(14N2)2 complexes lose their ligands stepwise during evacuation at 100 K, and two kinds of monoligand Ni+–14N2 species are formed (2252 and 2238 cm–1). After 15N2 adsorption, the Ni+(15N2)2 complexes were observed at 2211 and 2194 cm–1: the two Ni+–15N2 species at 2178 and 2163 cm–1, and the Ni2+–15N2 adducts at 2264 cm–1. To prove the geminal structure, coadsorption of 14N2 and 15N2 was studied. It resulted in formation of Ni+(14N2)(15N2) species that were characterized by 14N–14N and 15N–15N stretchings at 2277 and 2201 cm–1, ...

Coordination and Activation of Diazoalkanes in the Presence of Rh/Ru and Rh/Os Metal Combinations

The substituted diazoalkanes—ethyl diazoacetate (EDA), diethyl diazomalonate (DEDM), and trimethylsilyl diazomethane (TMSDM)—react readily with the methylene-bridged tricarbonyl species [RhM(CO)3(μ-CH2)(dppm)2][CF3SO3] (M = Os (5), Ru (6); dppm = μ-Ph2PCH2PPh2) to produce the corresponding substituted olefin (through loss of N2 and subsequent coupling of the diazoalkane-generated alkylidene fragment and the methylene unit), the known tetracarbonyl species [RhM(CO)4(dppm)2][CF3SO3] (M = Os (1), Ru (2)), and uncharacterized decomposition products. In the reaction of 5 with EDA at −20 °C the intermediate olefin adduct, [RhOs(CO)3(η2-CH2-CHR)(dppm)2][CF3SO3] (7; R = CO2Et) is observed, which decomposes with release of the olefin upon warming. The methylene-bridged tetracarbonyl species [RhM(CO)4(μ-CH2)(dppm)2][CF3SO3] (M = Os(3), Ru (4)) also react with these diazoalkanes to yield the same products, only at a much slower rate. Attempts to generate the alkylidene-bridged products, analogous to 3 and 4, by reaction of 1 or 2 with EDA, DEDM, and TMSDM accompanied by loss of N2 instead gave complexes containing the diazoalkane unit. In the reaction with EDA condensation of this unit with a carbonyl ligand occurs accompanied by migration of the diazoalkane hydrogen to the carbonyl oxygen, yielding [RhM(CO)3(μ-η1:η1-N2C(COH)CO2Et)(dppm)2][CF3SO3] (M = Os (8), Ru (9)). The new diazoalkane-like group bridges the metals via the terminal nitrogen, while also binding to the group 8 metal via the enol carbon that originated from a carbonyl group. In the related reaction involving DEDM, substitution of a carbonyl yields [RhM(CO)3(μ-η1:η1-N2C(CO2Et)2)(dppm)2][CF3SO3] (M = Os (10), Ru (11)), in which the intact diazoalkane ligand again bridges via the terminal nitrogen. However, in this case one of the ester carbonyls binds to the group 8 metal, replacing the carbonyl group that was displaced. Although the RhRu compound 2 does not react with TMSDM, the analogous RhOs compound (1) does react, yielding [RhOs(CO)3(η1-Ν2CHSiMe3)(dppm)2][CF3SO3]] (12), in which the TMSDM ligand binds terminally on Os opposite the Rh−Os bond.

Complexes of technetium(I) ( 99Tc, 99mTc) pentacarbonyl core with π-acceptor ligands ( tert-butyl isocyanide and triphenylphosphine): Crystal structures of [Tc(CO) 5(PPh 3)]OTf and [Tc(CO) 5(CNC(CH 3) 3)]ClO 4

A procedure was developed for preparing [ 99mTcX(CO) 5] (X = Cl, Br, I) in a reasonable yield by high-pressure carbonylation with CO of 99mTcO 4 − in aqueous solutions. In the synthesis, the substantial part of the target product is accumulated in the gas phase and can be transferred from the autoclave into various solvents when relieving the pressure. Compounds [ 99mTcX(CO) 5] (X = Cl −, Br −, I −) are stable in solutions for several hours, but in the course of longer storage they gradually decompose to give the tricarbonyl species. Substitution of the halide ligands in [ 99TcX(CO) 5] and [ 99mTcX(CO) 5] with tert-butyl isocyanide and triphenylphosphine was studied. The structures of the complexes [Tc(CO) 5(PPh 3)]OTf and [Tc(CO) 5(CNC(CH 3) 3)]ClO 4 are presented.

Kinetics and mechanisms of homogeneous catalytic reactions: Part 7. Hydroformylation of 1-hexene catalyzed by cationic complexes of rhodium and iridium containing PPh 3

Cationic rhodium and iridium complexes of the type [M(COD)(PPh 3) 2]PF 6 (M = Rh, 1a; Ir, 1b) are efficient precatalysts for the hydroformylation of 1-hexene to its corresponding aldehydes (heptanal and 2-methylhexanal), under mild pressures (2–5 bar) and temperatures (60 °C for Rh and 100 °C for Ir) in toluene solution; the linear to branched ratio ( l/ b) of the aldehydes in the hydroformylation reaction varies slightly (between 3.0 and 3.7 for Rh and close to 2 for Ir). Kinetic and mechanistic studies have been carried out using these cationic complexes as catalyst precursors. For both complexes, the reaction proceeds according to the rate law r i = K 1 K 2 K 3 k 4[M][olef][H 2][CO]/([CO] 2 + K 1[H 2][CO] + K 1 K 2 K 3[olef][H 2]). Both complexes react rapidly with CO to produce the corresponding tricarbonyl species [M(CO) 3(PPh 3) 2]PF 6, M = Rh, 2a; Ir, 2b, and with syn-gas to yield [MH 2(CO) 2(PPh 3) 2]PF 6, M = Rh, 3a; Ir, 3b, which originate by CO dissociation the species [MH 2(CO)(PPh 3) 2]PF 6 entering the corresponding catalytic cycle. All the experimental data are consistent with a general mechanism in which the transfer of the hydride to a coordinated olefin promoted by an entering CO molecule is the rate-determining step of the catalytic cycle.

FTIR Studies of CO Adsorption on Al2O3- and SiO2-Supported Ru Catalysts

The adsorption of CO on Al2O3- and SiO2-supported Ru catalysts has been investigated through FTIR spectroscopy. Deconvolution of the spectra obtained reveals the presence of 11 distinct bands in the case of Ru/Al2O3 and 10 bands in the case of Ru/SiO2, which were assigned to different carbonyl species adsorbed on reduced as well as partially oxidized Ru sites. Although most of these bands on both supports are similar, they exhibit substantial differences in terms of stability. In general, the analogous CO species on Ru/Al2O3 are adsorbed stronger than those on Ru/SiO2, with the most stable species observed being a dicarbonyl adsorbed on metallic Ru (i.e., Ru0(CO)2). Following sintering of the Ru, the ratio of multicarbonyl to monocarbonyl adsorption is reduced substantially because of the lack of isolated sites or small Ru clusters that enable the formation of multicarbonyl species via oxidative disruption. Finally, in the presence of O2, the main features observed correspond to monocarbonyl, dicarbonyl, and tricarbonyl species adsorbed on partially oxidized Run+. The intensities of all bands decrease drastically at temperatures above 210 degrees C because of the onset of CO oxidation, which results in substantially reduced surface coverage.

FT-IR study of CO and NO adsorption on a VSiBEA zeolite

A VSiBEA zeolite containing 2.1 wt.% V has been prepared by a two-step post-synthesis method, which consists of first creating vacant T-sites by dealumination of the BEA zeolite with nitric acid and then impregnation of the SiBEA zeolite with an aqueous solution of ammonium metavanadate (NH 4VO 3), used as V 5+ precursor. The sample has been studied by XRD analysis, FT-IR, TPR and diffuse reflectance UV–Visible spectroscopy. The disappearance of the IR band near 3520 cm −1 after impregnation of NH 4VO 3 indicates that a specific reaction has occurred between the vanadium precursor and silanol groups of vacant T-sites. As a result, tetrahedral V 5+ ions connected with OH groups are incorporated in the framework. In addition, weakly bound extraframework V 5+ species (tetrahedral and octahedral) exists. CO and NO were used as IR probes for establishing the state of reduced vanadium sites. It was found that NO was a better probe for this purpose, but CO provided valuable complementary information on the coordination state of the reduced vanadium sites. As expected, adsorption of both, CO and NO, was negligible on non-reduced sample. However, sample reduced with hydrogen at 673 K is characterised by a high concentration of V 4+ and V 3+ sites produced by the reduction of the extraframework sites. NO was found to form dinitrosyls with both V 4+ and V 3+ cations. The V 4+(NO) 2 species are characterised by ν s at 1902 cm −1 and ν as at 1755 cm −1. The dinitrosyls of V 3+ were registered at 1830 ( ν s) and 1687 cm −1 ( ν as). Reduction at 773 K led to increase in amount of the V 3+ species and formation of framework V 4+ cations (respective dinitrosyl bands at 1900 and 1729 cm −1). The spectra of CO adsorbed on the reduced sample are complex. Evidence of tricarbonyl species was found. It was concluded that CO is a better probe than NO for testing the coordination state of V 4+ and V 3+ sites.

A vibrational spectroscopic study of the thermal behavior of Re2(CO)10 on zeolite Y

This work describes the thermal decomposition of Re2(CO)10 in zeolite Y, which generates the zeolite-supported complex Re0(CO)3(O-Z)3, where (O-Z) represents a framework oxygen. The adsorption and thermal decomposition of Re2(CO)10 was performed on dehydrated and hydrated zeolite NaY. The conversion to Re0(CO)3(O-Z)3 was not significantly affected by the presence of water within the supercages as the supported complex formed at around 200 °C no matter what the initial water content of the zeolite was. However, when the zeolite sample was treated at ≥200 °C for long periods, the adsorbed H2O became involved in the reactivity, playing a role as an oxidant. The subcarbonyl complex Re0(CO)3(O-Z)3 was oxidized, generating isolated Re2O7 or HReO4, or a mixture of both, which was dispersed inside the zeolite host. This result suggests that thermal decomposition of Re2(CO)10 on a hydrated zeolite under mild conditions can be a convenient route for preparation of zeolite-supported Re2O7 catalysts. Re0(CO)3(O-Z)3 was also formed in siliceous zeolite Y (SiY) upon heating. But it quickly decomposes into metal Re at around 200 °C, suggesting that the tricarbonyl species is destabilized in the almost natural zeolite framework. The present study also shows that FT-Raman spectroscopy is a useful technique for monitoring the behavior of the metal carbonyl species in zeolitic hosts.Key words: Raman spectroscopy, zeolite Y, rhenium carbonyl, rhenium oxide.

CO Adsorption study of V/SiO 2: the low vanadium coverage regime

Adsorption of CO and its isotopic mixtures on vanadium particles in the very low coverage growth regime (0.02–0.05 MLV) on an ultra-thin ordered silica film is monitored by IRAS at 60 K. At different CO exposures, development of different vibrational peaks was observed. These peaks are assigned to either mono- or tri-carbonyl species [V(CO) x ; x=1,3] via isotopic mixture experiments. Comparing vanadium growth both on the alumina and silica films, it can be inferred from CO adsorption experiments that the metal–support interaction is weaker for vanadium growth on the silica film. The charge transfer between the vanadium metal center and the silica film is estimated based on a charge–frequency relationship to be +0.4e.

Selective coupling of methylene groups at a Rh/Os core, yielding C2, C3, or C4 fragments: roles of the adjacent metals in carbon-carbon bond formation.

The mixed-metal complex, [RhOs(CO)(4)(dppm)(2)][BF(4)] (1; dppm = micro-Ph(2)PCH(2)PPh(2)) reacts with diazomethane to yield a number of products resulting from methylene incorporation into the bimetallic core. At -80 degrees C the reaction between 1 and CH(2)N(2) yields the methylene-bridged [RhOs(CO)(3)(micro-CH(2))(micro-CO)(dppm)(2)][BF(4)] (2), which reacts further at ambient temperature to give the allyl methyl species, [RhOs(eta(1)-C(3)H(5))(CH(3))(CO)(3)(dppm)(2)][BF(4)] (4). At intermediate temperatures compounds 1 and 2 react with diazomethane to yield the butanediyl complex [RhOs(C(4)H(8))(CO)(3)(dppm)(2)][BF(4)] (3) by the incorporation and coupling of four methylene units. Compound 2 is proposed to be an intermediate in the formation of 3 and 4 from 1 and on the basis of labeling studies a mechanism has been proposed in which sequential insertions of diazomethane-generated methylene fragments into the Rh-C bond of bridging hydrocarbyl fragments occur. Reaction of the tricarbonyl species, [RhOs(CO)(3)(micro-CH(2))(dppm)(2)][BF(4)] with diazomethane over a range of temperatures generates the ethylene complex [RhOs(eta(2)-C(2)H(4))(CO)(3)(dppm)(2)][BF(4)] (7a), but no further incorporation of methylene groups is observed. This observation suggests that carbonyl loss in the formation of the above allyl and butanediyl species only occurs after incorporation of the third methylene fragment. Attempts to generate C(2)-bridged species by the reaction of 1 with ethylene gave no reaction, however, in the presence of trimethylamine oxide the ethylene adducts [RhOs(eta(2)-C(2)H(4))(CO)(3)(dppm)(2)][BF(4)] (7b; an isomer of 7a) and [RhOs(eta(2)-C(2)H(4))(2)(CO)(2)(dppm)(2)][BF(4)] (8) were obtained. The relationship of the above products to the selective coupling of methylene groups, and the roles of the different metals are discussed.

Methylene-Bridged Complexes of Rhodium/Ruthenium as Models for Bimetallic Fischer−Tropsch Catalysts: Comparisons with the Rh/Os and Ir/Ru Analogues

The cationic heterobinuclear complex [RhRu(CO)3(μ-H)2(dppm)2][X] (1) is prepared by protonation of the monohydride species [RhRu(CO)3(μ-H)(dppm)2] (dppm = μ-Ph2PCH2PPh2; X- = BF4-, CF3SO3-). Treatment of 1 with carbon monoxide affords the tetracarbonyl complex ion [RhRu(CO)4(dppm)2][X] (2), which yields the methylene-bridged product [RhRu(CO)4(μ-CH)2(dppm)2][X] (3), upon treatment with excess diazomethane at −78 °C. Reaction of 3 with trimethylamine-N-oxide results in CO removal, affording the methylene-bridged tricarbonyl species [RhRu(CO)3(μ-CH)2(dppm)2][X] (4). Although compound 3 is unreactive toward further treatment with CH2N2, compound 4 reacts readily with diazomethane, yielding a mixture of uncharacterized products. Compounds 3 and 4 react with PMe3 to yield [RhRu(PMe3)(CO)3(μ-CH)2(dppm)2][X] (5), in which coordination of PMe3 at the unsaturated Rh center occurs. The structures of compounds 2, 3, and 5 have been determined by X-ray methods. Comparisons of the reactivity of compound 3 with that of the analogous Ir/Ru and Rh/Os complexes toward diazomethane are presented.

Surface-mediated reductive carbonylation of SiO2-supported RuCl3 and Ru(NO)(NO3)3 studied by IR spectroscopy

The surface-mediated reductive carbonylation of SiO2-supported RuCl3 and Ru(NO)(NO3)3 has been studied by IR spectroscopy. Hydrated RuCl3/SiO2 reacts readily with CO (100–700Torr) to form a mixture of Ru(CO)Cl2(HOSi)3 and Ru(CO)2Cl2(HOSi)2 at 25°C, and a mixture of Ru(CO)Cl2(HOSi)3, Ru(CO)2Cl2(HOSi)2, Ru(CO)3Cl2(HOSi) (major product) and [Ru(CO)3Cl2]2 at 100°C. Hydrated Ru(NO)(NO3)3/SiO2 reacts readily with CO to give a mixture of Ru(CO)2(OSi)2 and Ru(CO)3(OSi)2 at 25°C. At 100°C, hydrated Ru(NO)(NO3)3/SiO2 is converted to a mixture of Ru(CO)2(OSi)2 and Ru(CO)3(OSi)2 under 100Torr of CO, and a mixture of Ru3(CO)12 (good yield) and Ru(CO)3(OSi)2 under 700Torr of CO. All these results are demonstrated by surface IR spectra and extraction experiments with organic solvents. While the carbonylation of hydrated Ru(NO)(NO3)3/SiO2 proceeds, the stoichiometric reductions of NO3− and NO: 2NO3−+3CO+2HOSi→2NO+3CO2+H2O+2OSi− and 2NO+CO→N2O+CO2 are suggested to occur on the surface, according to gaseous IR observation. The proportion of ruthenium(II) tricarbonyl species is found to increase with the increases of carbonylation temperature and CO pressure. In addition, the detrimental effect of calcination of RuCl3/SiO2 and Ru(NO)(NO3)3/SiO2 at 400°C on the reductive carbonylation is discussed.

The competitive and non-competitive hydroformylation of conjugated dienes starting with tetrarhodium dodecacarbonyl. An in-situ high-pressure infrared spectroscopic study

It is well known that the liquid-phase homogeneous unmodified rhodium catalysed hydroformylation of alkenes is poisoned by the presence of trace quantities of conjugated dienes. Nevertheless, some hydroformylation of conjugated dienes is possible with unmodified rhodium, and this reaction is in general slower than alkene hydroformylations at comparable reaction conditions. In the present contribution, we examined (A) the catalytic behaviour of alkenes in the presence of trace conjugated diene impurities and (B) the catalytic behaviour of a variety of dienes using Rh 4(CO) 12 in n-hexane solvent at 293 K under 1.0–4.0 MPa CO and 0.5–2.0 MPa H 2. The analytic method was in-situ high-pressure infrared spectroscopy. It was observed that (I) in the hydroformylation of poisoned alkenes, most of the rhodium reacts with the trace quantity of conjugated dienes and not the alkenes in this competitive situation and (II) the metal carbonyl spectra of the hydroformylation of a variety of dienes are very similar. The primary absorbance maxima observed in the hydroformylations of conjugated dienes occur at circa 2109, 2091, 2087, 2064, 2049, 2037, 2030, 2020, 2012, 1999, and 1990 cm −1. Given the known chemistry of Rh 4(CO) 12 under syngas, and the very well documented chemistry of Rh 4(CO) 12 under alkene hydroformylation conditions, the lack of bridging carbonyls in the present experiments strongly suggested that the new infrared vibrations are due to mononuclear rhodium species. Preliminary analysis suggests the presence of at least three new species. In particular, the formation of observable η 3 allyl rhodium tricarbonyl species, σ allyl rhodium tetracarbonyl species and even acyl rhodium tetracarbonyl species RCORh(CO) 4 (R=alkenyl and/or formylalkyl) seems probable. Characteristic wavenumbers of 2108, 2064, 2037, 2020 and 1700 cm −1 are tentatively assigned to the latter. The reduced hydroformylation activity in the competitive hydroformylation of alkenes arises due to the much higher affinity of rhodium complexes for conjugated dienes than for alkenes under otherwise similar reaction conditions.