Organometallic Catalyst Precursors Research Articles

ChemInform Abstract: Metatheases: Artificial Metalloproteins for Olefin Metathesis

AbstractReview: 45 refs.

Metatheases: artificial metalloproteins for olefin metathesis.

The incorporation of organometallic catalyst precursors in proteins results in so-called artificial metalloenzymes. The protein structure will control activity, selectivity and stability of the organometallic site in aqueous medium and allow non-natural reactions in biological settings. Grubbs-Hoveyda type ruthenium catalysts with an N-heterocyclic carbene (NHC) as ancillary ligand, known to be active in olefin metathesis, have recently been incorporated in various proteins. An overview of these artificial metalloproteins and their potential application in olefin metathesis is given.

One-Step Liquid-Phase Synthesis of Carbon Nanotubes with Catalyst Precursors of Organometallic Complexes

This paper describes a simple, low cost one-step liquid-phase process for the synthesis of highly aligned carbon nanotube (CNT) arrays (HACNTAs). Highly pure HACNTAs were grown on a stainless steel substrate by resistance-heating in methanol solution containing one of the organometallic complex catalyst precursors, ferrocene Fe(C5H5)2 and iron pentacarbonyl Fe(CO)5. Effects of the catalyst precursors on the formation and morphologies of HACNTAs were examined. A small amount of non-aligned multi-walled CNTs (MWCNTs) were grown from 1 mM Fe(C5H5)2 methanol solution. Highly pure HACNTAs composed of MWCNTs were readily grown from 10 and 40 mM Fe(C5H5)2 methanol solutions by this one-step liquid-phase process. From the Fe(CO)5 methanol solution, HACNTAs were prepared even at a very low Fe(CO)5 concentration of 0.01 mM, which was about 1/1000 lower than that of Fe(C5H5)2. The optimal low concentration is attributed to the low decomposition temperature of Fe(CO)5.

Artificial Transfer Hydrogenases Based on the Biotin−(Strept)avidin Technology: Fine Tuning the Selectivity by Saturation Mutagenesis of the Host Protein

Incorporation of biotinylated racemic three-legged d6-piano stool complexes in streptavidin yields enantioselective transfer hydrogenation artificial metalloenzymes for the reduction of ketones. Having identified the most promising organometallic catalyst precursors in the presence of wild-type streptavidin, fine-tuning of the selectivity is achieved by saturation mutagenesis at position S112. This choice for the genetic optimization site is suggested by docking studies which reveal that this position lies closest to the biotinylated metal upon incorporation into streptavidin. For aromatic ketones, the reaction proceeds smoothly to afford the corresponding enantioenriched alcohols in up to 97% ee (R) or 70% (S). On the basis of these results, we suggest that the enantioselection is mostly dictated by CH/pi interactions between the substrate and the eta6-bound arene. However, these enantiodiscriminating interactions can be outweighed in the presence of cationic residues at position S112 to afford the opposite enantiomers of the product.

Aqueous oxidation of alcohols catalyzed by artificial metalloenzymes based on the biotin–avidin technology

Based on the incorporation of biotinylated organometallic catalyst precursors within (strept)avidin, we have developed artificial metalloenzymes for the oxidation of secondary alcohols using tert-butylhydroperoxide as oxidizing agent. In the presence of avidin as host protein, the biotinylated aminosulfonamide ruthenium piano stool complex 1 (0.4 mol%) catalyzes the oxidation of sec-phenethyl alcohol at room temperature within 90 h in over 90% yield. Gel electrophoretic analysis of the reaction mixture suggests that the host protein is not oxidatively degraded during catalysis.

Design of artificial metalloenzymes

Homogeneous and enzymatic catalysis offer complementary means to generate enantiomerically pure compounds. For this reason, in a biomimetic spirit, efforts are currently under way in different groups to design artificial enzymes. Two complementary strategies are possible to incorporate active organometallic catalyst precursors into a protein environment. The first strategy utilizes covalent anchoring of the organometallic complexes into the protein environment. The second strategy relies on the use of non-covalent incorporation of the organometallic precursor into the protein. In this review, attention is focused on the use of semisynthetic enzymes to produce efficient enantioselective hybrid catalysts for a given reaction. This article also includes our recent research results and implications in developing the biotin–avidin technology to localize the biotinylated organometallic catalyst precursor within a well-defined protein environment. Copyright © 2005 John Wiley & Sons, Ltd.

Exploiting the Second Coordination Sphere: Proteins as Host for Enantioselective Catalysis

With the aim of exploring the role of the second coordination sphere in enantioselective catalysis, achiral organometallic catalyst precursors are anchored in proteins via non-covalent interactions. A chemogenetic procedure allows the activity and the enantioselectivity of the artificial metalloenzymes to be optimized, to yield hybrid catalysts with features reminiscent both of enzymatic and homogeneous catalysts.

Palladacycles − An Old Organometallic Family Revisited: New, Simple, and Efficient Catalyst Precursors for Homogeneous Catalysis

Nitrogen-, phosphorus-, and sulfur-containing palladacycles, typically containing four- or six-electron donor anionic metallated ligands, are emerging as a new family of organometallic catalyst precursors. These thermally and air-stable complexes are easy to handle and their synthesis is often straightforward. Palladacycles are now being successfully exploited in catalytic reactions ranging from classical hydrogenations to enantioselective aldol-type condensations. The main recent achievements pertaining to their use in homogeneous organometallic catalysis are outlined herein.

97/04544 Hydrodeoxygenation in low-rank coal liquefaction systems using novel organometallic catalyst precursors: Kirby, S. R. et al. Proc. Annu. Int. Pittsburgh Coal Conf., 1996, 13, (1), 466–471

Oxygen functionalities, especially phenols, are undesirable components of coal derived liquids. Removal of these compounds from the products of coal liquefaction is required. A beneficial alternative would be the removal of these functionalities, or the prevention of their formation, during the liquefaction process. Organometallic precursors of Co, Ni and Mo have been studied as catalysts. To ascertain the hydrodeoxygenation properties of these catalysts under liquefaction conditions, model compounds were investigated. Anthrone, Dibutylmethyl phenol, dinaphthyl ether and xanthene were studied to provide a comparison of conversions of deoxygenated products. Studies of the deoxygenating abilities of these catalyst precursors in coal liquefaction systems have also been performed. Improvements in conversion and product quality are observed. Both these factors are dependent on the coal used.

97/04529 Catalytic hydrodeoxygenation under coal liquefaction conditions using novel organometallic catalyst precursors: Virby, S. R. and Schobert, H. H. Prepr. Am. Chemical Soc., Div. Pet. Chemical, 1997, 42, (3), 643–647

97/04529 Catalytic hydrodeoxygenation under coal liquefaction conditions using novel organometallic catalyst precursors: Virby, S. R. and Schobert, H. H. Prepr. Am. Chemical Soc., Div. Pet. Chemical, 1997, 42, (3), 643–647

97/02705 Hydrodeoxygenation of O-containing polycyclic model compounds using a novel organometallic catalyst precursor

Polycyclic aromatic hydrocarbons (PAHs) are very toxic and highly persistent environmental pollutants which accumulate in soil and affect growth of the plants adversely. This study aims to investigate inhibitory effects of 3 major PAH particularly on photosynthetic processes in Arabidopsis thaliana grown in soil treated with PAH. The 3 PAH chosen differ from each other in aromaticity (number of rings) comprising their structure (2 rings: naphthalene, 3 rings: anthracene and 4 rings: pyrene). Several growth parameters and Chlorophyll a fluorescence was monitored in PAH treated plants. BN-PAGe analysis was done in order to get information about change in the protein conformation. PAH treatment led to increased value of Fo which collaborated with increase in the amount of free LHC as seen through BN-Page analysis. Thus PAH were found to inhibit PS II photochemistry and caused distinct change in pigment composition. However the results led us to infer that 3-ring anthracence is more inhibitory as compared to 2-ring naphthalene and 4-ring pyrene. This indicates that aromaticity of PAH is unrelated to their response on photosynthetic processes.

Effectiveness of dispersed catalysts in hydrocracking a coal liquefaction extract: a screening study

A coal liquefaction extract was hydrocracked in the presence of several metal carbonyls, organometallic catalyst precursors and a mixture of fullerites. Hydrocracking conversions and product quality achieved when using these materials (a set of metal carbonyls, Mo and Ni octoates and Mo naphthenate) were compared with the performance of a commercial presulfided NiMo/Al 2O 3 supported catalyst. Products were structurally characterized by size exclusion chromatography, u.v.-fluorescence spectroscopy and a t.g.a.-based method for determining boiling point distributions. In all cases, greater extents of reaction were observed during the first 30 min than during the rest of the reaction period (30–120 min). Molybdenum-based catalyst precursors were found to show greater activity than W(CO) 6, which in turn was more active than Fe(CO) 5 and Cr(CO) 6. Lower Mo loadings were required to achieve comparable or better conversions than Ni-based catalyst precursors; low loadings of Ni octoate led to conversions comparable with those observed in the absence of catalyst. The structural characteristics of products prepared in the presence of the fullerite mixture suggest that no particular advantage derives from the presence of this material; the results also suggest the possibility of adduction of the fullerites to coal-material. Differences between the activity of Mo-based catalyst precursors and the NiMo-supported catalyst in reducing >450°C b.p. materials to lower-boiling fractions were small. At 440°C, none of the catalyst precursors showed greater activity than the NiMo-supported catalyst; at lower reaction temperatures, however, some analyses suggested that Mo(CO) 6 was marginally more active. Furthermore, metal carbonyl catalyst precursors did not give significantly less gas production than the presulfided NiMo-catalyst. The present work describes experiments up to 2 h duration; unless it can be shown that finely dispersed catalysts are able to maintain high levels of activity and show better selectivity during longer exposure, the present evidence does not indicate demonstrably clear advantages for the preferential use of finely dispersed catalysts over conventional NiMo-supported catalysts in hydrocracking coal liquefaction extracts.

Hydrodeoxygenation of O-containing polycyclic model compounds using a novel organometallic catalyst precursor

Compounds containing oxygen functional groups, especially phenols, are undesirable components of coal-derived liquids. Removal of these compounds from the products of coal liquefaction is required. A beneficial alternative would be the removal of these compounds, or the prevention of their formation, during the liquefaction reaction itself, rather than as a separate processing step. A novel organometallic catalyst precursor containing Co and Mo has been studied as a potential hydrogenation catalyst for coal liquefaction. To ascertain the hydrodeoxygenation activity of this catalyst under liquefaction conditions, model compounds were investigated. Anthrone, 2,6-di-t-butyl-4-methyl-phenol, dinaphthyl ether, and xanthene were reacted in the presence of the Co-Mo catalyst precursor and a precursor containing only Mo over a range of temperatures, providing a comparison of conversions to deoxygenated products. These conversions give an indication of the hydrodeoxygenating abilities of organometallic catalyst precursors within a coal liquefaction system. For example, at 400°C dinaphthyl ether was converted 100% (4.5% O-containing products) in the presence of the Co-Mo organometallic precursor, compared to 76.5% conversion (7.4% O-products) in the presence of the Mo catalyst.

Characterization of large, polyanionic inorganic molecules: fast atom bombardment mass spectrometry of P2W15Nb3O629- and of the supported organometallic catalyst precursor (1,5-COD)Ir.cntdot.P2W15Nb3O628-

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCharacterization of large, polyanionic inorganic molecules: fast atom bombardment mass spectrometry of P2W15Nb3O629- and of the supported organometallic catalyst precursor (1,5-COD)Ir.cntdot.P2W15Nb3O628-Alessandro Trovarelli and Richard G. FinkeCite this: Inorg. Chem. 1993, 32, 26, 6034–6039Publication Date (Print):December 1, 1993Publication History Published online1 May 2002Published inissue 1 December 1993https://doi.org/10.1021/ic00078a022RIGHTS & PERMISSIONSArticle Views167Altmetric-Citations30LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Structural investigations of organometallic catalysts, catalyst precursors and ligands

Structural investigations of organometallic catalysts, catalyst precursors and ligands

PHOTOACTIVATION OF ORGANOMETALLIC CATALYSTS*

Abstract : Photochemistry offers a technique to synthesize unique catalysts, control catalytic reactions, and perturb and better understand conventional catalytic cycles. Recent studies in the author's laboratory concerning photoinduced catalysis using mono-, di-, and trinuclear organometallic catalyst precursors are summarized. Specific systems considered here are (M(CO)nL5-n) (M = Fe, Ru; L = PPh; n = 5,4,3), (M3(CO)12) (M = Fe, Ru, Os), (Ru3(CO)g(PPh3)3), and (Co2(CO)6L2) (L = P(n-Bu)3, P(OPh)3) used to effect catalytic chemistry of 1-pentene including isomerization, hydrogenation, and hydrosilation. (Author)