Metal carbonyl precursors

Kramer, J., Redel, E., Thomann, R. and Janiak, C. (2008) Use of ionic liquids for the synthesis of iron, ruthenium, and osmium nanopartides from their metal carbonyl precursors. Organometallics,... 

The rates of the water gas shift reactions were compared using different amounts of the mononuclear metal carbonyl precursor for all four cases (Fe(CO) and M(CO) where M = Cr, Mo, and W). In all cases the rates of hydrogen production were found to double as the concentration of the metal carbonyl was doubled. Thus all of the water gas shift reactions investigated... 

The above exposition shows that homo- and heteronuclear metal carbonyl precursors have been used successfully in the preparation of supported metal catalysts that behave better than those prepared by conventional methods. This is frequently... 

As mentioned above, appropriate hydride nucleophiles are capable of attacking coordinated CO [Eq. (3)]. This route to anionic formyl complexes was reported in 1976 by Casey, Gladysz, and Winter (29-34). All of the anionic formyl complexes in Table 1, including 22 [Eq. (4)], can be prepared by hydride attack on neutral metal carbonyl precursors. 

This catalytic labilization of carbonyl groups has been extended to the replacement of carbonyls in metal carbonyl clusters. Metal cluster complexes are at present the subject of extensive studies, partly because of their possible relevance as models for chemisorbed metal surfaces and because of their catalytic activity. The majority of these clusters contain carbonyl ligands, and these have been prepared from the vast number of metal carbonyl precursors generally available by a variety of synthetic methods usually without recourse to designed or rational procedures. In metal isocyanide chemistry, however, suitable precursors are lacking, and as a consequence, there are few routes to homoleptic metal-isocyanide clusters, and few isocyanide clusters are known (see Section IV,A). 

For the preparation of acyl and carbene complexes variation is not restricted to the metal carbonyl precursor. Besides PhLi, MeLi and BuLi, a number of different lithium... 

Alkene hydrogenation, alkane hydrogenolysis, and methanation of CO are used as test reactions for evaluating the catalytic activity of cluster-derived metal catalysts. Catalysts derived from noble metal carbonyl precursors such... 

Chemistry similar to that described above for iridium clusters has also been observed for rhodium clusters. Several authors [16-18] have prepared [Rh6(CO)i6] in NaY zeolite [R1i4(CO)i2] has also been formed [18], and each of these has been decarbonylated with minimal changes in the metal frame, as shown by EXAFS spectroscopy [18]. Thus there appears to be some generality to the method of forming small clusters in zeolite cages by synthesis of stable metal carbonyl precursors followed by decarbonylation. However, the method is limited. Attempts to use it to prepare zeolite-supported platinum clusters that are structurally simple and uniform have apparently not been successfiil. The literature of platinum carbonyl clusters in zeolites is not considered here because it is still contradictory. 

Sample Preparation. Cobalt catalysts were prepared by subliming Co2(C0)g into the pores of dehydrated NaX zeolite in a vacuum line at pressures of 1 x 10- f torr. Argon was flowed over the metal loaded zeolite sample at a pressure of 0.3 torr. A microwave plasma was induced with a static gun and the decomposition of the metal carbonyl precursor occurred for two hours. After total decomposition of the metal carbonyl which can be determined by the color of the plasma, the argon flow was stopped and the sample was sealed off by closing the Teflon stopcocks at both ends of the reactor. The sample was then brought into a drybox and loaded into catalytic reactors or holders for spectroscopic experiments. Further details of this procedure can be found elsewhere (11, 25). Iron samples were prepared in a similar fashion except ferrocene was used as a metal precursor. 

The IR characterization of dihydrides and alkyl hydrides are aided by three factors, comparison with literature spectra, the comparatively high wavenumber of the v(C-O) bands caused by the oxidation of the metal center relative to the metal carbonyl precursor [3] and in many cases direct observation of a weak IR band due to v(M-H) vibrations [28,29]. As with dihydrogen compounds, these... 

Examples given below illustrate synthesis of alkene polymerization catalysts, but these catalysts are simpler than the supported metallocenes used in industry, because they lack the promoter methylaluminoxane (MAO), an ill-defined material that greatly complicates characterization. Other examples given below illustrate (a) details of the surface chemistry of conversion of an organometallic precursor into a supported catalyst (b) synthesis of metal clusters of various sizes and compositions on a family of supports from metal carbonyl precursors and (c) synthesis of supported bimetallic clusters with combinations of noble (e.g., Pt) and oxophilic (e.g., W) metals that give quite stable catalysts with extremely high metal dispersions. 

Complex 20 has become a very useful metal carbonyl precursor for the preparation of CO-RMs. CO-RM 24 is prepared by reaction of 20 with tpm ligand 23 in the presence of NaPFe-... 

Stable ruthenium, rhodium, and iridium metal nanoparticles have been reproducibly obtained by facile, rapid, and energy-saving microwave irradiation under an argon atmosphere from their metal-carbonyl precursors [M(x)(CO)(y)] in the ionic liquid l-butyl-3-methylimidazolium tetrafluoroborate (Redel et al., 2009 Vollmer et al., 2010). The metal nanoparticles synthesized have a very small (<5 nm) and uniform size and are prepared without any additional stabilizers or capping molecules as long-term stable metal nanoparticles-ionic liquid dispersions. The ruthenium, rhodium, or iridium nanoparticles dispersed in ionic liquids are highly active and easily recyclable catalysts for the biphasic liquid-liquid hydrogenation of cyclohexene to cyclohexane. 

Microwave irradiation for the facile synthesis of transition-metal nanopartides (NPs) in ionic hquids (ILs) from metal-carbonyl precursors and Ru-, Rh-, and Ir-NP/IL dispersions as biphasic hquid-hquid hydrogenation nanocatalysts for cydohexene. Chemistry A European Journal, Vol.16, No.l2, (March 2010), pp. 3849-3858, ISSN 1521-3765... 

A different approach towards the incorporation of metal oxide clusters into zeo-litic pores via chemical vapor deposition has been studied extensively by Ozin et al. [236 - 240]. They developed a method denoted as intrazeolite metal carbonyl phototopotaxy . Metal carbonyls are used as precursors to obtain the occluded guest component because of their volatility, fitting molecular dimensions, ease of purification, ready availability, and facile and quantitative conversion to the respective metal oxide materials with minimal contamination by carbon [236, 240]. The metal carbonyl precursors are transformed into the metal oxides by photochemical oxidation. The term phototopotaxy is meant to indicate the similarity of this preparation method to epitactical growth of semiconducting oxide layers on planar surfaces commonly used to form low-dimensional quantum nanostructures for applications in electronic and optical devices [238]. 

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