Metal carbonyl compounds, supported

Metal bromides, 4 322-330 Metal can food packaging, 18 37-39 Metal-carbene complexes, 26 926 Metal-carbon compounds, 4 648, 650 Metal-carbon eutectic fixed points, 24 454 Metal carbonyl catalysts, supported, 16 75 Metal carbonyl complexes, 16 73 Metal carbonyls, 15 570 16 58-78 bonding and structure of, 16 59-64 from carbon monoxide, 5 12 in catalysis, 16 72-75 economic aspects of, 16 71 health and safety aspects of, 16 71 heteronuclear, 16 69-71 high nuclearity, 16 66-69 high nuclearity carbonyl clusters, 16 64-66... 

The use of highly dispersed catalysts from soluble salts of molybdenum is another approach to the reduction of catalyst amount because of their excellent activity despite their higher price. Recently, metal carbonyl compounds, such as Fe(CO)5, Ru3(CO)i2, and Mo(CO)6 have been investigated as metal cluster catalysts. Preparation involved their deposition and decomposition on catalyst support surfaces (71-73). 

Aluminum oxide itself catalyzes the metathesis reaction of propylene, although its activity is low. Catalysts that are obtained from oxides are active at temperatures ca 100 K higher than catalysts prepared from metal carbonyls. Compounds deposited on silica are catalytically active at temperatures which are higher by ca 200 K than compounds supported on aluminum oxide. However, because of the Si02 support these catalysts are more resistant to poisoning by polar compounds. Heterogeneous catalysts must be activated at 390-870 K before use. Catalysts obtained from metal carbonyls and alkyl compounds require lower temperatures of activation. Supported allyl complexes of Mo, W, and Re need no activation. 

Table I. Bimetallic catalysts obtained by interaction of metal carbonyl compounds with the surfaces of supported metals...

The 13C-NMR spectra of 4-7, 9-11 show a close similarity to the spectral data of analogous carbene complexes. The shift differences between the metal carbonyls of the silylene complexes and the related carbon compounds are only small. These results underline the close analogy between the silicon compounds 4-7, 9-11 and Fischer carbene complexes. This view is also supported by the IR spectral data. On the basis of an analysis of the force constants of the vco stretching vibration,... 

Tributyltin hydride reduction of carbonyl compounds. The reduction of carbonyl compounds with metal hydrides can also proceed via an electron-transfer activation in analogy to the metal hydride insertion into TCNE.188 Such a notion is further supported by the following observations (a) the reaction rates are enhanced by light as well as heat 189 (b) the rate of the reduction depends strongly on the reduction potentials of ketones. For example, trifluoroacetophenone ( re<1 = —1.38 V versus SCE) is quantitatively reduced by Bu3SnH in propionitrile within 5 min, whereas the reduction of cyclohexanone (Erea — 2.4 V versus SCE) to cyclohexanol (under identical... 

Homs, N. and d. 1. Piscina, P.R. (2009) Carbonyl compounds as metallic presursors of tailored supported catalysts, in Modern Surface Organometallic Chemistry (eds J.M. Bassett, R. Psaro, D. Boberto and R. Ugo), Chapter 8, Wiley-VCH, Weinheim. 

Carbonyl Compounds as Metallic Precursors of Tailored Supported Catalysts... 

Reasons for the Use of Metal Binary Carbonyl Compounds as Precursors in the Preparation of Tailored Supported Catalysts... 

In many cases, during the impregnahon a surface reaction between the organometallic compound and the surface takes place. The pretreatment of the support can be used to define the distribution of anchorage centers on the surface, and a homogeneous distribution of metal carbonyl surface species can be achieved. 

In many studies in which carbonyl compounds have been used as precursors in the preparation of catalysts there is no straightforward characterization in terms of the number of metallic atoms in the supported metaUic entities, there being uncertainties about true structural considerations. Analysis of the catalytic behavior is interpreted mainly in the Ught of electron microscopy analysis, and indirect characterization methods, such as infrared (IR) spectroscopic analysis of (de)carbonylation of the metal framework, and so on. 

Sections 8.3.1-8.3.3 present the use of iron, mthenium and osmium carbonyls, respectively, in the preparation of supported catalysts. Over non-inert supports, besides the characteristics of carbonyl compounds, the reactivity of the surface and that of the specific element, mainly related with its redox properties, will be covered for each metal. 

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