Carbonyl precursors

And here s the two representative methods one would use. Just imagine the carbonyl precursor as a P2P and the amine as methylamine. Visualize.,..man ... 

Alcohols also may serve as carbonyl precursors. The reaction with aliphatic alcohols is thought to go through a carbonyl intermediate, but since no hydrogen is actually consumed, the reaction appears to be an amination, as it... 

Erosion resistant coatings for gun steel barrels deposited with carbonyl precursor. 

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 examples represent Jl-heteroaromatic annulation involving the reaction of allyl anions whose double bond is a part of the heterocyclic ring system (Scheme 1). The corresponding a-oxoketene dithioacetals (1,3-electrophilic component) were generally derived from nonheterocyclic carbonyl precursors. Alternatively the Jl-heteroaromatic annulation can also be employed to a-oxoketene dithioacetals derived from heterocyclic ketones (1,3-bielectrophile) and hetero/nonheteroallyl anions (1,3-binucleophile). These reactions are described below. 

The a-oxoketene dithioacetal 6.40 is derived from indoxyl (l,2-dihydroindol-3-one), a heterocyclic carbonyl precursor, and its reaction with simple allyl anions will also yield the corresponding Jl-annulation product. Thus when 6.40 was reacted with allyl anions 65 the corresponding carbinol acetals 66 formed insitu underwent smooth BF3.Et20 assisted cyclization to afford the corresponding carbazoles 67 in high yields <99T11563>. 

Nitrate and carbonyl precursors of Co were used for the impregnation of ZnO support synthesized by the decomposition of 3ZnO 2ZnC03 3H20. Catalyst synthesized using carbonyl precursor was stable and selective for the production of CO-free H2... 

In this body of catalysts, the metal cluster is said to be formed around the carbonyl precursor. According to SEM and TEM imaging, it appears that the carbonyl clusters are on the order of 1 pm in diameter when supported on carbon.192 Analysis with FTIR has shown that the carbonyl is present.189 190 198-200 203 Non-noble metals have also been studied along side the noble-metals in this group of catalysts. Table 4 lists the non-noble metal carbonyl catalysts studied.189-192 198-200 The non-noble metal carbonyl catalysts studied produced mixed results for the ORR activity. 

Several reasons can be considered for using metal binary carbonyl precursors in the preparation of metal supported catalysts ... 

The use of hetero-metallic (MM )carbonyl complexes as precursors can lead to the preparation of supported catalysts having weU-defined bimetallic entities in which the intimate contact between M and M remains in the final catalyst and the atomic ratio M/M of the aggregates is that of the bimetallic carbonyl precursor used. This is illustrated in Figure 8.1, in which the definite interaction of the MjM (CO) complex with the functional group (F) of a surface (S) produces a new anchored surface species. This new surface species could evolve with an appropriate treatment producing tailored bimetallic particles. 

The accessibility of new techniques such as EXAFS brings researchers a powerful tool for unambiguous determination of the true core metallic framework of such systems. Thus, the relationship between the parent carbonyl precursor, the support and the final metal-supported particles has been studied at the structural atomic level in some cases. This can allow differentiation of the catalytic behavior of supported metal particles with bulk-like properties from that of supported metal clusters, opening the way to understanding the mechanism of metal-catalyzed reactions and extending the concept of sensitive or insensitive structure reactions from metal aggregates to clusters. 

The Pt-Re system has been studied extensively since the 1970s because adding Re to AhOs-supported platinum catalysts increases the resistance to deactivation of the catalysts used in naphtha reforming by preventing coke deposition. By using carbonyl precursors, well-defined bimetalhc species have been prepared. A proper characterization of these species allowed a relationship to be established between their structure and their catalytic behavior. Table 8.3 shows several Pt-Re bimetaUic catalytic systems prepared using different carbonyl species in which Pt-Re interactions determine the catalytic behavior. 

Supported ruthenium catalysts prepared from Ru3(CO),2 have been used in CO hydrogenation because of the highly dispersed metallic phase achieved when this carbonyl-precursor is used [70,107-109]. However, under catalytic reaction conditions the loss of ruthenium from the support could take place, ft has been reported that at low temperatures it takes place through the formation of Ru(CO)s species, whereas at high temperature dodecarbonyl formation occurs [110]. Decarbonylation of the initial deposited carbonyl precursor under hydrogen could minimize this problem [107]. 

Alumina-supported Ru catalysts derived from supported ruthenium carbonyls have been reported to be effective for carbon dioxide methanation, showing higher activity than other catalysts prepared from RUCI3. The catalytic activity depended on the nuclearity of the carbonyl precursor [111]. 

Ruthenium catalysts prepared from Ru3(CO)i2 and other related carbonyl-derived complexes have been widely used in reactions of hydrogenolysis, homologation and dimerization of alkanes [114—116]. Catalysts derived from carbonyl precursors usually show higher catalytic activities than conventionally prepared supported mthenium catalysts. This correlates well with the smaller crystallite size achieved by using carbonyl precursors. 

Zirconia-modified silica impregnated with Co2(CO)s and activated under H2 at 300 °C renders a catalyst more active and selective to diesel fraction, in the CO hydrogenation reaction, than that conventionally prepared from a nitrate salt solution. The selectivity patterns followed a Schulz-Flory distribution and catalysts prepared from carbonyl precursor exhibited low water-gas shift activity [146]. 

Continuing interest in cobalt catalysts used in the Fischer-Tropsch synthesis has led to the proposal of new methods of catalyst preparation that could determine the selectivity of the catalysts obtained. In this context, a highly selective material to produce C5+ hydrocarbons using a plasma-based method and carbonyl precursors has been prepared [147]. 

On an alumina support, independently of the cobalt carbonyl precursor used, complex cobalt sub-carbonyls compounds, [Co(CO)4] and hydrogencarbonate species formed [143, 149]. However, the reactivity of the alumina surface depends on the degree of hydroxylation highly hydroxylated alumina is more reactive against Co2(CO)g and facilitates decarbonylation, whereas dehydroxylated alumina favors the formation of high nuclearity species like [Co6(CO),5] , which would need higher temperatures than the initial Co2(CO)8 to be decarbonylated [149]. 

Zeolites have attracted much attention as cobalt catalyst supports ]151-155]. Co2(CO)8 reacts rapidly from the vapor phase with X and Y faujasite type zeolites Co4(CO)i2, subcarbonyl species and [Co(CO)4] species form inside the pores. Further migration of Co4(CO)i2 carbonyl is inhibited because of pore size hmita-tions, and subsequent decarbonylation can take place only above 150 °C. In contrast, the reaction of Co2(CO)g with an A-type zeolite is limited to the surface due to the inability of the carbonyl precursors to pass through the apertures of the cavities of the structure. 

Cobalt-based catalysts are effective in the ethanol reformation to hydrogen. Many oxides have been used to prepare supported cobalt catalysts of low cobalt content (circa 1 wt%) by impregnation from a solution of Co2(CO)8 catalysts were used in the ethanol reformation as prepared [156]. The performance of the catalysts in the steam reforming of ethanol was related with the presence, under reaction conditions, of metallic (ferromagnetic) cobalt particles and oxidized cobalt species. An easy exchange between small metallic cobalt particles and oxidized cobalt species was found. Comparison of Co/ZnO catalysts prepared from Co2(CO)8 or from nitrate precursor indicated that the catalyst prepared from the carbonyl precursor was highly stable and more selective for the production of CO-free hydrogen... 

Alumina-supported catalysts prepared using the bimetallic carbonyl precursors showed a better performance in alkene hydroformylation than conventional Co-Rh catalysts. This was related to the presence of highly dispersed Rh-Co clusters with frames corresponding to that of the parent carbonyl-precursor that were characterized by EXAFS [140, 183]. Silica-supported bimetallic entities RhCo3,... 

The study of propylene hydroformylahon reaction over the above-mentioned cluster-derived bimetallic catalysts showed that their activity followed the trend FeRhs < FeRh4 < Fe2Rh4 > Fe3Rh2. Moreover, hydroformylahon activity of these bimetallic systems was higher than that of the catalysts prepared by co-impregnahon using monometallic Rh and Fe carbonyl precursors in the same Rh/Fe metal ratios ]192]. 

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... 

Enrichment may be accomplished either thermally or photochemically, depending on the carbonyl involved, or labelled species may be prepared by the reaction of labelled CO with an incompletely carbonylated precursor. Substitution will lead to generation of multiply labelled species by successive replacement... 

In the case of the benzothiazole system, both aldehydes and mixed ketones have been synthesized by reduction or alkylation of the appropriate carbonyl precursors. The carbonyl compounds are in turn prepared from the benzothiazole-2-anion either directly by reaction with esters or indirectly by reaction with aldehydes followed by PCC oxidation (Scheme 154) (85H2467 91BCJ3256). 

Little work has been done in the field of fluorinated lysines 5-fluorolysine has been prepared by fluorination of lysine with CF3OF/HF under UV irradiation, " while preparation of 5,5-difluorolysine has been described by treatment of a suitable carbonyl precursor by SF4. ... 

Whereas the surface interaction between [Mo(CO)6] and oxide supports were extensively studied and reactivity features generally well described, in depth characterization of the final deposif was offen neglecfed in the spectroscopic studies. On the other hand, many CVD studies carried out with zerova-lent carbonyl precursors revealed that incorporation of significant amounts of carbon and oxygen takes place. Additional studies are thus needed to correlate the influence of the state of the surface of the substrate to the chemical purity of the deposited ultra-thin films or nanoparticles. Probably, and as shown in other cases, the addition of a reactive gas in the system could also improve the quality of the films. 

Although the reaction of dihydropyridinium ions produced by the electrophilic attack of dihydropyridines has promise in organic synthesis, this reaction has not been extensively exploited. Some examples of their potential are provided by the acid-catalyzed reactions with indoles (80TL2341). An application of this reaction for an efficient synthesis of ( )-deplancheine is shown in Scheme 25. An interesting feature of this reaction was the use of the alkoxy-substituted dihydropyridine as a carbonyl precursor. 

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