Catalytic decarbonylation

Walborski and Allen have shown that stiochiometric decarbonyla-tion of an optically active aldehyde with RhCl(PPh3)3 gives complete retention of configuration (5). Using [Rh(dppp)]BF4, (-) - (R)-2-phenyl-2-methylbutanal was decarbonylated catalytically at 165°C (0.4 turnovers hr-1) into (+) - (S)-2-phenylbutane with 100% retention of optical activity (21, 22). 

At elevated temperature, RhCl(PPh3)3 becomes a catalyst (or catalyst precursor) for the decarbonylation reaction. Acid chlorides are reported to be decarbonylated catalytically at A recent report has... 

Aldehydes are decarbonylated catalytically using solutions of bis(triphenylphosphine)(tetraphenylphorphyrinato)ruthenium(ii) at, or slightly above, room temperature. Decarbonylation of aromatic aldehydes takes place... 

Organomercurial carbonylation. Use of Co2(CO)g as a stoichiometric and as a catalytic reagent Organic synthesis reactions using palladium compounds Decarbonylation reactions using transition metal compounds... 

Dimethylmalonate 75 coordinates to a Fe(CO)4 species, yielding a ferrate species 128. This coordinates the allylic substrate under decarbonylation and by nucleophilic attack at the double bond an allyliron-species 131 is generated which undergoes substitution of the ferrate 132 by a dimethylmalonte molecule 75. Although there is some evidence of this catalytically active ferrate 128, until now it could not be fully analytically characterized and therefore the structure presented above still remains a hypothesis. 

In 1998, Wakatsuki et al. reported the first anti-Markonikov hydration of 1-alkynes to aldehydes by an Ru(II)/phosphine catalyst. Heating 1-alkynes in the presence of a catalytic amount of [RuCljlCgHs) (phosphine)] phosphine = PPh2(QF5) or P(3-C6H4S03Na)3 in 2-propanol at 60-100°C leads to predominantly anti-Markovnikov addition of water and yields aldehydes with only a small amount of methyl ketones (Eq. 6.47) [95]. They proposed the attack of water on an intermediate ruthenium vinylidene complex. The C-C bond cleavage or decarbonylation is expected to occur as a side reaction together with the main reaction leading to aldehyde formation. Indeed, olefins with one carbon atom less were always detected in the reaction mixtures (Scheme 6-21). 

The extremely low turnover rate (0.011 mmol CO/nmol Co/h, production of 0.003 mmol CH /mmol Co/h average), stimulated attempts to increase the efficiency of the reaction. Indeed, pretreatment involving removal of CO via vacuum thermolysis of CpCo(C0)2 5 to yield " CpCo", followed by its use in a Fischer-Tropsch reaction, led to improved activity (turnover of 0.130 mmol CO/irmol Co/h, production of 0.053 mmol CH /mmol Co/h average). It appears that decarbonylation is necessary for formation of the catalytically active species. 

The catalytic runs are performed with these adducts or with the materials recovered from their total decarbonylation at 200°C under vacuum. 

We recently reported briefly on an extremely efficient thermal catalytic decarbonylation of aldehydes using a system based on Ru(TPP)(PPI13)2 (6), and report here further studies on this system and one based on Ru(TPP)(CO)(tBu2P0H). 

Figure 1. Visible spectrum typical of solution no longer active for catalytic decarbonylation that shown here is for solution of Ru(TPP)(PPh3)2/nBu3P after decarbonylation of PhCH2CHO (----) same solution in presence of hydroquinone inac-...

The present paper focuses on the interactions between iron and titania for samples prepared via the thermal decomposition of iron pentacarbonyl. (The results of ammonia synthesis studies over these samples have been reported elsewhere (4).) Since it has been reported that standard impregnation techniques cannot be used to prepare highly dispersed iron on titania (4), the use of iron carbonyl decomposition provides a potentially important catalyst preparation route. Studies of the decomposition process as a function of temperature are pertinent to the genesis of such Fe/Ti02 catalysts. For example, these studies are necessary to determine the state and dispersion of iron after the various activation or pretreatment steps. Moreover, such studies are required to understand the catalytic and adsorptive properties of these materials after partial decomposition, complete decarbonylation or hydrogen reduction. In short, Mossbauer spectroscopy was used in this study to monitor the state of iron in catalysts prepared by the decomposition of iron carbonyl. Complementary information about the amount of carbon monoxide associated with iron was provided by volumetric measurements. 

Reactions that have led to other deoxyhalogeno sugars do not necessarily lead to deoxyfluoro sugars, as, for example, in the attempted decomposition of fluoroformates, the treatment of diazoketones and of 2-deoxy-2-diazohexonates with hydrogen fluoride, and the reaction of benzoxonium ions with halide ions. The reaction2281229 by which fluoroformates are thermally or catalytically decarbonylated to give alkyl fluorides has been applied to carbohydrates. Both thermal and catalytic treatment of 6-0-(fluoroformyl)-l,2 3,4-di-0-isopropylidene-... 

Morimoto, Kakiuchi, and co-workers were the first to show that aldehydes are a useful source of CO in the catalytic PKR [68]. Based on 13C-labeling experiments, it was proposed that after decarbonylation of the aldehyde, an active metal catalyst is formed. This was proven by the absence of free carbon monoxide. As a consequence CO, which is directly generated by previous aldehyde decarbonylation, is incorporated in situ into the carbonylative coupling. The best results were obtained using C5F5CHO and cinnamaldehyde as CO source in combination with [RhCl(cod)]2/dppp as the catalyst system. In the presence of an excess of aldehyde the corresponding products were isolated in the range of 52-97%. 

Di-rm-butylphenol dealkylation, 41 161, 171 Dodecacarbonylhexarhodium, reversible catalytic decarbonylation, 35 206-207 Dodecacarbonyltriiron, reaction on catalytic surfaces, 35 192-194 on alumina, 35 192 on silica, 35 190... 

It has been reported that the size of the metal cluster frame of Ru6Pt3(CO)2i( X3-H) ( X-H)3 remains on Y-AI2O3 and MgO after its impregnation and decarbonylation under He at 300 °C [65, 66]. The metallic clusters were rather strongly bound to both supports, Y-AI2O3 and MgO. The catalytic behavior of these materials in n-butane hydrogenolysis shows the suppression of the isomerization reaction according with an intimate association of Pt with Ru atoms. 

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]. 

Deposition of Co2(CO)g from the gas phase under a CO or N2 atmosphere on mesoporous high surface-area MCM-41 material has been reported [148]. Under CO, a Co2(CO)g monolayer coverage of up to 21 wt% cobalt was obtained. Although treatment at circa 150°C under N2 produced total decarbonylation, the surface area and pore size of the sample did not change and the presence of metalUc cobalt species could not be determined from the XRD patterns of decarbonylated samples these facts could indicate a good metal dispersion and capabilities for catalytic uses in hydrogenation reactions [148]. 

Iridium carbonyl clusters of several nuclearities (2, 4 and 6) have been prepared by a controlled carbonylation of [lr(CO)2(acac)] complex adsorbed in the cages of a NaY zeolite. Then, decarbonylation of the clusters gave rise to lr2, lr4 and Ir frames. Studies of the dependence of the catalytic activity on the size of the iridium frames in NaY zeolites show that there is no simple explanation for the variation in catalytic performance in ethene hydrogenation with cluster size [208]. 

The appropriate decarbonylation of surface carbonyl species can lead to the retention of the metal frame. When the original metal frame is preserved under reaction conditions, and it is properly characterized, a direct structure-catalytic properties relationship can be established, and the catalytic behavior of supported metaUic clusters can be differentiated from that of the supported metallic particles. 

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