Pyrolysis metal carbonyls

Iron, nickel, cobalt, molybdenum, and tungsten powders produced by the pyrolysis of the respective metal carbonyl (see Ch. 3).P 1... 

From studies of the reactions of 2-arylazirines it is evident that transition metal carbonyls can also effect reactions under mild conditions to give products that would be obtained from alternative pyrolysis procedures. 

Rearrangements of clusters, i.e. changes of cluster shape and increase and decrease of the number of cluster metal atoms, have already been mentioned with pyrolysis reactions and heterometallic cluster synthesis in chapter 2.4. Furthermore, cluster rearrangements can occur under conditions which are similar to those used to form simple clusters, e.g. simple redox reactions interconvert four to fifteen atom rhodium clusters (12,14, 280). Hard-base-induced disproportionation reactions lead to many atom clusters of rhenium (17), ruthenium and osmium (233), iron (108), rhodium (22, 88, 277), and iridium (28). And the interaction of metal carbonyl anions and clusters produces bigger clusters of iron (102, 367), ruthenium, and osmium (249). 

In the case of rhodium, however, it was demonstrated early that in the synthesis of [Rh6C(CO)l5]2 the encapsulated carbon atom originated as chloroform, which had reacted with the rhodium carbonyl anion [Rh7(CO)l6]3- (59). In the cobalt analog, [Co6C(CO)l5]2-, the carbon atom is derived indirectly from carbon tetrachloride [via Co3(CO)9CCl] (60) Both these syntheses are performed under mild conditions, and there are apparently no examples of carbidocarbonyl clusters of cobalt or rhodium prepared directly from the metal carbonyls under pyrolysis conditions. 

The reaction of a carbonylmetalate with a neutral metal carbonyl has been labeled a redox condensation by Chini et al. (40, 41) and has been as widely used as a pyrolysis reaction for synthesizing mixed-metal clusters. Carbonylmetalates usually react rapidly with most neutral carbonyls, even under very mild conditions. A large number of mixed-metal hydride clusters have been formed via this type of reaction, primarily because the initial products are anionic clusters that in many cases may be protonated to yield the neutral hydride derivative. 

The metal-n-cyclopenladienyl bond is somewhat stronger in n-cyclo-pentadienyl derivatives than the metal-carbon bond in metal carbonyl derivatives. However, stepwise loss of 7t-cyclopentadienyl ligands occurs in the mass spectra of 7t-cyclopentadienyl derivatives 24>. The following fragmentation of ferrocene is particularly important because of the occurrence of ferrocene as a pyrolysis product in numerous mass spectra ... 

In some polynuclear metal carbonyls of the first row (3d) transition metals the metal-metal bonds are too weak to survive complete loss of carbonyl groups. Thus in the mass spectrum of Fe3(CO)i2 stepwise loss of carbonyl groups occurs only as far as the tricarbonyltriiron ion Fe3(C0)s 2fl>. The rupture of the iron-iron bonds competes with the stepwise loss of carbonyl groups givingions such as Fe2(CO)4 and Fe(CO)4. The mass spectrum of Fe2(CO)9 exhibits the ion Fe(CO) which may represent pentacarbonyliron formed by the following pyrolysis process25) ... 

The mass spectra of some metal carbonyl halides with it-cyclopen-tadienyl, 7t-cycloheptatrienyl, 7i-allyl and Tt-indenyl ligands have been investigated 52,38) The usual losses of carbonyl groups and C2H2 fragments are observed. The mass spectra of the chlorides exhibited a strong iodine memory effect, since ions expected for the corresponding iodides were also observed in their mass spectra. Pyrolysis of the halides... 

The most common synthetic method (Fe, Ru, Os) is via pyrolysis of noncarbide metal carbonyl derivatives. It seems probable that the high temperature (140°-260°C) is not only responsible for formation of coor-dinatively unsaturated species and related condensations but also for the necessary disproportionation of carbon monoxide (58) ... 

Pyrolysis plant safety - carbon monoxide, metal carbonyls, carcinogens. 

Metal carbonyl clusters containing four or more metal atoms are made by a variety of methods osmium in particular forms a range of binary compounds and pyrolysis of Os3(CO)i2 yields a mix of products (equation 23.15) which can be separated by chromatography. 

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