Osmium pyrolysis

The pentanuclear carbido species Ms(CO)lsC (M = Fe, Ru, Os) have been prepared. The iron compound has been known for some considerable time (209), but the ruthenium and osmium complexes were prepared recently by pyrolysis reactions (210). The ruthenium adduct was only isolated in low yield (—1%), while the osmium complex was obtained in higher yield (—40%). The infrared spectrum and mass spectral breakdown pattern indicate a common structure to these compounds. The molecular structure of the iron complex is shown in Fig. 46. 

The formation of carbido-carbonyl cluster compounds with ruthenium and osmium appears to be common in pyrolysis reactions the basic reaction may be viewed as the transformation of the coordinated carbon monoxide to carbide and carbon dioxide. Small variations in... 

Two isomers of this compound (designated a and (3) have been claimed (see Table 10) although most preparations usually give the a-isomer which has the structure shown in Fig. 9. The osmium dihydride, Os4(CO)13H2, which is probably iso-structural with a-Ru4(CO)13H2, has been obtained from the mixture resulting on pyrolysis... 

Methylbenzene halogen complex of, 3 122 iodine monochloridecomplese, 3 109 Methylchlorosilanes hydrolysis, 42 149-150, 157 pyrolysis products of, 7 356-363 Methylcobalamin, 19 151, 152 Methyl-coenzyme M reductase, 32 323-325 EPR spectra, 32 323, 325 F43 and, 32 323-324 function, 32 324-325 Methyl-CoM reductase, 32 329 Methyl cyanide, osmium carbonyl complexes, reaction, 30 198-201 Methylcyclophosphazene salts, 21 70 synthesis, 21 109... 

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). 

The substitution reactions can be accompanied by subsequent reactions. Thus, Ru3(C0)i2 reacts with azobenzene (61) or fluorinated azobenzenes (60) to yield products like [47], and the pyrolysis of Ru3(CO)9L3 complexes leads to reactions similar to those discussed in Chapter 3.4. for the corresponding osmium clusters. Rearrangements and orthometalations were observed (65, 66), and one cluster formulated as [42] was isolated (65). 

The osmium analog was obtained in moderate yield by pyrolysis of Os CO) or Os3(CO),2 (20). Both the ruthenium (29) and osmium clusters (31) are isostructural with the original iron analog, 1 (2), the metal atoms describing a square pyramid, each vertex bearing three terminal carbonyls. The carbon atom lies fractionally below the center of the basal plane of the cluster, protruding 0.11 A below the Ru4 plane in 10 and 0.12 A below the Os4 plane in 11 [cf. a value of 0.08 A for Fe5C(CO)15 (2)] (see Fig. 11). 

Pyrolysis reactions of mononuclear carbonyls and low-nuclearity cluster compounds have been used extensively in the syntheses of HNCC of osmium (54, 72,80,95,108), ruthenium (18,20,29), and, more recently, rhenium (2-4). The reactions have been carried out either in inert solvents or, to facilitate the ejection of CO or other volatile ligands, in the solid state under vacuum. Condensation processes under pyrolytic conditions are rarely specific and, as such, lead to the formation of a wide range of products. In order to obtain optimum yields of a particular HNCC, the reaction conditions must be carefully screened. Solution reactions offer advantages such as the ability to monitor the progress of the reaction using IR spectroscopy. As they often give... 

A large number of HNCC of osmium have been produced from the vacuum pyrolysis of Os3(CO)i2 and some of its derivatives (Scheme 1). The reaction of Os3(CO)i2 has been shown to be extremely sensitive to temperature, time, and moisture, giving a series of products whose nuclearities range from 5 to 11 and possibly higher 41, 54, 80, 134). By optimizing the conditions, yields up to 80% of Os6(CO)ig have been obtained 41). High specificity has also been observed in the vacuum pyrolysis of Os3(CO)ii(C5H5N), from which [OsioC(CO)24j] has been obtained in 65% yield 80). 

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. 

This structure was confirmed by a partial synthesis of (81) from delphisine (82). Pyrolysis of (82) gave pyrodelphisine (83), which when hydrolysed afforded pyroneoline (84). Treatment of (84) with osmium tetroxide in pyridine/dioxane followed by aqueous sodium bisulfite gave 1sp-hydroxyneoline (81), which was identical in all respects with nagarine. ... 

Until recently, the favored route to higher nuclearity clusters has generally been via pyrolysis or thermolysis, and indeed the highest nuclearity, homonuclear osmium cluster anion to have been prepared, [Os2o(CO)4o], was isolated in reasonable... 

The parent heptanudear osmium cluster, [Os7(CO)2i], is prepared from the pyrolysis of [Os3(CO)i2]. The crystal structure confirms that the metal framework is a capped octahedron consistent with electron count of 98 e and the presence of seven skeletal electron pairs.The neutral carbonyl can be readily reduced to the dianion [Os7(CO)2o] with K/Ph2CO, and an X-ray analysis shows that the capped octahedral metal framework is retained (Fig. The reaction of this dianion... 

The bicapped octahedral octanuclear osmium cluster dianion [Osg(CO)22] can be prepared from the solid state pyrolysis of [Os3(CO)io(NCMe)2]. An X-ray analysis of the [N(PPh3)2j salt shows that the two Os(CO)3 caps occupy the 1 and 3 faces of the octahedron s as shown in Fig. 10, and the structure of the dianion is consistent with the electron count of 110 e and seven skeletal electron pairs. 

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