Unstable organometallics

The demonstration that stable and unstable organometallic compounds could be made in gram quantities from transition metal... 

Liquefied Xe and Kr have two features which make them particularly attractive as low-temperature solvents for examining the spectra of unstable organometallics. These solvents are inert, and this is important as the significant role of even innocuous solvents such as cyclohexane is more readily recognised in contrast to conventional solvents for IR spectroscopy they have no absorptions over a wide range of the spectrum, which also permits the use of special long path cells to overcome problems of low solubility. 

Fig. 1, the metal atoms may be generated in an electrically heated crucible and co-condensed with the substrate on the cold walls of the reaction vessel. To minimize gas-phase reactions, a good vacuum must be maintained in the reactor during this codeposition. An alternative procedure is to condense the metal vapor into a well-stirred solution of the reactant in a suitable solvent cooled to a temperature at which the vapor pressure of the solution is <10 3 torr. This method has special advantages for the preparation of unstable organometallic compounds and for reacting metal atoms with nonvolatile substrates.2... 

Metal atoms are oxidized on interaction with many compounds containing polar bonds R—X. This effect has already been noted in Section III in reactions of metal atoms with arenes containing electronegative substituents. The products of oxidation that can be isolated are of three types, namely, RMX, RM, and R2 + MX unstable organometallic products can be sometimes stabilized by addition of a ligand, L, at low temperatures to give RM(Ln)X or RML . 

The ability of n-arene metal complexes to coordinate additional metal atoms may be significant in the early stages of metallization of some phenyl-rich polymers. At the lowest coverages of say chromium on polystyrene, (arene)2Cr may be formed. With continued accumulation of metal these compounds may rapidly convert to thermally unstable organometallic cluster species that eventually expel the metal core. 

These results illustrate the utility of photochemical methods for preparing and characterizing thermally unstable organometallic intermediates via low-temperature irradiation. In many cases, photoinduced ligand loss can occur at temperatures low enough that intermediates thus formed do not have enough internal energy to further react so that they can be characterized. The subsequent thermal decomposition of such compounds can then be monitored upon warm-up of the solutions. 

The sp3 organometallic intermediates, which form the subject of this book, give the expected coupling products with primary alkyl bromides, the usual solvent being THF. The use of iodides does not offer special advantages except in alkylations of unstable organometallic compounds such as lithiated 2-methyldihydrooxazines,... 

Fig. 2.1-4 Handling of an unstable organometallic intermediate in a two-stage system.

In this reaction, the initial reactant methyl butyrate is reduced by diisobutyla-luminum hydride (Dibal-H) toluene to an unstable organometallic intermediate [38]. In a second step, the intermediate is further reduced to butyraldehyde, which is the desired product. A further reduction leads to the unwanted formation of... 

This thermally unstable organometallic radical is readily converted to triphenylthallium and metallic thallium, probably by way of diphenyl-thallium. 

He carried out the gas-liquid chromatography of thermally unstable organometallic compounds followed by combustion in a conventional micro-analytical furnace, absorption of water, and detection of the carbon dioxide with a Stuve katharometer (Stuve" ). The metal oxide deposited in the furnace gradually poisons the copper oxide furnace packing, and has to be replaced frequently. 

The use of aluminium in contact with gaseous or liquid methyl chloride is not recommended. Unstable organometallic compounds may form, which may explode in contact with air [5]. In the presence of moisture, the decomposition of methyl chloride into hydrochloric acid leads to pitting corrosion. 

There are few complexes known under this heading (see Table 23) and they are amongst the most reactive and unstable organometallic complexes known. 

All these reactions either have stable, isolable organometallic complexes as the catalyst or it is thought that they involve unstable organometallic intermediates. 

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