CARBON MONOXIDE EXCHANGE IN PENTACARBONYLIRON AND TETRACARBONYL(TRIPHENYLPHOSPHINE)IRON

The exchange of pentacarbonyliron and tetracarbonyl(triphenylphosphine)iron with labelled carbon monxide (either 13CO or C18O) is initiated by ultraviolet light. Statistical exchange of all the carbonyl groups is revealed by the infrared spectra of the 13CO and C18O enriched compounds. For Fe(CO)5, the reaction is catalysed with palladium supported on alumina or charcoal. The decomposition of Fe2(CO)9 to Fe(CO)5 in the presence of C18O leads to C18O incorporation in the Fe(CO)5. In a mixture of Fe(C16O)5 and Fe(C18O)5 scrambling is observed in the presence of ultraviolet light or palladium. The C18O exchange in Fe(CO)5 and Fe(CO)4P(C6H5)3 can also be catalysed by trifluoroacetic acid. A non-statistical mixture of labelled species is obtained in this case. With both compounds the monosubstituted product is disfavored with respect to higher substituted products. This can be explained by a mechanism in which two carbonyls exchange at once. © 1969.