Abstract
The CO replacement in higher technetium carbonyls (hexacarbonyltechntium cation, pentacarbonyltechnetium halides, and actually existing and hypothetical technetium tetracarbonyl complexes) was analyzed by quantum-chemical calculations. Dissociative and associative mechanisms of the reaction in a vacuum and in solvents were analyzed using the variational transition state theory. The solvent effect on the process was considered within the framework of PCM model and with explicit inclusion of different numbers of solvent molecules. The dissociative pathway was shown to better agree with the experimental data. Higher kinetic stability of the hexacarbonyl cation compared to pentacarbonyl halides and of pentacarbonyl halides compared to related tetracarbonyl complexes is mainly attributable to energetic features of the five-coordinate transition state (cis labilization effect exerted by π-donor ligands), as in related carbonyl complexes of other dmetals. Reactivity trends observed within the series of technetium pentacarbonyl and tetracarbonyl complexes were discussed.
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