Acrostichum indet.
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Abstract
The displacement of a CO ligand from an unusually labile
rhenium
carbonyl complex containing a bidentate carboxyaldehyde pyrrolyl ligand
by PPh<sub>3</sub> and pyridine has been investigated. The reaction
is found to proceed by an associative, preequilibrium mechanism. Theoretical
calculations support the experimental data and provide a complete
energetic profile for the reaction. While the Re–CO bond is
found to be intrinsically weak in these complexes, it is postulated
that the unusual lability of this species is due to the presence of
a weak aldehyde Re–O link that can easily dissociate to open
a coordination site on the metal center and accommodate an incoming
ligand prior to CO loss. The resulting intermediate complex has been
identified by IR spectroscopy. The presence of the hemilabile pyrrolyl
ligand provides a lower-energy reaction channel for the release of
CO and may be of relevance in the design of CO-releasing molecules