Structural and energetical characterization of reactive intermediates derived from toluene-Cr(CO)(3)

In order to gain a deeper understanding of the specific reactivity of arene - Cr(CO)(3) complexes, the structures and energies of the reactive interme diates formally generated by abstraction of a proton (H+), a hydride (H-.), or a hydrogen atom (H-) from the methyl group of toluene-Cr(CO)(3) (2) wer e computationally investigated by using density functional theory based qua ntum chemical techniques. The solid-state structure of the parent complex ( 2) was determined by low-temperature X-ray crystallography and this confirm ed the high accuracy of the computational methods. Besides calculating the geometry of the lowest energy conformation, particular emphasis was laid on the rotational barrier of the Cr(CO)(3) group as well as on that of the ex ocyclic carbon- carbon bond which exhibited a significant amount of double- bond character in all of the reactive intermediates investigated. The resul ts are put into broader perspective by discussing their relevance for the r ationalization and prediction of the selectivity of synthetically relevant reactions of arene chromium tricarbonyl complexes.