Importance of Dispersion on the Stability of the Concave-Bound CpM (M = Fe, Ru, Os) Complexes of Sumanene

The preference for concave mode binding
of the CpM unit with sumanene
in CpM­(η6-sumanene)+ (M = Fe, Ru, Os)
over the convex mode is analyzed by various density functional theory
based methods including (or not) dispersion and solvent effects. In
the case of the iron complex, the concave-bound isomer becomes energetically
more favorable than the convex form only after the proper inclusion
of dispersion effects, highlighting the importance of such contributions
to stabilize the former arrangement. For the ruthenium complex, both
the dispersion and solvent effects should be taken into account to
provide a correct trend. The noncovalent interaction index corroborates
the role of dispersion in concave selectivity. Our computations also
show that the presence of the counterion is not relevant for this
selectivity, discarding the previously reported argument made by Okumura
et al.