Importance of Dispersion on the Stability of the Concave-Bound CpM (M = Fe, Ru, Os) Complexes of Sumanene Saú l H. Martínez, † Sudip Pan, † Jose ́ Luis Cabellos, † Eugenia Dzib, † María A. Ferna ́ ndez-Herrera, †,‡ and Gabriel Merino* ,† † Departamento de Física Aplicada, Centro de Investigació n y de Estudios Avanzados, Km. 6 Antigua carretera a Progreso Apdo. Postal 73, Cordemex 97310, Me ́ rida, Me ́ xico ‡ Conacyt Research Fellow: Departamento de Física Aplicada, Centro de Investigació n y de Estudios Avanzados Unidad Mé rida, Km. 6 Antigua carretera a Progreso Apdo. Postal 73, Cordemex, 97310 Mé rida, Yucata ́ n, Mé xico * S Supporting Information ABSTRACT: The preference for concave mode binding of the CpM unit with sumanene in CpM(η 6 -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. ■ INTRODUCTION In 2007, Hirao and co-workers synthesized and characterized the first complex of sumanene, CpFe(η 6 -sumanene) + (1, Figure 1), 1 which is also the first example of a buckybowl with a concave selectivity. Previously, several metal complexes of sumanene were reported on paper. Some noteworthy examples are complexes of alkali metals, Pd(PH 3 ) 2 , and Pt(PH 3 ) 2 -bound sumanene and its different substituted derivatives. 2-4 In contrast to 1, these predicted complexes show an energetic preference for the convex-bound forms. Other buckybowl complexes such as corannulene with [C 5 Me 5 -Ru] + and hemifullerene with Li + also exhibit a convex preference. 5,6 Such concave selectivity is not only limited to 1. Three years later, the same group reported the next heavier analogue of 1, CpRu(η 6 -sumanene) + (2), which also prefers a concave mode binding in both the solid state and solution. 8 Using NMR, the authors found a solvent- and temperature-dependent bowl-to- bowl inversion of 2, which hints that the barrier for this process is lower in 2 than in 1. In 2013, Okumura et al. performed a series of density functional theory (DFT) computations to explore the main factors stabilizing the concave-bound form of the iron complex. 9 Their results obtained at the B3LYP/MIDI+pd/6-31G* level indicate that the convex-bound form is energetically more stable than the concave-bound isomer. They further argued that the coordination of counterion, AlCl 4 - , with 1 favors the concave isomer. In other words, the counterion is the key factor to explain the observed selectivity. In contrast to the results of Okumura et al., our DFT computations show that the presence of the counterion is not relevant for the selectivity. The crucial factors in understanding the relative preference of the concave mode binding of CpM unit with sumanene in CpM(η 6 -sumanene) + (M = Fe, Ru; Cp = cyclopentadienyl unit) complexes are mainly the intramolecular dispersion interactions. In particular, the dispersion interactions, which arise from the correlated motions of electrons, are ubiquitous in nature and their effects are important for an understanding of several kinds of phenomena. Focusing only on the arena of organometallic chemistry, several studies show that the inclusion of dispersion correction to the energy is crucial for a Received: April 13, 2017 Figure 1. Representative structure for the CpM(η 6 -sumanene) + (M = Fe, Ru) unit in the crystal. 7 Article pubs.acs.org/Organometallics © XXXX American Chemical Society A DOI: 10.1021/acs.organomet.7b00282 Organometallics XXXX, XXX, XXX-XXX