[60]Fullerene–Metal Cluster Complexes: Understanding Novel η¹ and η^2[6:5] Bonding Modes of Metallofullerenes

Abstract

We performed extensive density functional calculations on various metallofullerene complexes and their polyanions to gain insight into novel η1 and η2[6:5] metal (M)–C60 bonding modes. For LnMC60 (L = ligand), the η1 mode is calculated to be the most stable, followed by η2[6:5] and η2[6:6] for –3 anions, in contrast to η2[6:6] >> η2[6:5] ≈ η1 for neutral cases. This observation is responsible for the transformation from η2[6:6] to η1 for LnM3C60, such as [Os3(CO)9C60], upon successive electron reductions. Our energy partitioning analysis (EPA) indicates that the π‐type character of η2[6:6] is much larger than that of η2[6:5]. An electron addition decreases the π‐type interaction of both the η2[6:6] and η2[6:5] modes by about 35 %, whereas it has little effect on σ‐type interactions. Because of the large proportion of π‐character in η2[6:6] coordination, the stability of η2[6:6] coordination decreases steeply as electron reductions continue. On the basis of the EPA results, we could explain why the reaction of [Os3(CO)8(CNR)(μ3‐η2[6:6],η2[6:6],η2[6:6]‐C60)] (R = CH2Ph) with CNR (4e donor) produces [Os3(CO)8(CNR)(μ3‐CNR)(μ3‐η1,η2[6:5],η1‐C60)]. The η1 and η2[6:5] bonding modes of M–C60 are crucial to fully understand the bonding nature of M–C60 bonds in exohedral metallofullerene complexes.

Coordination chemistry on carbon surfaces

“…DFT calculations on various M C 60 complexes have been carried out in order to understand the differences between 1 and 2 coordination modes. The conclusions of the work point out that neutral M C 60 complexes prefers 2(6 6) followed by 2(6 5) and finally 1 , while the −3 anions bound stronger in 1 [486]. This behavior arises from the -type interactions.…”

Coordination Modes and Different Hapticities for Fullerene Organometallic Complexes

“…Besides this, a number of interesting theoretical studies exist, discussing this aspect as well as other features meriting comment [18]. …”

“…Almost all the available information referring to this topic has been discussed here, however it is important to note the interesting theoretical analysis carried out by Park and his group [18] where the electronic population of the bonds involved in the interaction of the metal plays a fundamental role in explaining hapticities η 1 , η 2 (6,5) and η 2 (6,6). They claim that η 2 (6,6) should represent the most stable structure out of the three in the case of neutral molecules, but the ionization of these as a result of successive electron reduction produces a stable η 1 (σ bond) species [24], therefore this may be a good strategy for preparing compounds of this kind.…”

“…, the π bonds are always formed in the junction of two six-member rings at the fullerene surface. The hapticity example pertaining to the (6,5) type previously mentioned in the Park study [18] may be important and will be analyzed at the end of this section.…”

“…With respect to the η 2 (6,5) mode, Park and his group have made interesting theoretical propositions in the same paper mainly focusing on the η 1 mode [18], arriving at the conclusion that in multiple substitutions and ionic species, the η 2 (6,5) mode may be more stable than its (6,6) counterpart. This phenomenon may be a consequence of both steric effects and a change in the electronic distribution of the ions.…”