[60]Fullerene as a Versatile Four-Electron Donor Ligand

How Can the η1-Type Fullerene-Metal Bond Survive? A Systematic Survey of Reactions between Mono-EMFs and (M'Ln)2 Dimers

Recently, one η¹-coordinated complex of endohedral metallofullerene (EMF) Y@C_2v(9)-C₈₂[Re(CO)₅] has been synthesized and characterized with a highly efficient radical-coupling methodology by performing a photochemical reaction between Y@C_2v(9)-C₈₂ and [Re(CO)₅]₂ complexes. Theoretical investigations with the density functional theory reveal that this complex is stabilized by an ionic C-Re bond. The reactions of M@C_2v(9)-C₈₂ (M = Sc, Y, La) with [Re(CO)₅]₂ suggest that the reaction energies differ little because of similar single occupied molecular orbitals (SOMOs) of M@C_2v(9)-C₈₂. In the reactions of Y@C_2v(9)-C₈₂ with various transition-metal complexes [M'L_n]₂ (M' = Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir), the C-M' bonds with Mn, Tc, Re, Fe, Ru, and Os can stably exist, whereas those with Co, Rh, and Ir are unstable. Further analyses disclose that, in each element group, the stability of the C-M' bond is mainly determined by the bond energy of the M'-M' bond, which is related to the d_σ orbital of the M'L_n species. Moreover, the very-low-energy d_σ orbitals and large geometrical distortions of M'(CO)₄ (M' = Co, Rh, Ir) lead to poor stabilities of the C-M' (M' = Co, Rh, Ir) bonds. As comparison, the reactions of Y@C_s(6)-C₈₂ and La@C₇₂ have been investigated. The Y@C_s(6)-C₈₂ structure is more reactive toward the [M'L_n]₂ complexes than Y@C_2v(9)-C₈₂ thanks to a lower SOMO of Y@C_s(6)-C₈₂ than that of Y@C_2v(9)-C₈₂, which derives from position change of the Y atom in C_s(6)-C₈₂ during the reactions. However, the formation of [Y@C_s(6)-C₈₂]₂ suppresses the formation of several C-M' bonds. The reactivity of La@C₇₂ is weak due to a high LUMO+1 of C₇₂, which leads to a high SOMO of La@C₇₂. We believe that this theoretical study provides primary principles of radical-coupling reactions of EMFs and will be valuable for future research of organometallic complexes of fullerene.

Coordination modes and different hapticities for fullerene organometallic complexes

The different coordination modes in fullerene organometallic complexes are reviewed. The main modes are η2 and η5, but there are some interesting studies about the other four, all of them are revised in order to show which is the state of art of this kind of compounds with the respect of the hapticity.

Two Metal Centers Bridging Two C60 Cages as a Wide Passage for Efficient Interfullerene Electronic Interaction

The reaction of Ir4(CO)8(PMe3)4 with excess C60 in refluxing 1,2-dichlorobenzene, followed by treatment by CNR (R = CH2C6H5) at 70 degrees C, affords a fullerene-metal sandwich complex Ir4(CO)3(mu4-CH)(PMe3)2(mu-PMe2)(CNR)(mu-eta2,eta2-C60)(mu4-eta1,eta1,eta2,eta2-C60) (1), which exhibits an interesting structural feature of two metal atoms bridging the two C60 centers as well as the first example of a mu4-eta1,eta1,eta2,eta2-C60 bonding mode. Compound 1 has been characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction study. A cyclic voltammetry study reveals strong electronic communication between the two C60 centers in 1, which is due to the presence of a wide channel of two metal centers between the two C60 cages for efficient electronic interaction.