A transition metal fullerene complex is a coordination complex wherein fullerene serves as a ligand. Fullerenes are typically spheroidal carbon compounds, the most prevalent being buckminsterfullerene, C<sub>60</sub>.
One year after it was prepared in milligram quantities in 1990, C<sub>60</sub> was shown to function as a ligand in the complex [Ph<sub>3</sub>P]<sub>2</sub>Pt(÷<sup>2</sup>-C<sub>60</sub>).
Since this report, a variety of transition metals and binding modes were demonstrated. Most transition metal fullerene complex are derived from C<sub>60</sub>, although other fullerenes also coordinate to metals as seen with C<sub>70</sub>Rh(H)(CO)(PPh<sub>3</sub>)<sub>2</sub>.
As ligands, fullerenes behave similarly to electron-deficient alkenes such as tetracyanoethylene. Thus, their complexes are a subset of metal-alkene complexes. They almost always coordinate in a dihapto fashion and prefer electron-rich metal centers. This binding occurs on the junction of two 6-membered rings. Hexahapto and pentahapto bonding is rarely observed.
In Ru<sub>3</sub>(CO)<sub>9</sub>(C<sub>60</sub>), the fullerene binds to the triangular face of the cluster.
C<sub>60</sub> forms stable complexes of the type M(C<sub>60</sub>)(diphosphine)(CO)<sub>3</sub> for M = Mo, W. A dirhenium complexes is known with the formula Re<sub>2</sub>(PMe<sub>3</sub>)<sub>4</sub>H<sub>8</sub>(÷<sup>2</sup>:÷<sup>2</sup>C<sub>60</sub>) where two of the hydrogen act as bridging ligands.
Many fullerene complexes are derived from platinum metals. An unusual cationic complex features three 16e Ru centers:
Vaska's complex forms a 1:1 adduct, and the analogous IrCl(CO)(PEt<sub>3</sub>)<sub>2</sub> binds 200x more strongly. Complexes with more than one fullerene ligand are illustrated by Ir<sub>4</sub>(CO)<sub>3</sub>(ü<sub>4</sub>-CH)(PMe<sub>3</sub>)<sub>2</sub>(ü-PMe)<sub>2</sub>(CNCH<sub>2</sub>Ph)(ü-÷<sup>2</sup>:÷<sup>2</sup>C<sub>60</sub>)(ü<sub>4</sub>-÷<sup>1</sup>:÷<sup>1</sup>:÷<sup>2</sup>:÷<sup>2</sup>C<sub>60</sub>). In this Ir<sub>4</sub> cluster two fullerene ligands with multiple types of mixed binding. Platinum, palladium, and nickel form complexes of the type C<sub>60</sub>ML<sub>2</sub> where L is a monodentate or bidentate phosphorus ligand. They are prepared by displacement of weakly coordinating ligands such as ethylene:
In [(Et<sub>3</sub>P)<sub>2</sub>Pt]<sub>6</sub>(÷<sup>2</sup>-C<sub>60</sub>), six Pt centers are bound to the fullerene.
Osmium tetraoxide adds to C<sub>60</sub> to give, in the presence of pyridine (py), the diolate C<sub>60</sub>O<sub>2</sub>OsO<sub>2</sub>(py)<sub>2</sub>.
The pentaphenyl anion C<sub>60</sub>Ph<sub>5</sub><sup>âÂÂ</sup> behaves as a cyclopentadienyl ligand.
In this example, the binding of the ligand is similar to ferrocene. The anion C<sub>60</sub>(PhCH<sub>2</sub>)<sub>2</sub>Ph functions as an indenyl-like ligand.
Fullerenes can also be substituents on otherwise conventional ligands as seen with an isoxazoline fullerene chelating to platinum, rhenium, and iridium compounds.
Although no application has been commercialized. non-linear optical (NLO) materials, and as supramolecular building blocks.