A transition metal fullerene complex is a

coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

wherein

fullerene A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ...

serves as a

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

Fullerenes A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ...

are typically spheroidal carbon compounds, the most prevalent being

buckminsterfullerene Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) made of twenty hexagons and twelve pentagons, and resembles a soccer ball. Each of its 60 carbon atoms is bonded ...

, C₆₀. One year after it was prepared in milligram quantities in 1990, C₆₀ was shown to function as a ligand in the complex h₃Psub>2Pt(η²-C₆₀). Since this report, a variety of

transition metals In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...

and binding modes were demonstrated. Most transition metal fullerene complex are derived from C₆₀, although other fullerenes also coordinate to metals as seen with C₇₀Rh(H)(CO)(PPh₃)₂.

Binding modes

As ligands, fullerenes behave similarly to electron-deficient

alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...

s such as

tetracyanoethylene Tetracyanoethylene (TCNE) is organic compound with the formula . It is a colorless solid, although samples are often off-white. It is an important member of the cyanocarbons. Synthesis and reactions TCNE is prepared by brominating malononitrile ...

. Thus, their complexes are a subset of

metal-alkene complex In organometallic chemistry, a transition metal alkene complex is a coordination compound containing one or more alkene ligands. Such compounds are intermediates in many catalytic reactions that convert alkenes to other organic products.Elschenbro ...

es. They almost always coordinate in a dihapto fashion and prefer electron-rich metal centers.Spessard, p. 162 This binding occurs on the junction of two 6-membered rings. Hexahapto and pentahapto bonding is rarely observed.Spessard, p. 165 In Ru₃(CO)₉(C₆₀), the fullerene binds to the triangular face of the cluster. file:Fullerene 4.png, h₃Psub>2Pt.html" ;"title="h₃Psub>2Pt">h₃Psub>2Ptsub>6(η²-C₆₀) file:Fullerene 2.png, Ru₃(CO)₉(C₆₀) file:Fullerene 5.png, Platinum complex of isoxazoline-modified fullerene.

Examples

C₆₀ forms stable complexes of the type M(C₆₀)(diphosphine)(CO)₃ for M = Mo, W. A dirhenium complexes is known with the formula Re₂(PMe₃)₄H₈(η²:η²C₆₀) 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: :3 Cp*Ru(MeCN)₃⁺ + C₆₀ → ³⁺ + 3 MeCN

Vaska's complex Vaska's complex is the trivial name for the chemical compound ''trans''-carbonylchlorobis(triphenylphosphine)iridium(I), which has the formula IrCl(CO) (C6H5)3sub>2. This square planar diamagnetic organometallic complex consists of a central iridi ...

forms a 1:1 adduct, and the analogous IrCl(CO)(PEt₃)₂ binds 200x more strongly. Complexes with more than one fullerene ligand are illustrated by Ir₄(CO)₃(μ₄-CH)(PMe₃)₂(μ-PMe)₂(CNCH₂Ph)(μ-η²:η²C₆₀)(μ₄-η¹:η¹:η²:η²C₆₀). In this Ir₄ cluster two fullerene ligands with multiple types of mixed binding. Platinum, palladium, and

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...

form complexes of the type C₆₀ML₂ where L is a mono

dentate Dentate may refer to: * A species having dentition * An energy-dissipating baffle block in a spillway * An individual not being edentulous * Dentate gyrus of the hippocampus * Dentate nucleus of the cerebellum * Denticity in chemistry * Dentat ...

or bidentate

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

ligand. They are prepared by displacement of weakly coordinating ligands such as

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene i ...

: : h₃Psub>2Pt(C₂H₄) + C₆₀ → h₃Psub>2Pt(η²-C₆₀) + C₂H₄ In Et₃P)₂Ptsub>6(η²-C₆₀), six Pt centers are bound to the fullerene.

Modified fullerenes as ligands

Osmium tetraoxide adds to C₆₀ to give, in the presence of pyridine (py), the diolate C₆₀O₂OsO₂(py)₂. The pentaphenyl anion C₆₀Ph₅⁻ behaves as a

cyclopentadienyl Cyclopentadienyl can refer to *Cyclopentadienyl anion, or cyclopentadienide, **Cyclopentadienyl ligand *Cyclopentadienyl radical, • *Cyclopentadienyl cation, See also *Pentadienyl In organic chemistry, pentadienyl refers to the organic radic ...

ligand. 260 px, center, Ferrocene-like complex of C₆₀Ph₅⁻.

In this example, the binding of the ligand is similar to

ferrocene Ferrocene is an organometallic compound with the formula . The molecule is a complex consisting of two cyclopentadienyl rings bound to a central iron atom. It is an orange solid with a camphor-like odor, that sublimes above room temperature, a ...

. The anion C₆₀(PhCH₂)₂Ph functions as an

indenyl In organometallic chemistry, a transition metal indenyl complex is a coordination compound that contains one or more indenyl ligands. The indenyl ligand is formally the anion derived from deprotonation of indene. The η5-indenyl ligand is related ...

-like ligand. Fullerenes can also be substituents on otherwise conventional ligands as seen with an isoxazoline fullerene chelating to platinum,

rhenium Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one ...

, and

iridium Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of ...

compounds.

Ongoing research

Although no application has been commercialized. non-linear optical (NLO) materials, and as

supramolecular Supramolecular chemistry refers to the branch of chemistry concerning chemical systems composed of a discrete number of molecules. The strength of the forces responsible for spatial organization of the system range from weak intermolecular forces ...

building blocks.

References

Bibliography

*Spessard, Gary; Miessler, Gary (2010). Organometallic Chemistry {{Coordination complexes Fullerenes Ligands