Platinum Metals Rev., 1996, 40, (1), 23
Platinum Group Metal Fullerenes
Some Recent Studies on Systems Containing C60
The C60 molecule, named 'buckminster-fullerene', is very stable physically, and its potential as a source of a number of useful materials has been suggested. For example, nonhydrostatic compression Of C60 transforms it into bulk polycrystalline diamond at room temperature (1); and when doped with alkali metals C60 gives the highest temperature organic superconductors seen to date (2–4). The soot deposits from arc evaporation contain near perfect nanotubes with potentially outstanding electronic and mechanical properties, and encapsulated palladium can act as the seed for the growth of a worm-like nanostructure (4, 5). The biological activity of unsubstituted buckminsterfullerene is also being investigated using C60 labelled with radioactive carbon-14 (6, 7). Potential biological applications for fullerenes are being sought in areas ranging from drug metabolism to agrochemicals.
In spite of its physical robustness, C60 readily undergoes chemical reactions and its organic chemistry has been widely investigated. In recent years there have also been reports of its reactions with inorganic species, including platinum group metals systems. These have given rise to the preparation of a number of platinum group metals complexes, the first such compound being: 
, an osmate ester with C-O-Os bonds, which was reported by Hawkins and co-workers (8,9). The first example of a compound with a direct metal-C60 bond, 
was described in 1991 (10), see Equation (i), below.
Addition of 
to C60 in toluene under nitrogen gave the C60 platinum complex indicated in Equation (i) as black microcrystals in 85 per cent yield; 
could be prepared by reaction with 
(11). The triemylphosphine complex was obtained in 68 per cent yield after purification by column chromatography on silica gel. The iriphenylphospnine complex is also formed when fuUerene-60 reacts with a binuclear heterometallic compound with a mercury-platinum bond, trans -
, or cis -
(12).
[60] Fullerene complexes have now been reported for all the platinum group metals. The reaction of C60 with excess 
proceeds as follows (13):
The first ruthenium carbonyl derivative of fullerene, 
, was prepared by the reaction between Ru(CO)5 and C60 in toluene solution under nitrogen. The product is more stable than the equivalent iron compound (14). The synthesis of a [60] fullerene derivative cova-lently linked to a ruthenium(II) tris(bipyridine) complex has been reported (15). 
complexes are photoactive (2), known to transfer energy in the excited state, and [60] fullerene has a high electron affinity and can reversibly accept up to six electrons in solution. Due to solubility problems, however, the reaction of
with the parent N-H fulleropyrrolidine gave a very insoluble stone-like material which could not be characterised (16); but when the fulleropyrrolidine (I) was synthesised and treated with 
in refluxing 1,2-dichloro-ethane, in the presence Of 
, compound (II) was produced, see Equation (iii), above.
Compound (II) is now being studied as a model for long-lived charge separated states, and is being compared with compounds which have conventional rigid spacers less flexible than the triethylene glycol chain.
A number of isomers of the bis-complex 
have been prepared (17); and C60 triosmium cluster compounds have been obtained from the reaction between a toluene solution of 
and one equivalent of C60 by heating at 80°C for 5 minutes. The products have the formulae 
,
, 
and 
(9).
A C60 rhodium complex 
, which is a dark green powder, has been prepared by the addition of one equivalent of 
in toluene to C60 in toluene (18). This rhodium complex may also be prepared in dichloromethane solution and obtained and isolated as green-black crystals (19). This product is more stable in solution than
which readily dissociates into C60 and 
. ‘Naked metal’ complexes M(C60) have been prepared for a number of metals including rhodium - the general approach involves the formation of M+ ions from pure metal targets by laser desorption, followed by interaction with C60 in the vapour state (20).
, was obtained as brown-black crystals when a purple solution of C60 in the dangerous solvent, benzene, was added to a yellow benzene solution of 
(21). The indenyl C60 complex 
was obtained by refluxing the indenyl cyclooctene complex 
and C60 in dichloro-methane (22). 
has been obtained in two conformational isomers (20, 23), and 
has been prepared by mixing solutions of C60 and 
in benzene (24).
has been reported (25) and the reaction between C60 and 
, where M is nickel, palladium or platinum, gives 
compounds. Addition 
to a solution of C60 in benzene produced 
(26), and analogous compounds of nickel and palladium have also been prepared (27). In the palladium product the molecule has a C60 core bearing six octahedrally-disposed 
groups (26).
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