Fullerene as initiator

In the previous section, devices with fullerenes as initial photoinduced electron acceptors in blends with conjugated polymers were discussed. Clearly one of their disadvantages is that only one of the two components is photoactive in the charge... 

Polymerization of a Monomer Using Charged or Functionalized Fullerenes as Initiators... 

Organometallic compounds, 14 550-551 25 71. See also Organometallics carbides contrasted, 4 648 as initiators, 14 256-257 iridium, 19 649-650 molybdenum(III), 17 27 osmium, 19 642-643 palladium, 19 652 platinum, 19 656-657 reaction with carbonyl groups, 10 505-506 rhodium, 19 645-646 ruthenium, 19 639 sodium in manufacture of, 22 777 titanium(IV), 25 105-120 Organometallic fullerene derivatives,... 

So in 1990 the Fullerenes became available in viable quantities and initiated a new and exciting field of chemistry. My colleagues Roger Taylor, David Walton and I set up a Fullerene and Nanoscience research programme at Sussex to explore the chemistry of the Fullerenes as well as the properties of carbon nanotubes. 

Silica gel with bonded aminopropyl groups (concentration of aminogroups is 0.8 mmol/g) with specific surface area s = 180 m /g and Silasorb Amin (CzR) with s = 200 m /g as initial adsorbents and fullerene Ceo (more than 99% purity) were used for the modification of silica surface. 

Alkali metal salts of fullerenes C ) (M ), were also tested as initiators for polymerization in polar solvents. Only the hexa-anion was able to initiate reactive monomers like methyl methacrylate, but not non-polar monomers hke styrene. In all cases, the initiation proceeds through electron transfer to the monomer so that no fullerene is incorporated [95]. The reduced fullerenes initiate polymerization like classical radical anions or dianions of aromatic or conjugated molecules and therefore this synthetic route is of limited interest. 

The tremendous burst of excitement which attended the initial isolation in 1990 of weighable amounts of separated fullerenes has been followed by an unparalleled and sustained surge of activity as chemists throughout the world rushed to investigate the chemical reactivity of these novel molecular forms of carbon. 

Wang IC, Tai LA, Lee DD, Kanakamma PP, Shen CK, Lull TY, Cheng CH, Hwang KC (1999) CW) and water-soluble fullerene derivatives as antioxidants against radical-initiated lipid peroxidation. J. Med. Chem. 42 4614 4620. 

On the other hand, the mechanochemical solid-state reaction was found to be the most suitable for this purpose. Thus, when the solid-state reaction was conducted for Cgo in the presence of one equivalent or less of KCN under the HSVM conditions for 30 min, a clean reaction took place to give the [2-1-2] fullerene dimer C120 (3) in 30% yield while 70% of Cgo was recovered unchanged (Scheme 2) [20]. It is to be noted that no cyanated fullerene such as 4 was obtained in comparison to the result of a liquid-phase reaction in o-dichloroben-zene (ODCB)-DMF [21]. This is apparently ascribed to the difference in reactivity of the initially formed cyanated Cgo anion with or without solvation. 

The NMR spectra of C qHR exhibits 37 resonances of the fuUerene carbons, with two of them in the sp region, proving Q-symmetry for the C oHR adducts. This is consistent with an addition to a double bond of a pole corannulene imit (1,2-addition), leading to l,2-dihydro[70]fullerene derivatives. These particular [6,6] bonds of Cyg, located between the carbons of the sets A and B, have almost the same bond length as the [6,6] bonds in Cjq [30], and the pole corannulene unit also exhibits bond alternation with longer [5,6] bonds. NMR data imply that the initial attack of the nucleophile occurred on C-1 and the protonation on C-2. 

Diazo compounds also undergo cycloaddition with fullerenes [for reviews, see (104),(105)]. These reactions are HOMO(dipole)-LUMO(fullerene) controlled. The initial A -pyrazoline 42 can only be isolated from the reaction of diazomethane with [60]fullerene (106) (Scheme 8.12) or higher substituted derivatives of Ceo (107). Loss of N2 from the thermally labile 42 resulted in the formation of the 6,5-open 1,2-methanofullerene (43) (106). On the other hand, photolysis produced a 4 3 mixture of 43 and the 6,6-closed methanofullerene (44) (108). The three isomeric pyrazolines obtained from the reaction of [70]fullerene and diazomethane behaved analogously (109). With all other diazo compounds so far explored, no pyrazoline ring was isolated and instead the methanofullerenes were obtained directly. As a typical example, the reaction of Cgo with ethyl diazoacetate yielded a mixture of two 6,5-open diastereoisomers 45 and 46 as well as the 6,6-closed adduct 47 (110). In contrast to the parent compound 43, the ester-substituted structures 45 and 46, which are formed under kinetic control, could be thermally isomerized into 47. The fomation of multiple CPh2 adducts from the reaction of Ceo and diazodiphenylmethane was also observed (111). The mechanistic pathway that involves the extrusion of N2 from pyrazolino-fused [60]fullerenes has been investigated using theoretical methods (112). 

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