Fullerenes bonds

Addition of diazomethane to a toluene solution of C70 generated a 12 1 2 mixture of pyrazolines. The structures of the three isomers are shown in Scheme 65. The formation of 174a and 174b in unequal amounts appears to be a well-characterized regioselective transformation at a fullerene bond. Photolysis and ther-... 

An excellent example of the use of the TB moiety as a chiral auxiliary in asymmetric synthesis is the preparation of the above-mentioned fullerene TB derivative 71a. The high asymmetric induction in the addition of 72 to fullerene C60 was attributed to the relatively large distance between the two reacting fullerene bonds spanned by the TB tether (04AG(E)1738). Sicker et al. used 1 for discrimination of enantiomeric cyclic hemiacetals and methylacetals finding a weakly discriminating effect (94MRC727). 

Fullerenes bonded to non-metallic elements (a) CgoO, (b) CgoBrg, and (c)C60[OsO4(pyBu)2]. 

Here again, typical chemical questions had to be solved, such as (i) the regioselectivtiy of the addition (see scheme 45) [265], (ii) the relative importance of mono- and higher adducts [264], and (iii) whether a ring-opening with cleavage of the original fullerene bonds could occur [258] in a cyclopropane derivative 193 (scheme 46). 

EQCM provides in situ measurement of mass changes accompanying electrochemical processes, namely, absorption, electrodeposition, electrocrystallization, electrodissolution, intercalation, electrochromism, etc. Studies dealing with, for instance, manganese oxides (Wu et al., 1997) and fullerenes (Bond et al., 2000, 2001) illustrate the capabilities of such technique in the context of the electrochemistry of porous materials. 

Jinno, K., Tanabe, K., Saito, Y., and Nagashima, H. (1997). Separation of polycyclic aromatic hydrocarbons with various fullerene bonded silica phases in microcolumn liquid chromatography. Analyst, 122, 787-91. 

Fig.4. The three most curved fullerene bond types a, p, and yin their local environments...

Cycloaddition of N-methylazomethine ylid to C70 yielded [70]fullero-pyrrolidine ( )-39 with the heterocycle fused across the fullerene bond C(7)-C(21) as a minor product besides the a- and -type adducts 40 and 41 [123] (Fig. 5). The isomeric assignment was based on H-NMR spectroscopy, the Cj-symmetrical C(7)-C(21) adduct being distinguished by two different methylene groups, each carrying two non-equivalent H-atoms. 

The low oxidation state of Pd(0) and the high rr-backbonding acceptor nature of fullerenes contribute to reinforce the Pd-fullerene bond strength. This facilitates the syntheses of these complexes, which can be easily prepared from C60 (or G70) and Pd(0) precursors, such as PdL4, Pd2(dba)3, or by ligand exchange from C6oPdL2 (Scheme 43).2 ... 

Recent theoretical calculations (DFT-NL) on M( 7 -C6o)(PH3)2 (M = Ni, Pd, Pt) reveal that the metal-fullerene bond-dissociation energies (Pd < Ni < Pt) are higher than the corresponding metal-ethylene complexes but lower than those of substituted ethylene (C2X4, X = F, CN). Similar studies on a series of complexes (7/ -C,) Pt(PH3)2 ( = 60, 70, 84 n = 1-6) indicate that the binding energy between the Pt(PH3)2 unit is almost independent of the size of the cage and the number of metals coordinated on the fullerene surface. In the C70 species, the most reactive site corresponds to the bond with the most pyramidalized carbon atoms in the free fullerene. ... 

The nature of the metal-fullerene bond, which is expected to be greatly influenced by the electron affinity of the fullerene discussed above, is also reflected in the changes in the coordination sphere of the metal atom induced by complex formation. A general feature in the coordination of alkenes to metal atoms is that the four groups attached to the alkene bend back away from the... 

The M-Ceo bonds are analyzed in terms of Charge Decomposition Analysis giving quantitative estimates of electron donation, back donation and repulsive polarization. The 7T back-donation has the dominant contribution to the metal-fullerene bond for the second and third row metal-fullerene bond for the second and third row metal MC60/C2H4 complexes. We found and interpreted the correlation between BDE and amount of tt back-donation and a donation. 

The aim of the present contribution is to identify the preferred structures of Ceo with two or more bare palladium atoms adsorbed, as well as to assess the associated Pd-fullerene bond energies. To this end we use density functional theory to optimize the geometry of the molecules and to compute the binding energy of palladium atoms at different sites. 

For the Pd dimer, the ground state was identified as a triplet spin state, having an equiiibrium bond length of 2.53 A. The computed bond dissociation energy (20.5kcal/mol) is in qualitative agreement with the experimental values (17 4, 26 5) [69]. Furthermore, it is much lower than twice the Pd-fullerene bond energy and clearly demonstrates that metal dimerization can not compete with metal adsorption onto the fullerene. 

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