Fullerene analogues

Compound 62 (as its aza[60]fullerene analogue 33) is unstable and decomposes slowly into insoluble products, which show carbonyl vibrations in IR. A rigorous proof of the structure of 61, using NMR, was impossible due to the low solubility of the material. 

The possible existence of fullerene analogues such as B30P30, B24P36, aud so on should be borne in mind (Figure 4.7). The existence of nitrogen analogues B30N30, and so on has been predicted else where [5]. Just as BN exists in more than two crystalline forms, the same may prove to be the case with BP. 

CALYPSO combined with ab initio calculations find an energetically stable Bgg fullerene analogue (Fig. 20(a)), which is a hollow cage with... 

The scope of tire following article is to survey the physical and chemical properties of tire tliird modification of carbon, namely [60]fullerene and its higher analogues. The entluisiasm tliat was triggered by tliese spherical carbon allotropes resulted in an epidemic-like number of publications in tire early to mid-1990s. In more recent years tire field of fullerene chemistry is, however, dominated by tire organic functionalization of tire highly reactive fullerene... 

Accordingly, the exterior surface is much more reactive than planar analogues, and is comparable to those of electron deficient polyolefins. This, in turn, rationalizes the high reactivity of the fullerene core towards photolytically and radiolytically generated carbon- and heteroatomic-centred radicals and also other neutral or ionic species [8]. The interior, in contrast, is shown to be practically inert [9]. Despite these surface related effects, the... 

Kuhn s carbanion analogues, [44 ], [45 ] and [46 ], have recently been synthesized, and the precursor hydrocarbons [44]-H, [45]-H and [46J-H dissociate into the respective anions in DMSO to show deep blue colours without any added base (Kinoshita et al., 1994). A fullerene anion, Bu Qb [47 ], has also been obtained as a stable carbanion (Fagan et al., 1992) its lithium salt has been isolated in the form Li [47 ]-4MeCN or Li [47"]-3-4THF. Several stable all-hydrocarbon anions of precursor hydrocarbons with low pKa values ( 7) are listed in Table 2, along with their oxidation potentials, ox-... 

Polycyclic aromatic hydrocarbons such as fluoranthrene or Cso-fullerene are structures of great interest A straightforward entrance to analogues and partial structure, respectively, has now been developed by de Meijere and coworkers [89], using a combination of a Suzuki and a Heck-type coupling. Thus, reaction of 1,8-dibromophenanthrene 6/1-166 and obromphenylboronic acid 6/1-167 employing 20 mol% of the Pd° catalyst led to 6/1-168 and 6/1-169 in 54% yield as a Id-mixture (Scheme 6/1.45). 

Hirsch and co-workers calculated NICS values for tetrahedral clusters of N, P, As, Sb, and Bi, as well as for the corresponding tetra-anions composed of Si, Ge, Sn, or Pb atoms, finding diatropic values for 2,n(n 1) jr-systems.296a b It was postulated by Hirsch, Schleyer, and their co-workers that for icosahedral fullerenes and their hetero-analogues the Hiickel rule, involving 4/2+2 //-electrons, should be replaced by the 2(/2+l)2 electron rule.296... 

Whether or not fullerenes have to be considered aromatic has been debated since their discovery [48]. This is because the definition of aromaticity [116-118] is controversial and has changed many times over the last 175 years. The structure of fullerenes, especially that of the icosahedral representatives such as Cjq, implies their consideration as three-dimensional analogues of benzene and other planar aromatics. In contrast to such classical systems, however, the sp -networks of... 

It is known from electrochemical studies that fullerenes are easily reduced. Up to 6 electrons can be added reversibly [19], and, as mentioned earlier, the excited states are even more easily reduced. A large number of electron donors were investigated including aromatic and alkyl amines [29,43,79,119-140,152,161], ni-troxide radicals [57,117], suspensions of Ti02 [118], polyaromatic compounds, [19,127] organo-silicon compounds, [133,158] phenothiazine, [133] acridine [145,154], (3-carotene [141], tetrathiafulvalenes [146], tetraethoxyethene [147], phthalocyanines [148], porphyrines [151,153], NADH and analogues [150,154, 155], borates [156,159], and naphtoles [23] to name a few representative cases. 

Contrary to the electron transfer in organic solvents, the reduction process of functionalized fullerenes in aqueous solutions is very complex. Although some adducts are sufficiently water-soluble (Fig. 22) no reduction could be observed [181,183,187], This is attributed to the irreversible formation of fullerene clusters in aqueous media, which seem to prevent electron transfer. Consequently, efficient triplet-triplet annihilation within the clusters is observed resulting in short triplet lifetimes (< 0.1 (xs compared to microseconds for their monomeric analogue) [182,187],... 

The radical anion Cw, can also be easily obtained by photoinduced electron transfer from various strong electron donors such as tertiary amines, fer-rocenes, tetrathiafulvalenes, thiophenes, etc. In homogeneous systems back-electron transfer to the reactant pair plays a dominant role resulting in a extremely short lifetime of Qo. In these cases no net formation of Qo is observed. These problems were circumvented by Fukuzumi et al. by using NADH analogues as electron donors [154,155], In these cases selective one-electron reduction of C6o to Qo takes place by the irradiation of C6o with a Xe lamp (X > 540 nm) in a deaerated benzonitrile solution upon the addition of 1-benzyl-1,4-dihydronicoti-namide (BNAH) or the corresponding dimer [(BNA)2] (Scheme 15) [154], The formation of C60 is confirmed by the observation of the absorption band at 1080 nm in the near infrared (NIR) spectrum assigned to the fullerene radical cation. 

The electronic structure of the hypothetical fulleroids also parallels that of the fullerenes in several significant respects. Properly closed n shells are found within the Hiickel approximation only for isolated p-gon isomers, and then only when the structure is either (a) leapfrogged from a smaller fulleroid of the same symmetry, or (b) a p-fold analogue of one of the fullerene carbon cylinder series (Fowler 1990). D1(l C84 is the smallest fulleroid with a properly closed shell (figure 3). 

P. W. Fowler (University of Exeter, U.K.). Please comment on finite analogues of your structures We have discussed previously the idea of making a Russian doll fullerene in which one fullerene is connected by tunnels to an outer shell. The matrix seems to comply with this. 

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