Cluster opened fullerene

Scheme 11.4 Photochemical reaction of 14 with singlet oxygen, leading to the cluster opened fullerene 19. (i) O2 hv, benzene (II) [2+2] cycloreversion, keto-enol tautomerization.

In a number of groundbreaking explorations,46 Wudl, Hummelen, and coworkers showed that photoinduced [2 + 2] cycloaddition of singlet oxygen to one of the electron-rich enamine-type double bonds of azahomo [60] fullerene derivative 53 (Scheme 1.8), followed by decomposition of the 1,2-dioxetane intermediate (not shown), led to ketolactam ( )-54, the first cluster-opened fullerene with a free orifice.153 Under synthetic conditions mimicking events observed in the gas phase,154 acid-induced loss of 2-methoxyethanol from... 

Lull and co-workers showed that the tethered bisazides such as 2,2-dibenzyl-l,3-diazidopropane (124) undergo [3-t2] cycloadditions to adjacent [6 6]-bonds (cis-l addition). Thermal extrusion of N2 afforded a mixture of the corresponding cis-1-1,2,3,4-bisimino[60]fullerenes and twofold cluster-opened 2,3,4,5-bis-aza-homo[60]-fullerenes [36, 37, 111]. The reaction of with optically active bisazides yielded enantiomerically pure bis-azafullerenes with the same addition pattern [111]. 

So far, all efforts to generate, isolate and characterize heterofuUerenes via Kratsch-mer-Huffman vaporization of graphite in the presence of hetero-element-containing compounds such as boron nitride (BN) or cyanogen (CN)2 have failed. An alternative route for the direct formation of heterofuUerenes is cluster rearrangement within exohedral fullerene derivatives such as iminofullerenes and azafuUeroids. The first hints of success by this approach were obtained from mass spectrometry investigations of the cis-l-diazabishomo[60]fullerene 3 [12], the n-butylamine adduct 4 [12] the 1,2-epiminofullerene 5 [11] and the cluster opened ketolactam 6 [2]. 

Scheme 12.2 Synthesis of the aza[60]fullerene dimer 2 starting from the cluster opened ketolactam 6.

Formation of cluster opened methano- and imino[60[fullerenes (fulleroids and azafUlleroids) Thermal [3+2]-cycloadditions ofdiazo compounds or azides leads to the formation of fulleropyrazolines or fullerotriazolines. Thermolysis of such adducts after extrusion of N2 affords as kinetic products the corresponding [5,6]-bridged methano and iminofullerenes with an intact 60 re-electron system and an open transannular bond (see Chapter 4) [88-91]. The corresponding [6,6]-bridged structures with 58 re-electrons and a closed transannular bond are formed only in traces. 

Framework Modifications of [60]Fullerene Cluster Opening Reactions and Synthesis of Heterofullerenes... 

The accessibility of the fullerenes [1] in macroscopic quantities [2] opened up the unprecedented opportunity to develop a rich three-dimensional chemistry of spherical and polyfunctional all carbon molecules. [3-8] A large multitude of fullerene derivatives like exohedral covalent addition products, salts, cluster opened and defined degradation products, heterofullerenes and endohedral derivatives can be imagined and numerous examples, especially of covalent adducts have been synthesized and characterized. [3-8] Within a few years the fullerenes became essential building blocks in organic chemistry. Most of the chemistry of fullerenes has so far been carried out with Ceo (1) with little work on C70 and few experiments with C76 and Cg4. This is simply due to the fact that Ceo... 

Here, a first review is provided which summarizes the more recent development framework modified fullerenes like cluster opened structures and heterofullerenes. The key steps for such framework modifications are always defined activations of the fullerene cluster due to specific covalent addition reactions. Therefore, the principles of covalent fullerene chemistry [3-8] will be considered first ... 

The prototype of all fullerenes is Buckminsterfullerene ,. Since it is the most abundant fiillerene obtained from macroscopic preparation procedures such as the classical Kratschmer-Huffman method, its chemical and physical properties were developed in very quick sucession soon after it became available in 1990. The icosahedral football shaped Buckminsterfrdlerene 60 is now the most intensively studied molecule of all. Many principles of the chemistry of C , are known. These allowone to tailor design new fuUerene derivates with specific properties useful for biological applications or as new materials. The main types of fullerene derivative are exohedral addition products, endohedral fullerenes, heterofullerenes and cluster opened systems. Whereas many examples of the first two groups are already known, sophisticated methods for the synthesis of the latter two groups have started to emerge only recently. 

The oxidative addition of allyl bromide to Os3(GO)io(NCMe)2 has also been studied. No carbon-nitrogen bonds are formed cluster opening to linear trinuclear clusters is of some interest.The reaction of lightly ligated triosmium clusters with fullerene G6o has been successfully attempted in this case also, no G-N bonds are formed. 

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