1. CHIRAL ALLOTROPES OF CARBON
The construction of chiral architectures through the use of two-dimensional systems or spherical shapes may seem at first glance a contradictory endeavour or a paradoxical eccentricity more typical of contemporary art than of chemistry. In fact, the new sp2 hybridized carbon allotropes, such as fullerenes, nanotubes or, more recently, graphene, would not seem at first sight to be suitable bricks for obtaining chiral structures. However, the network of conjugated double bonds, properly bent, can allow both the appearance of new interesting phenomena, such as chiroptic properties, and the fusion of the chiral information with the photo- and electro-activity typical of these conjugated structures.
1.1. Asymmetric catalysis on fullerenes and endofullerenes
A first direct approach toward chiral sp2 carbon nanostructures is based on the enantioselective functionalization of fullerenes. Despite of the non-coordinating nature of sp2 fullerene carbon atoms, we achieved their enantioselective functionalization by the chiral activation of a variety of different addends. Thus by the use of organo- and transition-metal catalysis we achieved the preparation of diverse chiral [60]-, [70]-, and endohedral fullerenes at will, which represents the first asymmetric catalysis of fullerenes reported in the literature.
Taking advantage of the aforementioned breakthrough, we have prepared a set of optically active fullerene hybrids with metal-centered chirality that have demonstrated great potential as chemical catalysts for some fundamental chemical reactions, as well as electro-chemical catalysts for oxygen reduction reactions.
Furthermore, we have used the chiral information stemming from optically active endohedral fullerenes to investigate reaction mechanisms in uncommon scenarios. Thus, we have reported on the role of incarcerated species in assisting the stereospecific cis/trans isomerization of 2,5-substituted pyrrolidines in carbon cages containing small molecules such as H2, HF or H2O.
1.2. Synthesis of chiral carbon nanostructures
Chirality is a property of asymmetry important in several branches of science. In the field of materials science, particularly chiral carbon nanostructures, promise outstanding applications namely asymmetric catalysis, supramolecular recognition of racemic mixtures or circular polarized emitters.
Controlling chirality in carbon nanostructures are a major challenge for the chemical community and there are a few examples in the literature. Our group described de preparation of several chiral carbon nanostructures introducing chiral moieties in fullerenes (1.1), graphene quantum dots or nanographenes.
The number of examples reported of the preparation of racemic mixtures of chiral carbon nanostructures is growing rapidly. These mixtures are then separated by chiral HPLC to measure its asymmetric properties. Our objective in this area goes beyond, we are immersed in the enantioselective synthesis of carbon nanostructures, especially the preparation nanographenes with inherently helical or atropisomeric chirality.