Subject Number : S-16-MS-0024
Support Type : Collaborative research
Proposal Title (English) : Theoretical Studies on the Reaction Mechanism of Fullerenes and Metallofullerenes
Username (English) : Xiang Zhao
Affiliation (English) : Xi’an Jiaotong University, China

1. Summary
Exohedral functionalizations of endohedral metallofullerenes (EMFs) have served as favorable approaches to isolate and modify EMF species, which facilitate their promising applications in materials science and medicine. Up to now, various organic reactions have been explored to obtain EMF exohedral derivatives. Here we will investigate the kinetics and thermodynamics of Bingel‒Hirsch and Prato reactions both thoroughly through the current state-of-the-art dispersion-corrected density functional theory calculations. The best addition sites and regioselectivities of M@C66 (M=Tb, La, Y, and Yb) towards these two functionalization approaches will be uncovered. In addition, solvent effects and Gibbs free energies are carried out to estimate the influence of reaction conditions on reactivities. Our collaborated work will enrich the exohedral cycloaddition reactions of IPR-violating EMFs and give support to predict and explain experimental results on addition sites.
2. Theoretical Details
In the electronic structure calculations, all Full geometry optimizations of all relevant structures were performed by using the dispersion-corrected density functional theory approach M06-2X with basis sets of 6-31G(d) for H, C, N and O atoms and Lanl2dz with the corresponding effective core potential for La and Yb atoms. Vibrational analyses upon the optimized structures are performed at the same level of theory to demonstrate the stationary points to be minimal for reactants, intermediates and adducts or saddle points for transition states. Intrinsic reaction coordinate (IRC) analyses are employed to confirm the transition states. Solvent effects have been considered by the polarizable continuum model (PCM).
3. Results and Discussion

It is indicated that this cage can be obtained in the novel form of mono-EMFs M@C2v(4348)-C66 (M = Tb, La, Y and Yb), which turn out to be the most stable and predominant isomers at the fullerene formation temperature region. As a consequence, a non-IPR fullerene #4348C66:C2v is capable of being obtained both exohedrally (C66Cl10:Cs) and endohedrally (by entrapping mono-metal rather than previously reported metallic cluster Sc2). Subsequent investigations on metal‒cage bonding characters demonstrate the covalent interaction between metal and DHCP moiety, indicating the combined role of ionic and covalent bonding in stabilizing #4348C66:C2v cage. The strong coordination of M‒DHCP induces significant variations in properties of DHCP moiety compared with hollow cage such as pyramidalization angles, NBO charges and chemical shifts of carbon atoms, distances of C‒C bonds, and aromatic properties of carbon rings. Due to the difficulty in isolation and purification of mono-EMFs M@C66, the concave‒convex complexation of [n]CPP (n = 9, 10 and 11) and Tb@C66 based on π‒π weak interaction is investigated through dispersion-corrected density functional theory (M06-2X) method. Results show that Tb@C2v(4348)-C66 favors to be stabilized by [10]CPP with “standing” orientation, leading to a size-suitable complex S-Tb@C2v(4348)-C66[10]CPP. Our present work verifies the existence of a carbon cage (#4348C66:C2v) shared by both endohedral and exohedral fullerene derivatives. The success in finding such a peculiar carbon cage will facilitate us to explore other similar fullerene isomers stabilized by endohedral and exohedral approaches and to explore whether it is possible to understand these two stabilization mechanisms in the same manner.

Figure:

Figure. Schlegel diagram of #4348C66:C2v cage consisting of 19 non-equivalent carbon atoms. The non-equivalent carbon atoms are classified into 556, 566 and 666 atom types, which are labelled with red, black and blue colored serial numbers, respectively. Bond critical points (BCPs) existed in C‒C and Tb‒C are marked with purple points for Tb@C2v(4348)-C66.

4. Others
N/A
5. Publication/Presentation
(1) P. Zhao, X. Zhao, M. Ehara, J. Org. Chem., 2016, 81, 8169-8174.
(2) P. Zhao, X. Zhao, M. Ehara, Inorganic Chemistry, 2017, 56, submitted for publication.

6. Patent
N/A