In a recent paper in Chemistry – a European Journal researchers from Girona and LA have studied the Diels-Alder reactivity of the endohedral metallofullerene Ti2C2@C78. Functionalized fullerenes have potentially important applications in non-linear optics, molecular magnets, radioimmunotherapy and many more.
The challenging task to find transition states for the reaction of s-cis-butadiene with any of the double bonds on the carbon sphere, has been achieved with QUILD’s efficient saddle-point searching techniques:
- TSRC enforcing the Hessian to have only 1 negative eigenvalue, along the user-specified reaction path
- adapted delocalized coordinates to deal with mixed strong and weak coordinates
Comparing the activation barriers with those for M3N@C78 and C78 revealed the empty fullerene to be the most reactive and the M3N@C78 least reactive, with significantly differing regio-selectivity between the (endohedral) fullerenes.
The effect of van der Waals interactions was assessed with Grimme’s D3 corrections and found to strongly affect the potential energy landscape. The dispersion interaction favors the formation of a collision complex between the diene and Ti2C2@C78 and furthermore lowers the activation barriers by about 50%.
Related paper, combined experiment and theory on endohedral C-80:
F.-F. Li, A. Rodriguez-Fortea, P. Peng, G. A. Campos Chavez, J. M. Poblet, L. Echegoyen, Electrosynthesis of a Sc3N@I-h-C-80 Methano Derivative from Trianionic Sc3N@I-h-C-80 J. Am. Chem. Soc., 134, 7480-7487 (2012).
transition states, dispersion-corrected DFT (GGA-D3), QUILD
M. Garcia-Borràs, S. Osuna, J. M. Luis, M. Swart, and M. Solà, The Exohedral Diels-Alder Reactivity of the Titanium Carbide Endohedral Metallofullerene Ti2C2@D3h-C78: Comparison with D3h-C78 and M3N@D3h-C78 (M=Sc and Y) Reactivity Chem. Eur. J., 18, 7141-7154 (2012).
S. Osuna, M. Swart, J. M. Campanera, J. M. Poblet and M. Solà, Chemical Reactivity of D3h C78 (Metallo)Fullerene: Regioselectivity Changes Induced by Sc3N Encapsulation J. Am. Chem. Soc., 130, 6206-6214 (2008).Key conceptsDispersion Reactivity