ENDOR Evidence of Electron–H2 Interaction in a Fulleride Embedding H-2

An endofulleropyrrolidine, with H-2 as a guest, has been reduced to a paramagnetic endofulleride radical anion. The magnetic interaction between the electron delocalized on the fullerene cage and the guest H-2 has been probed by pulsed ENDOR. The experimental hyperfine couplings between the electron and the H-2 guest were measured, and their values agree very well with DFT calculations. This agreement provides clear evidence of magnetic communication between the electron density of the fullerene host cage and H-2 guest. The ortho-H-2/para-H-2 interconversion is revealed by temperature-dependent ENDOR measurements at low temperature. The conversion of the paramagnetic ortho-H2 to the diamagnetic para-H-2 causes the ENDOR signal to decrease as the temperature is lowered due to the spin catalysis by the paramagnetic fullerene cage of the radical anion fulleride.