Spin-Preserving N@C60 Cyclopropane Addition: Revisiting N@C60 Reactivity and Stability

The paramagnetic molecule N@C₆₀ is a rare example of endohedral fullerene where the encapsulated nitrogen atom is almost completely isolated from the fullerene cage. This results in very long electron spin phase coherence times. Nitrogen is a very reactive element and indeed the N@C₆₀ molecule is a fragile entity that has to be carefully protected from heat and light. On the other hand, functionalization of N@C₆₀ can be achieved via chemical routes previously applied to C₆₀. Until today all reaction schemes that involve N@C₆₀ have resulted to some degree of electron spin signal loss during the reaction. In this talk, I will present our recent results for two cyclopropanation reactions that remarkably preserve all electron spin signal. The proposed methodology is facile and very effective. The reaction scheme can be successfully applied to both low-purity N@C₆₀/C₆₀ mixture and also significantly enriched material with very intense electron spin resonance (ESR) signal. I will show quantitative ESR evidence to support the above claim and I will propose a mechanism for suppressing any electron spin signal loss. I believe these results open up the road for more elaborate reaction schemes to be applied to N@C₆₀ and for the synthesis of multi spin-centre structures to be achieved. I will also provide an overview of the stability issues surrounding N@C₆₀ and its derivatives.