Highly regioselective complexation of tungsten with Eu@C82/Eu@C84: interplay between endohedral and exohedral metallic units induced by electron transfer

Interactions between the inner and outer units through a fullerene cage are of fundamental importance for the creation of molecular spintronics and machines but the mechanism of such through-cage interplay is still unclear. In this work, we have designed and synthesized two prototypical compounds which contain only a single europium atom inside the cage and merely a tungsten atom coordinating outside to clarify the interactions between the endohedral and exohedral metallic units. They are obtained by reacting a tungsten complex W(CO)4(Ph2PC2H4PPh2) (1) with the corresponding metallofullerenes in a highly regioselective manner (2a for Eu@C2(5)-C82 and 2b for Eu@C2(13)-C84). On the one hand, the endohedral Eu-doping has changed the LUMO distribution on C2(5)-C82/C2(13)-C84 dramatically, via electron transfer, which governs the addition pattern of the exohedral tungsten addition to show surprisingly high regioselectivity. On the other hand, the exohedral tungsten coordination onto Eu@C2(5)-C82/Eu@C2(13)-C84 has restricted the motion of the internal europium ion to some extent by changing the electrostatic potentials, as confirmed by the X-ray results of 2a, 2b and the corresponding pristine metallofullerenes cocrystallized with Ni(OEP) (OEP is the dianion of octaethylporphyrin). We now make it clear that the interplay between the endohedral and exohedral metallic units can be realized in a single system by means of intramolecular charge transfer, which may inspire the interests in the design and utilization of novel metallofullerene-based molecular devices.