Synthesis and properties of Di-π-[8]annulenecerium(IV), cerocene

An efficient synthesis of di-pi-([8] annulene)cerium(IV) (cerocene) is reported by the reaction of K[Ce(C8H8)(2)] with allyl bromide. Cerocenes can also be prepared by oxidation of the corrresponding cerates with silver iodide in THF, but this reaction is more variable. Cerocene m acts only slowly with UCl4 to give uranocene. K[Ce(C8H8)(2)] and cerocene undergo electron exchange on the NMR time scale. Electrochemical study of cerocene shows redox with the cerate ion, Ce(C8H8)(2)(-), to be reversible with a relatively low reduction potential (-0.6 V vs NHE). The corresponding praeseodymium salt, K[Pr(C8H8)(2)], does not undergo comparable reversible oxidation; its cyclic voltammetry is compared with that of K-2[Yb(C8H8)(2)]. The chemistry of cerocene resembles that of di-pi-([8]annulene)actinide(IV) compounds.