Multi-electron Oxidation of Ce(III) Complexes Facilitated by Redox-Active Ligands

A family of cerium complexes featuring a redox-active ligand in different oxidation states has been synthesized, including the the iminosemiquinone (isq)1- compound, Ce(dippisq)3 (1-Ceisq), and the amidophenolate (ap)2- species CeIII(dippap)3K3 (2-Ceap), [CeIII(dippap)3K][K(18-c-6)]2 (2-Ceap 18c6), and [CeIII(dippap)3K][K(15-c-5)2]2 (2-Ceap 15c5). Treating 2-Ceap 15c5 with dioxogen furnishes the cerium(IV) derivative [CeIV(dippap)3][K(15-c-5)2]2 (3-Ceap 15c5), and an analogous synthesis can be used to generate [CeIV(dippap)3][K(crypt)]2 (3-Ceap crypt). Similarly, addition of hexamethyldisiloxane produces an interesting bis(amidophenolate) species, [(Me3SiO)2CeIV(dippap)2][K(15-c-5)2]2 (4-CeOSiMe3). Full spectroscopic and structural characterization of each derivative was performed to establish the oxidation states of both the ligands and the cerium ions. Cerium(III) complexes with redox-active ligands in oxidation states L1- and L2- have been synthesized and fully characterized. Multielectron movement has been achieved by redox chemistry at the ligands. Sequestering counterions also introduces exciting reactivity, forming Ce(IV) species with dioxygen and oxidative addition of hexamethyldisiloxane to form a bis(siloxide) cerium(IV) species. image