Ceric Ammonium Nitrate and Ceric Ammonium Chloride as Precursors for Ceric Siloxides: Ammonia and Ammonium Inclusion

Abstract

Treatment of ceric ammonium nitrate (CAN) with sodium tris(tert‐butoxy)siloxide in THF afforded crystalline complexes [Ce{OSi(OtBu)3}3(NO3)(NH3)2(THF)] and [Ce{OSi(OtBu)3}4(NH3)2] featuring strong ammonia coordination. Conducting the CAN/NaOSi(OtBu)3 (1:4) reaction in acetonitrile gave ceric ate complex [Ce{OSi(OtBu)3}3(NO3)2(NH4)(NCCH3)] where the ammonium cation is embedded in the siloxy ligand sphere via hydrogen bonding. Salt‐metathetic conversion of ceric organo(R)ammonium hexachlorides (CACR, R = Me, Et) with NaOSi(OtBu)3 and sodium siloxides NaOSiR3 (R = Et, iPr) in THF allowed the isolation of ceric siloxide complexes [Ce{OSi(OtBu)3}4], [Ce(OSiEt3)4(THF)0.5], and [Ce(OSiiPr3)4]. Although the reaction products are prone to ate complex formation with the organoammonium chloride side products, the salt‐metathesis route gave good yields for homoleptic [Ce{OSi(OtBu)3}4]. The CACR/alkylsiloxide reaction mixtures also suffer from (photo)redox processes as revealed by the formation of trivalent [Ce(OSiiPr3)4(NMe4)], but can be further stabilized by pyridine coordination as shown for the solid‐state structure of [Ce(OSiiPr3)4(py)]. The siloxide complexes were characterized by NMR, DRIFT, UV/Vis spectroscopy and cyclic voltammetry, as well as paramagnetic susceptibility measurements, X‐ray structure, and elemental analysis. The electrochemical studies revealed an effective stabilization of the CeIV ion within the siloxy ligand environments.