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.

Dinuclear Ce(IV) Aryloxides: Highly Active Catalysts for Anhydride/Epoxide Ring-Opening Copolymerization

“…The solid-state structure (Figure ) indicates a distorted-octahedral geometry around the Ce IV centersboth metals are coordinated by two phenolate oxygens, three trimethylsiloxide ligands, and a single pyridine molecule. The average Ce–O phenolate distance (2.220 Å) is slightly longer than the average Ce IV –O siloxide distance (2.158 Å), but both are well within the range of literature Ce IV –O distances reported. ,,,− Specifically, the subset of average Ce–siloxide distances match very well with comparable six-coordinate complexes: e.g., 2.151 Å in [Ce­{OSi­(O t Bu) 3 } 4 (NH 3 ) 2 ] and 2.143 Å in [Ce­(OMe)­{OSi­(O t Bu) 3 } 3 (THF) 2 ] . The chelate angle of the TP ligand (O1–Ce1–O2) is 85.4° in 1*- p -Ad , which is slightly narrower than in similar TP complexes reported recently by us: the average O–M–O angle is 90.4° in [Ce IV 2 ( p TP t ) 2 (THF) 4 ], 89.0° in [{Ce III Cl­(py) 4 } 2 ( p TP t )], and 91.3° in [{U IV I 2 (THF) 2 } 2 ( p TP t )]. , …”

“…The proligands H 4 ( m TP t ) and H 4 ( p TP t ) (Chart ) have been reported previously; the adamantyl derivatives H 4 ( m TP Ad ) and H 4 ( p TP Ad ) and the terphenyl proligand H 4 ( mTer TP t ) are new and were synthesized in an analogous manner (see section S2.1 in the Supporting Information). We find that “Ce­(OSiR 3 ) 4 ” made in situ , as described recently by Anwander and co-workers from [NH 4 ] 2 [Ce­(NO 3 ) 6 ] or [NEt 4 ] 2 [CeCl 6 ], provides a clean, one-pot route to the target catalysts (Scheme ).…”

“…Neutral complexes can also be isolated and provide useful comparisons in the catalysis studies: [Ce 2 (OSiEt 3 ) 4 (pTP t )] (5) was synthesized by a protonolysis reaction of H 4 (pTP t ) and 2 equiv of the separately prepared Ce(OSiEt 3 ) 4 (Scheme 2). 51,59 Heating at 60 °C overnight and a straightforward workup gives 5 in 68% yield. The 1 H NMR spectrum of 5 shows four aromatic resonances of 2H, a singlet of 4H for the aromatic spacer, two singlets of 36H for the tert-butyl groups, and a triplet (36H at 1.13 ppm) and quartet (24H at 0.73 ppm) for the triethylsiloxide ligands (Figure S21).…”

“…Siloxide ligands have precedence in stabilizing Ce IV , as shown in work by the groups of Anwander and Mazzanti. 51,58 This also puts 1-p-t Bu among the most oxidizing Ce IV complexes yet reported, with a reduction potential similar to that of CeL(O t Bu) 2 (L = salfen; E pc = −2.39 V vs Fc/Fc + in THF) 10 by Diaconescu and the current record-holding imidophosphorane-supported Ce(NP(piperidinyl) 3 ) 4 complexes (reduction range of −2.30 < E pc < −2.88 V vs Fc/Fc + in THF) by La Pierre and co-workers. 60,61 Compounds 2-p-t Bu and 3 are also highly oxidizing, while the voltammogram of 1-m-t Bu is complicated and no clear redox process could be identified.…”

Tuning Organocerium Electrochemical Potentials by Extending Tris(cyclopentadienyl) Scaffolds with Terminal Halogenido, Siloxy, and Alkoxy Ligands

“…Moreover, the initial successful salt-metathetical exchange between chlorido species Cp′ 3 CeCl and KO t Bu disclosed a new approach toward ceric alkoxy derivatives . Alkoxy and siloxy ligands are known to strongly stabilize the cerium­(IV) center, as evidenced by a broad variety of homoleptic ceric alkoxides and siloxides. − The robust redox-insensitive siloxy ligands OSi­(O t Bu) 3 and OSiPh 3 even allowed for the isolation of molecular terbium­(IV) and praseodymium­(IV) complexes. − …”