Cerium(IV) Neopentoxide Complexes

Abstract

Treatment of ceric ammonium nitrate (CAN) with varying amounts of sodium neopentoxide led to the isolation of crystalline cerium(IV) complexes [Ce(OCHtBu)(NO)(HOCHtBu)], [Ce(OCHtBu)(NO)-(NCCH)], [Ce(OCHtBu)(NO)], and [Ce(OCHtBu)Na-(THF)] featuring Ce/(OR) ratios of 1:2, 1:3, 1:3.5, and 1:4.5, respectively. The complexes are light-sensitive and prone to ligand redistribution as evidenced by multicomponent NMR spectra as well as the formation of [{Ce(OCHtBu)}(THF)] and the mixed-valent complex [Ce(OCHtBu)(NO)]. The CAN protocol also gave access to the isopropoxide derivative [Ce(OiPr)(NO)(THF)]. The reaction of [EtN][CeCl] (CAC, ceric organoammonium chloride) with different equivalents of Na(OCHtBu) was also impaired by ligand reorganization and ate complexation as detected for the tetravalent cerium complex [Ce(OCHtBu)Cl][EtN]. Protonolysis of [Ce{N(SiHMe)}] with 4 equiv of HOCHtBu afforded donor-free homoleptic [Ce(OCHtBu)] in quantitative yield. All complexes were characterized by NMR, DRIFT, and UV-vis spectroscopy, as well as paramagnetic susceptibility measurements, X-ray structure analysis, and elemental analysis.

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

“…The cerium­(IV) alkoxides 5 (OR = OMe), 6 (OR = OEt), 7 (OR = OCH 2 t Bu), and 8 (OR = OCHMe 2 ) revealed characteristic NMR chemical shifts for the protons in the α-position of the alkoxy ligands (Ce–O–C– H ), as they appear heavily shifted downfield (Table ). Such a deshielding effect was also observed for the homoleptic cerium­(IV) alkoxides [Ce­(OCHMe 2 ) 4 ] 3 and [Ce­(OCH 2 t Bu) 4 ] 2 (thf), albeit to a minor extent. , The latter complexes show the relevant proton signals at 5.25 and 4.53 ppm, respectively, significantly shifted to lower field in comparison to 4.01 and 3.28 ppm in the free alcohol in CDCl 3 . ,, However, the 1 H NMR signals of the CH 2 moieties in neopentoxy derivatives Cp′ 3 Ce­(OCH 2 t Bu) ( 7a and 7b ) are detected at 5.87 and 6.09 ppm, respectively. This indicates a decrease in electron density at the respective protons close to the cerium­(IV) center, possibly caused by the +M effect of the alkoxy ligand.…”

“…Such a deshielding effect was also observed for the homoleptic cerium(IV) alkoxides [Ce(OCHMe 2 ) 4 ] 3 and [Ce(OCH 2 tBu) 4 ] 2 (thf), albeit to a minor extent. 22,39 The latter complexes show the relevant proton signals at 5.25 and 4.53 ppm, respectively, significantly shifted to lower field in comparison to 4.01 and 3.28 ppm in Scheme 1. Oxidation of Cp R 3 Ce(thf) (1), 14,32 to Form Cerium(IV) Halogenides 2-4 The ceric tris(cyclopentadienyl) complexes under study could be obtained as needlelike microcrystals via crystallization from n-hexane.…”

“…For further comparison, the terminal Ce–O distances in homoleptic [Ce­(O t Bu) 4 ] 2 and [Ce­(OCH 2 t Bu) 4 ] 3 range from 2.058(3) to 2.065(3) Å and from 2.029(1) to 2.030(2) Å, respectively, while the terminal Ce–O­(methoxy) distance in Ce­[OSi­(O t Bu) 3 ] 3 (OCH 3 )­(thf) 2 is 2.094(1) Å . Generally, the Ce–O distances span a wide range depending on the coordination number and terminal/μ x -bridging mode: e.g., as detected for ceric Ce 3 (μ 3 -O i Pr) 2 (μ s -O i Pr) 3 (O i Pr) 7 (2.061(4)–2.721(3) Å) .…”

“…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. − …”

Crystallographic and Spectroscopic Investigations on Oxidative Coordination in the Heteroleptic Mononuclear Complex of Cerium and Benzoxazine Dimer

“…At a closer inspection into the preparation of Ce(IV) complexes, there are two main synthetic approaches to obtain the desired materials, namely the ligand substitution reactions of Ce(IV) precursors and the one-electron oxidation of Ce(III) complexes [ 4 ]. Considering the ligand substitution approach, CeO 2 , [CeCl 6 ] 2− , and ceric ammonium nitrate (CAN) are commonly used as the starting precursors [ 10 , 11 ]. However, the ligands possessing a reducing property may disturb the preservation of the desired tetravalent oxidation state [ 12 ].…”