Synthesis and Characterization of Cerium(IV) Metallocenes

Abstract

By applying a salt metathesis approach between Ce(O t Bu3)2(NO3)2(THF)2 and the potassium salts of mono-and ditrimethylsilyl substituted cyclopentadienes, we were able to isolate two new Ce(IV) metallocenes, including to the best of our knowledge, the first structurally characterized bis-cyclopentadiene Ce(IV) compound.

Ceric Cyclopentadienides Bearing Alkoxy, Aryloxy, Chlorido, or Iodido Co‐Ligands

“…The 1 H NMR resonances for the Cp′ protons of 4 at 6.35, 5.67, and 0.45 ppm are shifted to higher fields in comparison with those of the Ce IV compounds 2 b , 3 b , and 3 c . The signal for the tert ‐butoxide ligand at 1.81 ppm lies well within the expected range . Furthermore, the magnetic susceptibility of 4 ( χ mol =4.93×10 −4 , μ =0.15 emu mol −1 , see Table S1 in the Supporting Information), as well as its molar absorptivities at 298 nm ( ϵ 298 =2283 L mol −1 cm −1 ) and 422 nm ( ϵ 422 =6974 L mol −1 cm −1 , Figure S28) are in line with the monomeric tris(cyclopentadienyl) Ce IV complexes 3 a – c .…”

“…Cp 3 CeCl was the first chlorido‐functional species of this type and, following Cp 3 Ce(O i Pr) and Cp 3 Ce(O t Bu), the third well‐defined tris(cyclopentadienyl)cerium(IV) complex known so far. More recently, the synthesis and X‐ray structure analysis of the bis(cyclopentadienyl) bis(alkoxy) derivatives Cp′ 2 Ce(O t Bu) 2 and Cp′′ 2 Ce(O t Bu) 2 (Cp′=C 5 H 4 SiMe 3 , Cp′′=C 5 H 3 ‐1,3‐(SiMe 3 ) 2 ) were reported using CAN as the Ce IV precursor . Overall, chlorido ligands provide a less stabilizing environment for non‐ionic Ce IV complexes, as clearly evidenced by the unstable “CeCl 4 ” compared with the thermally rather stable Ce(OR) 4 complexes …”

Pentamethylcyclopentadienyl‐Supported Cerocene(III) Complexes

“…Although trivalent cerium Cp* compounds have been investigated relatively thoroughly, tetravalent cerium Cp* complexes are unknown. Overall, fully characterized Ce IV cyclopentadienyl complexes are limited to those of [Cp 3 CeCl], [Cp 3 Ce(OR)] (R = t Bu, i Pr), [Cp′ 2 Ce(O t Bu) 2 ] (Cp′ = C 5 H 4 SiMe 3 ), and [Cp′′ 2 Ce(O t Bu) 2 ] [Cp′′ = C 5 H 4 (SiMe 3 ) 2 ‐1,3] . Of these five compounds, [Cp 3 CeCl] is the only example accessed by oxidation of a trivalent precursor (here [Cp 3 Ce]).…”

Reversible Formation of a Cerium‐Bound Terminal Hydride: Ce(C5Me4SiMe3)2(H)(thf)

“…The bulky Cp′ (Cp′ = C 5 Me 4 SiMe 3 ) ligand meanwhile shows promise for stabilizing a new type of cerium terminal hydride complex, and we have recently utilized the bis‐substituted version of this ligand to stabilize the first structurally characterized bis‐cyclopentadiene Ce IV complex . Hou et al have also used this ligand to effectively stabilize terminal lanthanide hydride complexes of the type Ln(Cp′) 2 (H)(thf) (Ln = Y, Nd, Sm, Dy and Lu, see Scheme ), but did not report the cerium member of this series, presumably because their synthetic route could not be applied to this metal center, owing to the instability of the analogous starting material.…”