Stabilization of the Oxidation State +IV in Siloxide‐Supported Terbium Compounds

Abstract

The synthesis of lanthanides other than cerium in the oxidation state +IV has remained a desirable but unmet target until recently, when two examples of TbIV with saturated coordination spheres were isolated. Here we report the third example of an isolated molecular complex of terbium(IV), where the supporting siloxide ligands do not saturate the coordination sphere. The fully characterized six‐coordinate complex [TbIV(OSiPh3)4(MeCN)2], 2‐TbPh, shows high stability and the labile MeCN ligands can be replaced by phosphinoxide ligands. Computational studies suggest that the stability is due to a strong π(O−Tb) interaction which is stronger than in the previously reported TbIV complexes. Cyclic‐voltammetry experiments demonstrate that non‐binding counterions contribute to the stability of TbIV in solution by destabilizing the +III oxidation state, while alkali ions promote TbIV/TbIII electron transfer.

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

“…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. Switching to toluene/n-hexane mixtures resulted in crystals of suitable size for X-ray diffraction (XRD) analyses.…”

“…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. − …”

Heterometallic Clusters with Multiple Rare Earth Metal–Transition Metal Bonding

“…RE metals in molecular complexes usually exhibit a stable +III oxidation state; the synthesis and characterization of +IV RE species remains a challenge. Cerium, as one of the most abundant RE metals, can adopt a +IV oxidation state in molecular complexes. − Recently, the +IV oxidation state of RE was extended to Tb and Pr independently by the groups of Mazzanti and La Pierre. − However, an example of a +IV RE complex with a metal–metal bond has not been reported.…”

Molecular Complexes of Emerging Tetravalent Rare‐Earth Metals

“…continued their work on tetravalent rare‐ earth chemistry and reported another molecular complex of Tb(IV) 4 from Ph 3 SiO‐substitued trivalent precursor 3 (Scheme 1). [ 7 ] This six‐coordinate complex shows high stability and the MeCN ligands can be replaced by phosphinoxide ligands (Et 3 PO and Ph 3 PO). Unlike 2 , the supporting ligands (OSiPh 3 ) 4 do not saturate the coordination sphere but can also stabilize this complex.…”

“…Since then, four examples of Tb(IV) and Pr(IV) molecular complexes have been reported. [ 6‐9 ] In this emerging topic, we will for the first time cover the field of rare‐earth (except Ce) chemistry contributed to the +4 oxidation state. Meanwhile, we hope that this topic will open a new avenue for the development of tetravalent rare‐earth organometallic chemistry.…”