Synthesis and Structures of Oxide -Centred Alkali Metal (K, Li)/Lanthanoid (Ln3 or 4) 3,5-Dimethylpyrazolate Cages - Herbert Schumann Revisited.

Reaction of lanthanoid tris(3,5-dimethylpyrazolate) compounds, [Ln(Mepz)(thf)] (Ln=La 1 a, Ce, Pr, Dy 1 b, Yb, Lu) with potassium or lithium bistrimethylsilylamide and with or without added 3,5-dimethylpyrazole, or of lanthanoid tris(bistrimethylsilyl)amide complexes with potassium bistrimethylsilylamide and 3,5-dimethylpyrazole have yielded a variety of oxide centred Ln or Ln/(K or Li) multinuclear cages, namely, [LaO(Mepz) K(thf)] (2 a), [LaO(Mepz)Li(MepzH)]⋅0.5Hexane (2 b), [LaO(Mepz)(MepzH)] (2 c) (from heating 1 a in toluene), [CeO(Mepz)K(dme)] (3 a), [CeO(Mepz)Li(thf)]⋅0.5Hexane (3 b) and [Ce(Mepz)Li(thf)] (3 c), which crystallized together, [CeO(Mepz)K(thf)] (3 d), [PrO(Mepz)K(thf)] (4), [DyO(Mepz)K(thf)]⋅THF (5), [YbO(Mepz)K(thf)]⋅THF (6), and [LuO(Mepz)K(thf)]⋅THF (7). Crystals of {[K(Mepz)(thf)]⋅THF} (8) were also obtained from the preparation of 7. From reaction of [Ce(Mepz)(thf)] with potassium tert-butoxide in toluene, the cerium(IV) heterobimetallic polymer [Ce(Mepz)(OtBu)K] (9) was isolated. In the LnO and the LnO cages, the Ln atoms have triangular and distorted tetrahedral arrangements about the central oxygen, respectively. The relationship of the alkali metals to the central oxygen varies considerably. Thus in 2 a, 2 b, there is no bonding, in 3 a, both K atoms interact weakly, in 3 b one of the two Li atom is bound, in 3 d, 4, one of three K atoms in bound, whilst in 5-7, both K atoms are bound. All metals are bound to the cages by a variety of pyrazolate binding modes, with up to five different exhibited in some structures, and a new coordination mode, μ-1κ(N):2κ(N'):η:η, was observed in two complexes. In the structure of 2 c, the coordinated MepzH ligand binds to two metals through a single nitrogen, the first time this has been observed for a pyrazole donor. The complex 9 is polymeric with all metals bridged by butoxide donors as well as by Mepz groups.