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(Me₂pz)₃(thf)]₂ (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 Ln₃ or Ln₄/(K or Li)_1-3 multinuclear cages, namely, [La₄O(Me₂pz)₁₁ K(thf)₂] (2 a), [La₄O(Me₂pz)₁₁Li(Me₂pzH)]⋅0.5Hexane (2 b), [La₄O(Me₂pz)₁₀(Me₂pzH)] (2 c) (from heating 1 a in toluene), [Ce₃O(Me₂pz)₉K₂(dme)₂] (3 a), [Ce₃O(Me₂pz)₉Li₂(thf)₂]⋅0.5Hexane (3 b) and [Ce(Me₂pz)₅Li₂(thf)₃] (3 c), which crystallized together, [Ce₃O(Me₂pz)₁₀K₃(thf)₃] (3 d), [Pr₃O(Me₂pz)₁₀K₃(thf)₃] (4), [Dy₃O(Me₂pz)₉K₂(thf)₂]⋅THF (5), [Yb₃O(Me₂pz)₉K₂(thf)₂]⋅THF (6), and [Lu₃O(Me₂pz)₉K₂(thf)₂]⋅THF (7). Crystals of {[K₈(Me₂pz)₈(thf)₂]⋅THF}_∞ (8) were also obtained from the preparation of 7. From reaction of [Ce(Me₂pz)₃(thf)]₂ with potassium tert-butoxide in toluene, the cerium(IV) heterobimetallic polymer [Ce₂(Me₂pz)₆(OtBu)₄K₂]_∞ (9) was isolated. In the Ln₃O and the Ln₄O 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, μ₄-1κ(N):2κ(N'):η⁵:η⁵, was observed in two complexes. In the structure of 2 c, the coordinated Me₂pzH 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 Me₂pz groups.