Potassium and lithium pyrazolates: The interplay of electronic and steric factors on the hapticity of the pyrazolate ligand and the influence of Lewis bases on nuclearity

The oligomeric potassium complex [(Me2pzH)(Me2pz)2(18-crown-6)(THF)K2]2 (1) and the lithium dimer [(tBu2pz)(THF)Li]2 (2) were synthesized. Both complexes were fully characterized by spectroscopic methods and single crystal X-ray diffraction. Complex 1 crystallized in the triclinic space group P1¯, the structure shows an oligomer capped with 18-crown-6 and THF in both ends. This oligomer may be thought as the result of exscind an infinite single ladder structure in which η2-coordinated pyrazolate ligands to potassium ions are the steps of the stair, and the crown ether acting as a scissor. The potassium ions that form the truncated stair are coordinated in a η5-fashion to one pyrazolate ligand and in a η1-fashion to one pyrazolate and one pyrazolyl ligand, respectively. The potassium ions in the cavity of the 18-crown-6 ligand complete their coordination spheres with η5-coordination to one pyrazolate ligand and one THF molecule. Complex 2 is formed from the nucleophilic addition of THF to the lithium pyrazolate tetramer, [(tBu2pz)Li]4. Complex 2 crystallized in the monoclinic space group C2/c. The molecular structure shows a dimer in which the pyrazolate ligands are coordinated in a μ-η1:η 1 fashion to two Li ions. These ions complete their respective coordination spheres with THF.

Graphical abstractThe oligomeric potassium complex [(Me2pzH)(Me2pz)2(18-crown-6)(THF)K2]2 (1) and the lithium dimer [(tBu2pz)(THF)Li]2 (2) were synthesized. Both complexes were fully characterized by spectroscopic methods and single crystal X-ray diffraction. Complex 1 shows π-bound pyrazolate ligands to potassium in a η5-fashion. Complex 2 was obtained by nucleophilic addition of THF to [(tBu2pz)Li]4.Figure optionsDownload full-size imageDownload as PowerPoint slide