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

Abstract

The oligomeric potassium complex [(Me 2pzH)(Me 2pz) 2(18-crown-6)(THF)K 2] 2 ( 1) and the lithium dimer [( t Bu 2pz)(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 P 1 ¯ , 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 η 2-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 η 5-fashion to one pyrazolate ligand and in a η 1-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 η 5-coordination to one pyrazolate ligand and one THF molecule. Complex 2 is formed from the nucleophilic addition of THF to the lithium pyrazolate tetramer, [( t Bu 2pz)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-η 1:η 1 fashion to two Li ions. These ions complete their respective coordination spheres with THF.