Synthesis and structural characterization of ferrocene-based bis(pyrazol-1-yl)borate ligands: FcB(Me)pz 2 K, Fc 2 Bpz 2 K, and 1,1′-fc[B(Me)pz 2 ] 2 K 2 (Fc: ferrocenyl, fc: ferrocenylene, pz: pyrazolyl)

Reaction of the ferrocenyl(dimethylamino)boranes FcB(Me)NMe 2, Fc 2 BNMe 2, and 1,1′-fc[B(Me)NMe 2 ] 2 with 1:1 mixtures of pyrazole and potassium pyrazolide in refluxing THF gave the potassium salts of the ferrocene-based bis(pyrazol-1-yl)borate ligands FcB(Me)pz 2 K, Fc 2 Bpz 2 K, and 1,1′-fc[B(Me)pz 2 ] 2 K 2 in good yield (Fc: ferrocenyl, fc: ferrocenylene, pz: pyrazolyl). In the solid state, FcB(Me)pz 2 K and Fc 2 Bpz 2 K form centrosymmetric dimers with short K⋯Cp contacts suggesting an η 5 coordination mode of the potassium ion. The crystal lattice of the ditopic ligand 1,1′-fc[B(Me)pz 2 ] 2 K 2 consists of coordination polymer strands featuring essentially the same structural motif that has been observed for the monotopic derivatives. All three scorpionate ligands are thus promising building blocks for the preparation of ferrocene-containing multiple-decker sandwich complexes.