Sterically demanding ferrocene-based tris(1-pyrazolyl)borate ligands

Ferrocene-based mono- and bifunctional tris(1-pyrazolyl)borates bearing either methyl or phenyl substituents at the 3-positions of their pyrazolyl rings have been obtained from FcB(NMe2)(2) and 1,1'-fc[B(NMe2)(2)](2) (Fc: ferrocenyl; fc: ferrocenylene) and the corresponding pyrazole derivatives via a transamination reaction. All novel ligands have been characterized as their thallium(I) complexes, and the molecular structure of FcB(pz(Ph))(3)Tl (pz(Ph):3-phenylpyrazolyl) has been determined by X-ray crystallography. The compound features monomeric units with tridentate [FcB(pz(Ph))(3)](-) ligands in the crystal lattice, which is in striking contrast to the sterically less congested complex FcB(pz)(3)Tl, that forms polymeric rods in the solid state. For the purpose of comparison, the single crystal X-ray structure of the ferrocene-free parent compound HB(pz)(3)Tl (pz:pyrazolyl) has also been investigated, which again revealed the conventional structural motif of monomeric complexes. (C) 1998 Elsevier Science Ltd. All rights reserved.