STERICALLY DEMANDING FERROCENE-BASED TRIS(1-PYRAZOLYL)BORATE LIGANDS

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