Synthesis and structural characterization of fluorenyltris(pyrazol-1-yl)borate ligands as new examples of cyclopentadienyl/scorpionate hybrid ligands

Two fluorenyl/tris(pyrazol-1-yl)borate hybrid ligands, FlBpz3Li and FlB(pz3-tBu)3Li, have been synthesized and structurally characterized by X-ray crystallography (Fl: 9-fluorenyl; pz: pyrazolyl). From the reaction of FlBpz3Li and ZnCl2 in THF, the dinuclear complex (THF)3Lipz(Fl)Bpz2ZnCl2 was obtained in which a ZnCl2 moiety is chelated by two pyrazolyl ligands while the third pz ring coordinates to an Li(THF)3 fragment. Acetonitrile solutions of the compound gradually transform into the mononuclear species Fl(pz)Bpz2Znpz2B(pz)Fl featuring a distorted tetrahedral ZnN4 core. In all molecular structures of [FlBpz3]− or [FlB(pz3-tBu)3]− complexes investigated so far, the hybrid ligands adopt very similar conformations with only two pyrazolyl rings bonded to the central metal, whereas the third pyrazolyl acts as dangling substituent. The fluorenyl substituent of FlBpz3Li may be deprotonated with KH in quantitative yield.