The synthesis of half-sandwich bis(pentafluorophenyl)boryl-substituted cyclopentadienyl zirconium, niobium and tantalum complexes and the isolation and moecular structure of a zwitterionic niobocene

摘要

Reaction of B(C_5H_4SiMe_3)(C_6F_5)_2 with MCl_5 (M = Nb, Ta) leads to the first group 5 borylcyclopentadienyl half-sanwich complexes MCl_4{C_5H_4B(C_5F_5)_2} (1 and 2). In contrast, the reaction with ZrCl_4 gives the metallocene ZrCl_4{C_5H_4B(C_6F_5)_2}_2 (3). The use of ZrCl_4(SMe_2)_2 instead of ZrCl_4 as starting material allows the isolation of the monocyclopentadienyl zirconium complex ZrCl_3{C_5H_4B(C_6F_5)_2(SMe_2)} (4). The utility of LiCp' as a general route to zirconocenes is demonstrated by the synthesis of ZrCl_3(Cp){C_5H_4B(C_6F_5)_2(SMe_2)} (5) and ZrCl_3(Ind){C_5H_4B(C_6F_5)_2(SMe_2)} (6) (Ind = eta~5-indenyl). Boron-substituted niobocenes are prepared through the dehalostannylaion reaction between the half-sandwich complexes and tin-substituted cyclopentadienes. They adopt zwitterionic structures in which a chlide ligand is transferred to boron, for example Nb~(+)Cl(C_5F_4SMe_3)C_5F_4B~(-)(Cl)(C_6F_5)_2} (9). The crystal structure of 9 has been determined by X-ray crystallography. Reaction of the strong base, pyridine, with the borylcyclopentadienyl complexes, TiCl_3(C_5F_4B(C_6F_5)_2) TiCl_2(Cp)(C_5F_4B(C_6F_5)_2)} and 1-6 leads to the generation of a series of pyridine adducts (10-17) in which the pyridine is bound to boron. The solid-state structures of the four coordinate adducts TiCl_2(Cp)(C_5F_4B(C_6F_5)_2(py)) (10) and TiCl_3(C_5F_4B(C_6F_5)_2(py)) (14) are described. The half-sandwich zirconium and niobium complexes 15 and 16 are shown by spectroscopic and structural methods to coordinate a further one (Nb) or two (Zr) equivalents of pyridine to attain an octahedral geometry at the metal centre. The zwitterionic complexes 8 and 9 do not react with pyridine.