Synthesis and Characterization of Zirconium Complexes Containing a Linked Amido-Fluorenyl Ligand

Abstract

Zirconium complexes containing an amido-fluorenyl ligand bridged by a dimethylsilylene group, C13H8SiMe2NCMe3, have been synthesized. The dichloro complexes Zr(η5:η1-C13H8-SiMe2NCMe3)Cl2(L) (L = THF, Et2O) were prepared by reacting ZrCl4l2 with Li2[C13H8-SiMe2NCMe3] and characterized as labile mono(solvent) adducts. Reaction with MeMgCl gives the thermally sensitive dimethyl complex Zr(η5:η1-C13H8SiMe2NCMe3)Me2(THF), whereas solvent-free dialkyl derivatives Zr(η5:η1-C13H8SiMe2NCMe3)Ph2 and Zr(η5:η1-C13H8-SiMe2NCMe3)(CH2SiMe3)2, all under preservation of the chelate structure, are obtained with PhMgCl and Me3SiCH2MgCl, respectively. Variable-temperature 1H NMR spectroscopic data reveal a sterically congested ligand sphere around the zirconium atom which is confirmed by a single-crystal X-ray diffraction study in the case of the bis(trimethylsilylmethyl) derivative. The substituted fluorenyl ligand is pentahapto-bonded with some variation of the zirconium-ring carbon bond lengths. The amido nitrogen is trigonal planar as a result of significant π-donation to the zirconium. The two (trimethylsilyl)methyl groups do not appear to be strongly distorted despite being bound to a 12-electron d0 center but give rise to a conformation in which the repulsion between the trimethylsilyl and the tert-butyl groups is minimized. This compound crystallizes from pentane in the monoclinic space group P21/n with a = 9.326(3), b = 16.806(5), and c = 19.638(6) Å, β= 93.23(2)°, V = 3073(2) Å3, Z = 4, R = 0.0308, Wr2 = 0.079. © 1995, American Chemical Society. All rights reserved.