Synthesis of Cyclopentadienyl-, Indenyl-, and Fluorenylbis(pentafluorophenyl)boranes as Ligands in Titanium and Zirconium Half-Sandwich Complexes. The Crystal Structures of C13H9B(C6F5)2·t-BuNH2, C13H8SiMe3B(C6F5)2, and {η5-C5H4B(C6F5)2}TiCl3
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Abstract
Bis(pentafluorophenyl)boron fluoride (C6F5)2BF·OEt2 (1), readily accessible from BF3·OEt2 and 2 equiv of C6F5MgBr, reacts with fluorenyllithium to give (Flu)B(C6F5)2 (4), while the reaction with indenyllithium leads to the regioisomers 1- and 2-IndB(C6F5)2 5 and 6, which are separated by fractional crystallization. 4 and 5 form crystalline adducts with tert-butylamine. The trimethylsilyl derivatives Flu(SiMe3)B(C6F5)2 (9) and Ind(SiMe3)B(C6F5)2 (10) are similarly prepared. Heating (C6F5)2BF·OEt2 leads to ether cleavage and formation of (C6F5)2BOEt. Treatment of 5 and 6 with Zr(NMe2)4 at room temperature gives indenylzirconium amido half-sandwich complexes; however, the reaction is accompanied by the unexpected exchange of one boron-C6F5 substituent by NMe2, to form 1- and 2-{C9H6B(C6F5)(NMe2)}Zr(NMe2)3. Reaction with SiClMe3 affords the trichlorides 1- and 2-{C9H6B(C6F5)(NMe2)}ZrCl3. The NMe2 substituent reduces the Lewis acidity of boron, so that donor ligands such as THF or DME coordinate exclusively to zirconium. Whereas 9 and 10 fail to react with group 4 metal chlorides, the cyclopentadienylborane C5H4(SiMe3)B(C6F5)2 undergoes smooth dehalosilylation with TiCl4 to give {C5H4B(C6F5)2}TiCl3. Both 2-{C9H6B(C6F5)(NMe2)}ZrCl3 and {C5H4B(C6F5)2}TiCl3 in the presence of low concentrations of AlEt3 are active ethene polymerization catalysts, while under comparable conditions mixtures of AlEt3 and either IndZrCl3 or CpTiCl3 are inactive. The molecular structures of (Flu)B(C6F5)2·NH2CMe3, Flu(SiMe3)B(C6F5)2, and {C5H4B(C6F5)2}TiCl3 have been determined by X-ray diffraction.
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