SYNTHESIS OF CYCLOPENTADIENYLBIS(PENTAFLUOROPHENYL)BORANES, INDENYLBIS(PENTAFLUOROPHENYL)BORANES, AND FLUORENYLBIS(PENTAFLUOROPHENYL)BORANES AS LIGANDS IN TITANIUM AND ZIRCONIUM HALF-SANDWICH COMPLEXES - THE CRYSTAL-STRUCTURES OF B(C6F5)(2)CENTER-DOT-T-BUNH2,C13H8SIME3B(C6F5)(2), AND (ETA(5)-C5H4B(C6F5)(2))TICL3

Bis(pentafluorophenyl)boron fluoride (C6F5)(2)BF.OEt2 (I), readily acc essible from BF3.OEt2 and 2 equiv of C6F5MgBr, reacts with fluorenylli thium to give (Flu)B(C6F5)(2) (4), while the reaction with indenyllith ium leads to the regioisomers 1- and 2-IndB(C6F5)(2) 5 and 6, which ar e separated by fractional crystallization. 4 and 5 form crystalline ad ducts with tert-butylamine. The trimethylsilyl derivatives Flu(SiMe3)B (C6F5)(2) (9) and Ind(SiMe3)B(C6F5)(2) (10) are similar ly prepared. H eating (C6F5)(2)BF.OEt2 leads to ether cleavage and formation of (C6F5 )(2)BOEt. Treatment of 5 and 6 with Zr(NME2)(4) at room temperature gi ves indenylzirconium amido half-sandwich complexes; however, the react ion is accompanied by the unexpected exchange of one boron-C6F5 substi tuent by NMe2, to form 1- and 2-{C9H6B(C6F5)(NMe2)}Zr(NMe2)(3). Reacti on with SiClMe3 affords the trichlorides 1- and 2-{C9H6B(C6F5)(NMe2)}Z rCl3. 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 cycl opentadienylborane C5H4(SiMe3)B(C6F5)(2) undergoes smooth dehalosilyla tion with TiCl4 to give {C5H4B(C6F5)(2)}TiCl3. Both 2-{C9H6B(C6F5) (NM e2)}ZrCl3 and {C5H4B(C6F5)(2)}TiCl3 in the presence of low concentrati ons of AlEt3 are active ethene polymerization catalysts, while under c omparable conditions mixtures of AlEt3 and either IndZrCl(3) or CpTiCl 3 are inactive. The molecular structures of (Flu)B(C6F5)(2).NH2CMe3, F lu(SiMe3)B(C6F5)(2), and {C5H4B(C6F5)(2)}TiCl3 have been determined by X-ray diffraction.