Anionic ansa-zirconocenes with pentafluorophenyl-substituted borato bridges

The ansa-borane complex (Me2S)(C6H5)B(C5H4)(2)ZrCl2 (1) reacts selectively with 2 equiv of LiC6F5 to give (Me2S)(C6H5)B(C5H4)(2)Zr(C6F5)(2) (2) and wi th 3 equiv LiC6F5 to form the borato-bridged complex [Li(Et2O)(3)][(C6F5)(C 6H5)B(C5H4)(2)Zr(C6F5)(2)] (3a) The C6F5 groups are exchanged for Me by rea ction with AlMe3 to form [Li(Et2O)(x)][(C6F5)(C6H5)B(C5H4)(2)ZrMe2] (4). Tr eatment of BCl3 with (SiMe3)(SnMe3)C5H4 affords BCl(C5H4SiMe3)(2) (5), whic h undergoes a dehalosilylation reaction with ZrCl4(Me2S)(2) to give Cl(Me2S )B(C5H4)ZrCl2 (6). The reaction of 6 with LiC6F5 proceeds in a fashion simi lar to that of 2, leading first to (Et2O)ClB(C5H4)(2)Zr(C6F5)(2) (7) and wi th 5 equiv of LiC6F5, to [Li(Et2O)(4)][(C6F5)(2)B(C5H4)(2)Zr(C6F5)(2)] (9a) in 28% yield. The yield is improved through the use of C6F5MgBr at 60 degr eesC. The C6F5 groups are readily exchanged for Me through reaction with Li Me to give [Li(Et2O)(4)][(C6F5)(2)B(C5H4)(2)ZrMe2] (10a). Complexes 3, 9, a nd 10 are catalysts for ethene polymerization when activated with MAO or Al Bu3i/[CPh3][B(C6F5)(4)].