Anionicansa-Zirconocenes with Pentafluorophenyl-Substituted Borato Bridges

The ansa-borane complex (Me2S)(C6H5)B(C5H4)2ZrCl2 ( 1 ) reacts selectively with 2 equiv of LiC6F5 to give (Me2S)(C6H5)B(C5H4)2Zr(C6F5)2 ( 2 ) and with 3 equiv LiC6F5 to form the borato-bridged complex [Li(Et2O)3][(C6F5)(C6H5)B(C5H4)2Zr(C6F5)2] ( 3a ). The C6F5 groups are exchanged for Me by reaction with AlMe3 to form [Li(Et2O)x][(C6F5)(C6H5)B(C5H4)2ZrMe2] ( 4 ). Treatment of BCl3 with (SiMe3)(SnMe3)C5H4 affords BCl(C5H4SiMe3)2 ( 5 ), which 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 similar to that of 2 , leading first to (Et2O)ClB(C5H4)2Zr(C6F5)2 ( 7 ) and with 5 equiv of LiC6F5 to [Li(Et2O)4][(C6F5)2B(C5H4)2Zr(C6F5)2] ( 9a ) in 28% yield. The yield is improved through the use of C6F5MgBr at 60 °C. The C6F5 groups are readily exchanged for Me through reaction with LiMe to give [Li(Et2O)4][(C6F5)2B(C5H4)2ZrMe2] ( 10a ). Complexes 3 , 9 , and 10 are catalysts for ethene polymerization when activated with MAO or AlBui3/[CPh3][B(C6F5)4].