CATIONIC METALLOCENE POLYMERIZATION CATALYSTS BASED ON TETRAKIS(PENTAFLUOROPHENYL)BORATE AND ITS DERIVATIVES - PROBING THE LIMITS OF ANION NONCOORDINATION VIA A SYNTHETIC, SOLUTION DYNAMIC, STRUCTURAL, AND CATALYTIC OLEFIN POLYMERIZATION STUDY

The synthesis and properties of two soluble, weakly coordinating deriv atives of the tetrakis(perfluoroaryl)borate anion B(4-C6F4TBS)(4)(-) a nd B(4-C6F4TIPS)(4)(-) (TBS = tert-butyldimethylsilyl and TIPS = triis opropylsilyl) are reported. Reaction of the trityl salts of the above anions with a variety of zirconium and thorium L(2)MMe(2) complexes in benzene or toluene affords the cationic ion-paired methyl complexes L (2)MMe(+)X(-) or the corresponding hydride complexes L(2)MH(+)X(-) (L( 2) = bis(cyclopentadienyl)- or cyclopentadienylamido-type ligand) when the reaction is carried out under dihydrogen. The solid state structu re of the complex (Me(5)Cp)(2)ThMe(+)B(C6F5)(4)(-) has been characteri zed by X-ray diffraction. The B(C6F5)(4)(-)-based zirconocenium methyl complexes L(2)MMe(+) are unstable at room temperature with respect to , among other factors, intramolecular C-H activation of the ligand fra mework. In general, the thermal stabilities of the B(C6F4TBS)(4)(-)- a nd B(C6F4TIPS)(4)(-)-derived complexes are greater than those of the c orresponding B(C6F5)(4)(-)- and MeB(C6F5)(3)(-)-derived analogues. The relative coordinative tendencies of MeB(C6F5)(3)(-), B(C6F5)(4)(-), B (C6F4TBS)(4)(-), and B(C6F4TIPS)(4)(-) are estimated from the solution spectroscopic information and the structural dynamics of the ion-pair s and follow the order MeB(CBF5)(3)(-) > B(C6F4TBS)(4)(-) approximate to B(C6F4TIPS)(4)(-) > B(C6F5)(4)(-). The coordination of the neutral metallocene precursors to the cationic metallocenes is found to compet e with counteranion coordination. Arene solvent coordination to the zi rconium constrained geometry cation [(Me(4)Cp)SiMe(2)(N(t)Bu)]ZrMe(+) is also observed when B(C6F5)(4)(-) is the counteranion. (1,2-Me(2)Cp) (2)ZrMe(+)B(C6F4TBS)(4)(-) undergoes slow decomposition under an inert atmosphere to afford [(1,2-Me(2)Cp)(2)ZrF](2)(mu-F)B-+(C6F4TBS)(4)(-) , which has been characterized by X-ray diffraction. The olefin polyme rization activity and thermal stability of the zirconocene catalysts r eaches a maximum when B(C6F4TBS)(4)(-) and B(C6F4TIPS)(4)(-) are used as counteranions. The polymerization activity of the zirconium constra ined geometry complex also reaches a maximum in aromatic solvents when B(C6F5)(4)(-) is used as the counteranion, apparently due to solvent coordination.