Base-free Cationic Mono(cyclopentadienyl)zirconium Complexes - Synthesis, Structural Characterization, and Catalytic Activity In Olefin Polymerization

Mono(cyclopentadienyl) Lewis-base-free cationic complexes [(C5R5)Zr(CH2Ph)2]+-[B(CH2Ph)(C6F5)3]- (R = H (1), Me (2)) have been synthesized by abstraction of one benzyl ligand from the corresponding neutral (C5R5)Zr(CH2Ph)3 precursors with the strong Lewis acid B(C6F5)3. A single-crystal X-ray diffraction analysis of 1 shows; that the formally 10-electron [(C5H5)Zr(CH2Ph)2]+ cation is stabilized by pi-coordination of the Ph ring of the [B-(CH2Ph)(C6F5)3]- anion. The coordination geometry around Zr is tetrahedral, with normal, undistorted eta1-benzyl ligands, while a considerable deviation from planarity is observed for the pi-coordinated Ph ring. Crystal data are a = 15.813(7) angstrom, b = 11.014(8) angstrom, c = 25.402(11) angstrom, beta = 102.65(3)-degrees, V = 4316.7 angstrom3, Z = 4, space group P2(1)/n. A dynamic equilibrium involving the dissociation of the counteranion is observed in solution by variable-temperature NMR spectroscopy for both 1 and 2. Both 1 and 2 react rapidly with THF, affording the Lewis-base adducts [(C5R5)Zr(CH2Ph)2(THF)2]+[B(CH2Ph)(C6F5)3]- (3 and 4), and initiate the ring-opening polymerization of THF. 1 and 2 promote the polymerization of ethene at 25-degrees-C and 1 atm of monomer pressure with fairly high activity, while under the same conditions polymerization of propene proceeds sluggishly