H-1-NMR spectroscopic study of cationic intermediates in solvent and oil constituents of the catalytic systems Cp2ZrMe2/AlMe3/[CPh3][B(C6F5)(4)] and Cp2ZrMe2/AlMe3/[CPh3][B(C6F5)(4)] in benzene

摘要

Using H-1-NMR spectroscopy, mutual transformations and stability of cationic complexes [(CP2ZrMe)(2)(mu-Me)](+) [B(C6F5)(4)](-) (1), [Cp2ZrMe+B-...(C6F5)(4)(-)] (2) and [Cp2Zr(mu-Me)(2)AlMe2](+)[B(C6F5)(4)](-) (3) formed in catalytic systems Cp2ZrMe2/[CPh3][B(C6F5)(4)] and Cp2ZrMe2/AlMe3/[CPh3][B(C6F5)(4)] in benzene were studied both in the solution and in the oil deposit formed whenever the total zirconocene concentration is high enough. It was shown that at high zirconocene concentrations, the decay rate of complexes I and 2 in the oil constituent of the reaction mixture is at least a factor ten lower than that in the solvent. Complexes 1-3 are close in energy to each other and can be readily converted to one another by changing the ratio between Cp2ZrMe2, [CPh3][B(C6F5)(4)] and AlMe3, Complex 1 reacts with excess [CPh3][B(C6F5)(4)] to yield 2 with first order rate constant of 4 x 10(-4) s(-1) at 20 degreesC. Complex 3 reacts with excess [CPh3][B(C6F5)(4)] to yield 2 with a half-life of 1 h at 20 degreesC. Addition of 1-hexene to samples containing various relative amounts of complexes 1-3, and further H-1-NMR spectroscopic monitoring of the polymer/monomer ratio, showed that 1 - 3 have comparable polymerization activities. (C) 2003 Elsevier Science B.V. All rights reserved. [References: 11]