Reduction of(eta5-cyclonentadienyl)zirconium dichloride in the presence of methylalumoxane

The reaction occurring between bis(eta5-C5H5)ZrCl2 (C5H5 = cyclopentadienyl) and methylalumoxane (MAO) has been studied by means of electron paramagnetic resonance (EPR) spectroscopy at different zirconium concentrations and Al/Zr mole ratios. The toluene solution of bis(eta5-C5H5)ZrCl2/methylalumoxane, in the absence of ethylene, was verified to be more stable than the catalytic system based on bis(eta5-C5H5)TiCl2/AlR3 (R = alkyl). Zr(IV) was reduced to Zr(III) in small amounts with a Lande factor g = 1,998 and a hyperfine interaction splitting constant alpha (Zr-91) = 7 G. The presence of ethylene strongly increased the efficiency of the Zr(IV) to Zr(III) reduction. Simultaneously it modified the chemical electronic surrounding of the Zr nucleus as revealed by the sharp increase of a (Zr-91) = 12 G