Isolated Ti(III) Species on the Surface of a Pre-active Ziegler Natta Catalyst

The nature of Ti(III) species, introduced in working models of industrial Ziegler Natta catalyst precursors, consisting of MgCl2/TiCl4 binary systems, eventually containing different Lewis basis, are studied by a combination of X- and Q-band CW and pulse EPR spectroscopy. In Ziegler Natta catalysts, Ti(III) play the double role of active catalytic species and unconventional spin probes. On the binary system, two dominant Ti(III) species, characterized by distinctively different EPR spectra, are observed. 35,37Cl Q-Band HYSCORE spectra allow estimating the hyperfine and nuclear quadrupole interactions of directly coordinated Cl, characterized by a hyperfine dipolar contribution of the order of 5 MHz and nuclear quadrupole interactions of the order of e2qQ/h = 9 MHz. Interestingly, the two dominant EPR active species are selectively suppressed by the presence of different Lewis bases, indicating the possibility to address the long standing issue of the influence of Lewis bases in driving specific morphological configurations and influencing the catalytic properties of Ti(III) active sites.