## 3 Results and Discussion  
The Oxidation State of Titanium in the Active Component of Ti-Mg Catalysts of Different Composition According to ESR Data  
The same MgCl\({}_{2}\) support was prepared according to ref. [24] (the mean particle size of 6-7 \(\upmu\)m, S\({}_{\rm sp}\) = 176 m\({}^{2}\)/g) was used to synthesize a series of highly active supported TMCs of different compositions. The TMC-1 catalyst was prepared by depositing on MgCl\({}_{2}\) a compound with the composition [n\({}^{6}\)-BenzeneTiAl\({}_{2}\)Cl\({}_{8}\)]. This catalyst contains only monomeric Ti(II) ions bound with two aluminum chloride molecules [18]. The TMC-1-2 catalyst was obtained by treating the TMC-1 catalyst with chloropentafluorobenzene; its active component is represented by monomeric compounds of Ti(III) ([\(\eta^{6}\)-BenzeneTiAl\({}_{2}\)Cl\({}_{8}\)]/ MgCl\({}_{2}\)/C\({}_{6}\)F\({}_{5}\)Cl). TMC containing mostly the associated Ti(III) compounds (60-90%) after the interaction with AlR\({}_{3}\) (TMC-2 and TMC-3 catalysts) were prepared as the reference catalysts. TMC-2 catalyst was prepared by depositing the TiCl\({}_{3}\)-nDBE soluble complex on the MgCl\({}_{2}\) support, and the TMC-3 catalyst was prepared by depositing the TiCl\({}_{4}\) on the MgCl\({}_{2}\) support. Our earlier data [18] on the content of titanium in different valent states and in different coordination environments in the catalysts synthesized using different titanium compounds, which were employed in this study, are listed in Table 1.  
One can see in Table 1 that the TMC-1 catalyst (exp. 1), which was synthesized using a complex with the composition [\(\eta^{6}\)-BenzeneTiCl\({}_{2}\)-2 AlCl\({}_{3}\)], contains only the isolated Ti(II) ions. These data were obtained after the treatment of TMC-1 with water or chloropentafluorobenzene, leading to the oxidation of Ti(II) ions in the catalyst to Ti(III) ions, which were identified by ESR [18]. It should be noted that additional evidence indicating the presence of divalent titanium in TMC-1 is the result of ethylene polymerization in the absence of an organoaluminium co-catalyst on this catalyst (the activity of 146 kg PE/(gTi \(\times\) h) at 80 \({}^{\circ}\)C and 4 bar C\({}_{2}\)H\({}_{4}\)). The literature data [27; 28] allow the conclusion that, among Ti-containing catalytic systems, only the catalysts based on divalent titanium can perform ethylene polymerization without an organoaluminium co-catalyst. The TMC-1-2 catalyst obtained by the interaction of TMC-1 with chloropentafluorobenzene contains only the mononuclear compounds of trivalent titanium (isolated Ti(III) ions) (Table 1, exp. 2). The interaction of this catalyst with aluminum trialkyl (TIBA/Ti = 15 mol/mol) does not change the valent state of titanium (Table 1, exp. 2-1). The isolated state of titanium ions in these two catalysts may be caused by the composition of the initial titanium complex [\(\eta^{6}\)-Benzene TiCl\({}_{2}\)-2 AlCl\({}_{3}\)], namely, by the presence of two AlCl\({}_{3}\) groups, which hinder the mutual interaction of titanium ions on the magnesium chloride surface. According to ESR data, the TMC-2 catalyst with the composition TiCl\({}_{3}\)/MgCl\({}_{2}\), which was prepared by depositing the TiCl\({}_{3}\)-nDBE complex on MgCl\({}_{2}\), contains 35% of isolated Ti(III) ions and 65% of Ti(III) as associates of Ti(III) titanium ions, which are observed in the ESR spectrum after treating the catalyst with pyridine [18]. After the interaction of this catalyst with TIBA at 298 K (Al/Ti = 15 mol/mol), a small part of the associated titanium ions (\(\sim\)5-10%) is reduced to the divalent state (Table 1, exp. 3-1). The TMC-3 catalyst with the composition TiCl\({}_{4}\)/MgCl\({}_{2}\) after the interaction with TIBA (Al/Ti = 15 mol/mol, 298 K) contains a wide set of titanium compounds with different oxidation states of titanium ions and coordination states of Ti(III) ions (Table 1, exp. 4-1). Therewith, the major part of trivalent titanium (ca.