Spectroscopic and voltametric studies in titanium tris(pyrazolyl)borate catalysts

The ethylene polymerization using TpMs*TiCl3 (1) (TpMs* = HB(3-mesitylpyrazolyl)2(5-mesitylpyrazolyl)−) and TpMsTiCl3 (2) (TpMs = HB(3-mesityl-pyrazolyl)3−) was performed in toluene or hexane at 60 °C in the presence of MAO or TiBA/MAO (1:1) as cocatalysts. Higher activities were found for the polymerization reactions carried out in hexane, and using a combination of TiBA/MAO as cocatalysts. Absorciometric measurements in the UV-vis region and cyclic voltammetric have shown that such complexes when activated by MAO were not stable. Measurements carried out in the presence 1-hexene have demonstrated the necessity to add the cocatalyst in the presence of an olefin, i.e., ethylene or hexene-1 in order to stabilize the active species. Furthermore, these studies have revealed that after the activation process most of Ti remains as TiIV.