Studies on the active species in olefin polymerisation generated from phenoxo-amido titanium “chiral-at-metal” compounds

Treatment of RHN-CH2-(3,5-tBu2C6H2-2-OH) (R = C6H51a, p-MeC6H41b, Cy 1c; Cy = cyclohexyl) with 1 equiv of TiCp∗Cl3 (Cp∗ = η5-C5Me5) in the presence of 2.5 equiv of NEt3 in pentane or hexane at room temperature gives the monocyclopentadienyl phenoxo-amido monochloro complexes [TiCp∗{RN-CH2-(3,5-tBu2C6H2-2-O)}Cl] (R = C6H52, p-MeC6H44, Cy 5). In a more polar solvent the phenoxo-amino complex [TiCp∗{(C6H5)(H)N–CH2-(3,5-tBu2C6H2-2-O)}Cl2] (3) is obtained from the reaction with 1a. The reaction of TiCp∗Cl3 with tBu(H)N–CH2-(3,5-tBu2C6H2-2-OH) (1d) affords the complex [TiCp∗{tBu(H)N–CH2-(3,5-tBu2C6H2-2-O)}Cl2] (6) in which no coordination of the amino group to the metal centre is observed as a consequence of the high steric requirements of the amino substituent in the phenol-amine. All the reported compounds were characterised by the usual analytical and spectroscopic methods and the molecular structures of 2 and 5 were determined by X-ray diffraction analysis from suitable single crystals.Studies of catalytic activity for ethylene or propylene polymerisation using boron or aluminium reagents as cocatalysts were performed under different conditions. In general the trends observed for the phenoxo-amido precatalysts with the aluminium reagent as cocatalyst in the α-olefin polymerisation reactions might suggest a catalyst decomposition process through ligand abstraction by sMAO. The activity found for ethylene or propylene polymerisation when B(C6F5)3 or [CPh3][B(C6F5)4] are used as cocatalysts is related to the strength of the cation-anion interactions.

Graphical abstractThe synthesis and characterisation of monocyclopentadienyl phenoxo-amido complexes [TiCp∗{RN–CH2-(3,5-tBu2C6H2-2-O)}Cl] and phenoxo-amino derivatives [TiCp∗{(C6H5)(H)N–CH2-(3,5-tBu2C6H2-2-O)}Cl2] and [TiCp∗{tBu(H)N–CH2-(3,5-tBu2C6H2-2-O)}Cl2] are described. These compounds contain a titanium asymmetric centre. Studies of catalytic activity for ethylene or propylene polymerisation are performed. Key Topic: Asymmetric titanium-centre derivatives; chelating alkoxo-amido.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Phenoxo-amido and phenoxo-amino titanium derivatives with asymmetric metal centres. ► Monocyclopentadienyl titanium derivatives as polymerisation catalysts. ► Studies on ethylene and propylene polymerisation. ► Boron and aluminium cocatalyst. ► Formation of the active species.