Imido titanium compounds bearing the 6-dimethylamino-1,4,6-trimethyl-1,4-diazacycloheptane ligand: synthesis, structures, solution dynamics and ethylenepolymerisation capability

Abstract

Reaction of Me₄DACH (6-dimethylamino-1,4,6-trimethyl-1,4-diazacycloheptane) with Ti(N^tBu)Cl₂(py)₃ or Ti(N^tBu)Cl₂(NHMe₂)₂ gave Ti(N^tBu)(Me₄DACH)Cl₂ (1) which in CD₂Cl₂ solution exists as a mixture of trans and cis isomers (defined with respect to the imido ligand and the exocyclic NMe₂ donor of Me₄DACH). Aryl imido analogues of 1 were prepared from Ti(NAr)Cl₂(NHMe₂)₂ and Me₄DACH forming Ti(NAr)(Me₄DACH)Cl₂ (Ar = 2,6-C₆H₃Me₂ (2), 2,6-C₆H₃ⁱPr₂ (3), 2-C₆H₄^tBu (4), 2-C₆H₄CF₃ (5)) which also exist as isomers in solution. The activation parameters for the interconversion of trans- and cis-3 were measured by VT NMR spectroscopy. The solid state structures of trans-1, 3 and 4 and cis-2 have been determined. In the presence of MAO or dried MAO the compounds 1–5 act as moderatley productive ethylene polymerisation catalysts, with a modest productivity gain found on moving from the 1/MAO to 1/dried MAO catalyst system.