The syntheses of ketimide titanium complexes of the type Ti(NC t Bu 2 ) 3 X (X=Cl, Cp, Ind), Ti(NC t Bu 2 ) 4 and the zirconium complex CpZr(NC t Bu 2 ) 2 Cl are described. When activated by MAO, all compounds are ethylene polymerisation catalysts. In the conditions studied, the most active catalyst is CpZr(NC t Bu 2 ) 2 Cl, with an activity of 2.7×10 5 kg/(molZr [E] h). Titanium complexes are less active by about two orders of magnitude. The polyethylene produced is linear, as determined by NMR spectroscopy. Molecular structures of Ti(NC t Bu 2 ) 3 X (X=Cl, Cp, Ind) and Ti(NC t Bu 2 ) 4 were determined by X-ray single crystal diffraction.