Two new precatalysts for ethylene and a-olefin trimerization, (FI)Ti(CH2SiMe3)(2)Me and (FI)Ti(CH2CMe3)(2)Me (FI = phenoxy-imine), have been synthesized and structurally characterized by X-ray diffraction. (FI)Ti(CH2SiMe3)(2)Me can be activated with 1 equiv of B(C6F5)(3) at room temperature to give the solvent-separated ion pair [(FI)Ti(CH2SiMe3)(2)][MeB(C6F5)(3)], which catalytically trimerizes ethylene or 1-pentene to produce 1-hexene or C-15 olefins, respectively. The neopentyl analogue (FI)Ti(CH2CMe3)(2)Me is unstable toward activation with B(C6F5)(3) at room temperature, giving no discernible diamagnetic titanium complexes, but at -30 degrees C the following can be observed by NMR spectroscopy: (i) formation of the bis-neopentyl cation [(FI)Ti(CH2CMe3)(+), (ii) alpha-elimination of neopentane to give the neopentylidene complex [(FI)Ti(=CHCMe3)](+), and (iii) subsequent conversion to the imido-olefin complex [(MeOAr2N=)-Ti(OArHC=CHCMe3)](+) via an intramolecular metathesis reaction with the imine fragment of the (FI) ligand. If the reaction is carried out at low temperature in the presence of ethylene, catalytic production of 1-hexene is observed, in addition to the titanacyclobutane complex [(FI)Ti(CH(CMe3)CH2CH2)](+), resulting from addition of ethylene to the neopentylidene [(FI)Ti(=CHCMe3)](+). None of the complexes observed spectroscopically subsequent to [(FI)Ti(CH2CMe3)(2)](+) is an intermediate or precursor for ethylene trimerization, but notwithstanding these off-cycle pathways, [(FI)Ti(CH2CMe3)(+) is a precatalyst that undergoes rapid initiation to generate a catalyst for trimerizing ethylene or 1-pentene.