Iron Phosphinimide and Phosphinimine Complexes:  Catalyst Precursors for Ethylene Polymerization

Reaction of Li[NP t -Bu 3 ] with FeCl 2 affords [Cl 3 Fe 2 (μ-NP t -Bu 3 ) 2 ] 1 in 71% yield. This mixed valent Fe(III)−Fe(II) undergoes reversibly one-electron oxidation to generate [Cl 3 Fe 2 (μ-NP t -Bu 3 ) 2 ] + . Chemical oxidation with [Cp 2 Fe]PF 6 yields [Cl 2 Fe(μ-NP t -Bu 3 )] 2 2 . The reaction of Li[NP t -Bu 3 ] with FeBr 3 affords [Br 4 Fe 2 (μ-NP t -Bu 3 ) 2 ] 3, while the reaction of FeCl 3 with Me 3 SiNPCy 3 gives [Cl 2 Fe(μ-NPCy 3 )] 2 4 . Hydrolysis of 3 yields the species [( t- Bu 3 PNH)Br 2 Fe] 2 (μ-O) 5 . These species have also been evaluated as catalysts for the polymerization of ethylene and copolymerization of ethylene/octene. These species were found to be single-site catalysts even under rather demanding conditions (50−160 °C, 100−300 psig ethylene), although the activities are generally low. Compound 5 affords polymer similar to that produced by 3, suggesting that MAO dehydrates 5 generating a catalyst similar to that derived from 3 . Compounds 1, 2, 4, and 5 have been crystallographically characterized.