Iron Phosphinimide and Phosphinimine Complexes: Catalyst Precursors for Ethylene Polymerization

Reaction of Li[NPt-Bu3] with FeCl2 affords [Cl3Fe2(μ-NPt-Bu3)2] 1 in 71% yield. This mixed
valent Fe(III)−Fe(II) undergoes reversibly one-electron oxidation to generate [Cl3Fe2(μ-NPt-Bu3)2]+. Chemical oxidation with [Cp2Fe]PF6 yields [Cl2Fe(μ-NPt-Bu3)]2 2. The reaction of
Li[NPt-Bu3] with FeBr3 affords [Br4Fe2(μ-NPt-Bu3)2] 3, while the reaction of FeCl3 with Me3SiNPCy3 gives [Cl2Fe(μ-NPCy3)]2 4. Hydrolysis of 3 yields the species [(t-Bu3PNH)Br2Fe]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.