Cationic Nickel Complexes Containing Bulky Phosphine Ligands: Catalyst Precursors for Styrene Polymerization

The cationic complexes [Ni(η3-CH2C(R)CH2)(P)2][BPh4] (R = Me, H; (P)2 = (PMeiPr2)2, (PPhiPr2)2, 1,2-bis(diisopropylphosphino)ethane (dippe)) and [Ni(η-2-MeInd)(P)2][BPh4] (2-MeInd = 2-methylindenyl; (P)2 = (PMeiPr2)2, (PPhiPr2)2, dippe) have been prepared and characterized. These materials are catalyst precursors for the nonliving polymerization of styrene to polystyrene without the need of a cocatalyst such as methylaluminoxane. The polymerization reactions are carried out in refluxing 1,2-dichloroethane, using a 1:1000 catalyst to styrene ratio, yielding essentially atactic polystyrenes with Mn in the range 14 500−155 000 Da and polydispersities between 1.89 and 9.70. The mass properties of the polymers and the overall yield depend much on the nature of the catalyst precursor.