Indenyl nickel complexes: synthesis, characterization and styrene polymerization catalysis

Neutral indenyl nickel complexes with the general formula (η-1-R–Ind)Ni(PPh3)Cl (R=cyclopentyl (1), benzyl (2)) have been prepared and characterized by 1H-NMR spectroscopy and single-crystal X-ray analysis. The results of X-ray crystal structural determination reveal that the hapticity of indenyl ligand in complex 1 or 2 is significantly distorted away from an idealized η5 mode to an unsymmetrical η3 mode. Furthermore, the structures of (R–Ind)Ni(PPh3)Cl exhibit a progressively more distorted coordination of the indenyl ring from cyclopentyl to benzyl. Both of them are inert toward the insertion of styrene, however, they are able to catalyze the polymerization of styrene effectively in the presence of NaBPh4 and PPh3 to give syndio-rich atactic poly(styrene) with Mw values in the range of 104. The NaBPh4·1·PPh3 system shows the higher catalytic activity than the NaBPh4·2·PPh3 system.