Indenyl-Nickel Complexes Bearing a Pendant, Hemilabile Olefin Ligand: Preparation, Characterization, and Catalytic Activities

The reaction of (PPh 3 ) 2 NiCl 2 with Li[Ind∧CH CH 2 ] gave the neutral complexes (η:η 0 -Ind∧CH CH 2 )Ni(PPh 3 )Cl (Ind = indenyl; ∧ = (CH 2 ) 2, 1a; Si(Me) 2 CH 2, 1b ), which were subjected to Cl - abstraction to give the corresponding cationic complexes [(η:η 2 -Ind∧CH CH 2 )Ni(PPh 3 )] + (∧ = (CH 2 ) 2, 2a; Si(Me) 2 CH 2, 2b ). The bis(phosphine) derivatives [(η:η 0 -Ind-CH 2 CH 2 CH CH 2 )Ni(PPh 3 ) 2 ] + ( 3a ) and [(η 3 -allyl)Ni(PPh 3 ) 2 ] + ( 4 ) formed gradually from room-temperature solutions of 2a and 2b, respectively, even in the absence of added PPh 3 . On the other hand, [(η:η 0 -Ind-SiMe 2 CH 2 CH CH 2 )Ni(PPh 3 ) 2 ] + ( 3b ) was detected only when PPh 3 was added to a CD 2 Cl 2 solution of 2b . The lability of the vinyl moiety in 2 allows these complexes to act as single-component precatalysts for the polymerization and hydrosilylation of styrene; the latter reaction requires little or no induction period with the hydrosilanes PhRSiH 2 (R= Ph, Me, H) and proceeds with up to 1000 catalytic turnovers. Compounds 1a, 1b, 2a, 3a, and 4 have been characterized by NMR and single-crystal X-ray diffraction studies, whereas 2b and 3b were identified by NMR spectroscopy. Structural information gleaned from both solid-state and solution data provide important information on the Ni−olefin bonding in 2a and 2b and indicate that the Ni−Ind interactions in these complexes are affected by the significant trans influence of the chelating olefin moiety.