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

The reaction of (PPh3)2NiCl2 with Li[Ind∧CHCH2] gave the neutral complexes
(η:η0-Ind∧CHCH2)Ni(PPh3)Cl (Ind = indenyl; ∧ = (CH2)2, 1a; Si(Me)2CH2, 1b), which were
subjected to Cl- abstraction to give the corresponding cationic complexes [(η:η2-Ind∧CHCH2)Ni(PPh3)]+ (∧ = (CH2)2, 2a; Si(Me)2CH2, 2b). The bis(phosphine) derivatives [(η:η0-Ind-CH2CH2CHCH2)Ni(PPh3)2]+ (3a) and [(η3-allyl)Ni(PPh3)2]+ (4) formed gradually from room-temperature solutions of 2a and 2b, respectively, even in the absence of added PPh3. On
the other hand, [(η:η0-Ind-SiMe2CH2CHCH2)Ni(PPh3)2]+ (3b) was detected only when PPh3
was added to a CD2Cl2 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
PhRSiH2 (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.