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Structure and Reactivity of the Cationic Nickel Compound [(η31-Ind(CH2)2NMe2)Ni(PPh3)][BPh4]

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journal contribution
posted on 26.07.2001, 00:00 by Laurent F. Groux, Davit Zargarian
The solid-state structure of the first nickel compound containing a chelating amino−indenyl ligand, [(η31-Ind(CH2)2NMe2)Ni(PPh3)][BPh4] (2), has been resolved and confirms the chelation of the amine tether to the nickel center. Complex 2 acts as a precatalyst for the oligomerization of norbornene, the dimerization of phenylsilane, and the polymerization of styrene. The results of these catalytic reactions are qualitatively different from those catalyzed by the cationic species generated in situ from the precursor complex (η30-Ind(CH2)2NMe2)Ni(PPh3)Cl (1). Phosphines displace the amine tether in 2 to give the bis(phosphine) cations [(η30-Ind(CH2)2NMe2)Ni(Ph2PCH2CH2PPh2)]+ (3) and [(η30-Ind(CH2)2NMe2)Ni(PPh3)(PR3)]+ (4, R = Ph; 5, R = Me), whereas LiI reacts to form the neutral compound [(η30-Ind(CH2)2NMe2)Ni(PPh3)I]·LiBPh4 (7). The displacement of the amine tether by pyridine and its methyl-substituted derivatives leads to an equilibrium between 2 and [(η30-Ind(CH2)2NMe2)Ni(PPh3)L]+ (6) with Keq values of 9 (6a, L = pyridine), 2.0 (6b, L = 2-picoline), 23 (6c, L= 3-picoline), 33 (6d, L = 4-picoline), and 16 (6e, L = 3,5-lutidine).

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