Aminoalkyl-substituted indenyl-nickel compounds: Tuning reactivities as a function of the pendant, hemilabile moiety

Article abstract of DOI:10.1021/om030241q

Indenyl ligands bearing three different aminoalkyl substituents have been used to prepare the complexes (IndNR₂)Ni(PPh₃)Cl (IndNR₂ = 2-(1-indenylmethyl)pyridine (1), N-(1-indenylethyl)pyrrolidine (2), and N-(1-indenylethyl)diisopropylamine (3)). The solution NMR spectra of complexes 1 and 2 point to the existence of a dynamic process involving the reversible coordination of the pendant amine moieties to the Ni center, but no N-Ni interaction is evident in complex 3. Abstraction of Cl^- from the neutral precursors 1-3 yields the corresponding cationic derivatives [(η³:η¹-IndNR₂)Ni(PPh₃)] ⁺ (4-6) wherein the amino tether is chelated to the nickel center. Complexes 1-5 have been isolated and fully characterized by multinuclear NMR spectroscopy and, in the case of 1 and 4, by single-crystal X-ray diffraction studies. The isolation of complex 6 is complicated by its partial conversion to the bis(phosphine) derivative [{η³:η⁰-IndCH₂CH₂N(i-Pr) ₂}Ni(PPh₃)₂]⁺ (7). Studies on the displacement of the chelating amine moiety in 4 and 5 by dppe, PPh₃, and pyridine showed the pyridine moiety to be the least labile. Cyclic voltammetry studies have shown that the reduction potentials of the complexes vary as a function of the Ni-N interaction, the complexes bearing the NMe₂ moieties showing the strongest resistance to reduction. Olefin polymerization reactions also showed that the nature of the N-moiety has a considerable influence on the catalytic reactivity of the cationic complexes.