Synthesis and Oxidative Reactivity of 2,2′-Pyridylpyrrolide Complexes of Ni(II)

Synthesis and characterization of divalent nickel complexed by 2-pyridylpyrrolide bidentate ligands are reported, as possible precursors to complexes with redox active ligands. Varied substituents on the pyrrolide, two CF₃ (L²), two ^tBu (L⁰), and one of each type (L¹) are employed and the resulting Ni­(L^<i>n</i>)₂ complexes show different Lewis acidity toward CO, H₂O, tetrahydrofuran (THF), or MeCN, the L² case being the most acidic. Density functional theory calculations show that the frontier orbitals of all three Ni­(L^<i>n</i>)₂ species are localized at the pyrrolide groups of both ligands and Ni­(L^<i>n</i>)₂⁺ can be detected by mass spectrometry and in cyclic voltammograms (CVs). Following cyclic voltammetry studies, which show electroactivity primarily in the oxidative direction, reactions with pyridine N-oxide or Br₂ are reported. The former yield simple <i>bis</i> adducts, Ni­(L²)₂(pyNO)₂ and the latter effects electrophilic aromatic substitution of the one pyrrolide ring hydrogen for both chelates, leaving it brominated