Synthesis and characterization of nickel(II) complex containing 2-(t-butylaminomethyl)pyrrole

Two aminopyrroles, 2-(t-butylaminomethyl)pyrrole (HL1) and 2,5-di(t-butylaminomethyl)pyrrole (HL2), were synthesized and the hydrogen-bond interactions were observed in the single-crystal X-ray structures of HL1-HCl and HL2. Bis[2-(t-butylaminomethyl)pyrrole]nickel(II) [Ni(L1)₂] was prepared by treatment of the NiCl₂ with 2 equiv. of mono-deprotonated HL1 in THF solvent. The solid-state structure of Ni(L1)₂ shows the N₄-coordinated nickel atom, with a geometry corresponding to a square-planar structure, in which two intramolecular C-H⋯Ni interactions are present at the axial positions with contact distances of 2.77 Å. The complex displays an irreversible reduction response at -0.66 V (vs. Fc ⁺/Fc) in CH₃CN. Furthermore, ¹H, ¹³C-HSQC NMR experiments performed at room temperature revealed that the two methylene protons of the chelating L1^-1 are chemically nonequivalent and one of them is coupled to the amino proton. The coupling constants (J_HH') observed are close to the values predicted from the vicinal Karplus correlation diagram.