Syntheses and structural studies of lithium complexes of 2-amino-6-methylpyridine

Abstract

Lithiation of 2-amino-6-methylpyridine (C₅H₃NMeNH₂) occurred smoothly in diethyl ether (OEt₂) or hexane–N,N,N′,N′-tetramethylethylenediamine (tmeda) affording [Li(C₅H₃NMeNH)(OEt₂)_0.5] 1 or [Li(C₅H₃NMeNH)(tmeda)] 2. These complexes are extremely moisture sensitive and rapidly yield [Li₈(C₅H₃NMeNH)₆(O)(OEt₂)₂] 3 and [Li₈(C₅H₃NMeNH)₆(O)(tmeda)₂] 4 respectively, upon exposure to limited amounts of water. On treatment of 1 with dimethylsilicone, insertion of dimethylsilicone into the Li–N bond occurs affording [Li₄(C₅H₃NMeNHSiMe₂O)₄] 5. All complexes were characterised by spectroscopic and X-ray crystallographic methods. Complexes 3 and 4 reveal octanuclear centrosymmetric structures with an octahedral oxygen centre bound by six lithium atoms, and in 4 a monodentate tmeda ligand is identified. Compound 5 is tetranuclear with an Li₄O₄ pseudo-cubane core with each of these lithium atoms involved in six-membered chelate rings comprised of N–C–N–Si–O atoms with the lithium bound to the terminal N and O heteroatoms.