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

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 [Li-8(C5H3NMeNH)(6)(O)(OEt2)(2)] 3 and [Li-8(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 [Li-4(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.