Synthesis and Characterization of Extremely Bulky Aminopyridinate Ligands and a Series of Their Groups 1 and 2 Metal Complexes

High-yielding synthetic routes to five new extremely bulky aminopyridine pro-ligands were developed, viz. (C₅H₃N-6-Ar¹)N(H)Ar²-2; Ar¹ = Trip, Ar² = TCHP (HAmPy¹), Ar* (HAmPy²) or Ar^† (HAmPy³); Ar¹ = TCHP, Ar² = Ar* (HAmPy⁴) or Ar^† (HAmPy⁵) (Trip = 2,4,6-triisopropylphenyl, TCHP = 2,4,6-tricyclohexylphenyl, Ar* = C₆H₂(CHPh₂)₂Me-2,6,4, Ar^† = C₆H₂(CHPh₂)₂Prⁱ-2,6,4. Four of these were deprotonated with LiBuⁿ in diethyl ether to give lithium aminopyridinate complexes which were dimeric for the least bulky ligand, [{Li(AmPy¹)}₂] or monomeric for the bulkier aminopyridinates, i.e., in [Li(AmPy²⁻⁴)(OEt₂)]. One aminopyridine was deprotonated with MeMgI to give monomeric [Mg(AmPy³)I(OEt₂)₂]. When treated with sodium or potassium mirrors or 5% w/w Na/NaCl, over-reduction occurred, leading to the alkali metal aminopyridinates, [M(AmPy³)(η⁶-toluene)] (M = Na or K) or [{Na(AmPy³)}_∞]. An attempted reduction of [Mg(AmPy³)I(OEt₂)₂] with a dimagnesium(I) compound led only to partial loss of diethyl ether and the formation of [(AmPy³)Mg(μ-I)₂Mg(AmPy³)(OEt₂)]. All prepared complexes have potential as ligand transfer reagents in salt metathesis reactions with metal halide complexes.