Synthesis of Bis(amino)pyridines by the Stepwise Alkylation of Bis(imino)pyridines: An Unexpected and Selective Alkylation of the Aminoiminopyridine by AlMe₃

Bis­(imino)­pyridines 2-[2,6-(R¹)₂C₆H₃NC­(CH₃)]-6-[2,6-(R²)₂C₆H₃NC­(CH₃)]­(C₅H₃N) (<b>1a</b>, R¹ = R² = <i>i</i>-Pr; <b>1b</b>, R¹ = <i>i</i>-Pr, R² = CH₃; <b>1c</b>, R¹ = R² = CH₃) were first alkylated by AlMe₃ and then hydrolyzed to aminoiminopyridines 2-[2,6-(R¹)₂C₆H₃NC­(CH₃)]-6-[2,6-(R²)₂C₆H₃NHC­(CH₃)₂]­(C₅H₃N) (<b>3a</b>, R¹ = R² = <i>i</i>-Pr; <b>3b</b>, R¹ = <i>i</i>-Pr, R² = CH₃; <b>3c</b>, R¹ = R² = CH₃). When the aminoiminopyridines were treated with AlMe₃, the expected methane elimination was not found; alkylation at the imine functional group led to the aluminum complexes {2-[2,6-(R¹)₂C₆H₃NC­(CH₃)₂]-6-[2,6-(R²)₂C₆H₃NHC­(CH₃)₂]­(C₅H₃N)}­AlMe₂ (<b>4a</b>, R¹ = R² = <i>i</i>-Pr; <b>4b</b>, R¹ = <i>i</i>-Pr, R² = CH₃; <b>4c</b>, R¹ = R² = CH₃), which were further hydrolyzed to the bis­(amino)­pyridines 2-[2,6-(R¹)₂C₆H₃NHC­(CH₃)₂]-6-[2,6-(R²)₂C₆H₃NHC­(CH₃)₂]­(C₅H₃N) (<b>5a</b>, R¹ = R² = <i>i</i>-Pr; <b>5b</b>, R¹ = <i>i</i>-Pr, R² = CH₃; <b>5c</b>, R¹ = R² = CH₃). The selective alkylation over elimination may come from the noninnocent property of the conjugated iminopyridine group. New magnesium, yttrium, and zirconium complexes supported by <b>5a</b> ({2,6-[2,6-(<i>i</i>-Pr)₂C₆H₃NC­(CH₃)₂]₂(C₅H₃N)}­Mg­(THF) (<b>6</b>), {2,6-[2,6-(<i>i</i>-Pr)₂C₆H₃NC­(CH₃)₂]₂(C₅H₃N)}­Y­(CH₂SiMe₃)­(THF) (<b>7</b>), and {2,6-[2,6-(<i>i</i>-Pr)₂C₆H₃NC­(CH₃)₂]₂(C₅H₃N)}­Zr­(CH₂SiMe₃)₂ (<b>8</b>)) were formed via the alkane elimination method