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) (1a, R1 = R2 = i-Pr; 1b, R1 = i-Pr, R2 = CH3; 1c, 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) (3a, R1 = R2 = i-Pr; 3b, R1 = i-Pr, R2 = CH3; 3c, 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 (4a, R1 = R2 = i-Pr; 4b, R1 = i-Pr, R2 = CH3; 4c, 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) (5a, R1 = R2 = i-Pr; 5b, R1 = i-Pr, R2 = CH3; 5c, 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 5a ({2,6-[2,6-(i-Pr)2C6H3NC­(CH3)2]2(C5H3N)}­Mg­(THF) (6), {2,6-[2,6-(i-Pr)2C6H3NC­(CH3)2]2(C5H3N)}­Y­(CH2SiMe3)­(THF) (7), and {2,6-[2,6-(i-Pr)2C6H3NC­(CH3)2]2(C5H3N)}­Zr­(CH2SiMe3)2 (8)) were formed via the alkane elimination method.