Synthesis of Bis(amino)pyridines by the Stepwise Alkylation of Bis(imino)pyridines: An Unexpected and Selective Alkylation of the Aminoiminopyridine by AlMe 3

Bis(imino)pyridines 2-[2,6-(R-1)(2)C6H3N=C(CH3)]-6-[2,6-(R-2)(2)C6H3N=C(CH3)](C5H3N) (1a, R-1 = R-2 = i-Pr; 1b, R-1 = i-Pr, R-2 = CH3; 1c, R-1 = R-2 = CH3) were first alkylated by AlMe3 and then hydrolyzed to aminoiminopyridines 2-[2,6-(R-1)(2)C6H3N=C(CH3)]-6-[2,6-(R-2)(2)C6H3NHC(CH3)(2)](C5H3N) (3a, R-1 = R-2 = i-Pr; 3b, R-1 = i-Pr, R-2 = CH3; 3c, R-1 = R-2 = 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-(R-1)(2)C6H3NC(CH3)(2)]-6-[2,6-(R-2)(2)C6H3NHC(CH3)(2)](C5H3N)}AlMe2 (4a, R-1 = R-2 = i-Pr; 4b, R-1 = i-Pr, R-2 = CH3; 4c, R-1 = R-2 = CH3), which were further hydrolyzed to the bis(amino)pyridines 2-[2,6-(R-1)(2)C6H3NHC(CH3)(2)]-6-[2,6-(R-2)(2)C6H3NHC(CH3)(2)](C5H3N) (5a, R-1 = R-2 = i-Pr; 5b, R-1 = i-Pr, R-2 = CH3; 5c, R-1 = R-2 = 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)(2)C6H3NC(CH3)(2)](2)(C5H3N)}Mg(THF) (6), {2,6-[2,6-(i-Pr)(2)C6H3NC(CH3)(2)](2)(C5H3N)}Y(CH2SiMe3)(THF) (7), and {2,6-[2,6-(i-Pr)(2)C6H3NC(CH3)(2)](2)(C5H3N)}Zr(CH2SiMe3)(2) (8)) were formed via the alkane elimination method.