Synthesis and metal(II) ion complexation of pyridine-2,6-diamides incorporating amino alcohols

Reaction of 2,6-bis(methoxycarbonyl)pyridine with two equivalents of a β-amino alcohol yields pyridine-2,6-diamides C6H3N(CONH–CR1R2–CHR3–OH)2 [(1) R1 = R2 = R3 = H; (2) R1 = R2 = H, R3 = CH3; (3) R1 = CH3, R2 = R3 = H; (4) R1 = C2H5, R2 = R3 = H; (5) R1 = C6H5CH2, R2 = R3 = H; (6) R1 = O2NC6H4CH(OH), R2 = R3 = H; (7) R1 = R2 = CH3, R3=H] incorporating the amino alcohols, several of which are chiral, whereas the free diamide ligands show no capacity toward deprotonation up to pH > 12. In the presence of metal(II) ions they undergo concomitant deprotonation and complexation to form [M(L-2H)] compounds. Formation constants have been determined for Cu(II), Ni(II), and Zn(II) complexes of the suite of ligands. Determined values for the two observed steps of log β ML-2H and log β ML-3H (where additional alcohol or coordinated water deprotonation occurs) are approximately −10 and −20, respectively. As pK a values of the diamide cannot be determined independently, absolute log K ML-2H values for the di-deprotona...