Abstract
An amide bond of a terpyridine-appended substrate, 6-(L-phenylalanylamino)-2,2′:6′,2″-terpyridine ( 2a), was cleaved to yield phenylalanine methyl ester quantitatively in the presence of catalytic amounts of Cu 2+ not only in methanol but also in aqueous methanol at 30 °C. The reaction proceeds via formation of an N 3O (three terpyridine nitrogens and one carbonyl oxygen) type 1:1 metal complex 2a-Cu 2+. From spectral titration, the structure of the 2a-Cu 2+ complex was confirmed to have three different protonation states, i.e., A (non-deprotonated amide with α-ammonium), D1 (deprotonated-amide with α-ammonium) and D2 (deprotonated-amide with α-amino) states. Among them, the complex in the D2 state was exclusively responsible for the observed mild, rapid and selective alcoholysis, showing the first-order rate constant of 6 × 10 −3 s −1 or half-decay time of 2 min in methanol at 30 °C. Acidity of the amide proton was found to be higher than that of the ammonium proton in the complex, allowing formation of the highly reactive amide-deprotonated D2 state in methanol even without addition of external bases. Factors contributing to the high reactivity of the complex were discussed.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.