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Mild, rapid and selective alcoholysis of terpyridine-appended amide substrates by Cu2+-catalysis: protonation state and reactivity of the complex
- Source :
-
Inorganica Chimica Acta . Mar2005, Vol. 358 Issue 4, p947-956. 10p. - Publication Year :
- 2005
-
Abstract
- 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 Cu2+ not only in methanol but also in aqueous methanol at 30 °C. The reaction proceeds via formation of an N3O (three terpyridine nitrogens and one carbonyl oxygen) type 1:1 metal complex 2a-Cu2+. From spectral titration, the structure of the 2a-Cu2+ 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. [Copyright &y& Elsevier]
- Subjects :
- *PHOTOSYNTHETIC oxygen evolution
*METHANOL
*NONMETALS
*ORGANIC compounds
Subjects
Details
- Language :
- English
- ISSN :
- 00201693
- Volume :
- 358
- Issue :
- 4
- Database :
- Academic Search Index
- Journal :
- Inorganica Chimica Acta
- Publication Type :
- Academic Journal
- Accession number :
- 19180799
- Full Text :
- https://doi.org/10.1016/j.ica.2004.10.008