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Proton and metal‐ion activation of C–H exchange in five‐membered azoles by Erwin Buncel; Ikenna Onyido is a Medicine article available to read on EtoBox.

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## Abstract Factors influencing C–H isotopic exchange rates in five‐membered azoles, that is imidazoles and thiazoles, under catalysis by H^+^ and M^__n__+^, especially transition metals, Pt(II) and Co(III) are discussed. Hydrogen ion catalysis through N(3) protonation of azoles **1–3** is generally the most efficient, with rate enhancements in the range 10^2^–10^9^ over the neutral process being attained. Metal‐ion coordination also results in effective catalysis, though less so than catalysis by protons. Catalysis of C–H exchange by M^__n__+^ can be studied through addition of the metal salts to a buffered solution of the heterocycle in which labile complexes exist, or on synthesized complexes such as **4–13** which are substitution‐inert thus precluding complications from unknown dissociation equilibria. A delicate balance of factors influence the ease of C–H exchange, including: (1) the magnitude of the fractional charge located at N(3) of the heterocycle through M^__n__+^–N(3) __σ__ bond polarization; (2) metal‐to‐ligand __π__ back‐bonding; (3) the electronic structure of the metal ions. These considerations have obvious consequences for deuterium‐ and tritium‐labelling of a n

Who reads Proton and metal‐ion activation of C–H exchange in five‐membered azoles?

Author

Erwin Buncel; Ikenna Onyido

Publisher

John Wiley and Sons; Wiley (John Wiley & Sons); John Wiley & Sons Inc.; Wiley (ISSN 0022-2135)

Published

2002

Language

EN

Field

Medicine (Life Sciences)