Premium
4′‐Hydrazone Derivatives of 2,2′:6′,2"‐Terpyridine: Protonation and Substituent Effects
Author(s) -
Beves Jonathon E.,
Constable Edwin C.,
Housecroft Catherine E.,
Neuburger Markus,
Schaffner Silvia,
Zampese Jennifer A.
Publication year - 2008
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200800301
Subject(s) - chemistry , imine , substituent , protonation , hydrogen bond , steric effects , intramolecular force , terpyridine , stereochemistry , crystal structure , crystallography , medicinal chemistry , molecule , organic chemistry , ion , metal , catalysis
Abstract Four 4′‐hydrazone derivatives of 2,2′:6′,2"‐terpyridine which vary in their N ‐ and C ‐substitution in the R′NN=CRPh unit have been prepared and structurally characterized. Protonation studies and solution behaviour of these compounds are described, as well as representative crystal structures of mono‐ and diprotonated derivatives. In the solid‐state structures of each neutral compound, the tpy domain adopts the anticipated trans , trans ‐conformation, and intramolecular steric factors compete with π‐stacking effects to control the amount to which the C ‐phenyl substituent twists out of the plane of the tpy unit. When R′ = H, the imine NH group engages in hydrogen bonding interactions in the solid state, except where R = Ph. In solution, variable temperature 1 H NMR spectroscopy shows that on going from R = Me to Ph (with R′ = H), the barrier to rotation about the C py –N imine bond increases; with R = R′ = H, the hydrogen bonding capabilities of the solvent to the imine NH influence this dynamic process. In the N ‐methyl derivative (R = H and R′ = Me), rotation about the C py –N imine bond is facile at room temperature. Protonation of the derivative with R = R′ = H results in an increase in the activation barrier to rotation, consistent with a greater π‐contribution to the C py –N imine bond. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)