Theoretical studies of the energetics of the imidazole molecule have established that it is 29 kcal mol-1 lower in energy than its NHC tautomer, which suggests that tautomoerization to NHC is thermodynamically unfavoured.1 Following this, a theoretical investigation carried out by Crabtree et al. on the thermodynamic preference for N- vs. C- coordination in imidazoles went on to show that the opposite of this is observed when each is bound to a soft, late transition metal complex. It was therefore concluded through this study that while first row elements prefer binding via N, second and third row elements prefer binding via C.2 A few imidazole to NHC tautomerizations by transition metal complexes have been reported in the literature;1,3 and a simple, clean, base promoted transformation of imidazoles to NHCs was of interest to our group due to the ease with which such conditions could be attained in the biological system.This study posits that DNIC-bound imidazoles will be effective to establish controlling factors for metal-assisted, base-mediated conversion to NHCs, which also provides an additional route to the synthesis of asymmetric/bioconjugated carbenes and open a new field of bioorganometallic chemistry based on NHC-DNIC compounds and their NO-releasing capabilities.4-51. Ruiz, J.; Perandones, B. F.; Van der Maelen, J. F.; Garcia-Granda, S. Organometallics 2010  , 29, 4639-4642.2. Sini, G.; Eisenstein, O.; Crabtree, R. H. Inorg. Chem. 2002  , 41, 602� 604.3. Ruiz, J.; Perandones, B. F. J. Am. Chem. Soc. 2007  , 129, 9298-92994. Hsieh, C.-H.; Darensbourg, M. Y. J. Am. Chem. Soc., 2010  , 132, 14118-14125.5 Hess, J. L.; Hsieh, C.-H.; Reibenspies, J. H.; Darensbourg, M. Y. Inorg. Chem. 2011  , 50, 8541�8552.

Base-promoted tautomerization of imidazoles to N-heterocyclic carbenes (NHCs): Via a dinitrosyl iron scaffold

244th National Meeting (2012)

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