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From annelation to an elation: The surprising stability of pyridoannelated imidazol-2-ylidenes (see scheme) in comparison with the heavier Group 14 homologues suggests broad tuning potential and control of the reactivity by the lone pair of electrons at the carbon atom. The asymmetric distribution of π-electron density, which destabilizes the heavier homologues, does not markedly diminish the kinetic stability of the N-heterocyclic carbenes (NHCs).
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Ullah et al. (2007) studied this question.
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