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Updated: Aug 8, 2026

Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
Published on: November 29, 2018
Migratory insertion in N-heterocyclic carbene-containing Fe carbonyl complexes: an experimental and theoretical study
Simon A Llewellyn1, Malcolm L H Green, Jennifer C Green
1Inorganic Chemistry Laboratory, South Parks Road, Oxford, UKOX1 3QR.
Abstract:
The compound [Fe(eta-C5H5)(CO)2(Me)] reacts thermally with N-heterocyclic carbenes (L) to give both alkyl, [Fe(eta-C5H5)(L)(CO)(Me)], and acyl, [Fe(eta-C5H5)(L)(CO)(COMe)], derivatives. The reaction temperature has been shown to affect the product distribution. The alkyl and acyl derivatives exist in an equilibrium that is more easily perturbed than in the tertiary phosphine analogues. DFT studies on the reactivity of [Fe(eta-C5H5)(CO)2(Me)] with PH3 and dihydroimidazole-2-ylidene (IH) have shown that CO exchange is energetically favoured for IH, and energetically disfavoured for PH3. The products of CO-induced migratory insertion, [Fe(eta-C5H5)(L)(CO)(COMe)], are more stable than the parent alkyl, [Fe(eta-C5H5)(L)(CO)(Me)], compounds. This stabilisation is larger when L = IH than when L = PH3. Stabilisation of the transition state by agostic interactions was seen in both instances, but this was significantly more pronounced for L = IH.
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Stability of Substituted Cyclohexanes
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...