Tuning the Electronic and
Ligand Properties of Remote
Carbenes: A Theoretical Study
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Abstract
The
effect of annulation and carbonylation on the electronic and
ligating properties of remote N-heterocyclic carbenes (rNHCs) has
been studied quantum-chemically. The thermodynamic stability of these
complexes has been assessed on the basis of their hydrogenation and
stabilization energies, while HOMO–LUMO gaps are used to measure
the kinetic stabilities. Annulated/carbonylated rNHCs are found to
be weaker σ donors but better π acceptors compared with
the parent rNHCs. The reactivity of these rNHCs has been studied by
evaluating their nucleophilicity and electrophilicity indices. The
nucleophilicity values are in good agreement with the σ basicities
of all of the rNHCs. The <sup>31</sup>P NMR chemical shifts of the
corresponding rNHC–phosphinidene adducts have been calculated
and found to correlate well with the π acidities of these rNHCs