NHC-Stabilised Acetylene—How Far Can the Analogy Be Pushed?

Experimental studies suggest that the compound (NHC^bz)₂C₂H₂can be considered as a complex of a distorted acetylene fragment which is stabilised by benzoannelated N-heterocyclic carbene ligands (NHC^bz)→(C₂H₂)←(NHC^bz). A quantum chemical analysis of the electronic structures shows that the description with dative bonds is more favourable than with electron-sharing double bonds (NHC^bz)=(C₂H₂)=(NHC^bz).