Lone‐Pair‐π Bond Strength Unveiled by a Combined Experimental and Computational Study

Abstract

A series of naphthalene‐diimide (NDI) and perylene‐diimide (PDI) connected bis‐N‐heterocyclic carbene complexes of iridium (III) have been prepared and fully characterized. The analysis of their NMR spectroscopic features, together their molecular structures show that these species display lone pair‐p interactions between the chloride ligands of the Ir(III) complex and the heterocycles of the NDI/PDI moieties. The detection of this type of interaction in solution is due to the formation of two atropisomers, which are formed as a result of the restricted rotation about the Ir‐Ccarbene bond imposed by the (Cl)lp…p interaction. Variable temperature 1H NMR analysis allowed to determine the strength of this non‐covalent interaction, which lies between DH = 6.6‐10 kcal/mol. The computational studies performed fully support the experimental findings. Our study demonstrates that this type of lp…p interaction is comparable to strong hydrogen bonding.