Postmodification of the Electronic Properties by Addition of π-Stacking Additives in N-Heterocyclic Carbene Complexes with Extended Polyaromatic Systems

Abstract

A series of iridium complexes containing phenanthro[4,5--abc]phenazino[11,12--d]imidazol--2--ylidene and ace-- [11,12--d]imidazol--2--ylidene ligands have been obtained and fully characterized. These com--plexes display highly extended polyaromatic systems attached to the backbone of the N--heterocyclic carbene. The pres--ence of this extended polyaromatic system makes the electron--donating character of these ligands sensitive to the pres--ence of π--stacking additives, such as pyrene and hexafluorobenzene. The computational studies predict that the addition of pyrene affords an increase of the electron--donating character of the polyaromatic ligand (TEP decreases), while the addition of hexafluorobenzene has the opposite effect (TEP increases). This prediction is experimentally corroborated by IR spectroscopy, by measuring the shift of the CO stretching bands of a series of IrCl(NHC)(CO) 2 complexes, where NHC is the N--heterocyclic carbene ligand with the polyaromatic system. Finally, the energy of the π--stacking interaction of one of the key Ir(I) complexes with pyrene and hexafluorobenzene has been estimated by using the Benesi--Hildebrand treat--ment, based on the δ--shifts observed by 1 H NMR spectroscopy.

Platinum‐Based Organometallic Folders for the Recognition of Electron‐Deficient Aromatic Substrates

“…[11] Parallel to this research, we also designed as eries of di-and tritopic NHC ligands bearing rigid polyaromatic linkers, [12] and found that the catalytic performances of the corresponding metal complexes were highly influenced by supramolecular effects,w hich we attributed to the p-p stacking interactions betweent he polyaromatic spacers of the ligands and the aromatic substrates. [13] In order to study the nature of these supramolecular interactions, as eries of complexes with monodentate NHCl igandsw ith rigid polyaromatic backbones wereo btained, [14] and by well-known host-guest chemistry approaches, we were ablet od etermine the nature of the supramolecular interactions, and also quantify the extent of the non-covalent binding. [14b] The binding affinities that we found between the p-stackinga dditives andt he metal complexes were low, [12d, 14b] because the host-guest interactions werep roduced on the open surfaceo ft he metal complex, rather than in the interior of ac avity.F rom our point of view,t hese results established the basis for the use of monometallicc omplexes as receptors for molecular recognition, as an alternative to using the commons elf-assembly polymetallic architectures.…”

Improving Catalyst Activity in Hydrocarbon Functionalization by Remote Pyrene–Graphene Stacking

“…Peris and co-workers have demonstrated as imilar pyrene-to-polyaromatic electron density flux. [20] This remote pyrene-graphene stacking effect explains the enhancement of reactionr ate and yields observed with 1-rGO compared with those with soluble 1.…”

Structural Features of Mono‐ and Dimetallic Complexes of Palladium Combining Two Types of Aromatic NHC Ligands

“…Not less important is that the presence of the polyaromatic moieties provides new photophysical properties to the complexes (mainly fluorescence), thus affording an interesting approach to combine them with the intrinsic features of transition metals. In this regard, several mono‐NHCs containing an annulated polyaromatic backbone have been synthesized (Scheme ) and coordinated to transition metals furnishing new complexes with very interesting photophysical properties , …”

“…In this regard, several mono-NHCs containing an annulated polyaromatic backbone have been synthesized (Scheme 2) and coordinated to transition metals furnishing new complexes with very interesting photophysical properties. [18,[26][27][28][29][30][31][32][33] Scheme 2. Selected examples of mono-NHC ligands decorated with polyaromatic backbones.…”