Coordination‐Driven Hierarchical Organization of π‐Conjugated Systems: From Molecular to Supramolecular π‐Stacked Assemblies

Abstract

The reaction of U-shaped, bimetallic, Cu(I) complexes, assembled from a heteroditopic pincer, with cyano-capped pi-conjugated linkers gives a straightforward access to pi-stacked metallocyclophanes in good yields. In these assemblies, the pi-walls have an almost face-to-face arrangement. The versatility of this rational supramolecular synthesis is demonstrated with the use of linkers that have nanoscale lengths (up to 27.7 A), different chemical compositions (oligo(para-phenylenevinylene)s OPVs, oligo(phenylene)s, oligo(phenylethynylene)s), and alternative geometries (linear, angular). Linkers that incorporate an internal pyridyne moiety can also be employed. X-ray diffraction studies revealed that the metallocyclophanes based on linear linkers self-organize into infinite pi-stacked columns in the solid state with intermolecular distances of about 3.6 A. This approach, based on coordination-driven self-assembly, provides a novel and rational strategy for the stacking of extended pi-systems in the solid state.

Dissymmetrical U‐Shaped π‐Stacked Supramolecular Assemblies by Using a Dinuclear CuI Clip with Organophosphorus Ligands and Monotopic Fully π‐Conjugated Ligands

“…In all cases, the 31 P{ 1 H} NMR spectra of the mother solutions exhibited a broad signal with a chemical shift at approximately d = + 8 ppm (Table 2), which is similar to those ob-served for the corresponding free molecular clip A [11] and most of the supramolecular assemblies obtained from A (see Table S1 in the Supporting Information). [10,13] These data indicate that the structure of the Cu I dimer, which features a bridging P-center, is maintained throughout these reactions. The 31 P{ 1 H} NMR signals observed at room temperature are broad, mostly due to the hemilabile behavior of ligand B in the coordination sphere of the Cu I centers of the {(Cu I ) 2 (B) 2 } fragments.…”

Chiroptical Properties of Carbo[6]Helicene Derivatives Bearing Extended π‐Conjugated Cyano Substituents

“…The cyano group was then reduced to an aldehyde using DIBAL‐H in toluene at 30°C, giving carbo[6]helicene‐2‐carbaldehyde H6 with 85% yield. The final step was a Horner‐Emmons reaction between the produced aldehyde H6 and an already prepared 4‐cyanobenzylphosphonate, yielding the desired product H3 as a 30:70 cis / trans isomeric mixture. HPLC separation over a Chiralpak IB column (hexane/EtOH 8:2 as the mobile phase, see SI) enabled to obtain the final enantiopure P ‐ and M ‐ H3 in their pure trans form (Supporting Fig.…”

“…i ) 4‐cyano‐benzaldehyde, n ‐BuLi, THF, Ar, r.t., 3 h, 85% ; ii ) hν, cat. I 2 , toluene, 1 night, 45%; iii ) DIBAL‐H, toluene, Ar, r.t., 2 h, 80%; iv ) 4‐cyanobenzylphosphonate, NaH, THF, Ar, 2 h, 80%; v ) HPLC separation over a chiral stationary phase (see text and SI).…”

“…Synthesis of enantiopure P ‐ and M ‐ H4 . i ) 4‐iodobenzaldehyde, PdCl 2 (PPh 3 ) 2 , CuI, Et 3 N, Ar, 50°C, 1 night, 92%; ii ) 4‐cyanobenzylphosphonate, NaH, THF, Ar, 2 h, 82%; iii ) HPLC separation over a chiral stationary phase (see text and SI).…”

“…This case study of carbo[6]helicenes bearing extended π‐conjugated cyano substituents nicely illustrates how the electronic and optical properties of a [6]helicene can be molecularly engineered by simply grafting a π‐conjugated arm of different vinyl or ethynyl substituents and of different lengths therefore enabling modification of the chiroptical properties of helicenic systems. In the future, the ability of these phenyl‐ethynyl and/or vinyl substituted carbo[6]helicenes bearing cyano groups to be used as ligands for helicene‐based coordination chemistry will be investigated.…”