Can Coordination-Driven Supramolecular Self-Assembly Reactions Be Conducted from Fully Aliphatic Linkers?

The reaction between a preassembled CuI bimetallic molecular clip with a short intermetallic distance and a series of fully aliphatic cyano-capped ditopic linkers with increasing lengths was investigated. It is shown that, depending on the length of the ditopic linkers, the rational design of unprecedented supramolecular compact metallacycles containing fully aliphatic walls is possible. The specific preorganized molecular arrangement of the molecular clip used favors stabilizing interlinker London dispersion interactions, which allow, as the length of the linkers increases, the selective formation of discrete compact metallacycles at the expense of 1D coordination polymers. The generalizability of this approach was demonstrated by the reaction of fully aliphatic cyano-capped linkers with two other types of preassembled CuI bimetallic molecular clips that also had short intermetallic distances.

Bimetallic Gold(I) Complexes with Ethynyl-Helicene and Bis-Phosphole Ligands: Understanding the Role of Aurophilic Interactions in their Chiroptical Properties.

Monometallic gold(I)-alkynyl-helicene complexes (1 a,b) and bimetallic gold(I)-alkynyl-helicene architectures featuring the presence (2 a,b) or absence (3 a,b) of aurophilic intramolecular interactions were prepared by using different types of phosphole ligands (mono-phosphole L1 or bis-phospholes L2,3). The influence of the Au(I) d(10) metal center(s) on the electronic, photophysical, and chiroptical properties of these unprecedented phosphole-gold(I)-alkynyl-helicene complexes was examined. Experimental and theoretical results highlight the importance of ligand-to-ligand-type charge transfers and the strong effect of the presence or absence of Au(I) -Au(I) interactions in 2 a,b.

Ruthenium-Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching.

The properties of mono- and bis-Ru-vinyl[6]helicene complexes (2 a and 2 b, respectively), recently synthesized by using molecular engineering of helicenes based on the grafting of lateral organometallic substituents on the π-helical backbone through a vinyl bridge, are presented. These helicene derivatives are thoroughly characterized, with special attention given to their chiroptical properties and redox switching activity. The UV/Vis and electronic circular dichroism (ECD) spectra of P and M enantiopure species, both in the neutral and oxidized states ([2 a](·+), [2 b](·+), and [2 b](2+)), are analyzed with the aid of quantum-chemical calculations. The extended π-conjugation facilitated by the vinyl moiety, clearly visible in the electronic structures of 2 a,b, introduces new active bands in the ECD spectra that consequently lead to a significant increase in optical rotation of Ru-vinylhelicenes compared with the organic precursors. The vibrational circular dichroism (VCD) spectra were measured and calculated for both the organic and organometallic species and constitute the first examples of VCD for metal-based helicene derivatives. Finally, the redox-triggered chiroptical switching activity of 2 a,b is examined in detail by using ECD spectroscopy. The modifications of the ECD spectra in the UV/Vis and NIR region are well reproduced and rationalized by calculations.

Synthesis, electronic properties and WOLED devices of planar phosphorus-containing polycyclic aromatic hydrocarbons.

We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P-containing PAHs exhibit properties expected for an emitter in white organic light-emitting diodes (WOLEDs).

Phosphorus centers of different hybridization in phosphaalkene-substituted phospholes.

Phosphole-substituted phosphaalkenes (PPAs) of the general formula Mes*P=C(CH(3))-(C(4)H(2)P(Ph))-R 5 a-c (Mes*=2,4,6-tBu(3)Ph; R=2-pyridyl (a), 2-thienyl (b), phenyl (c)) have been prepared from octa-1,7-diyne-substituted phosphaalkenes by utilizing the Fagan-Nugent route. The presence of two differently hybridized phosphorus centers (σ(2) ,λ(3) and σ(3) ,λ(3)) in 5 offers the possibility to selectively tune the HOMO-LUMO gap of the compounds by utilizing the different reactivity of the two phosphorus heteroatoms. Oxidation of 5 a-c by sulfur proceeds exclusively at the σ(3) ,λ(3) -phosphorus atom, thus giving rise to the corresponding thioxophospholes 6 a-c. Similarly, 5 a is selectively coordinated by AuCl at the σ(3),λ(3) -phosphorus atom. Subsequent second AuCl coordination at the σ(2),λ(3) -phosphorus heteroatom results in a dimetallic species that is characterized by a gold-gold interaction that provokes a change in π conjugation. Spectroscopic, electrochemical, and theoretical investigations show that the phosphaalkene and the phosphole both have a sizable impact on the electronic properties of the compounds. The presence of the phosphaalkene unit induces a decrease of the HOMO-LUMO gap relative to reference phosphole-containing π systems that lack a P=C substituent.

Dissymmetrical U-shaped π-stacked supramolecular assemblies by using a dinuclear Cu(I) clip with organophosphorus ligands and monotopic fully π-conjugated ligands.

Reactions between the U-shaped binuclear Cu(I) complex A that bears short metal-metal distances and the cyano-capped monotopic π-conjugated ligands 1-5 that carry gradually bulkier polyaromatic terminal fragments lead to the formation of π-stacked supramolecular assemblies 6-10, respectively, in yields of 50-80 %. These derivatives have been characterized by multinuclear NMR spectroscopic analysis and X-ray diffraction studies. Their solid-state structures show the selective formation of U-shaped supramolecular assemblies in which two monotopic π-conjugated systems present large (6, 7, and 9) or medium (8 and 10) intramolecular π overlap, thus revealing π-π interactions. These assemblies self-organize into head-to-tail π-stacked dimers that in turn self-assemble to afford infinite columnar π stacks. The nature, extent, and complexity of the intermolecular contacts within the head-to-tail π-stacked dimer depend on the nature of the terminal polyaromatic fragment carried by the cyano-capped monotopic ligand, but it does not alter the result of the self-assembling process. These results demonstrate that the dinuclear molecular clip A that bears short metal-metal distances allows selective supramolecular assembly processes driven by the formation of intra- and intermolecular short π-π interactions in the resulting self-assembled structures; thus, demonstrating that their shape is not only dictated by the symmetry of the building blocks. This approach opens perspectives toward the formation of extended π-stacked columns based on dissymmetrical and functional π-conjugated systems.

1,2-dihydrophosphete: a platform for the molecular engineering of electroluminescent phosphorus materials for light-emitting devices.

The discovery and molecular engineering of novel electroluminescent materials is still a challenge in optoelectronics. In this work, the development of new π-conjugated oligomers incorporating a dihydrophosphete skeleton is reported. Variation of the substitution pattern of 1,2-dihydrophosphete derivatives and chemical modification of their P atoms afford thermally stable derivatives, which are suitable emitters to construct organic light-emitting diodes (OLEDs). The optical and electrochemical properties of these new P-based oligomers have been investigated in detail and are supported by DFT calculations. The OLED devices exhibit good performance and current-independent CIE coordinates.

Diastereo- and enantioselective synthesis of organometallic bis(helicene)s by a combination of C-H activation and dynamic isomerization.

Homochiral and heterochiral cis-bis-cycloplatinated-[6]helicene derivatives 1b(1,2), as representative examples of platina[6]helicenes that share a common platinum center, have been prepared. A diastereo- and enantioselective synthesis, which combines CH activation and dynamic isomerization from heterochiral structure 1b(2) into homochiral structure 1b(1), is also described. Overall, this isomerization process results in the transfer of chiral information from one helicene moiety to the other one. The chiroptical properties of homochiral (P)- and (M)-1b(1) were greatly modified upon oxidation into their corresponding (P)- and (M)-diiodo-Pt(IV) complexes (5). The changes were also analyzed by performing theoretical calculations. C-H activation in the synthesis of organometallic helicenes is further demonstrated by the preparation of cis-bis-cycloplatinated-[8]helicene 1c.

Synthesis of small tetranuclear Cu(I) metallacycles based on bridging pseudohalogenide ions.

Three new 'short' metallacycles are selectively obtained from the reaction of a bimetallic Cu(I) 'U-shape' molecular clip with, respectively, the cyano CN(-), tricyanomethanide C(CN)(3)(-), and azido N(3)(-) pseudohalogenide ions. These supramolecular assemblies have been characterized by spectroscopic methods, single-crystal X-ray diffraction, and elemental analysis. The single-crystal X-ray structures of these complexes reveal no short contact interaction between the pseudohalogenide ions within these self-assembled structures despite the short Cu(I)···Cu(I) distances within the molecular clips. The formation of these discrete metallacycles is rationalized by analyzing the structural features of the Cu(I) 'U-shape' molecular clip.

Dibenzophosphapentaphenes: exploiting P chemistry for gap fine-tuning and coordination-driven assembly of planar polycyclic aromatic hydrocarbons.

A synthetic route to planar P-modified polycylic aromatic hydrocarbons (PAHs) is described. The presence of a reactive σ(3),λ(3)-P moiety within the sp(2)-carbon scaffold allows the preparation of a new family of PAHs displaying tunable optical and redox properties. Their frontier molecular orbitals (MOs) are derived from the corresponding phosphole MOs and show extended conjugation with the entire π framework. The coordination ability of the P center allows the coordination-driven assembly of two molecular PAHs onto a Au(I) ion.

Ruthenium-vinylhelicenes: remote metal-based enhancement and redox switching of the chiroptical properties of a helicene core.

Introducing metal-vinyl ruthenium moieties onto [6]helicene results in a significant enhancement of the chiroptical properties due to strong metal-ligand electronic interactions. The electro-active Ru centers allow the achievement of the first purely helicene-based redox-triggered chiroptical switches. A combination of electrochemical, spectroscopic, and theoretical techniques reveals that the helicene moiety is a noninnocent ligand bearing a significant spin density.

Aurophilicity versus mercurophilicity: impact of d10-d10 metallophilic interactions on the structure of metal-rich supramolecular assemblies.

Treatment of U-shaped, binuclear Cu(I) complexes 1,1' (1, counterion: BF(4)(-); 1', counterion: PF(6)(-)) with metal cyanide linear linkers K[Au(CN)(2)] (3) and Hg(CN)(2) (4) lead to formation of new supramolecular assemblies 5,5' and 6,6', respectively, in good yield. These derivatives have been characterized by NMR spectroscopy, IR, and X-ray diffraction studies. Derivative 5,5' are supramolecular metallacycles in which intramolecular aurophilic interactions between the Au(I) metal centers of the linkers are observed. Derivative 5 crystallizes as a single solid phase, whereas derivative 5' is characterized in the solid state as four different pseudo-polymorphs (5'a-d). Notably in the case of phase 5'd, a dimer of supramolecular metallacycles bounded by intermolecular aurophilic interactions is formed. Conversely, derivatives 6,6' present large structural diversity depending on the nature of the counterion. Derivative 6 is a supramolecular rectangle in which the Hg(II)-Hg(II) metal distance suggests mercurophilic interaction, whereas 6' crystallizes as two different pseudo-polymorphs 6'a,b, that is, a one-dimensional coordination polymer and one oligomer with no short Hg(II)-Hg(II) metal contacts, respectively. In derivatives 6,6', short contacts between the Hg(II) metal centers and fluorine atoms of the counterions are also observed, which may explain the counterion structural dependence of these supramolecular assemblies based on Hg(II) metal cyanide linker. Comparison of the different solid-state structures characterized highlights the importance of weak secondary interactions between the linkers for the formation supramolecular metallacycles from molecular clips 1,1' and suggests the range of energies required for these interactions to form metallacycles and to induce self-aggregation.

Tunable acetylene sorption by flexible catenated metal-organic frameworks.

The safe storage of flammable gases, such as acetylene, is essential for current industrial purposes. However, the narrow pressure (P) and temperature range required for the industrial use of pure acetylene (100 < P < 200 kPa at 298 K) and its explosive behaviour at higher pressures make its storage and release challenging. Flexible metal-organic frameworks that exhibit a gated adsorption/desorption behaviour-in which guest uptake and release occur above threshold pressures, usually accompanied by framework deformations-have shown promise as storage adsorbents. Herein, the pressures for gas uptake and release of a series of zinc-based mixed-ligand catenated metal-organic frameworks were controlled by decorating its ligands with two different functional groups and changing their ratio. This affects the deformation energy of the framework, which in turn controls the gated behaviour. The materials offer good performances for acetylene storage with a usable capacity of ~90 v/v (77% of the overall amount) at 298 K and under a practical pressure range (100-150 kPa).

From hetero- to homochiral bis(metallahelicene)s based on a Pt(III)-Pt(III) bonded scaffold: isomerization, structure, and chiroptical properties.

Hetero- and homochiral diastereomeric bis(metallahelicene)s have been synthesized. They possess a rare Pt(III)-Pt(III) scaffold bridged by benzoato ligands. It is shown that heterochiral (P,M)-bis(Pt(III)-[6]helicene) can isomerize into the homochiral (P,P)- and (M,M)-bis(Pt(III)-[6]helicene). A theoretical study shows a unique σ-π conjugation between the two π-helices and the σ-Pt(III)-Pt(III) scaffold that impacts the strong chiroptical properties.

Simultaneous end-on/side-on coordination modes of a diphosphorus tetrahedral complex imposed by pre-organization of oligometallic Cu(I) acceptors.

The reaction of the [{CpMo(CO)(2)}(2)(µ,η(2):η(2)-P(2))] (Cp=cyclopentadienyl) metallo-ligand 2 with pre-organized Cu(I) bi- and trimetallic precursors afforded new coordination complexes with unprecedented coordination modes for a Mo(2)P(2) complex. Variable-temperature solution and solid-state (31)P NMR spectroscopy measurements were performed and X-ray diffraction studies revealed an η(2):η(1) coordination mode for the Mo(2)P(2) unit of 2 in the Cu(I) bimetallic complexes 3 and 4. DFT calculations were carried out to highlight the bonding situation of this unprecedented coordination mode in the Cu(I) bimetallic compound 3. It is built up from a side-on coordination of the P-P σ bond to one copper ion and from the interaction of the lone pair of one phosphorus atom with the second copper ion. The remaining available lone pair of the second phosphorus atom can be involved as well to interact with an additional metal centre, as evidenced in the Cu(I) trimetallic compound 5 in which an η(2):η(1):η(1) coordination mode of the ligand 2 is observed. Derivative 3 can be used as a molecular clip to obtain discrete π-stacked dimers through a ligand exchange reaction between acetonitrile ligands and cyano-capped π-conjugated systems, indicating the stability of the new η(2):η(1) coordination mode.

Chiral and extended π-conjugated bis(2-pyridyl)phospholes as assembling N,P,N pincers for coordination-driven synthesis of supramolecular [2,2]paracyclophane analogues.

Chiral, π-conjugated 3,4-butano-1-phenyl-2,5-bis(2-pyridyl)phosphole derivatives 1a(2,2') and 1a(3) with chiral trans-1,2-diol moieties and fused pinene derivatives, respectively, were prepared from the corresponding chiral diynes by using the Fagan-Nugent method. Their UV/Vis absorption and chiroptical properties (optical rotation and circular dichroism) were studied. Their behavior as N,P,N chelates towards coordination of Cu(I) and formation of chiral supramolecular assemblies with π-conjugated ditopic dicyano ligands was investigated. Chiral C(2)-symmetric rectangles that are [2,2]paracyclophane analogues were obtained, as demonstrated by X-ray crystallography. During the course of this study, the first stable water-soluble phosphole derivative (1a(2)·2 HCl) was prepared. Furthermore, achiral 3,4-butano-1-phenyl-2,5-bis(aza[4]helicene)phosphole 1a(4) was synthesized and displays extended π conjugation. A supramolecular rectangle was obtained by coordination to Cu(I) and assembly with a dicyano stilbene. This coordination-driven supramolecular assembly contains a total of four aza[4]helicene moieties and displays two types of π-π stacking interactions in the solid state, that is, between two helicene moieties and between one helicene and a bridging dicyano ligand. All the supramolecular arrangements are discussed by comparing them with previous work on the parent 3,4-butano-1-phenyl-2,5-bis(2-pyridyl)phosphole.

Multifunctional and reactive enantiopure organometallic helicenes: tuning chiroptical properties by structural variations of mono- and bis(platinahelicene)s.

Acetylacetonato-platina[6]- and -platina[7]helicenes have been prepared from 2-pyridyl-substituted benzophenanthrene ligands by following a two-step cycloplatination reaction. The photophysical properties (UV-visible absorption and emission behavior) and chiroptical properties (circular dichroism and molar rotation) of the resolved enantiomers have been measured. These metallahelicenes constitute a novel family of easily accessible helicene derivatives that exhibit large and tuneable chiroptical properties that can be rationalized theoretically and compared to the parent [6]- and [7]carbohelicenes. Furthermore, they are red phosphors at room temperature and their large chiroptical properties can be modulated by oxidation of the metal center to Pt(IV). Hetero- and homochiral diastereomeric bis(metallahelicene)s that possess a rare Pt(III)-Pt(III) scaffold bridged by benzoato ligands have also been prepared. It is shown that the heterochiral (P,M)-bis(Pt(III)-[6]helicene) 9a(1) can isomerize into the homochiral (P,P)- and (M,M)-bis(Pt(III)-[6]helicene) 9a(2). Spectral assignments and an analysis of the optical rotation of these systems were made with the help of time-dependent density functional theory. The calculations highlight the contributions of the metal centers to the chiroptical properties. For 9a(1) and 9a(2), σ-π conjugation between the helicenes and the Pt-Pt moiety may contribute strongly to the optical rotation and electronic circular dichroism.

Folding of a supramolecular framework based on a tetrametallic clip driven by π-π interactions.

Supramolecular extended frameworks based on a rotational molecular clip and having the same "primary structure" can exhibit either an unfolded or a folded framework. This process is driven by intramolecular π-π interactions, resulting in the formation of an infinite π-stacked column within the folded supramolecular framework.

Coordination-driven hierarchical organization of pi-conjugated systems: from molecular to supramolecular pi-stacked assemblies.

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.

3,4-Dithiaphosphole and 3,3',4,4'-tetrathia-1,1'-biphosphole π-conjugated systems: S makes the impact.

Conjugated systems based on phospholes and 1,1'-biphospholes bearing 3,4-ethylenedithia bridges have been prepared using the Fagan-Nugent route. The mechanism of this organometallic route leading to intermediate zirconacyclopentadienes has been investigated by using theoretical calculations. This study revealed that the oxidative coupling leading to zirconacyclopentadienes is favored over oxidative addition within the S-C≡C bond both thermodynamically and kinetically. The impact of the presence of the S atoms on the optical and electrochemical behavior of the phospholes and 1,1'-biphospholes has been systematically evaluated both experimentally and theoretically. A comparison with their "all-carbon" analogues is provided. Of particular interest, this comparative study revealed that the introduction of S atoms has an impact on the electronic properties of phosphole-based conjugated systems. A decrease of the HOMO-LUMO separation and a stabilization of the LUMO level were observed. These general trends are also observed with 1,1'-biphospholes exhibiting σ-π conjugation. The P atom of the 3,4-ethylenedithiaphospholes can be selectively oxidized by S(8) or O(2). These P modifications result in a lowering of the HOMO-LUMO separation as well as an increase of the reduction and oxidation potentials. The S atoms of the 3,4-ethylenedithia bridge of the 2,5-phosphole have been oxidized using m-chloroperoxybenzoic acid. The resulting 3,4-ethylenesulfoxide oxophosphole was characterized by an X-ray diffraction study. Experimental and theoretical studies show that this novel chemical manipulation results in an increase of the HOMO-LUMO separation and an important decrease of the LUMO level. The electropolymerization of 2-thienyl-capped 3,4-ethylenedithiathioxophosphole and 1,1'-biphosphole is reported. The impact of the S substituents on the polymer properties is discussed.