Aryl-Aryl Interactions in (Aryl-Perhalogenated) 1,2-Diaryldisilanes

Geometrical and Electronic Structure of Fluorinated and Non-Fluorinated Platinum(II) Tetraphenylporphyrin Complexes

The composition of the saturated vapors of two platinum complexes with the macrocyclic ligands 5,10,15,20-tetraphenylporphyrin (PtTPP) and 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (PtTF5PP) and their structures were determined by synchronous gas-phase electron diffraction/mass spectrometry (GED/MS). These porphyrin complexes are those with the heaviest metal atom in the coordination cavity that have been structurally investigated in the gas phase. The mass spectra confirm the presence of a single molecular form of each, PtTPP (T=629 K) and PtTF5PP (T=597 K). Their structures can serve as references for related complexes in the crystalline state or solutions. Differences between the geometries of PtTPP and PtTF5PP in the crystalline and gaseous states include a significant deformation of the tetrapyrrole macrocycle in solid PtTPP. The experimental Pt-N bond lengths of both complexes are in agreement with quantum chemical calculations (DFT/B97D/ECP(Pt)) taking into account relativistic effects. The effect of lanthanide contraction is evident from the similarity of the Pd-N and Pt-N internuclear distances of analogous compounds. The strong electron density transfer from the porphyrin backbone to the metal ion and the resulting low effective positive charge on the platinum atom, studied by NBO and QTAIM methods, helps to rationalize the high catalytic activity of such platinum compounds.

Phase-Dependence of Molecular Structures Arising from Weak London Dispersion Interactions

ConspectusThe structures of molecules can be different in different phases. Intermolecular forces, even those of weak noncovalent interactions (WNCIs), can lead to a preference for quite different conformations in the solid, the gas, and the liquid phases. WNCIs can cause variations in bond lengths, angles, and torsional angles. Since structure is a fundamental concept in chemistry, the knowledge of structural changes with phase is important to understand the source and effects of distorting contributions from WNCIs but also as a predictive tool for the design and stabilization of new bonding situations.X-ray crystallography is ubiquitous and now mostly straightforward to perform, but facilities for the determination of accurate gas-phase structure determination are rare, and gas-phase work is laborious and time-consuming. There are currently about 1.25 million crystal structures and more than 12 500 experimental gas-phase structures, but the intersection of the two data sets that can tell us about the structural differences of the same molecule in different phases is surprisingly small.In this Account, we describe several cases of WNCI-dominated systems for which accurate experimental structure determinations exist for both the gas phase and the solid state and, in one case, also for solution. The examples include aryl-aryl, aryl-alkyl, and alkyl-alkyl interactions; systems with chalcogen and halogen bonding; and fluorine-based interactions in arylboranes. We work out the role of WNCIs in stabilizing large, strained, or sterically overloaded molecules. We will show how flexible molecules will fold under the action of WNCIs when isolated in the gas and how they fold or unfold when they are embedded in an environment of neighbors in crystals. We will show how they can vary in strength when the substitution patterns in aryl groups are changed by different halogens and how intramolecular WNCIs, such as those forming rings, change when such systems experience additional intermolecular WNCIs.Overall, we hope that this Account will give the reader an idea of the type and magnitude of structural changes that can be expected from a free molecule in the gas phase or a single molecule calculated by quantum chemistry compared with one embedded in a crystal. This should define the limits of comparability and provide some predictive concepts of the distortions and variations to be expected.

Disilane-bridged architectures: an emerging class of molecular materials

Disilanes are organosilicon compounds that contain saturated Si-Si bonds. The structural characteristics of Si-Si single bonds resemble those of C-C single bonds, but their electronic structure is more similar to that of C[double bond, length as m-dash]C double bonds, as Si-Si bonds have a higher HOMO energy level. These organosilicon compounds feature unique intramolecular σ electron delocalization, low ionization potentials, polarizable electronic structure, and σ-π interaction. It has been demonstrated that the employment of disilane units (Si-Si) is a versatile and effective approach for finely adjusting the photophysical properties of organic materials in both solution and solid states. In this review, we present and discuss the structure, properties, and relationships of novel σ-π-conjugated hybrid architectures with saturated Si-Si σ bonds. The application of disilane-bridged σ-conjugated compounds as optoelectronic materials, multifunctional solid-state emitters, CPL, and non-linear optical and stimuli-responsive materials is also reviewed.

Bis(amidophenolato)phosphonium: Si-H Hydride Abstraction and Phosphorus-Ligand Cooperative Activation of C-C Multiple Bonds

The first bis(amidophenolato)phosphonium salts are prepared and fully characterized. The perfluorinated derivative represents the strongest monocationic phosphorus Lewis acid on the fluoride and hydride ion affinity scale isolable to date. This affinity enables new reactions, such as hydride abstraction from Et₃ SiH, the first phosphaalkoxylation of an alkyne or a phosphorus catalyzed intramolecular hydroarylation. All properties and reactions are scrutinized by theory and experiment. Substantial σ- and π-acidity provides the required affinity for substrate activation, while phosphorus-ligand cooperativity substantially enriches the reactivity portfolio of phosphonium ions.

Silyl Groups Are Strong Dispersion Energy Donors

We present an experimental and computational study to investigate noncovalent interactions between silyl groups that are often employed as "innocent" protecting groups. We chose an extended cyclooctatetraene (COT)-based molecular balance comprising unfolded (1,4-disubstituted) and folded (1,6-disubstituted) valance bond isomers that typically display remote and close silyl group contacts, respectively. The thermodynamic equilibria were determined using nuclear magnetic resonance measurements. Additionally, we utilized Boltzmann weighted symmetry-adapted perturbation theory (SAPT) at the sSAPT0/aug-cc-pVDZ level of theory to dissect and quantify noncovalent interactions. Apart from the extremely bulky tris(trimethylsilyl)silyl "supersilyl" group, there is a preference for the folded 1,6-COT valence isomer, with London dispersion interactions being the main stabilizing factor. This makes silyl groups excellent dispersion energy donors, a finding that needs to be taken into account in synthesis planning.

Noncovalent Synergy: Aurophilicity and Aryl Stacking in Bis(gold(I)aryl)-dmpm Complexes

Bis(dimethylphosphino)methane (dmpm) was used as a ligand to synthesize four semi-supported dinuclear gold(I) complexes, dmpm(AuR)₂ (R = Cl, C₆H₅, C₆Cl₅, and C₆F₅), which were studied concerning the synergistic effects of two weak noncovalent interactions: aurophilic and aryl-aryl stacking interactions. The chloro-substituted complex was synthesized by the ligand substitution of (tht)AuCl with dmpm and further functionalized by the reaction with PhMgBr or in situ-generated C₆Cl₅Li to afford the phenyl- and pentachlorophenyl-substituted compounds, respectively. The pentafluorophenyl-substituted gold complex was generated by the ligand substitution of (tht)Au(C₆F₅) with dmpm. All complexes were characterized by multinuclear NMR spectroscopy, CHN analyses, and X-ray diffraction experiments. Additionally, the basic photoluminescence properties of dmpm(AuCl)₂, dmpm(AuC₆Cl₅)₂, and dmpm(AuC₆F₅)₂ were examined. The aggregation behavior of dmpm(AuC₆F₅)₂ was further investigated by variable-temperature diffusion-ordered NMR spectroscopy experiments.

Conformational Switch of Benzanilide Derivative Induced by Acid; Effect of Pentafluorobenzoyl Group

Amide-based molecular switches had its limitation on structural diversities. In this work, we designed and synthesized a series of pentafluorobenzoyl-based benzanilide compounds. The conformational ratio of these compounds in solution was correlated linearly with Hammett's σ_p value of the substituent on the anilide ring, reflecting the repulsive interaction between the carbonyl group and the electron-rich aryl group. The addition of acid into the solution of 6, bearing pentafluorobenzoyl group, switched the stable amide conformation. In addition, the sizeable rotational barrier of 6 induced by the pentafluorobenzoyl moiety enabled us to monitor the conformational transition by means of ¹H NMR spectroscopy.

Synthesis, structural and photophysical properties of dimethylphosphino(perfluoro-)phenylene-based gold(I) dimers

Starting with 1,2-dibromobenzene and 1,2,3,4-tetrafluorobenzene, dimethyl(2-(trimethylstannyl)phenyl)phosphane, Me₂P(o-C₆H₄)SnMe₃, and dimethyl-[2,3,4,5-tetrafluoro-6-(trimethylstannyl)phenyl]phosphane, Me₂P(o-C₆F₄)SnMe₃, were synthesized and used in tin-gold exchange reactions to prepare two gold(I) dimers, bis[(2-dimethylphosphino)phenyl]di-gold(I), [Au₂(μ-2-C₆H₄PMe₂)₂], and bis[(2-dimethylphosphino)-3,4,5,6-tetrafluorophenyl]di-gold(I), [Au₂(μ-2-C₆F₄PMe₂)₂], respectively. Both tin precursor molecules, as well as the gold(I) complexes, were characterized by multinuclear NMR spectroscopy, CHN analysis and X-ray diffraction experiments. Both gold(I) dimers were further investigated by the means of computational as well as photophysical methods.

Co-Crystal Formation of Partially Fluorinated 1,3,5-Tris(phenylethynyl)benzenes

Several rigid 1,3,5-tris(phenylethynyl)benzenes with different fluorination patterns were synthesized through selective Sonogashira-Hagihara coupling reactions to analyze the packing behavior in solid-state structures. The aggregation is dominated by various intermolecular interactions between aryl substituents, triple bonds, C-H bonds and H⋅⋅⋅F contacts. Co-crystallization experiments for the analysis of preferred aryl-aryl-interactions led to 1 : 1 complexes. Intermolecular phenyl-perfluorophenyl interactions with short centroid-centroid distances are dominating these co-crystal structures. They lead to melting point increases of up to 49 °C for the co-crystals compared to the pure substances.

Chalice-Type Tridentate Silicon Lewis Acids of C3 Symmetry in a Single Step Starting from Hexadehydrotribenzo[12]annulene

Tridentate Lewis acids with aligned functions were synthesized based on the rigid framework hexadehydrotribenzo[12]annulene. The backbone and its fluorinated analogue were synthesised in one-pot syntheses, with alkyne deprotection and Sonogashira cross coupling reaction being carried out in one step. Hydrosilylation of the annulene with chlorohydrosilanes proceeded highly selectively and afforded rigid poly-Lewis acids with three SiCl3 or SiCl2 Me substituents perfectly oriented to one side of the molecule in a single step. The progress of hydrosilylation was investigated by time-correlated NMR spectroscopic studies. The crystal structures show that the framework is symmetrically functionalised and the silyl substituents are aligned in one direction. To increase the acidity of the Lewis acids the chlorosilyl substituents were fluorinated with SbF3 . Further investigation of hydrometallation reactions (M=B, Al, Ga, Sn) did not lead to corresponding structures.

Inter- and Intramolecular Aryl-Aryl Interactions in Partially Fluorinated Ethylenedioxy-bridged Bisarenes*

Several ethylenedioxy‐bridged bisarenes with a variety of type and number of aryl groups were synthesized to study non‐covalent dispersion‐driven inter‐ and intramolecular aryl–aryl interactions in the solid state and gas phase. Intramolecular interactions are preferably found in the gas phase. DFT calculations with and without dispersion correction show larger interacting aromatic groups increase the stabilization energy of folded conformers and decrease the intermolecular centroid–centroid distance. Single‐molecule structures generally adopt folded conformations with short intramolecular aryl–aryl contacts. Gas electron diffraction experiments were performed exemplarily for 1‐(pentafluorophenoxy)‐2‐(phenoxy)ethane. A new procedure for structure refinement was developed to deal with the conformational complexity of such molecules. The results are an experimental confirmation of the existence of folded conformations of this molecule with short intramolecular aryl–aryl distances in the gas phase. Solid‐state structures are dominated by stretched structures without intramolecular aryl–aryl interactions but interactions with neighboring molecules.

London dispersion-driven hetero-aryl-aryl interactions in 1,2-diaryldisilanes

Non-covalent aryl-aryl interactions for the molecular structures of three 1,2-diaryltetramethyldisilanes X5C6-(SiMe2)2-C6Y5 (X ≠ Y; X, Y = H, F, Cl) were studied by single crystal X-ray and gas electron diffraction as well as by SAPT calculations. Aryl-aryl interactions cause all to adopt exclusively rather untypical eclipsed syn-conformers in the gas phase, and C6F5-(SiMe2)2-C6Cl5 also in the solid state.

Aryl-Aryl Interactions in (Aryl-Perhalogenated) 1,2-Diaryldisilanes

Three 1,2-diaryltetramethyldisilanes X5 C6 -(SiMe2 )2 -C6 X5 with two C6 H5 , C6 F5 , or C6 Cl5 groups were studied concerning the importance of London dispersion driven interactions between their aryl groups. They were prepared from 1,2-dichlorotetramethyldisilane by salt elimination. Their structures were determined in the solid state by X-ray diffraction and for free molecules by gas electron-diffraction. The solid-state structures of the fluorinated and chlorinated derivatives are dominated by aryl-aryl interactions. Unexpectedly, Cl5 C6 -(SiMe2 )2 -C6 Cl5 exists exclusively as an eclipsed syn-conformer in the gas phase with strongly distorted Si-C6 Cl5 units due to strong intramolecular interactions. In contrast, F5 C6 -(SiMe2 )2 -C6 F5 reveals weaker interactions. The contributions to the total interaction energy were analyzed by SAPT calculations.