An official website of the United States government
Abstract Reaction of {LiC6H2−2,4,6‐Cyp3⋅Et2O}2(Cyp=cyclopentyl) (1) of the new dispersion energy donor (DED) ligand, 2,4,6‐triscyclopentylphenyl with SnCl2afforded a mixture of the distannene {Sn(C6H2−2,4,6‐Cyp3)2}2(2), and the cyclotristannane {Sn(C6H2−2,4,6‐Cyp3)2}3(3).2is favored in solution at higher temperature (345 K or above) whereas3is preferred near 298 K. Van't Hoff analysis revealed the3to2conversion has a ΔH=33.36 kcal mol−1and ΔS=0.102 kcal mol−1 K−1, which gives a ΔG300 K=+2.86 kcal mol−1, showing that the conversion of3to2is an endergonic process. Computational studies show that DED stabilization in3is −28.5 kcal mol−1per {Sn(C6H2−2,4,6‐Cyp3)2unit, which exceeds the DED energy in2of −16.3 kcal mol−1per unit. The data clearly show that dispersion interactions are the main arbiter of the3to2equilibrium. Both2and3possess large dispersion stabilization energies which suppress monomer dissociation (supported by EDA results).
more »
« less
1,3,5–2,4,6‐Functionalized Benzene Molecular Cage: An Environmentally Responsive Scaffold that Supports Hierarchical Superstructures
Abstract New stimulus‐responsive scaffolds are of interest as constituents of hierarchical supramolecular ensembles. 1,3,5–2,4,6‐Functionalized, facially segregated benzene moieties have a time‐honored role as building blocks for host molecules. However, their user as switchable motifs in the construction of multi‐component supramolecular structures remains poorly explored. Here, we report a molecular cage 1, which consists of a bent anthracene dimer3paired with 1,3,5‐tris(aminomethyl)‐2,4,6‐triethylbenzene2. As the result of the pH‐inducedababab↔bababaisomerization of the constituent‐functionalized benzene units derived from2, this cage can reversibly convert between an open state and a closed form, both in solution and in the solid state. Cage 1was used to create stimuli‐responsive hierarchical superstructures, namely Russian doll‐like complexes with [K⊂18‐crown‐6⊂1]+and [K⊂cryptand‐222⊂1]+. The reversible assembly and disassembly of these superstructures could be induced by switching cage 1from its open to closed form. The present study thus provides an unusual example where pH‐triggered conformation motion within a cage‐like scaffold is used to control the formation and disassociation of hierarchical ensembles.
more »
« less
- Award ID(s):
- 2304731
- PAR ID:
- 10576438
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 63
- Issue:
- 36
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Herein, the first report on the isolated and unambiguously proven benzene radical trianion is presented. This unprecedented radical oxidation state of benzene is stabilized through two trivalent rare earth (RE) metal cations each supported by a bis(guanidinate) scaffold. Specifically, the one‐electron chemical reduction of the neutral inverse‐sandwich yttrium complex [[{(Me3Si)2NC(NiPr)2}2Y]2(μ–ƞ6:ƞ6–C6H6)]1, containing a benzene dianion, with potassium graphite (KC8) in the presence of [2.2.2]‐cryptand yielded the title complex [K([2.2.2]‐cryptand)][[{(Me3Si)2NC(NiPr)2}2Y]2(μ–ƞ6:ƞ6–C6H6•)]2, featuring a benzene radical trianion. Analyses through single‐crystal X‐ray diffraction, EPR and UV–vis spectroscopy, elucidated its molecular structure and revealed strong [YIII–(C6H6)3–•–YIII] metal–radical interactions. Although the Y centers remain in the +3 oxidation state, the spin density of the unpaired electron resides primarily on the benzene trianion moiety and extends toward the YIIIions. Density functional theory (DFT) calculations on2corroborate this assignment and further suggest weak aromaticity for the benzene radical trianion.more » « less
-
ABSTRACT The pursuit of sustainable organic synthesis has renewed interest in photochemistry, as sunlight‐driven reactions provide eco‐friendly alternative methods. Although the relationships among structure, properties, and reactivity are well established for ground‐state molecules, the understanding of excited states and reactive intermediates, such as triplet and singlet arylnitrenes, remains limited. Herein, we investigated the properties of triplet and singlet 4‐nitrenopyridine‐1‐pyridine oxide (1N), 3‐nitrenopyridine‐1‐pyridine oxide (2N), and phenylnitrene (PhN) using density functional theory (DFT), complete active space self‐consistent field (CASSCF(10,9)), and complete active space second‐order perturbation theory (CASPT2(10,9)) calculations. Bond length analysis demonstrated that31Nand11N, as well as12Nand1PhN, exhibit significant imine biradical character, whereas the structures of32Nand3PhNare better described as benzene‐like. Nucleus‐independent chemical shift (NICS(0), NICS(1.7)ZZ) and anisotropy of induced current density (ACID) calculations were performed to compare the induced magnetic currents in these molecules. These analyses demonstrated that31Nis weakly aromatic, whereas32Nand3PhNare best described as having Baird aromaticity. In contrast, singlet nitrenes11N,12N, and1PhNare nonaromatic. In addition, irradiation of1in argon matrices verified that31Nreacts photochemically to form corresponding ketenimine1K. Finally, the absorption difference spectrum of31Nin a frozen 2‐methyltetrahydrofuran (mTHF) matrix exhibited resolved vibrational structure, suggesting the vibrational coupling to another electronic state. These insights into the structure and aromaticity of heterocyclic nitrenes could provide new avenues for modulating the reactivity of triplet ground state and triplet excited molecules.more » « less
-
Abstract 2,6‐Bis(pyrrol‐2‐yl)pyridines are important building blocks for supramolecular assemblies and photoluminescent main group and transition metal compounds. Sterically encumbered 2,6‐bis(5‐(2,4,6‐trimethylphenyl)‐3‐phenyl‐1H‐pyrrol‐2‐yl)pyridine, H2MesPDPPh, can adopt monomeric and dimeric structures in the solid state and in solution, controlled by competing inter‐ and intramolecular hydrogen bonds. Deprotonation in the presence of lithium cations provides Li2MesPDPPh, which can be isolated in monomeric and dimeric forms depending on solvent polarity. Protonation of H2MesPDPPhdisrupts intramolecular hydrogen bonding and provides the monomeric pyridinium salt [H3MesPDPPh]Cl. Independent of solvent polarity, all three derivatives exhibit intense fluorescence in solution. The absorption and emission spectra are highly sensitive to the level of protonation, which can be rationalized by the effects of (de)protonation on the HOMO and LUMO of the tricyclic π‐system.more » « less
-
2,4,6-Triaminopyrimidine is an interesting and challenging molecule due to the presence of multiple hydrogen-bond donors and acceptors. Its noncovalent interactions with a variety of carboxylic acids provide several supramolecular aggregates with frequently occurring molecular synthons. The present work focuses on the supramolecular interactions of 2,4,6-triaminopyrimidinium 3-(indol-3-yl)propionate–3-(indol-3-yl)propionic acid (1/1), C4H8N5+·C11H10NO2−·C11H11NO2, (I), 2,4,6-triaminopyrimidinium 2-(indol-3-yl)acetate, C4H8N5+·C10H8NO2−, (II), 2,4,6-triaminopyrimidinium 5-bromothiophene-2-carboxylate, C4H8N5+·C5H2BrO2S−, (III), and 2,4,6-triaminopyrimidinium 5-chlorothiophene-2-carboxylate, C4H8N5+·C5H2ClO2S−, (IV). All four salts exhibit robust homomeric and heteromericR22(8) ring motifs. Salts (I) and (II) develop sextuple [in (I)] and quadruple [in (I) and (II)] hydrogen-bonded arrays through fused-ring motifs. Salt (II) exhibits a rosette-like architecture. Salt (IV) is isostructural and isomorphous with salt (III), exhibiting an identical crystal structure with a different composition and an identical supramolecular architecture. In salts (III) and (IV), a linear hetero-tetrameric motif is formed and, in addition, both salts exhibit halogen–π interactions which enhance the crystal stability. All four salts develop a supramolecular hydrogen-bonded pattern facilitated by several N—H...O and N—H...N hydrogen bonds with multiple furcated donors and acceptors.more » « less
