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A new series of [Pd2(L)4] cages based on photochromic dithienylethene (DTE) ligands allowed us to gain insight into the successive photoswitching of multiple DTE moieties in a confined metallo-supramolecular assembly. Three new X-ray structures of [Pd2(o-L4)4], [Pd2(o-L1)2(c-L1)2] and [Pd2(c-L1)4] (o-L and c-L = open and closed forms of DTE ligands, respectively) were obtained. The structures deliver snapshots of three different combinations of DTE photoisomeric states within the cage, facilitating a comparison of the all-open with the all-closed, and most notably, an intermediate form where open and closed switches co-exist in the same cage. Moreover, a series of spherical anionic borate clusters was introduced in order to study their roles in the light-controllable host–guest chemistry. The binding guests show higher affinities with the flexible open cage [Pd2(o-L1)4] than with the rigid closed cage [Pd2(c-L1)4]. For the [B12F12]2− guest, thermodynamic data obtained from NMR experiments was compared to results from isothermal titration calorimetry (ITC).
The isolation and structural characterization of the cyanido-substituted metalated ylides [Ph3P−C−CN]M (1-M; M=Li, Na, K) are reported with lithium, sodium, and potassium as metal cations. In the solid-state, most different aggregates could be determined depending on the metal and additional Lewis bases. The crown-ether complexes of sodium (1-Na) and potassium (1-K) exhibited different structures, with sodium preferring coordination to the nitrogen end, whereas potassium binds in an unusual η2-coordination mode to the two central carbon atoms. The formation of the yldiide was accompanied by structural changes leading to shorter C−C and longer C−N bonds. This could be attributed to the delocalization of the free electron pairs at the carbon atom into the antibonding orbitals of the CN moiety, which was confirmed by IR spectroscopy and computational studies. Detailed density functional theory calculations show that the changes in the structure and the bonding situation were most pronounced in the lithium compounds due to the higher covalency.
The rhodium(I) complex [Rh(κ3-P,O,P-Xantphos)(η2-PhC≡CPh)][BArF4] (ArF = 3,5-(CF3)2C6H4) is an effective catalyst for the cis-selective hydroboration of the alkyne diphenylacetylene using the amine-borane H3B·NMe3. Detailed mechanistic studies, that include initial rate measurements, full simulation of temporal profiles for a variety of catalyst and substrate concentrations, and speciation experiments, suggest a mechanism that involves initial coordination of alkyne and a saturation kinetics regime for amine-borane binding. The solid-state molecular structure of a model complex that probes the proposed resting state is also reported, [Rh(κ3-P,O,P-Xantphos)(NCMe)(η2-PhC≡CPh)][BArF4].
Two different chromophores, namely a dipolar and an octupolar system, were prepared and their linear and nonlinear optical properties as well as their bioimaging capabilities were compared. Both contain triphenylamine as the donor and a triarylborane as the acceptor, the latter modified with cationic trimethylammonio groups to provide solubility in aqueous media. The octupolar system exhibits a much higher two‐photon brightness, and also better cell viability and enhanced selectivity for lysosomes compared with the dipolar chromophore. Furthermore, both dyes were applied in two‐photon excited fluorescence (TPEF) live‐cell imaging.
Cyclic (amino)(aryl)carbenes (cAArCs) based on the isoindoline core were successfully generated in situ by α‐elimination of 3‐alkoxyisoindolines at high temperatures or by deprotonation of isoindol‐2‐ium chlorides with sodium or copper(I) acetates at low temperatures. 3‐Alkoxy‐isoindolines 2 a,b‐OR (R=Me, Et, iPr) have been prepared in high yields by the addition of a solution of 2‐aryl‐1,1‐diphenylisoindol‐2‐ium triflate (1 a,b‐OTf; a: aryl=Dipp=2,6‐diisopropylphenyl; b: Mesityl‐, Mes=2,4,6‐trimethylphenyl) to the corresponding alcohol (ROH) with NEt3 at room temperature. Furthermore, the reaction of 2 a,b‐OMe in diethyl ether with a tenfold excess of hydrochloric acid led to the isolation of the isoindol‐2‐ium chlorides 1 a,b‐Cl in high yields. The thermally generated cAArC reacts with sulfur to form the thioamide 3 a. Without any additional trapping reagent, in situ generation of 1,1‐diphenylisoidolin‐3‐ylidenes does not lead to the isolation of these compounds, but to the reaction products of the insertion of the carbene carbon atom into an ortho C−H bond of a phenyl substituent, followed by ring‐expansion reaction; namely, anthracene derivatives 9‐N(H)aryl‐10‐Ph‐C14H8 4 a,b (a: Dipp; b: Mes). These compounds are conveniently synthesized by deprotonation of the isoindol‐2‐ium chlorides with sodium acetate in high yields. Deprotonation of 1 a‐Cl with copper(I) acetate at low temperatures afforded a mixture of 4 a and the corresponding cAArC copper(I) chloride 5 a, and allowed the isolation and structural characterization of the first example of a cAArC copper complex of general formula [(cAArC)CuCl].
The electron‐precise binary boron subhalide species [B\(_2\)X\(_6\)]\(^{2−}\) X=F, Br, I) were synthesized and their structures confirmed by X‐ray crystallography. The existence of the previously claimed [B\(_2\)Cl\(_6\)]\(^{2−}\), which had been questioned, was also confirmed by X‐ray crystallography. The dianions are isoelectronic to hexahaloethanes, are subhalide analogues of the well‐known tetrahaloborate anions (BX\(_4\)\(^−\)), and are rare examples of molecular electron‐precise binary boron species beyond B\(_2\)X\(_4\), BX\(_3\), and [BX\(_4\)]\(^−\).
Die elektronenpräzisen binären Borsubhalogenide [B\(_2\)X\(_6\)]\(^{2−}\) (X=F, Br, I) wurden synthetisiert und strukturell im Festkörper untersucht. Zudem konnte die vermutete Existenz von [B\(_2\)Cl\(_6\)]\(^{2−}\) mittels Röntgendiffraktometrie nachgewiesen werden. Diese Dianionen sind isoelektronisch zu den Hexahalogeniden des Ethans und können als Homologe des Tetrahalogenborat‐Anions BX\(_4\)\(^−\) betrachtet werden. Darüber hinaus gehören sie zu den seltenen Beispielen von elektronenpräzisen binären Borverbindungen (B\(_2\)X\(_4\), BX\(_3\), [BX\(_4\)]\(^−\)).
Eine effiziente, einstufige Synthese von 1,1,1‐Trialkylalkanen durch die sequenzielle, dehydrierende Borylierung und zweifache Hydroborierung von terminalen Alkinen mit Pinakolboran (HBpin) wurde unter Verwendung des kostengünstigen und einfach zugänglichen Kupfersalzes Cu(OAc)2 als Katalysator realisiert. Das Verfahren zeichnet sich durch ein breites Substratspektrum, eine außerordentliche Selektivität und eine hohe Toleranz gegenüber funktionellen Gruppen aus. Zudem kann die Reaktion ohne Ausbeuteverlust im Gramm‐Maßstab durchgeführt werden. Die somit erhaltenen 1,1,1‐Trialkylalkane können Anwendungen in der Herstellung von synthetisch wertvollen und bislang schwer zugänglichen α‐Vinylboronaten und zyklischen Boryl‐Verbindungen finden. Verschiedene Alkylgruppen können stufenweise über eine basenvermittelte deborylierende Alkylierung eingeführt werden, um racemische, tertiäre Alkylboronate herzustellen, die einfach in nützliche tertiäre Alkohole umgewandelt werden können.
The steric and electronic properties of aryl substituents in monoaryl borohydrides (Li[ArBH\(_3\)]) and dihydroboranes were systematically varied and their reactions with [Ru(PCy\(_3\))\(_2\)HCl(H\(_2\))] (Cy: cyclohexyl) were studied, resulting in bis(σ)‐borane or terminal borylene complexes of ruthenium. These variations allowed for the investigation of the factors involved in the activation of dihydroboranes in the synthesis of terminal borylene complexes. The complexes were studied by multinuclear NMR spectroscopy, mass spectrometry, X‐ray diffraction analysis, and density functional theory (DFT) calculations. The experimental and computational results suggest that the ortho‐substitution of the aryl groups is necessary for the formation of terminal borylene complexes.
The photophysical properties (absorption, fluorescence and phosphorescence) of a series of triarylboranes of the form 4-D-C\(_6\)H\(_4\)-B(Ar)\(_2\) (D=\(^t\)Bu or NPh\(_2\); Ar=mesityl (Mes) or 2,4,6-tris(trifluoromethylphenyl (Fmes)) were analyzed theoretically using state-of-the-art DFT and TD-DFT methods. Simulated emission spectra and computed decay rate constants are in very good agreement with the experimental data. Unrestricted electronic computations including vibronic contributions explain the unusual optical behavior of 4-\(^t\)Bu-C\(_6\)H\(_4\)-B(Fmes)\(_2\) 2, which shows both fluorescence and phosphorescence at nearly identical energies (at 77 K in a frozen glass). Analysis of the main normal modes responsible for the phosphorescence vibrational fine structure indicates that the bulky tert-butyl group tethered to the phenyl ring is strongly involved. Interestingly, in THF solvent, the computed energies of the singlet and triplet excited states are very similar for compound 2 only, which may explain why 2 shows phosphorescence in contrast to the other members of the series.