Reactivity of Organolithium Reagents to 2,3,4,5-Tetraphenylcyclopentadienone and Crystal Structures of Addition Products

The conjugate addition reactions of four organolithium reagents to 2,3,4,5-tetraphenylcyclopentadienone (tetracyclone) were investigated to reveal the reactivity of organolithium reagents to tetracyclone. The results show that 1,2-addition products 2,3,4,5-tetraphenyl-1-(2-thienyl)-2,4-cyclopentadien-1-ol(1), 1-n-butyl-2,3,4,5-tetraphenyl-2,4-cyclopentadien-1-ol(2) and 1,2,3,4,5-pentaphenyl-2,4-cyclopentadien-1-ol(3) were synthesized in excellent yields while tetracyclone reacted with 2-thienyllithium, n-butyllithium and phenyllithium, respectively. Interestingly, three 1,2-, 1,4- and 1,6-addition isomers 1-tert-butyl-2,3,4,5-tetraphenyl-2,4-cyclopentadien-1-ol(4), 4-tert-butyl-2,3,4,5-tetraphenyl-2-cyclopenten-l-one(5) and 2-tert-butyl-2,3,4,5-tetraphenyl-3-cyclopenten-l-one(6), were simultaneously obtained by the conjugate addition reaction of tert-butyllithium with larger steric hindrance to tetracyclone. Compounds 1-6 were characterized by ¹H and ¹³C NMR spectra, Fourier transform infrared(FTIR) spectra and mass spectra(MS). The crystal and molecular structures of compounds 1, 2 and isomers 5, 6 were determined by X-ray single crystal diffraction technique. The results imply that the steric hindrance of tert-butyllithium probably play a key role in controlling the conjugate addition reaction. The conjugate addition mechanism of organolithium reagents to tetracyclone was proposed.     

Metal coordination architectures of N-acyl-salicylhydrazides: The effect of metal ions and steric repulsion of ligands to their structures of polynuclear metal complexes

Three polynuclear transition metal complexes [Mn₈(DMF)₈(L1)₈] · 4DMF (1), [Mn₆(DMF)₆(L2)₆] · [Mn₆(DMF)₄(H₂O)₂(L2)₆] · 2DMF (2), [Cu₃(L3)₂(py)₂] (3) of the pentadentate ligands N-acyl-salicylhydrazides were synthesized and characterized, their crystal structures were investigated. The oxidation state and properties of the central metal ions are important in crystal structure formation, trivalent Mn(III) ion which easily form stable octahedral coordination metallamacrocycle complexes, metallacrowns 1 and 2 were obtained; while bivalent Cu(II) ion is easier to form square planar, trinuclear complexes 3 was obtained. The steric effect of the N-acyl side chains also plays an important role in the structures of these polynuclear complexes. The magnetic property of 1 was also investigated.     

Sol–gel transitions of sodium montmorillonite dispersions by cationic end-capped poly(ethylene oxides) (surface modification of bentonites, IV)

Poly(ethylene oxides), PEO, end-capped with hexadecyl dimethylammonium, HDDMA⁺, and trimethylammonium hexyldimethylammonium, THA²⁺, changed distinctly the sol–gel transition of sodium montmorillonite dispersions. In the presence of HDDMA⁺-PEO 1,500 and 4,000, domains of sol with increased salt tolerance (c _k=550–1,000 mmol NaCl/l) were found at high polymer and low montmorillonite contents. The corresponding PEO of higher molar mass (20,000 and 35,000) led to extended fields of flocs. THA²⁺-PEO 1,500 formed attractive gels at polymer concentrations >2–5 g/l and montmorillonite contents >0.5%. These gels showed very high yield values. THA²⁺-PEO of higher molar mass acted as stabilizing agents. The salt tolerance was highest (300–750 mmol/l) in the presence of THA²⁺-PEO 20,000. The observed sol–gel diagrams reveal the interplay between polymer end-group fixation on the clay mineral particles, polymer conformation, and colloidal stabilization and destabilization mechanisms.

Synthesis and Characterization of [(1-benzylpyrazole) [<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-bis(2-aminoethyl)-1,2-ethanediamine]copper(II)] Diperchlorate,a Structure with a Sterically Strained,Distorted-Trigonal-Bipyramidal Cation

Abstract  The synthesis, characterization, and molecular structure of the title compound, [(1-benzylpyrazole)[N,N-bis(2-aminoethyl)-1,2-ethanediamine]copper(II)] diperchlorate, [(nbp)(tren)Cu(II)](ClO₄)₂, 2  · 2ClO₄, is reported. The salt crystallized in the monoclinic space group P2₁/n with a = 10.1453(5) ?, b = 17.5250(8) ?, c = 13.6021(6) ?, β = 100.737(19)° and V = 2376.06(19) ?³ with Z = 4. The structure contains copper(II) (nbp)(tren) cations, each with a distorted-trigonal-bipyramidal CuN₅ coordination geometry, separated by perchlorate anions. The cations exhibit steric strain associated primarily with close contacts between the methylene protons of the nbp ligand and one of the amine groups of the tren ligand. The strain has a noticeable effect on the coordination geometry and certain physical properties of the complex. Graphical Abstract  In the title structure, steric strain in the (nbp)(tren)Cu(II) cations, associated with close contacts between protons of the nbp ligand and two of the amine groups of the tren ligand (dashed lines in the figure below) affects certain physical properties of the cation and is consistent with an anomalously long Cu(II)–N(pyrazole) distance (Cu–N41) and an unusually large axial–equatorial angle, N41–Cu–N12.      

新型有机-无机杂化碱性介孔材料的合成——空间位阻对催化性能的影响

通过直接合成方法制备了2个二级胺功能化的SBA-15型有机-无机杂化碱性介孔材料. 粉末X射线衍射分析、氮气吸附-脱附和透射电镜表征表明, 合成的材料保持了SBA-15的有序介孔孔道结构, 而热重、红外光谱和元素分析表明有机功能团被成功引入. 在对硝基苯甲醛和丙酮的羟醛缩合反应中, 相对于一级胺功能化的材料, 二级胺功能化的SBA-15展示了极大改进的催化活性, 这可能是由于具有更大空间位阻效应的有机功能团的引入导致了碱性胺中心催化活性增强.     

Carbon-13NMR spectra of isomeric diazaphenanthrenes,II δ-Effects in sterically crowded methyl derivatives

Steric downfield shifts due to a -CH moiety and a -nitrogen lone pair are similar in methylated diazaphenanthrenes. Most probably steric distortions are responsible for the -effects observed, and this might be quoted as a further evidence for a nearly equal steric requirement of a hydrogen atom and a nitrogen lone pair.

---

C-13 NMR-Spektren isomerer Diazaphenanthrene, II. -Effekte in sterisch gehinderten Methylderivaten

Zusammenfassung Sterisch bedingte Tieffeldverschiebungen infolge von -CH-Molekülteilen und -lone pairs von Stickstoffatomen sind in methylierten Diazaphenanthrenen ähnlich. Die gemessenen -Effekte dürften auf sterische Deformationen zurückzuführen sein, was als weiteres Indiz für den nahezu gleichgroßen Raumbedarf eines Wasserstoffatoms und eines freien Elektronenpaars am Stickstoff gewertet werden kann.

     

Mechanochromic luminescence of soft crystals: Recent systematic studies in controlling the molecular packing and mechanoresponsive properties

Soft crystals are a class of smart materials that can switch their photophysical or mechanical properties in response to gentle external stimuli. A representative stimuli-responsive behavior of soft crystals is mechanochromic luminescence (MCL), i.e., a reversible color change of solid-state photoluminescence induced by external mechanical stimuli. Together with the rapid growth in the area of solid-state photoluminescence including fluorescence, room-temperature phosphorescence (RTP), thermally activated delayed fluorescence (TADF), white-light emission (WLE), and circularly polarized luminescence (CPL), a number of soft crystals that exhibit MCL behaviors have been reported during the past decade. In the typical MCL of soft crystals, the emission color switches in the bathochromic direction upon amorphization by grinding and recovers to the original color upon recrystallization by heating or exposure to organic solvents. Relatively few are known to exhibit hypsochromically shifted MCL, two-step MCL, self-recovering MCL, or mechanical-stimuli-induced single-crystal-to-single-crystal (SCSC) transitions. Rational design guidelines to control the mechanoresponsive properties of soft crystals have not yet been established. This review summarizes the systematic studies on the substituent effect to control the MCL properties of soft crystals. Recent studies provide useful insights into the effects of electronic and steric differences of substituents on crystal structure, luminescence properties, and mechanoresponsive behaviors.     

Convenient synthesis of selected meta- and ortho-substituted pentaarylpyridines via the Suzuki-Miyaura cross-coupling reaction

The first synthesis of sterically demanding, stable at room temperature atropisomeric derivatives of penta-(ortho-substituted phenyl)pyridines is described. The Suzuki-Miyaura cross-coupling reaction of pentabromopyridine and selected meta- and ortho-tolylboronic acids afforded a series of pentaarylpyridine derivatives. The structures of two room temperature stable atropisomeric derivatives of penta-(o-tolyl)pyridines were confirmed by single-crystal X-ray analysis. Racemic atropisomers were examined by ¹H NMR spectroscopy with a chiral solvating agent in order to visualize the presence of individual enantiomers.     

Blue-shifting intramolecular CH O(S) contacts in sterically strained systems

A group of model systems which may form chelate-type structures with intramolecular CH  Y (Y = O, S) contact is investigated computationally. The existence of several conformers permits to identify a reference molecule without the CH  Y intramolecular contact and to establish the blue-shifting character of this interaction. The CH stretching frequency in chelate forms is found to increase with respect to its value in the reference system. A parallel decrease of the CH bond distance is also established. The blue-shifting character of the intramolecular CH  Y contact is interpreted in terms of the sterically enforced repulsion between the hydrogen atom in CH and the electron donor Y. This interpretation is supported by the negative (repulsive) estimates of the energy contribution due to CH  Y contacts.