Aromaticity in stable tiara nickel thiolates: computational and structural analysis

Quantum chemical calculations as well as crystallographic analyses show that the Ni(n) rings in the tiara Ni thiolates, [NiS2]n and [Ni(SR)2]n (n = 3-6), have highly symmetric polygonal structures. We find that such structural features primarily arise from the effective delocalization of the d-orbital electrons across the Ni(n) rings leading to bond length equalization and thereby aromaticity. We introduce the d-orbital aromaticity for the first time to explain the experimentally observed polygonal structures of these cyclic metal rings bridged by thiol linkages.     

4-Silapiperidine and 4-silapiperidinium derivatives: syntheses and structural characterization

A series of novel 4-silapiperidine and 4-silapiperidinium derivatives, with two silicon-bound aryl groups and various N-organyl groups, have been synthesized and structurally characterized (solution ¹H, ¹³C, ¹⁹F, and ²⁹Si NMR spectroscopy; eight crystal structure analyses). These synthetic and structural investigations provide the basis for the development of novel silicon-based drugs containing a 4-silapiperidine or 4-silapiperidinium skeleton.     

Rigid nitronyl-nitroxide-labelled anchoring molecules: syntheses, structural and magnetic investigations

The syntheses of two rigid organic molecular rods bearing a nitronyl-nitroxide radical and a terminal nitrogen-based functionality like a pyridine or a cyano group are reported. Both new paramagnetic molecules are fully characterized, including crystal structure analysis. Furthermore their magnetic behaviours in the crystalline state are investigated and their spin concentration corroborate their excellent purity. While the pyridine functionalized rod is synthesized by converting the corresponding benzaldehyde to the phenyl-nitronyl-nitroxide radical, the synthesis of the cyano functionalized rod demonstrates the accessibility of highly sophisticated spin-labelled molecules via cross-coupling reaction with a meta-iodo-phenyl-nitronyl-nitroxide moiety.     

Aromatic core-modified twisted heptaphyrins[1.1.1.1.1.1.0]: syntheses and structural characterization

[reaction: see text] First examples of aromatic core-modified twisted heptapyrrolic systems with six meso links have been obtained via a general [3 + 4] acid-catalyzed condensation method. Despite the twisted conformation, these heptaphyrins exhibit aromaticity in solution, unlike most of the all-aza analogues.     

Tethered dithiacyclopropenones. syntheses and structural properties of tetrathiacyclopropenonophanes

The reaction of the cyclic tetrathiadiynes 4(m.n) (where m and n indicate the number of methylene groups between the dithiaacetylene units) with sodium trichloroacetate and subsequent hydrolysis of the gem-dichlorocyclopropenes afforded the mono- and biscyclopropenone derivatives 5(m.n) and 6(m.n) in moderate yields. Investigation of the X-ray crystal structures revealed small torsion angles between the CH(2)-S bond and the C-C double bond, indicating conjugation between the sulfur 3p lone pair and the cyclopropenone ring. The maintenance of the conjugation determines the secondary structure of both (5, 6) ring systems.     

Hydrothermal syntheses and structural characterization of two sandwich-type arsenotungstates

Two new organic–inorganic composite sandwich-type arsenotungstates [H₂dap]₆H₈[Ni₄(H₂O)₂(B-α-AsW₉O₃₄)₂]₂ · 33H₂O (1) and {[Ni(dap)₂(H₂O)]₂[Ni(dap)₂]₂[Ni₄(Hdap)₂(B-α-AsW₉O₃₄)₂]} · 4H₂O (2) (dap = 1,2-diaminopropane) have been hydrothermally synthesized by reaction of Na₈[A-α-HAsW₉O₃₄] · 11H₂O with NiCl₂ · 6H₂O in the presence of 1,2-diaminopropane and characterized by elemental analysis, IR spectra, X-ray single-crystal diffraction, and thermogravimetric analysis. 1 crystallizes in the triclinic P 1 space group with a = 16.351(6) Å, b = 16.423(6) Å, c = 19.894(7) Å, α = 110.630(6)°, β = 92.684(7)°, γ =104.946(7)°, V = 4774(3) ų, Z = 1, GOOF = 1.033, R ₁ = 0.0517, wR ₂ = 0.1086. 2 also crystallizes in the triclinic P 1 space group with a = 13.305(4) Å, b = 13.882(4) Å, c = 17.031(5) Å, α = 68.109(5)°, β = 71.511(4)°, γ = 88.407(5)°, V = 2753.5(14) ų, Z = 1, GOOF = 1.051, R ₁ = 0.0491, wR ₂ = 0.1150. Notably, 1 is a discrete structure, composed of two tetra-Ni^II substituted sandwich-type polyoxoanions [Ni₄(H₂O)₂(B-α-AsW₉O₃₄)₂]^10? with different spatial orientation, whereas 2 displays a organic–inorganic composite 2-D sheet architecture constructed by tetra-Ni^II sandwiched [Ni₄(H₂O)₂(B-α-AsW₉O₃₄)₂]^10? units by means of [Ni(dap)₂]²⁺ bridges. Some previously reported transition-metal-substituted sandwich-type polyoxotungstates have been summarized.     

Figure-eight aromatic core-modified octaphyrins with six meso links: syntheses and structural characterization

The synthesis and structural characterization of the first examples of aromatic core-modified figure-eight octaphyrins with six meso links and their formation with and without acid catalysts are highlighted.     

26pi aromatic core-modified hexaphyrins: syntheses, characterization, and structural diversities

Synthesis and characterization of several 26pi core-modified hexaphyrins are reported. The synthetic methodology involved a well-known acid-catalyzed MacDonald-type condensation reaction of the required tripyrrane with electron deficient pentafluorobenzaldehyde. The nature of the product and yield depends on the nature of the acid catalyst and its concentration. Dioxahexaphyrin 9 was isolated only when 0.5 equiv of TFA was used as a catalyst, while dithiahexaphyrin 10 and diselenahexaphyrin 11 were formed with TFA, PTSA, and even in the absence of catalyst. The detailed 1H and 2-D COSY as well as HSQC experiments reveal the solution structure as well as the conformational mobility of hexaphyrins. In the tetracationic state, 10 and 11 exhibit a four heterocyclic ring inverted structure, while only two completely inverted heterocyclic rings were observed for 9. The other four heterocyclic rings are only partially inverted in 9. All the hexaphyrins reported here show aromatic character inferred from large Deltadelta values (difference in chemical shift between the most shielded and the most deshielded protons). Electronic absorption spectral studies also support the conformational changes observed upon protonation.     

Synthesis of selenolates from stannyl and silyl alkylselenides

Stannyl and silyl alkylselenides have been efficiently transformed to the corresponding alkylselenolates on reaction with butyllithiums. Other conditions proved to be limited.     

Cyclopentadienylaluminum thiolates - synthesis and structure

The dicyclopentadienylaluminum thiolates [Cp₂Al(μ-SR)]₂, where R = Et (1), ⁱPr (2), were obtained by reacting Cl₂AlSR with CpNa at the molar ratio 1:2, respectively. Use of CpLi instead of CpNa at the same molar ratio of reagents leads to the formation of cyclopentadienyl(chloro)aluminum thiolates [Cp(Cl)Al(μ-SR)]₂, exclusively, where R = Et (3), ⁱPr (4), ⁱBu (5), and ⁿBu (6). The compounds were characterized by ¹H, ¹³C, and ²⁷Al NMR spectroscopy. The structures of the compounds 1 and 4 were determined by X-ray crystallography.     

Total syntheses of spiroviolene and spirograterpene A: a structural reassignment with biosynthetic implications

The recent natural product isolates spiroviolene and spirograterpene A are two relatively non-functionalized linear triquinane terpenes with a large number of structural homologies. Nevertheless, three significant areas of structural disparity exist based on their original assignments, one of which implies a key stereochemical divergence early in their respective biosyntheses. Herein, using two known bicyclic ketone intermediates, a core Pd-catalyzed Heck cyclization sequence, and several chemoselective transformations, we describe concise total syntheses of both natural product targets and propose that the structure of spiroviolene should be reassigned. As a result, these natural products possess greater homology than previously anticipated.

Concise syntheses of spiroviolene and spirograterpene A have been achieved from a common intermediate, indicating a structure revision of one is necessary along with implications for its biosynthesis.     

Four triarylantimony(V) carboxylates: syntheses,structural characterization and in vitro cytotoxicities

Four new organoantimony carboxylates, (R–COO)₂SbR′₃ [R–COOH = (±)-2-phenoxypropionic acid and R′ = phenyl (1), 4-fluorophenyl (2), 3-fluorophenyl (3), 3,4,5-trifluorophenyl (4)], were synthesized and structurally characterized by elemental analysis, ¹H, ¹³C NMR, IR and X-ray single crystal diffraction. Structural analyses reveal that 1–3 show similar five-coordinate trigonal bipyramidal geometries, binding with three aryl groups and two deprotonated unidentate ligands. Unexpectedly, 4 exhibits pentagonal bipyramidal arrangement accompanied by two Sb–O (carbonyl) coordination bonds. In vitro cytotoxic activities of 1–4 have been determined by the MTT method against four cancer cell lines. Studies reveal that 1–4 have an activity similar to cisplatin on lung cancer cell line A549 and but also exhibit excellent cytotoxicity against cisplatin-insensitive colon cancer cell lines HCT-116, Caco-2 and human promyelocytic leukemia cell line HL-60. Additionally, the results showed that most of these triarylantimony(V) complexes exhibited enhanced cytotoxicity compared with the ligand and four triarylantimony dichloride precursors, which clearly implied a positive synergistic effect. Also interestingly, it was found that 3- or 4- mono-fluoro-substituted triphenylantimony, compounds 2 and 3, exhibit higher in vitro cytotoxicities toward the four cancer cell lines than the tri-3,4,5-trifluoro-substituted and without-fluoro-substituted triphenylantimony complexes. The structure-activity relationship of the cytotoxicity of 1–4 is discussed.     

Sterically stabilized cyclopropenonophanes and an electronically stabilized cyclopropenethionophane: syntheses, structural properties, and reactivity

The syntheses of sterically stabilized cyclopropenonophanes as well as an electronically stabilized cyclopropenethionophane are reported, and their molecular structures in the solid state are elucidated. The sulfur of the CS moiety in cyclopropenethiones was shown to react as a nucleophile. Temperatures of more than 240 degrees C favor the extrusion of CO in the cyclopropenonophane to afford an alpha,alpha'-tetramethyl-substituted cyclodiyne. [reaction: see text]     

Thiolates, selenolates, and tellurolates of the s-block elements

The potential of alkali and alkaline earth metal chalcogenolates in synthetic chemistry and various technical applications has sparked the recent interest in the chemistry of alkali and alkaline earth metal thiolates, selenolates and tellurolates. As a result, an increasing body of work concerned with exploring synthetic routes to the target compounds, analyzing the influence of metal, ligand and donor on the structural chemistry, and correlating structure and function has appeared in the literature, most of which during the last few years. This article describes recent trends in this area of alkali and alkaline earth chemistry, by discussing synthetic access routes, analyzing structure determining factors such as metal, donor and ligand influence, comparing structural similarities and disparities in alkali and alkaline earth chemistry, and discussing structure–function relationships.     

Synthesis and reactivity of cyclopentadienyl iron complexes containing ferrocenyl selenolates

New homo-trimetallic complexes of general formula?1,1??-fc[SeFeCp(CO)₂]₂ (fc?=?Fe(??⁵-C₅H₄)₂) are accessible in high yield by the reaction of 1,1??-fc(SeLi)₂, which is generated from 1,1??-fc(SeSiMe₃)₂ and n-BuLi, with two equivalents of CpFe(CO)₂I. Photolytic CO-substitution reactions of the organoiron diselenolate with bis-phosphines at ?50?°C using 1:2 (metal/ligand) molar ratio afforded 1,1??-fc(SeFeCp(P^P)₂. All these complexes were characterized by physicochemical and spectroscopic methods.     

Facile syntheses, structural characterizations, and isomerization of disiloxane-1,3-diols

In the hydrolysis reaction of dichlorosilanes having an intramolecular coordinating atom, dcisiloxane-1,3-diols, [(OH){o-(CH₃)₂NCH₂-C₆H₄}RSi]₂O(R=CH₂CH (1), C₆H₅ (2), o-(CH₃)₂NCH₂C₆H₄ (3), Me (4)), were obtained in high yields. The results of the crystal structure analyses of meso-2, rac-2a, rac-2b and 3 are reported. They showed strong intramolecular hydrogen bondings between the hydroxy group and the nitrogen atom. We have also found that the diastereomeric isomerization of meso-2 to rac-2 in CDCl₃ solvent containing moisture occurred to result in the 55:45 equilibrium mixtures of the isomers and vice versa.     

Erbium-formate frameworks templated by diammonium cations: syntheses, structures, structural transition and magnetic properties

Two structurally different Er-formate frameworks, one NaCl-like [dmenH(2)][Er(HCOO)(4)](2) (1) and the other pillared-layer type [tmenH(2)][Er(HCOO)(4)](2) (2), were obtained when templated by the corresponding protonated N,N'-dimethylethylenediamine (dmenH(2)) and N,N,N',N'-tetramethyl- ethylenediamine (tmenH(2)). The shape and size of the template cations dictate the different coordination geometries of erbium and consequently the framework topologies, though erbium adopts eight coordination in the two compounds. In the NaCl-like structure of 1, erbium is coordinated by eight anti-anti bridging formates in a square antiprism, while in the pillared-layer structure of 2, it is coordinated by six anti-anti bridging formates and one chelating formate in a pentagonal bipyramid. 2 exhibits a structural phase transition around -70 °C which is related to the disorder-order transition of the template cation. Both compounds behave as paramagnets between 2 and 300 K. However, they display field-dependent ac-susceptibilities with complicated field-induced magnetic relaxation processes, and the major slow ones probably results from spin-lattice relaxation.     

新型二茂稀土烃硫基配合物的合成与表征

本文用三茂基稀土[(C~5H~5)~3Ln(Ln=Ho(1)，Yb(2)，La(3)，Y(4)]与等摩尔的2-巯基嘧啶(HSC:NCH:CHCH:N·)在四氢呋喃溶剂中于室温下反应，合成了四个对空气敏感的二茂稀土嘧啶巯基配合物。产物经元素分析、红外光谱及质谱鉴定确定其组成为：(C~5H~5)~2LnSC:NCH:CHCH:N·THF[Ln=Ho(1)，Yb(2)，La(3)，Y(4)]。