13-8-13-Membered Tricyclic Ladder-Type Siloxanes Hybridized with BINOLs: Synthesis, Characterization, and Fluorescence Sensing of Fluorides.

Developing fluorescent chemosensors with sensitivity and high specificity for recognizing fluorides is still challenging. Herein, four innovative compounds based on 13-8-13-membered tricyclic ladder-type siloxanes hybridized with BINOLs (abbreviated as TLS-BINOLs) were prepared through the B(C6F5)3-catalyzed Piers-Rubinsztajn reaction. The well-defined ladder-type structure of the TLS-BINOLs was determined by X-ray crystallographic analysis. Additionally, the fluorescent sensing ability of the TLS-BINOLs toward anions was studied. Our finding revealed that all four ladder-type compounds (TLS-BINOLs) exhibited high specificity in recognizing fluorides through fluoride-triggered structural decomposition. The detection limits for fluorides were determined to be 0.37, 0.35, 0.39, and 0.48 µM for the respective TLS-BINOLs. The nonemissive product induced by the fluorides was also determined using single-crystal X-ray diffraction analysis.

New Janus Tricyclic Laddersiloxanes: Synthesis, Characterization, and Reactivity.

The synthesis of four novel syn-type tricyclic laddersiloxanes bearing eight or six alkenyl groups is presented. These compounds possess reactive alkenyl groups on both the bridged and side silicon atoms, and their structures were determined through characterization using multinuclear 1D and 2D NMR spectroscopy, mass spectrometry, and elemental analysis techniques. To investigate their reactivity, the compounds were subjected to hydrosilylation using two different silanes, and the resulting fully hydrosilylated compounds were thoroughly analyzed. Remarkably, all the synthesized laddersiloxanes displayed high thermal stability, suggesting their potential as promising precursors for the development of new hybrid materials. Additionally, preliminary findings indicate the possibility of exploiting the reactivity difference between the alkenyl groups attached to the D- and T-unit silicon atoms for the synthesis of Janus molecules. These findings highlight the potential of the reported compounds as valuable building blocks in the construction of innovative materials.

Synthesis of Octachloro- and Octaazido-Functionalized T8-Cages and Application to Recyclable Palladium Catalyst.

Unprecedented T8-cages bearing eight chloromethyldimethylsilylethyl substituents were obtained in excellent yield from the readily and commercially available octavinylsilsesquioxane. The chloro groups can be quantitatively substituted by azido ones to yield the corresponding octaazido T8 without rearrangement of the cage. The syntheses of both functionalizable POSSs are scalable (gram-scale). The azido-functionalized T8 compound constitutes a versatile building block able to undergo copper-catalyzed azide-alkyne [3 + 2] cycloaddition. As a proof of concept, it was allowed to react with 2-ethynylpyridine to give rise to a multidentate ligand bearing eight 2-pyridyl-triazole moieties (N,N-pincers). The coordination of the eight N,N-bidentate ligands to palladium(II) led to the corresponding octa-palladium complex shown to successfully promote the coupling reaction between anisole and phenylboronic acid. The low solubility of this catalytic complex in the reaction medium enabled (or facilitated or made possible) its straightforward recovery and recycling with four cycles with no loss of activity.

Synthesis of Tricyclic Laddersiloxane with Various Ring Sizes (Bat Siloxane).

A new synthetic method for tricyclic laddersiloxanes, ladder-type silsesquioxanes with defined structures, is developed based on intramolecular cyclization of hydrosilyl-functionalized cyclic siloxanes. This method enables the construction of unprecedented laddersiloxanes with various ring sizes. Herein, the preparation of tricyclic laddersiloxanes containing 6-8-6-, 8-8-8-, or 12-8-12-membered-ring systems is reported. These products can be considered as bat-shape siloxanes, owing to their rigid inorganic siloxane body with flexible oligosiloxane "wings" as side rings. The synthesized compounds are potential building blocks for well-defined nanomaterials, porous materials, and host molecules.

Synthesis of Tetrachloro, Tetraiodo, and Tetraazido Double-Decker Siloxanes.

A convenient and scalable (gram-scale) route to unprecedented T8D2-double-decker siloxanes (DDSQs) bearing four chloro (3b) or four azido (5b) groups is reported. Both compounds were characterized and proved to undergo successful nucleophilic substitution for 3b (with iodide or azide) and copper-catalyzed azide-alkyne [3 + 2] cycloaddition for 5b. All of these transformations occurred under mild conditions, and the corresponding DDSQs were prepared in very high yields. Beyond the enhanced multivalency as compared to the previously described disubstituted D2T8 structures, the reported tetrafunctional DDSQs are formed as a single isomer and readily isolated in very high yields. Moreover, the tetra-azido DDSQ 5b constitutes a multipurpose nanobuilding block for the further preparation of new inorganic-organic hybrid materials where the covalent incorporation of a DDSQ moiety brings valuable properties.

Synthesis, Structures, and Thermal Properties of Symmetric and Janus "Lantern Cage" Siloxanes.

Symmetric and asymmetric (Janus-type) new "lantern cage" siloxanes (PhSiO1.5 )4 (Me2 SiO)4 (RSiO1.5 )4 (R=Ph or iBu) were synthesized through reaction of all-cis-[PhSi(OSiMe2 Br)O]4 with all-cis-[RSi(OH)O]4 (R=Ph or iBu). These precursors were obtained by facile two or three-step reactions from commercially available compounds. The spectroscopic properties of the resulting products were fully characterized and they showed high thermal stability and sublimation without decomposition. The crystal structures clearly indicated that the internal vacancy volumes of the lantern cages are considerably larger than that of octaphenylsilsesquioxane (PhSiO1.5 )8 . DFT calculations of the lantern cage showed a distinctly different electronic state from that of octasilsesquioxane. These results suggest that lantern cage siloxanes have a characteristic "field" in the molecule.

Synthesis, Characterization, and Functionalization of Tetrafunctional Double-Decker Siloxanes.

Novel tetravinyl- and tetraallyl-substituted closed double-decker siloxanes (DDSQs) were synthesized and characterized, and their structures were elucidated by X-ray crystallographic analysis. Moreover, it was shown that peripheral olefins could successfully undergo hydrosilylation quantitatively. Such tetrafunctionalizable DDSQs (DDSQ-Vinyl4 and DDSQ-Allyl4) thus constitute promising building blocks for more complex inorganic-organic hybrid materials.

Lithium-Templated Formation of Polyhedral Oligomeric Silsesquioxanes (POSS).

A coordination complex, lithium hepta(i-butyl)silsesquioxane trisilanolate (1; Li-T7), a stable intermediate in silsesquioxane (SQ) syntheses, was successfully isolated in 65% yield and found to be highly soluble in nonpolar solvents such as hexane. The structure of Li-T7 was confirmed by NMR, IR spectroscopy, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, electrospray ionization mass spectrometry, and computational simulation, providing detailed elucidation of the intermolecular self-association of the SQ cage with a box-shaped Li6O6 polyhedron through strong coordination bonds. After acid treatment, Li-T7 undergoes lithium-proton cationic exchange, yielding hepta(i-butyl)silsesquioxane trisilanol (2; H-T7) quantitatively. The high yield of H-T7 seems to be influenced by Li-O bonding in the Li-T7 complex that affects the selective formation of hepta(i-butyl)silsesquioxane trisilanolate and the bulky i-butyl groups which may prevent decomposition or SQ cage-rearrangement even at reflux under alkaline conditions. Single-crystal X-ray crystallography confirms the presence of the dumbbell-shaped SQ partial cages through strong intermolecular hydrogen bonds. Interestingly, lowering the polarity of the reaction solution by adding dichloromethane results in formation of the cubic octa(i-butyl)silsesquioxane (3; T8) cage in a good yield (47%), which is isolated by crystallization from the reaction solution.

Synthesis and Characterization of Unsymmetrical Double-Decker Siloxane (Basket Cage).

The one-pot synthesis of an unsymmetrical double-decker siloxane with a novel structure via the reaction of double-decker tetrasodiumsilanolate with 1 equiv. of dichlorotetraphenyldisiloxane in the presence of an acid is reported herein for the first time. The target compound bearing all phenyl substituents on the unsymmetrical siloxane structure was successfully obtained, as confirmed by 1H-NMR, 13C-NMR, 29Si-NMR, IR, MALDI-TOF, and X-ray crystallography analyses. Additionally, the thermal properties of the product were evaluated by TG/DTA and compared with those of other siloxane cage compounds.

Janus-Cube Octasilsesquioxane: Facile Synthesis and Structure Elucidation.

A perfect "Janus-cube" octasilsesquioxane, a nanometer-scale Janus particle with two different types of substituents, was synthesized through the cross-coupling of a "half-cube" cyclic sodium siloxanolate with another half-cube cyclic fluorosiloxane. The structure was confirmed by X-ray crystallography to be a Janus cube. The overall synthesis is simple and does not require drastic separation methods compared with previous methods. The synthesis of the Janus cube demonstrates a novel siloxane bond-forming reaction involving the coupling a silanol salt and fluorosilane. The reaction is mild, does not result in acid generation, and could be applied to the construction of other novel siloxane compounds.

Synthesis and characterization of sulfide/sulfone-containing 18-8-18-membered-ring ladder-type siloxanes.

Innovative macrocyclic 14-membered molecule (5) and tricyclic 18-8-18-membered-ring ladder-type siloxane-based compound (7), with sulfide units inserted in the backbone were prepared through B(C6F5)3-catalyzed Piers-Rubinsztajn reaction. Further oxidation of 5 and 7 with m-CPBA enables the synthesis of the novel sulfonyl-containing cyclic and ladder-type compound (8 and 9) in high yields. Both tricyclic ladder-type products (7 and 9) show superior thermostability and their well-defined syn-type structures were determined by X-ray crystallographic analysis. The compounds 7 and 9 may become promising building blocks for various new materials.

BINOL and triazole-containing Janus rings and 29-8-29-membered tricyclic ladder-type hybridized siloxane: application in the fluorescence sensing of anions.

Tetrachloro- and tetraazide-substituted all-cis-tetraphenylcyclotetrasiloxanes (all-cis-T4) 2 and 3 were synthesized in high yields and were fully characterized. Then the precursor 3 underwent CuAAC click reaction with monopropargyl BINOL 4 and dipropargyl BINOL 6 to give the novel BINOL and triazole-containing all-cis-T4 cyclic siloxane 5 and the 29-8-29-membered-ring ladder-type hybrid siloxane 7. The sensing ability of compounds 5 and 7 towards anions was studied as well, and it was observed that 7 could selectively recognize iodides through synergistic C-H⋯I hydrogen bonding, resulting in an impressive fluorescence quenching with a Ksv of 8.10 × 104 M-1.

Vinyl-Functionalized Janus Ring Siloxane: Potential Precursors to Hybrid Functional Materials.

A vinyl-functionalized all-cis-tetrasiloxycyclotetrasiloxane [ViSi(OSiMe2H)O]4 (Vi = vinyl group) Janus precursor was prepared from potassium cyclotetrasiloxane silanolate. The Janus precursor was selectively modified at its dimethylhydrosilyl groups [-SiMe2H] via the Piers-Rubinsztajn reaction to obtain a family of new tetravinyl-substituted Janus rings [ViSi(OR')O]4 containing various functional groups in moderate yields. Remarkably, the tetravinyl groups on the structure remained intact after modification by the Piers-Rubinsztajn reaction. Since these synthesized compounds possess multiple functional groups (up to eight per molecule), they are potential precursors for advanced hybrid organic-inorganic functional materials.

Synthesis and characterization of tetrathiol-substituted double-decker or ladder silsesquioxane nano-cores.

Tetra(3-mercaptopropyl)-silsesquioxanes with double-decker (DDSQ) or ladder nano-cores were easily prepared from the corresponding tetraallyl derivatives through fast and convenient thiol-ene reactions. An additional tetrathiol-DDSQ with more flexible arms was also synthesized in high yield from the corresponding tetrachloro-DDSQ derivative. The three novel tetrathiol silsesquioxanes described represent versatile building blocks for the preparation of hybrid organic-inorganic materials.

Janus ring siloxane: a versatile precursor of the extended Janus ring and tricyclic laddersiloxanes.

All-cis-tetrasiloxycyclotetrasiloxanes (Janus ring siloxanes) were facilely prepared from all-cis-cyclotetrasiloxanetetraol or sodium cyclotetrasiloxane silanolates. Moreover, we demonstrated the synthesis of extended Janus rings, [RSi(OR')O]4, containing various functional groups, via the Piers-Rubinsztajn reaction using a Janus ring siloxane as a precursor. Remarkably, we discovered the formation of an unexpected all-cis tricyclic laddersiloxane as a by-product. These synthesized compounds can be potential monomers of well-defined cage silsesquioxanes, Janus-type nanomaterials, and porous materials.

Crystal structure of chlorido-{tris-[2-(iso-propyl-sulfan-yl)phen-yl]phosphane-κ4 P,S,S',S''}nickel(II) tri-fluoro-methane-sulfonate.

The complex cation of the title compound, [NiCl{P(C6H4-2-S-i-Pr)3}](CF3SO3), has a slightly distorted trigonal-bipyramidal coordination geometry in which three S atoms are located in the equatorial plane, and one P and one Cl atom in the apical positions. In the cation, there are two intra-molecular C-H⋯S hydrogen bonds. In the crystal, there are some inter-molecular C-H⋯O and C-H⋯F hydrogen bonds formed between the cation and the anion. The tri-fluoro-methane-sulfonate anion and one of the methyl groups are both disordered over two sets of sites with occupancies of 0.629 (17):0.371 (17) and 0.786 (14):0.214 (14), respectively.

Synthesis of a "Butterfly Cage" Based on a Double-Decker Silsesquioxane.

Novel polyhedral structures were prepared with a butterfly-shape composed of oligosiloxane wings and a double-decker silsesquioxane (DDSQ) body. The compounds were synthesized in two steps from commercially available alkoxysilanes, and their structures were confirmed using spectroscopic methods and X-ray crystallography. Not like other phenyl-substituted cage silsesquioxanes, these butterfly cages show very good solubility in common organic solvents. The crystal structures clearly showed their unique features: a larger space with longer siloxane chains and a very flexible framework. Moreover, these compounds are thermally stable with a Td5 (5 % weight loss temperature) over 320 °C.

Synthesis of octacarboxy spherosilicate.

feasible new preparation was reported for an octacarboxylphenyl functionalized spherosilicate, octakis[(pcarboxyphenyl) dimethylsilyl]silicate, which was a versatile monomer leading to other functional spherosilicate derivatives. The synthesis was started from octakis[dimethyl(p-methylphenyl)silyl]silicate. Octakis[dimethyl(pmethylphenyl) silyl]silicate was brominated by NBS to produce octakis[dimethyl(4-tribromomethylphenyl)silyl]silicate. Finally, octakis[dimethyl(4-tribromomethylphenyl)silyl]silicate was hydrolyzed in the presence of AgNO3 and formic acid to give the desired compound. Octakis[(pcarboxyphenyl) dimethylsilyl]silicate was fully characterized by FTIR, 1H NMR, 13C NMR, 29Si NMR spectra, ESI-MS, and elemental analysis.

Stereoisomerization of Cyclic Silanols.

Stereoisomerization of readily available all-cis-1,3,5,7-tetrahydroxy-1,3,5,7-tetraisobutylcyclotetrasiloxane (1 a) was carried out under acidic conditions to afford cis-trans-cis (1 b), all-trans (1 c), and cis-cis-trans (1 d) isomers. The compounds in the reaction mixture could be easily separated into 1 a and a mixture of 1 b, 1 c, and 1 d by the treatment with chloroform. Compounds 1 b, 1 c, and 1 d were further separated and isolated, and each structure was identified. The experimental results indicated that the most plausible mechanism is a substitution reaction at the silicon center via a pentacoordinate intermediate without a cyclic siloxane bond cleavage reaction. The obtained isomer 1 a or 1 b further reacted with dichlorodiphenylsilane in the presence of triethylamine to give syn-type laddersiloxane (2 a) or anti-type laddersiloxane (2 b), respectively.

Unusual carbon-sulfur bond cleavage in the reaction of a new type of bulky hexathioether with a zerovalent palladium complex.

The reaction of a bulky hexathioether, TbtS(o-Phen)S(o-Phen)SS(o-Phen)S(o-Phen)STbt (o-Phen = o-phenylene, Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl) (1), with 3 molar amounts of Pd(PPh3)4 afforded trinuclear palladium complex bridged by two benzenedithiolato ligands via a three-step palladium insertion reaction into one sulfur-sulfur and two carbon-sulfur bonds of 1.