Intramolecular hydrogen bond activation: Thiourea-organocatalyzed enantioselective 1,3-dipolar cycloaddition of salicylaldehyde-derived azomethine ylides with nitroalkenes

An organocatalytic strategy for the synthesis of tetrasubstituted pyrrolidines with monoactivated azomethine ylides in high enantiomeric excess and excellent exo/endo selectivity is presented. The key to success is the intramolecular activation via hydrogen bonding through an o-hydroxy group, which allows the dipolar cycloaddition to take place in the presence of azomethine ylides bearing only one activating group. The intramolecular hydrogen bond in the azomethine ylide and the intermolecular hydrogen bond with the catalyst have been demonstrated by DFT calculations and mechanistic proofs to be crucial for the reaction to proceedThe Spanish Government (CTQ2015-64561-R, CTQ2016- 76061-P) and the European Research Council (ERC-CG, contract number 647550) are acknowledged. We acknowledge the generous allocation of computing time at the CCC (UAM). S.D.-T. gratefully acknowledges the “Ramón y Cajal” program (RYC-2010-07019). Financial support from the Spanish Ministry of Economy and Competitiveness, through the “Maria de Maeztu” Program of Excellence in R&D (MDM- 2014-0377

Aggregation-Induced Enhanced Emission (AIEE) from <i>N</i>,<i>N</i>‑Octyl-7,7′-diazaisoindigo-Based Organogel

A new kind of low molecular-mass organic gelator (LMOG) π-electron-deficient <i>N</i>,<i>N</i>-octyl-7,7′-diazaisoindigo (<b>1</b>) with aggregation-induced enhanced emission (AIEE) phenomenon is described. This organogel is capable of self-assembling through intermolecular H-bonding and π–π interactions between diazaisoindigo molecules. Its rheological properties, X-ray diffraction pattern, optical properties and theoretical calculations were investigated. The AIEE effect is exhibited in fluorescence during the formation of the supramolecular organogel, which persisted in the xerogel state, and the spectral red-shifts suggest the formation of <i>J</i>-type aggregates during the gelation process via π–π interactions in microbelts or 3D networks. Fluorescence lifetime and quantum yield significantly increase from dilute solution to the aggregate state. From a theoretical perspective, the effect of the aggregation of <b>1</b> on the photophysical properties was also studied by means of the density functional theory (DFT). In this sense, the lowest energy electronic transitions were calculated for both the single molecule and different size aggregates in order to predict spectral shifts. In addition, the geometry and molecular properties of the excited state were analyzed in different material states

Cubic Octasilsesquioxanes, Cyclotetrasiloxanes, and Disiloxanes Maximally Functionalized with Silicon-Bridged Interacting Triferrocenyl Units

Redox-active, highly symmetrical cubic octasilsesquioxanes (OS) peripherally decorated with 24 ferrocenyl units, linked in threes around the periphery of a cubic cage, namely, [Fc₃Si­(CH₂)₂Me₂SiO]₈Si₈O₁₂ (<b>6</b>) and [Fc₃Si­(CH₂)₂]₈Si₈O₁₂ (<b>7</b>) (Fc = (η⁵-C₅H₄)­Fe­(η⁵-C₅H₅)), have been synthesized. Such integrally ferrocenyl-functionalized cubic macromolecules <b>6</b> and <b>7</b>, as well as the related small-molecule models hexaferrocenyldisiloxane [Fc₃Si­(CH₂)₂Me₂Si]₂O (<b>4</b>) and dodecaferrocenyl cyclotetrasiloxane [Fc₃Si­(CH₂)₂MeSiO]₄ (<b>5</b>), have been prepared by covalently linking, via Karstedt’s-catalyzed hydrosilylation, triferrocenylvinylsilane (CH₂CH)­Si­(Fc)₃ (<b>3</b>) around the surface of octasilsesquioxane cages T₈(OSiMe₂H)₈ and T₈H₈ and linear [Me₂SiH]₂O and cyclic [MeSiHO]₄ siloxane scaffolds, respectively. All new polyferrocenyl oligosiloxanes have been thoroughly characterized using a combination of elemental analysis, multinuclear (¹H, ¹³C, ²⁹Si) NMR spectroscopy, FT-IR, and MALDI-TOF mass spectrometry. The molecular structure of disiloxane <b>4</b>, in the solid state, has been determined by single-crystal X-ray analysis. Hexametallic <b>4</b> shows a bent arrangement of the ferrocenyl-substituted disiloxane linkage (Si–O–Si angle of 147.6(5)°). Polyferrocenyl-OS <b>6</b> and <b>7</b> show good thermal stability and form iron-containing ceramics when pyrolyzed under nitrogen. The electrochemical behavior of polyferrocenyl OS and model linear and cyclic siloxanes has been examined by cyclic and square wave voltammetries, in dichloromethane solution using PF₆^– and B­(C₆F₅)₄^– as supporting electrolyte anions of different coordinating ability. The novel maximally ferrocenyl-functionalized oligosiloxanes exhibit a three-wave redox pattern, suggesting appreciable electronic interactions between the silicon-bridged triferrocenyl moieties as they are successively oxidized. OS <b>6</b> and <b>7</b> undergo remarkable oxidative precipitation in CH₂Cl₂/<i>n-</i>NBu₄PF₆ and are able to form stable electroactive films on platinum electrode surfaces. They are the first redox-active OS showing significant electronic interactions between metal sites on the cage surface

Cubic Octasilsesquioxanes, Cyclotetrasiloxanes, and Disiloxanes Maximally Functionalized with Silicon-Bridged Interacting Triferrocenyl Units

Redox-active, highly symmetrical cubic octasilsesquioxanes (OS) peripherally decorated with 24 ferrocenyl units, linked in threes around the periphery of a cubic cage, namely, [Fc₃Si­(CH₂)₂Me₂SiO]₈Si₈O₁₂ (<b>6</b>) and [Fc₃Si­(CH₂)₂]₈Si₈O₁₂ (<b>7</b>) (Fc = (η⁵-C₅H₄)­Fe­(η⁵-C₅H₅)), have been synthesized. Such integrally ferrocenyl-functionalized cubic macromolecules <b>6</b> and <b>7</b>, as well as the related small-molecule models hexaferrocenyldisiloxane [Fc₃Si­(CH₂)₂Me₂Si]₂O (<b>4</b>) and dodecaferrocenyl cyclotetrasiloxane [Fc₃Si­(CH₂)₂MeSiO]₄ (<b>5</b>), have been prepared by covalently linking, via Karstedt’s-catalyzed hydrosilylation, triferrocenylvinylsilane (CH₂CH)­Si­(Fc)₃ (<b>3</b>) around the surface of octasilsesquioxane cages T₈(OSiMe₂H)₈ and T₈H₈ and linear [Me₂SiH]₂O and cyclic [MeSiHO]₄ siloxane scaffolds, respectively. All new polyferrocenyl oligosiloxanes have been thoroughly characterized using a combination of elemental analysis, multinuclear (¹H, ¹³C, ²⁹Si) NMR spectroscopy, FT-IR, and MALDI-TOF mass spectrometry. The molecular structure of disiloxane <b>4</b>, in the solid state, has been determined by single-crystal X-ray analysis. Hexametallic <b>4</b> shows a bent arrangement of the ferrocenyl-substituted disiloxane linkage (Si–O–Si angle of 147.6(5)°). Polyferrocenyl-OS <b>6</b> and <b>7</b> show good thermal stability and form iron-containing ceramics when pyrolyzed under nitrogen. The electrochemical behavior of polyferrocenyl OS and model linear and cyclic siloxanes has been examined by cyclic and square wave voltammetries, in dichloromethane solution using PF₆^– and B­(C₆F₅)₄^– as supporting electrolyte anions of different coordinating ability. The novel maximally ferrocenyl-functionalized oligosiloxanes exhibit a three-wave redox pattern, suggesting appreciable electronic interactions between the silicon-bridged triferrocenyl moieties as they are successively oxidized. OS <b>6</b> and <b>7</b> undergo remarkable oxidative precipitation in CH₂Cl₂/<i>n-</i>NBu₄PF₆ and are able to form stable electroactive films on platinum electrode surfaces. They are the first redox-active OS showing significant electronic interactions between metal sites on the cage surface

Water-Soluble Mono- and Dimethyl N‑Heterocyclic Carbene Platinum(II) Complexes: Synthesis and Reactivity

A family of water-soluble dimethyl complexes of formula <i>cis</i>-[PtMe₂(dmso)­(NHC·Na)] (<b>2</b>), in which NHC is an anionic N-heterocyclic carbene bearing a sulfonatopropyl chain on one of the nitrogen atoms and a sulfonatopropyl (<b>a</b>), methyl (<b>b</b>), mesityl (<b>c</b>), or 2,6-diisopropylphenyl group (<b>d</b>) on the other, have been prepared. The hydrolytic stability of the Pt–C bonds in these complexes under different neutral, alkaline, and acidic aqueous conditions has also been studied. Complexes <b>2</b> were found to be quite stable at room temperature in water under neutral or alkaline conditions. Degradation occurred at higher temperatures but involved C sp³–H activation and C–C reductive elimination processes in addition to Pt–Me bond hydrolysis. Hydrolytic cleavage of the platinum–methyl bonds was favored by good nucleophiles. Thus, the addition of KCN to an aqueous solution of <b>2</b> resulted in formation of the monomethyl complexes K­[PtMe­(CN)₂(NHC·Na)] (<b>9</b>), whereas the dimethyl complexes K­[PtMe₂(CNR)­(NHC·Na)] (<b>10</b>) were formed with the isocyanide CNCH₂COOK. The addition of stoichiometric amounts of protic acids to aqueous solutions of <b>2</b> resulted in the clean cleavage of one or both platinum­(II)–methyl bonds. Thus, the reaction of <b>2</b> with HCl afforded the complexes [PtClMe­(dmso)­(NHC·Na)] (<b>3</b>) and [PtCl₂(dmso)­(NHC·Na)] (<b>4</b>), whereas [PtMe­(OH₂)­(dmso)­(NHC)] (<b>5</b>) and [Pt­(OH₂)₂(dmso)­(NHC)]­[BF₄] (<b>7</b>) were obtained upon treatment with HBF₄. The crystal structure of <b>9a</b> is remarkable in light of the longitudinal channels around 6 Å in diameter internally decorated with Pt–Me bonds

Tuning of Adsorption and Magnetic Properties in a Series of Self-Templated Isostructural Ni(II) Metal−Organic Frameworks

An isomorphous series of five metal–organic frameworks of formula [Ni₄(O₂CR)­(OH)₂­(4-pyc)₅] [4-pyc = 4-pyridinecarboxylate or isonicotinate; R = C₆H₅ (<b>1</b>), 4-OMe-C₆H₄ (<b>2</b>), 2,6-(OMe)₂-C₆H₃ (<b>3</b>), 3,5-(OMe)₂-C₆H₃ (<b>4</b>), 3,4,5-(OMe)₃-C₆H₂ (<b>5</b>)] were obtained by solvothermal reactions. These compounds display a three-dimensional framework where the nickel atoms are coordinated to the hydroxyde anions and two different organic ligands: isonicotinate and phenylcarboxylate. Both hydroxyde (μ₃-OH) and phenylcarboxylate (μ₃-1κ<i>O</i>,2κ<i>O</i>,3κ<i>O</i>′) ligands are coordinated to nickel atoms of the same secondary building unit (SBU). The SBU consists of four edge-sharing NiA₆ octahedra (A = O, N). The isonicotinate ligands, however, act as linkers between SBUs displaying three different coordination modes: μ-1κ<i>N</i>,2κ<i>O</i>; μ₃-1κ<i>N</i>,2κ<i>O</i>,3κ<i>O</i>′; and μ₄-1κ<i>N</i>,2:3κ²<i>O</i>,4κ<i>O</i>′. Nitrogen adsorption measurements were done to obtain textural parameters of these microporous networks. Micropore size distributions indicate cylindrical pores with diameters of approximately 0.80 nm. The values of Brunauer–Emmett–Teller surface areas (<i>S</i>_BET) obtained are in the range of 382–488 m²/g, and the micropore volumes are between 0.13 cm³/g and 0.19 cm³/g. Both parameters are influenced by the substitution grade and position of the methoxy groups of the phenylcarboxylate ligand. The magnetic properties, which also depend on the arylcarboxylate ligands, vary from compound <b>1</b> (with only antiferromagnetic interactions) to compound <b>5</b>, which shows a spin glass behavior (<i>T</i>_g = 15 K)

Tuning of Adsorption and Magnetic Properties in a Series of Self-Templated Isostructural Ni(II) Metal−Organic Frameworks

An isomorphous series of five metal–organic frameworks of formula [Ni₄(O₂CR)­(OH)₂­(4-pyc)₅] [4-pyc = 4-pyridinecarboxylate or isonicotinate; R = C₆H₅ (<b>1</b>), 4-OMe-C₆H₄ (<b>2</b>), 2,6-(OMe)₂-C₆H₃ (<b>3</b>), 3,5-(OMe)₂-C₆H₃ (<b>4</b>), 3,4,5-(OMe)₃-C₆H₂ (<b>5</b>)] were obtained by solvothermal reactions. These compounds display a three-dimensional framework where the nickel atoms are coordinated to the hydroxyde anions and two different organic ligands: isonicotinate and phenylcarboxylate. Both hydroxyde (μ₃-OH) and phenylcarboxylate (μ₃-1κ<i>O</i>,2κ<i>O</i>,3κ<i>O</i>′) ligands are coordinated to nickel atoms of the same secondary building unit (SBU). The SBU consists of four edge-sharing NiA₆ octahedra (A = O, N). The isonicotinate ligands, however, act as linkers between SBUs displaying three different coordination modes: μ-1κ<i>N</i>,2κ<i>O</i>; μ₃-1κ<i>N</i>,2κ<i>O</i>,3κ<i>O</i>′; and μ₄-1κ<i>N</i>,2:3κ²<i>O</i>,4κ<i>O</i>′. Nitrogen adsorption measurements were done to obtain textural parameters of these microporous networks. Micropore size distributions indicate cylindrical pores with diameters of approximately 0.80 nm. The values of Brunauer–Emmett–Teller surface areas (<i>S</i>_BET) obtained are in the range of 382–488 m²/g, and the micropore volumes are between 0.13 cm³/g and 0.19 cm³/g. Both parameters are influenced by the substitution grade and position of the methoxy groups of the phenylcarboxylate ligand. The magnetic properties, which also depend on the arylcarboxylate ligands, vary from compound <b>1</b> (with only antiferromagnetic interactions) to compound <b>5</b>, which shows a spin glass behavior (<i>T</i>_g = 15 K)

Structural Diversity in Paddlewheel Dirhodium(II) Compounds through Ionic Interactions: Electronic and Redox Properties

Reactions of dinuclear rhodium­(II) tetracarboxylates, [Rh₂­(O₂CR)₄] (R = Me, Et), with halides (Br^– and I^–) or pseudohalides (OCN^–) yield dinuclear complexes with intriguing supramolecular architectures based on ionic interactions. The solid-state arrangement of the complexes presented here has been studied using single-crystal X-ray diffraction. Discrete anionic units with the axial positions occupied by isocyanate, Na₂­[Rh₂­(O₂CMe)₄­(NCO)₂]·4H₂O (<b>1</b>), water and isocyanate, Na­[Rh₂­(O₂CMe)₄­(NCO)­(H₂O)] (<b>2</b>), iodide, {K₂­[Rh₂­(O₂CEt)₄­I₂]·H₂O}_n (<b>3</b>), and bromide ligands, {K₂­[Rh₂­(O₂CEt)₄­Br₂]·H₂O}<i>_n</i> (<b>4</b>) and K­[Rh₂­(O₂CEt)₄­(Br)_0.5]₂­[Rh₂­(O₂CEt)₄­(H₂O)₂] (<b>5</b>), have been found. Complex <b>1</b> shows monodimensional polymeric chains stabilized through ionic interactions, while complexes <b>2</b>–<b>4</b> consist of two-dimensional layers. Finally, a three-dimensional network containing two kinds of dirhodium moieties has been found in complex <b>5</b>. Speciation of the [Rh₂­(O₂CR)₄]/X^– (R = Me, Et; X = OCN, Br, I) systems was investigated in aqueous solution by UV–visible titrations, helping us to rationalize the obtention of different Rh–X stoichiometries in the crystal state. By cyclic voltammetry, we have evaluated the effect of X^– coordination on the oxidation properties of these dirhodium­(II) units

Structural Diversity in Paddlewheel Dirhodium(II) Compounds through Ionic Interactions: Electronic and Redox Properties

Reactions of dinuclear rhodium­(II) tetracarboxylates, [Rh₂­(O₂CR)₄] (R = Me, Et), with halides (Br^– and I^–) or pseudohalides (OCN^–) yield dinuclear complexes with intriguing supramolecular architectures based on ionic interactions. The solid-state arrangement of the complexes presented here has been studied using single-crystal X-ray diffraction. Discrete anionic units with the axial positions occupied by isocyanate, Na₂­[Rh₂­(O₂CMe)₄­(NCO)₂]·4H₂O (<b>1</b>), water and isocyanate, Na­[Rh₂­(O₂CMe)₄­(NCO)­(H₂O)] (<b>2</b>), iodide, {K₂­[Rh₂­(O₂CEt)₄­I₂]·H₂O}_n (<b>3</b>), and bromide ligands, {K₂­[Rh₂­(O₂CEt)₄­Br₂]·H₂O}<i>_n</i> (<b>4</b>) and K­[Rh₂­(O₂CEt)₄­(Br)_0.5]₂­[Rh₂­(O₂CEt)₄­(H₂O)₂] (<b>5</b>), have been found. Complex <b>1</b> shows monodimensional polymeric chains stabilized through ionic interactions, while complexes <b>2</b>–<b>4</b> consist of two-dimensional layers. Finally, a three-dimensional network containing two kinds of dirhodium moieties has been found in complex <b>5</b>. Speciation of the [Rh₂­(O₂CR)₄]/X^– (R = Me, Et; X = OCN, Br, I) systems was investigated in aqueous solution by UV–visible titrations, helping us to rationalize the obtention of different Rh–X stoichiometries in the crystal state. By cyclic voltammetry, we have evaluated the effect of X^– coordination on the oxidation properties of these dirhodium­(II) units

Structural Diversity in Paddlewheel Dirhodium(II) Compounds through Ionic Interactions: Electronic and Redox Properties

Reactions of dinuclear rhodium­(II) tetracarboxylates, [Rh₂­(O₂CR)₄] (R = Me, Et), with halides (Br^– and I^–) or pseudohalides (OCN^–) yield dinuclear complexes with intriguing supramolecular architectures based on ionic interactions. The solid-state arrangement of the complexes presented here has been studied using single-crystal X-ray diffraction. Discrete anionic units with the axial positions occupied by isocyanate, Na₂­[Rh₂­(O₂CMe)₄­(NCO)₂]·4H₂O (<b>1</b>), water and isocyanate, Na­[Rh₂­(O₂CMe)₄­(NCO)­(H₂O)] (<b>2</b>), iodide, {K₂­[Rh₂­(O₂CEt)₄­I₂]·H₂O}_n (<b>3</b>), and bromide ligands, {K₂­[Rh₂­(O₂CEt)₄­Br₂]·H₂O}<i>_n</i> (<b>4</b>) and K­[Rh₂­(O₂CEt)₄­(Br)_0.5]₂­[Rh₂­(O₂CEt)₄­(H₂O)₂] (<b>5</b>), have been found. Complex <b>1</b> shows monodimensional polymeric chains stabilized through ionic interactions, while complexes <b>2</b>–<b>4</b> consist of two-dimensional layers. Finally, a three-dimensional network containing two kinds of dirhodium moieties has been found in complex <b>5</b>. Speciation of the [Rh₂­(O₂CR)₄]/X^– (R = Me, Et; X = OCN, Br, I) systems was investigated in aqueous solution by UV–visible titrations, helping us to rationalize the obtention of different Rh–X stoichiometries in the crystal state. By cyclic voltammetry, we have evaluated the effect of X^– coordination on the oxidation properties of these dirhodium­(II) units