A versatile synthesis of benzothieno-annelated 1,2-dihydropyridine and 1,2,3,4-tetrahydropyridine derivatives: the effect of the structure of benzothieno-annelated pyridinium salts on their reduction by sodium borohydride

Abstract  

Benzothieno[2,3-c]pyridinium and benzothieno[2,3-c]quinolinium salts were synthesized either by quaternization of benzothieno[2,3-c]pyridines, or recyclization of benzothieno[2,3-c]pyrylium salts with primary amines. One-pot synthesis of benzothieno[3,2-g]indolizinium salts from 1-(3-chloropropyl)-benzothieno[2,3-c]pyrylium included consequent recyclization of the pyrylium core by ammonia into a pyridine intermediate and its further intramolecular quaternization reaction. Depending on the structure of benzothieno-annelated pyridinium salts, their reaction with sodium borohydride in methanol results in reduction of the pyridine core into tetrahydropyridine or dihydropyridine derivatives. Whereas reduction of benzothieno[2,3-c]pyridinium and benzothieno[3,2-g]indolizinium salts readily yields benzothieno-annelated tetrahydropyridines as a complex mixture of stereoisomers, reduction of benzothieno[2,3-c]quinolinium salts results in dihydropyridine derivatives. The structure of the latter, in particular, was confirmed by single-crystal X-ray diffraction analysis.     

Alkyl chains of surface ligands affect polytypism of cdse nanocrystals and play an important role in the synthesis of anisotropic nanoheterostructures

We show that the length of the alkyl chain of surface ligands can shift the equilibrium between the wurtzite and zinc blende polytypes of CdSe nanocrystals. In-situ wide-angle X-ray scattering measurements reveal that short-chain (e.g., propyl) phosphonic acids stabilize CdSe nanocrystals with the zinc blende phase whereas octadecylphosphonic acid stabilize nanocrystals with the wurtzite phase. We also demonstrate how this effect can be used to improve the shape selectivity in the synthesis of anisotropic CdSe/CdS and ZnSe/CdS nanoheterostructures.     

Nanocrystal superlattices with thermally degradable hybrid inorganic-organic capping ligands

Colloidal metallic and semiconductor nanocrystals (NCs) functionalized with metal chalcogenide complexes (MCCs) have shown a promise for designing materials that combine high carrier mobility with the electronic structure of strongly quantum-confined solids. Here we report a simple and general methodology for switching the repulsive forces responsible for colloidal stabilization of MCC-capped NCs from long-range electrostatic to short-range steric through the formation of tight ionic pairs with cationic surfactants. This noncovalent surface modification remarkably improved the ability of MCC-capped NCs to self-assemble into long-range ordered superlattices. These NCs are highly soluble in nonpolar solvents and compatible with various technologically relevant organic molecules and polymers. The hybrid inorganic-organic coating can be thermally decomposed at significantly lower temperatures compared to those required for removal of conventional organic ligands.     

How does the type of counterion influence the polymerization rate and thermal properties of tailored choline-based linear- and star-shaped poly(ionic liquid)s PILs?

The synthesis of tailored [2-(methacryloyloxy)ethyl]-trimethylammonium chloride (ChMA/Cl⁻) and bis(trifluoromethanesulfonate) imide (ChMA/NTf₂⁻)-based ionic homopolymers by sustainable activators generated by electron transfer atom transfer radical polymerization (ATRP) method has been demonstrated. Linear and four-arm star-shaped macromolecules were obtained with the use of two synthetic strategies: (a) direct polymerization of ionic monomers with counterions differing in hydrophilicity (prepolymerization) and (2) modification by ion exchange from Cl⁻ to NTf₂⁻ (postpolymerization) using both classical ATRP initiator and pentaerythritol-based initiator. The effect of counterions on the polymerization kinetics and the physicochemical and thermodynamical properties of resulted poly(ionic liquid)s (PILs) has been investigated. Results showed that polymerizations of ChMA/NTf₂⁻ proceeded with higher rate in comparison to ChMA/Cl⁻ one independently on the predetermined topologies (linear and four-arm star-shaped). From thermodynamical point of view, the glass transition temperature T_g increased with molecular weight M_n for linear- and star-shaped PILs for both types of counterion. In addition, star-shaped polymers of comparable M_n to linear ones were characterized by slightly higher T_g values. The resulting polyelectrolytes, after modification via exchange of Cl⁻ anions to NTf₂⁻ ones were characterized by much higher T_g in comparison to those produced by direct polymerization of ionic monomer, indicating the crucial role of postpolymerization modification on thermodynamical properties of PILs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2681–2691     

Guest induced reversible on–off switching of elastic frustration in a 3D spin crossover coordination polymer with room temperature hysteretic behaviour

A binary reversible switch between low-temperature multi-step spin crossover (SCO), through the evolution of the population γ_HS(T) with high-spin (HS)-low-spin (LS) sequence: HS₁LS₀ (state 1) ↔ HS_2/3LS_1/3 (state 2) ↔ HS_1/2LS_1/2 (state 3) ↔ HS_1/3LS_2/3 (state 4) ↔ HS₀LS₁ (state 5), and complete one step hysteretic spin transition featuring 20 K wide thermal hysteresis centred at 290 K occurs in the three-dimensional (3D) Hofmann-type porous coordination polymer {Fe^II(3,8phen)[Au(CN)₂]₂}·xPhNO₂ (3,8phen = 3,8-phenanthroline, PhNO₂ = nitrobenzene), made up of two identical interpenetrated pcu-type frameworks. The included PhNO₂ guest (x = 1, 1·PhNO₂) acts as a molecular wedge between the interpenetrated 3D frameworks via PhNO₂-3,8phen intermolecular recognition and is the source of the strong elastic frustration responsible for the multi-step regime. Detailed X-ray single crystal analysis reflects competition between spatial periodicities of structurally inequivalent HS and LS SCO centres featuring: (i) symmetry breaking (state 3) with ⋯HS–LS⋯ ordering with γ_HS = 1/2; and (ii) occurrence of spatial modulation of the structure providing evidence for stabilization of local or aperiodic ordered mixed spin states for states 2 and 4 (with γ_HS ≈ 2/3) and 4 (with γ_HS ≈ 1/3), respectively. Below c.a. 20 K, structural and magnetic analyses show the photogeneration of a metastable HS*, state 6. The room-temperature single-step hysteretic regime appears with release of the guest (x = 0, 1) and the elastic frustration, and reversibly switches back to the original four-step behaviour upon guest re-adsorption. Both uncommon relevant SCO events meeting in the same material represent a rare opportunity to compare them in the frame of antiferro- and ferro-elastic transitions.

Reversible switch between a robust bistable two-state room temperature spin crossover (SCO) and its transformation in a four-stepped elastically frustrated SCO due to guest inclusion in a metal–organic Hofmann framework.     

Post‐Synthesis Stabilization of Germanosilicate Zeolites ITH,IWW, and UTL by Substitution of Ge for Al

Germanosilicate zeolites often suffer from low hydrothermal stability due to the high content of Ge. Herein, we investigated the post‐synthesis introduction of Al accompanied by stabilization of selected germanosilicates by degermanation/alumination treatments. The influence of chemical composition and topology of parent germanosilicate zeolites ( ITH , IWW , and UTL ) on the post‐synthesis incorporation of Al was studied. Alumination of ITH (Si/Ge=2–13) and IWW (Si/Ge=3–7) zeolites resulted in the partial substitution of Ge for Al (up to 80 %), which was enhanced with a decrease of Ge content in the parent zeolite. In contrast, in extra‐large pore zeolite UTL (Si/Ge=4–6) the hydrolysis of the interlayer Ge?O bonds dominated over substitution. The stabilization of zeolite UTL was achieved using a novel two‐step degermanation/alumination procedure by the partial post‐synthesis substitution of Ge for Si followed by alumination. This new method of stabilization and incorporation of strong acid sites may extend the utilization of germanosilicate zeolites, which has been until now been limited.