Tin Lewis Acid Research Articles

Efficient Tin-Based Perovskite Solar Cell with a Cesium Acetate Pre-buried PEDOT:PSS Hole Transport Layer.

The strong Lewis acid tin halide leads to an excessively fast crystallization rate, resulting in more defects in the film and degraded device performance. In this work, a cesium acetate (CsAc) pre-buried poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer acts as nucleation points during the crystallization of tin-based perovskite, which can induce preferential orientation growth of crystals and increase the grain size to improve the quality of crystallization. The addition of CsAc not only can increase the conductivity of PEDOT:PSS but also can improve the wettability of the perovskite precursor solution to enhance the interface contact between the hole transport layer and perovskite layer. Because of the incorporation of CsAc in PEDOT:PSS, the average short-circuit current density increases from 23.80 to 27.60 mA cm-2. Furthermore, a power conversion efficiency of 10.99% is achieved for a tin-based perovskite solar cell with CsAc-doped PEDOT:PSS as the hole transport layer.

Phosphanyl-substituted tin half-sandwich complexes.

Phosphanyl-substituted tin(ii) half sandwich complexes are reported. Due to the Lewis acidic tin center and Lewis basic phosphorous atom they form head-to-tail dimers. Their properties and reactivities were investigated both experimentally and theoretically. Furthermore, related transition metal complexes of these species are presented.

Oligomeric ricinoleic acid synthesis with a recyclable catalyst and application to preparing non-isocyanate polyhydroxyurethane

As a consequence of the great demand and extended application of polyurethanes in various fields, the development of green processes for their production and functional polyurethane materials has received widespread attention. In this regard, the biomass-derived polyurethane via the non-isocyanate route could be promising. In this work, the castor-based polyurethanes were designed and synthesized through a non-isocyanate route by employing ricinoleic acid as the starting material, in which the oligomeric ricinoleic acid (ORA) with variable average polymerization degree was used as the key intermediate. To access the ORA with different average polymerization degree, the solid Lewis acid tin(II) oxide (SnO) was developed as the efficient and recyclable catalyst and the average polymerization degree of ORA was regulated by the reaction time at 210 °C. After sequential esterification, epoxidation, cycloaddition with CO2 and polyaddition with 1,6-hexamethylene diamine (HMDA) or isophorone diamine (IPDA), a series of polyhydroxyurethanes (PHUs) with different tensile strength and elongation at break as well as the thermal stability and the glass transition temperature were obtained depending on the type of diamine and the average polymerization degree of ORA, indicating the functional role of the polymerization degree of ORA in regulating the mechanical and thermal properties of the resulting materials. This protocol for the castor-based PHUs preparation in this work not only represents a green and sustainable way to produce bio-based material, but also provides a convenient way to change the average polymerization degree of ORA and then alter the properties of resulting polyurethanes.

Synthesis and catalytic testing of Lewis acidic nano zeolite Beta for epoxide ring opening with alcohols

Lewis acidic zeolites are robust catalytic materials that are capable of a range of important chemistry for fine chemical production, including the epoxide ring opening with alcohols. The crystalline structure imposes diffusion limitations for large molecules that are overcome through reducing the particle size to produce nano zeolite beta substituted with Lewis acidic tin (nSnBeta). nSnBeta is characterized using standard methods to demonstrate that tin is efficiently incorporated into the zeolite framework with open and closed sites similar to the micron-sized conventional Sn-Beta (cSnBeta). While nSnBeta exhibits comparable catalytic activity to cSnBeta for reactions involving small substrates such as epichlorohydrin and methanol, an improvement in catalytic performance is observed for nSnBeta relative to cSnBeta when using large substrates such as 1,2-epoxyoctane and ethanol. nSnBeta and cSnBeta convert a cyclic epoxide too large to enter the pores to similar extents, indicating that the improved performance is not associated with an increased number of catalytic sites on the external surface. Catalyst reuse experiments demonstrate that organic accumulation on the material reduces catalytic activity that can be partially restored through calcination. Overall, the results demonstrate that nano zeolite beta can be synthesized with small particle sizes (i.e., 150 nm) to help overcome diffusion limitations for bulky substrates for the alcohol ring opening of epoxides.

Synthesis and catalytic testing of Lewis acidic nano-MFI zeolites for the epoxide ring opening reaction with alcohol

Zeolites have well-defined pores that can impart shape selectivity, but can also cause diffusion limitations, reducing catalytic performance. While several strategies have been investigated to overcome diffusion limitations for Brønsted acidic zeolites, limited research has investigated modifying material properties for Lewis acidic zeolites. In this work, diffusion limitations for catalytic reactions are overcome through the low temperature synthesis of nanozeolites containing Lewis acidic tin sites. The growth of the tin-substituted zeolites is monitored using dynamic light scattering, showing that including tin as a heteroatom at a 200:1 (Si:Sn) in the zeolite synthesis gel does not impact the zeolite growth rate. While similar growth rates are observed for pure silica and tin-substituted MFI, the low temperature synthesis methods result in low tin incorporation that can be overcome through adding more tin precursor to the synthesis gel while still producing nanoparticles. The nano-sized zeolites are demonstrated to overcome apparent diffusion limitations that conventional Sn-substituted zeolite MFI encounter for the epoxide ring opening reaction with alcohol. Indeed, conventional Sn-MFI materials can catalyze the ring opening of 1,2-epoxyhexane with methanol and achieve only 55% conversion after 24 h; the nano Sn-MFI zeolites achieve >95% conversion in the same amount of time. Catalyst reuse experiments demonstrate that the nano zeolite does not leach Sn, but that organic accumulation in the pores causes loss in apparent catalytic activity. The organic can be removed through calcination, enabling recovery of the catalytic activity. Overall, engineering of zeolites with reduced crystal size provides an efficient route to overcome diffusion limitations of bulky molecules.

The first report of Lewis acid reagents in the intramolecular Rauhut–Currier reaction

The first report of Lewis acid use in intramolecular Rauhut–Currier reactions is described. Titanium Lewis acids lead to rapid Rauhut–Currier reactions in the case of two classic substrates. More importantly, titanium and tin Lewis acids were the only successful reagent for a more complex substrate, thereby illustrating the potential for Lewis acid reagents to facilitate challenging intramolecular Rauhut–Currier reactions that fail with traditional reagents.

Accelerating Reactive Compatibilization of PE/PLA Blends by an Interfacially Localized Catalyst.

We show catalyst localized at the interface can compatibilize polyethylene (PE) and polylactide (PLA) blends. Telechelic hydroxyl functional PE was synthesized by ring opening metathesis polymerization, which reacted with PLA in melt mixing (shown by adhesion and droplet size reduction). Lewis acid tin catalysts were examined as interfacial reaction promoters, with the goal of interfacial localization. Stannous octoate was shown to localize at the interface by transmission electron microscopy with energy dispersive X-ray spectroscopy and improved dispersion of PLA in PE as compared to uncatalyzed materials and a nonlocalized tin chloride dihydrate.

Active Sites in Sn-Beta for Glucose Isomerization to Fructose and Epimerization to Mannose

Framework Lewis acidic tin sites in hydrophobic, pure-silica molecular sieves with the zeolite beta topology (Sn-Beta) have been reported previously to predominantly catalyze glucose−fructose isomerization via 1,2 intramolecular hydride shift in water and glucose–mannose epimerization via 1,2 intramolecular carbon shift in methanol. Here, we show that alkali-free Sn-Beta predominantly isomerizes glucose to fructose via 1,2 intramolecular hydride shift in both water and methanol. Increasing extents of postsynthetic Na+ exchange onto Sn-Beta, however, progressively shifts the reaction pathway toward glucose–mannose epimerization via 1,2 intramolecular carbon shift. Na+ remains exchanged onto silanol groups proximal to Sn centers during reaction in methanol solvent, leading to nearly exclusive selectivity toward epimerization. In contrast, decationation occurs with increasing reaction time in aqueous solvent and gradually shifts the reaction selectivity to isomerization at the expense of epimerization. Decat...

Evaluation of 18F-labeled BODIPY dye as potential PET agents for myocardial perfusion imaging

Despite the great potential of positron emission tomography/computed tomography (PET/CT) in cardiovascular disease imaging, one of the major limitations is the availability of PET probes with desirable half-lives and reasonable cost. In this report, we hypothesized that lipophilic cationic BODIPY dye could be selectively accumulated in cardiac muscle, possibly for the development of novel PET myocardial perfusion imaging (MPI) probes. A (18)F-labeled BODIPY dye ([(18)F]1) was synthesized efficiently through a fluoride exchange reaction catalyzed by the Lewis acid tin chloride (SnCl₄). The compound was first evaluated by a cellular uptake assay in vitro, followed by biodistribution and microPET imaging studies in vivo. [(18)F]1 was obtained in more than 90% labeling yield, with >98% radiochemical purity. The HEK-293 cellular uptake assay showed that the preferential uptake of [(18)F]1 could be related to the cell membrane potential. The biodistribution data demonstrated high levels of [(18)F]1 accumulation in the heart. In the biodistribution study in mice, the radioactivity uptake in the heart, blood, liver and lung was 3.01 ± 0.44, 0.39 ± 0.09, 0.69 ± 0.07, 1.71 ± 0.27%ID/g, respectively, at 3h post-injection (p.i.). The heart-to-lung and heart-to-liver ratios are 1.76 ± 0.14 and 4.37 ± 0.51 at 3h p.i., respectively. Volume-of-interest analysis of the microPET images correlated well with the biodistribution studies in mice. The heart was clearly visualized in normal rats, with 0.72 ± 0.18, 0.69 ± 0.18, 0.67 ± 0.20 and 0.59 ± 0.17%ID/g uptake at 0.5, 1, 2 and 4h p.i., respectively. (18)F-labeled BODIPY dye showed good heart uptake and heart-to-blood and heart-to-lung contrast. A (18)F-labeled BODIPY dyes may represent a new category of cationic PET agents for myocardial perfusion imaging.

Control of thermal properties and hydrolytic degradation in poly(lactic acid) polymer stars through control of isospecificity of polymer arms

AbstractThe synthesis of a family of polymer stars with arms of varied tacticities is discussed. The effect of polymer tacticity on the physical properties of these polymer stars is dramatic. Dipentaerythritol cores support six poly(lactic acid) arms. Lewis acidic tin and/or aluminum catalysts control the polymerization to afford polymer stars of variable tacticity. Analysis of these polymers by 1H NMR spectroscopy, thermogravimetric analysis, powder X‐ray diffraction, and differential scanning calorimetry reveals the effects of tacticity control on the physical properties of the polymer stars. Hydrolytic decomposition studies suggest that the degradation profile of a polymer star may also be tuned by stereochemical control. Differences between isotactic samples derived from rac‐lactide and L‐lactide are heightened by longer arms of 50 and 100 monomer units. Control of polymer isospecificity shows that a ∼70% isotacticity bias is necessary to induce crystallinity and alter the thermal and degradation properties of the material. Above 70% isotacticity, the degradation properties and thermal transitions can be further tuned across a relatively wide range. This technique allows for significant tunability to the physical properties of aliphatic polyester polymer stars. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Chromiumpentacarbonyl-Coordinated Organotin(II) Cation

The synthesis of the novel chromiumpentacarbonyl complex [2,6-(MeOCH2)2C6H3](Cl) SnCr(CO)5 (1) is reported. Compound 1 was used for the synthesis of novel chromiumpentacarbonyl coordinated organotin(II) cations [{2,6-(MeOCH2)2C6H3}SnCr(CO)5]+X− (X = OTf or CB11H12). The strongly Lewis acidic tin(II) center of the latter organotin(II) cations coordinates H2O or THF molecules yielding the corresponding organotin(II) cations [{2,6-(MeOCH2)2C6H3}(H2O)SnCr(CO)5]+ [OTf]− (2) and [{2,6-(MeOCH2)2C6H3}(H2O)SnCr(CO)5]+ [CB11H12]− (3). Compounds 1−3 were characterized by means of elemental analyses, 1H, 13C, 119Sn NMR spectroscopies, and single crystal X-ray diffraction analysis.

Tacticity Control in the Synthesis of Poly(lactic acid) Polymer Stars with Dipentaerythritol Cores

The synthesis of a family of polymer stars with arms of varied tacticities is discussed. The effect of polymer tacticity on the physical properties of these polymer stars is presented. Dipentaerythritol cores support six poly(lactic acid) (PLA) arms. Lewis acidic tin and aluminum catalysts control the polymerization to afford polymer stars of variable tacticity. The analysis of these polymers by NMR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and differential scanning calorimetry reveals the effects of tacticity control on the physical properties of the polymer stars. Preliminary decomposition studies suggest that the biodegradation profile of a polymer star may also be tuned by stereochemical control. This is the first systematic altering of tacticity in PLA polymer stars, showing that polymer tacticity can have a great impact on star properties.

Binding of a 2-pyridyl moiety to a B/Sn bidentate Lewis acid

Reaction of the bidentate Lewis acid 1,2-Fc(SnMe 2Cl)(B(Me)Cl) ( 1, Fc = 1,2-ferrocenylene) with 2-trimethylstannylpyridine gave a complex ( 2), in which the 2-pyridyl group forms a bridge between the Lewis acidic tin and boron centers. The structure of 2 was confirmed by multinuclear and two-dimensional NMR, single crystal X-ray diffraction, and elemental analysis. The crystal structure shows that the pyridyl moiety is positioned endo relative to the substituted Cp ring and UV–Vis spectroscopy revealed an enhancement of the ferrocene-centered dd transition in comparison to related complexes with pyridine as a terminal ligand.

Peculiarities of Sn-Beta and potential industrial applications

In the search for new environmentally friendly processes Sn-Beta has been developed as a heterogeneous catalyst. Its reactivity is different from similar materials, i.e. titanium containing molecular sieves. The origin of its singularity is described by means of density functional theory (DFT), in situ IR spectroscopy of deuterated acetonitrile and catalytic studies. All results point to a bi-functional active site that involves a Lewis acid tin centre and an adjacent oxygen atom capable to accept hydrogen bonding from water or hydrogen peroxide. The catalyst may be employed for Baeyer-Villiger oxidations taking part in multi-step synthesis of industrial interest, achieving more than 10,000 turnovers per tin centre.

Highly Diastereoselective Hydrostannylation of Allyl and Homoallyl Alcohols with Dibutyl(trifluoromethanesulfoxy)stannane.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A new, alternative, halogen-free synthesis for the fragrance compound Melonal using zeolites and mesoporous materials as oxidation catalysts

At present Melonal (2,6-dimethyl-5-hepten-1-al) fragrance is industrially produced by a Darzens reaction from 6-methyl-5-hepten-2-one, with ethylchloroacetate as reagent. We present here a novel halogen-free synthesis strategy that involves the chemoselective oxidation of Citral (3,7-dimethyl-6-octen-1-al), a common compound in the fragrance industry, with H 2O 2 and Sn-Beta or Sn-MCM-41 as catalysts. The performance of tin Lewis acid sites is compared with other potential catalytic sites, and it is found that aluminium Brønsted acid sites and zirconium or titanium Lewis acid sites are less efficient and selective than Sn. In the case of Ti, epoxidation by-products could be found. The re-usability of Sn-Beta zeolite is discussed, as is the heterogeneity of the reaction.

Highly Diastereoselective Hydrostannylation of Allyl and Homoallyl Alcohols with Dibutyl(trifluoromethanesulfoxy)stannane

Dibutyl(trifluoromethanesulfoxy)stannane (Bu2Sn(OTf)H, 1a) was found to be very valuable for highly diastereoselective homolytic hydrostannylation of allyl and homoallyl alcohols. alpha,beta-Disubstituted allyl alcohols and alpha,gamma-disubstituted homoallyl alcohols were converted into gamma- and delta-stannylated alcohols with high 1,2-syn and 1,3-syn diastereoselectivity, respectively. The origin of the stereochemical outcomes can be rationalized by conformational fixation of the intermediary beta-stannylalkyl radical by coordination of the hydroxy group to the Lewis acidic tin center.

Highly Regio‐ and Stereoselective Hydrostannylation of Alkynols with a New Lewis Acidic Hydrostannane.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly Regio- and Stereoselective Hydrostannylation of Alkynols with A New Lewis Acidic Hydrostannane

[reaction: see text] Bu2Sn(OTf)H (1a), easily prepared from Bu2SnH2 and TfOH, was found to be very valuable for highly regio- and stereoselective hydrostannylation of various propargyl alcohols leading to (Z)-gamma-stannylated allyl alcohols. The stannylation with 1a is applicable to the synthesis of hydroxy-substituted (Z)-vinylstannanes from terminal alkynes bearing a hydroxy group at the homoallylic or bishomoallylic position. The coordination of the hydroxy group to the Lewis acidic tin center plays an important role for the observed regio- and stereochemistry.

Chemistry of odorants: stereoselective synthesis of octahydronaphthalene-based perfumery Georgywood, (+,−)-1-[(1 R∗,2 S∗)-1,2,3,4,5,6,7,8-octahydro-1,2,8,8-tetramethylnaphthalen-2-yl]ethan-1-one

A straightforward synthesis of octahydronaphthalene-based fragrance, such as Georgywood, is described. The Lewis acid tin (IV) chloride catalyzed efficiently an original one-pot sequential cycloaddition–clyclization process by reaction of myrcene with 3-bromo-but-3-en-2-one, leading directly to the octahydronaphthalene skeleton in very good yields (85%). Then, dehydrohalogenation with DBU gave the key 2,4-dienone intermediate in excellent yield (85%). Regioselective Michael addition gave rise to the formation of the addition product as a trans/ cis diastereoisomeric mixture, by reaction either with CH 3Cu·BF 3 (6:1 ratio, 70%) or (CH 3) 2CuLi/TMSCl reagents (3:1 ratio, 80%). The generation of thermodynamically more stable enolate by treatment of the diastereoisomeric mixture with sodium hydride in tetrahydrofuran in the presence of an excess of methyl iodide, allowed stereoselective introduction of the methyl group at C2, leading to the formation of Georgywood in good yield (60%), as the only diastereoisomer, with a trans stereochemistry of the two methyl groups as demonstrated by NMR experiments.