Zeolite synthesis using degradable structure-directing agents and pore-filling agents

Zeolites and molecular sieves are synthesized using organic structure-directing agents (SDAs) that have the potential to be degraded into fragments within the pore space so that they can be readily extracted at mild conditions. The zeolites and molecular sieves, VPI-8, ZSM-12, and ZSM-5, are synthesized using the ketal-containing SDA, 8,8-dimethyl-1,4-dioxa-8-azoniaspiro[4,5]decane (SDA-1). As expected, solids with unidimensional pore systems (VPI-8, ZSM-12) are much more difficult to process by this methodology than solids containing multidimensional pore systems (ZSM-5). Pore-filling agents (PFAs) such as isobutylamine and cyclopentylamine are used together with the ketal-containing SDA-1 to prepare ZSM-5. Extraction of the PFA is shown to be feasible, and its removal provides space for components to enter the zeolite micropores where they react with and cleave SDA-1. Removal of the cleavage fragments from SDA-1 gives ZSM-5 that has the appropriate pore volume, framework aluminum (measured by 27Al NMR), and catalytic behavior. Reasons for desiring this new type of zeolite synthesis method are enumerated.     

在无有机导向剂条件下采用乙醇为助剂合成高硅沸石

高硅沸石具有优异的热稳定性、水热稳定性、大的微孔体积、高表面积和均匀的微孔孔道,因而广泛应用于催化领域.然而,高硅沸石的合成往往需要使用有机结构导向剂,不但增加了沸石合成成本,而且还产生了大量的三废排放.为了解决这个问题,我们发展了在无有机导向剂存在条件下采用沸石晶种诱导合成沸石的方法,但是该方法合成的沸石产物骨架富铝...     

Monomers that form conducting polymers as structure-directing agents: synthesis of microporous molecular sieves encapsulating poly-para-phenylenevinylene

We have developed a novel concept that uses monomers required for making conducting polymers as organic structure-directing agents, for the synthesis of microporous molecular sieves. We show that these monomers facilitate the formation of crystalline and amorphous molecular sieves depending on the synthesis procedure. The monomers filling the pores of the silicates can be polymerized under certain conditions, resulting in a polymer immobilized and protected inside the matrix. The concept was exemplified with para-phenylenemethylene-bis(1-tetrahydrothiophenium) and para-phenylenemethylene-bis(trimethylammonium) that were used to template microporous molecular sieves and subsequently to obtain poly-para-phenylenevinylene (PPV) inside the matrix. The organic self-assembled organic-inorganic material was extensively characterized and the implication on electrical conductivity is presented.     

Solvothermal synthesis of new open-framework metal phosphites with structure-directing agents generated in situ

By using amide molecules and a urea derivative as the source of structure-directing agents (SDAs), three open-framework metal phosphites, (CH₃NH₃)₂·[Be₃(HPO₃)₄] (1), (CH₃CH₂NH₃)₂·[Be₃(HPO₃)₄] (2), and [(CH₃)₂NH₂]_1.5·(H₃O)_0.5·[Al₄(HPO₃)₇(H₂O)₃]·(H₂O)_0.5 (3), have been synthesized under solvothermal conditions. Compound 1 has left- and right-handed helical channels running along the [001] directions. Compound 2 possesses zigzag 12-ring channels running along the [001] direction. Compound 3 contains multidirectional 12-ring channels running along the [100], [010], and [110] directions. It is noteworthy that the direct use of methylamine, ethylamine and dimethylamine as SDAs can't produce corresponding single crystals of compounds 1–3, demonstrating the slow release of amines from amide molecules and urea derivative is a key process for the crystal growth.     

Acylmethanesulfonamides as new acylating agents for primary amines

A new, simple and efficient procedure for the preparation of secondary amides through internal condensation of acylmethanesulfonamides ammonium salts is described. The selective acylation of mixed primary-secondary amines could be an attractive application of the new method.     

A study of piperidinium structure-directing agents in the synthesis of silica molecular sieves under fluoride-based conditions

This study is a continuation of our efforts to understand the interplay in the self-assembly chemistry for formation of molecular sieves from guest organocations and inorganic silicon oxide. In this particular study we focus on the competitive interplay of the organocations and the synthesis cofactor fluoride anion. The anions play a key role in structure determination, as a function of net solution concentration. They compete with the role for the space-filling organocation in determining which molecular sieve host structure will be specified. In this study we look at this competition in the synthesis for a series of 33 different organocations derived from the piperidine ring system. Derivatives were prepared which both fixed substituents on the carbon and nitrogen centers on the ring. Results were discussed in terms of product selectivity from synthesis as a function of solution concentration for the reactants. A total of 17 different host topologies were found in this series, and a correlation was seen for (a) open-framework lattices (low framework densities) under the most concentrated reaction conditions and then (b) high framework density products once the conditions were more dilute. Some surprising synthesis differences are seen in comparing the performance of these structure directing agents (SDAs) in fluoride media vs hydroxide media (the more conventional environment for zeolite/molecular sieve syntheses involving silicate chemistry). Finally molecular modeling was used to understand some of the trends in product selectivity for closely related guest (SDA) candidates.     

Urotropine as a ligand for the efficient synthesis of metal-organic frameworks

Russian Chemical Bulletin - Urotropine is a cheap and promising ligand for the synthesis of metal-organic frameworks containing uncoordinated nitrogen atoms. The reactions between urotropine,...     

Heteroacyl azides as acylating agents for aromatic or heteroaromatic amines

The possibility of formation of substituted heterocyclic amides from heteroacyl azides and aromatic or heteroaromatic amines was investigated. Although acylation proceeded in some cases under mild reaction conditions, formation of N,N′-disubstituted ureas was the main process at elevated temperatures.     

Nanoscale metal-organic frameworks as potential multimodal contrast enhancing agents

Nanoscale metal-organic frameworks (NMOFs) based on Gd3+ centers and benzenedicarboxylate and benzenetricarboxylate bridging ligands were synthesized using reverse microemulsions and characterized using SEM, PXRD, and TGA. These NMOFs exhibit extraordinarily large R1 and R2 relaxivities because of the presence of up to tens of millions of Gd3+ centers in each nanoparticle and are thus efficient T1 and T2 contrast agents for MRI. The NMOFs can also be made highly luminescent by doping with Eu3+ or Tb3+ centers. The results from this work suggest that NMOFs can be used as potential contrast agents for multimodal imaging.     

P-derived organic cations as structure-directing agents: synthesis of a high-silica zeolite (ITQ-27) with a two-dimensional 12-ring channel system

Recently, efforts have been made to synthesize large-pore, multidimensional zeolite frameworks as a basis for new catalysts to improve various hydrocarbon conversions. A new aluminosilicate zeolite, ITQ-27, has been prepared using the phosphorus-containing structure-directing agent, dimethyldiphenylphosphonium. Its crystal structure was determined in its calcined form by direct methods (FOCUS) on synchrotron powder diffraction data (lambda = 0.8702 A) after the unit cell and space group were determined from tilt electron diffraction experiments on individual microcrystals. The material crystallizes in space group Fmmm, where a = 27.7508(5) A, b = 25.2969(7) A, and c = 13.7923(4) A. The final model, refined by Rietveld methods, comprises seven unique T-sites forming a framework with straight 12-MR channels that are connected by 14-MR openings between them. (Corresponding 12-ring pore dimension is 6.94 A x 6.20 A.) Since access from one 14-MR opening to the next is through the 12-MR channel, the structure is best described as a two-dimensional, 12-MR framework.     

Macrocyclic amines as catalysts of the hydrolysis of the triphosphate bridge of the mRNA 5'-cap structure

The reactions of a 5'-cap model compound P1-(7-methylguanosine) P3-guanosine 5',5'-triphosphate, m7GpppG, were studied in the presence of three different macrocyclic amines (2-4) under neutral conditions. The only products observed in the absence of the macrocycles resulted from the base-catalysed imidazole ring-opening and the acid-catalysed cleavage of the N7-methylguanosine base, whereas in the presence of these catalysts hydrolysis of the triphosphate bridge predominated. The latter reaction yielded guanosine 5'-monophosphate, guanosine 5'-diphosphate, 7-methylguanosine 5'-monophosphate and 7-methylguanosine 5'-diphosphate as the initial products, indicating that both of the phosphoric anhydride bonds were cleaved. The overall catalytic activity of all three macrocycles was comparable. The hydrolysis to guanosine 5'-diphosphate and 7-methylguanosine 5'-monophosphate was slightly more favoured than the cleavage to yield guanosine 5'-monophosphate and 7-methylguanosine diphosphate. All the macrocycles also enhanced the subsequent hydrolysis of the nucleoside diphosphates, 2 being more efficient than 3 and 4.     

New agents for alkoxycarbonylation of amines

Alkoxycarbonylated pyrazinols and pyrazinethiols were prepared. These compounds were shown to be convenient agents for alkoxycarbonylation of aliphatic amines.     

Coordination-bond-directed synthesis of hydrogen-bonded organic frameworks from metal–organic frameworks as templates

Controlled synthesis of hydrogen-bonded organic frameworks (HOFs) remains challenging, because the self-assembly of ligands is not only directed by weak hydrogen bonds, but also affected by other competing van der Waals forces. Herein, we demonstrate the coordination-bond-directed synthesis of HOFs using a preformed metal–organic framework (MOF) as the template. A MOF (Cu^I-TTFTB) based on two-coordinated Cu^I centers and tetrathiafulvalene-tetrabenzoate (TTFTB) ligands was initially synthesized. Cu^I-TTFTB was subsequently oxidized to the intermediate (Cu^II-TTFTB) and hydrated to the HOF product (TTFTB-HOF). Single-crystal-to-single-crystal (SC-SC) transformation was realized throughout the MOF-to-HOF transformation so that the evolution of structures was directly observed by single-crystal X-ray diffraction. The oxidation and hydration of the Cu^I center are critical to breaking the Cu–carboxylate bonds, while the synergic corbelled S⋯S and π⋯π interactions in the framework ensured stability of materials during post-synthetic modification. This work not only provided a strategy to guide the design and discovery of new HOFs, but also linked the research of MOFs and HOFs.

The MOF-to-HOF transformation was realized in a single-crystal-to-single-crystal manner by the oxidation and hydration of the Cu^I center in Cu^I-TTFTB. The corbelled S⋯S and π⋯π interactions ensured the framework stability during transformation.     

Epoxyamide-based strategy for the synthesis of polypropionate-type frameworks

A new approach to the stereoselective synthesis of polypropionate-type frameworks is reported utilizing reactions of amide-stabilized sulfur ylides with chiral aldehydes. To establish a new strategy for macrolide fragment synthesis, the stereoselectivity of these reactions in the construction of epoxy amides was the most important aspect of this study. In this aspect, we found a strong influence of the protecting groups employed in the starting aldehydes upon the stereochemical outcome of their reactions with the sulfur ylide 1. Thus, numerous aldehydes showed remarkable stereofacial differentiation, providing a major diastereoisomer, in contrast to others that displayed a poor or no stereoselectivity. Despite the difficulties encountered for some cases with respect to their diastereomeric yields, we were able to prepare various stereotetrads and stereopentads, thus enhancing the synthetic value of this new methodology for the preparation of typical polypropionate frameworks found in many natural products, in particular the macrolide class of antibiotics.     

Supramolecular chemistry in the structure direction of microporous materials from aromatic structure-directing agents

A combination of fluorescence spectroscopy, thermogravimetric analysis, and molecular mechanics calculations has been used to study the structure-directing effect of the aromatic benzylpyrrolidine (BP) molecule (and its monofluorinated derivatives), and (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM) in the synthesis of the microporous AFI structure. The results clearly show that, while all molecules form supramolecular aggregates in concentrated water solution, BPM molecules have a much more pronounced trend to aggregate as dimers within the AFI structure due to the development of interdimer H-bond interactions. Instead, BP (and its ortho- and meta-fluorinated derivatives) SDAs tend to incorporate in the AFI structure as monomers but with the simultaneous occlusion of water molecules, while para-fluorinated BP derivatives do not form compact dimers able to be accommodated in the AFI structure. We propose a crystallization mechanism where the presence of dimers is required for the nucleation step to occur, while crystal growth takes place through the simultaneous occlusion of SDA monomers and water (when the synthesis is performed with BP and derivatives) or through the occlusion of SDA dimers (in the synthesis with BPM).     

1,1-Diacyloxy-1-phenylmethanes as versatile N-acylating agents for amines

1,1-Diacyloxy-1-phenylmethanes and 1-pivaloxy-1-acyloxy-1-phenylmethanes have been used as bench stable N-acylating reagents for primary and secondary amines and anilines under solvent-free conditions to afford their corresponding amides in good yield.