Post-synthetic Transformation Research Articles

Leveraging ordered voids in microporous perovskites for intercalation and post-synthetic modification.

We report the use of porous organic layers in two-dimensional hybrid organic-inorganic perovskites (HOIPs) to facilitate permanent small molecule intercalation and new post-synthetic modifications. While HOIPs are well-studied for a variety of optoelectronic applications, the ability to manipulate their structure after synthesis is another handle for control of physical properties and could even enable use in future applications. If designed properly, a porous interlayer could facilitate these post-synthetic transformations. We show that for a series of copper-halide perovskites, a crystalline arrangement of designer ammonium groups allows for permanently porous interlayer space to be accessed at room temperature. Intercalation of the electroactive molecules ferrocene and tetracyanoethylene into this void space can be performed with tunable loadings, and these intercalated perovskites are stable for months. The porosity also enables reactivity at the copper-halide layer, allowing for facile halide replacement. Through this, we access previously unobserved reactivity with halogens to perform halide substitution, and even replace halides with pseudohalides. In the latter case, the porous structure allows for stabilization of new phases, specifically a novel copper-thiocyanate perovskite phase, only accessible through post-synthetic modification. We envision that this broad design strategy can be expanded to other industrially relevant HOIPs to create a new class of highly adjustable perovskites.

Palladium-Catalyzed Strain-Enabled [2π + 2σ] Cycloadditions of Vinyl Bicyclo[1.1.0]butanes with Methyleneindolinones.

A palladium-catalyzed [2π + 2σ] cycloaddition of vinyl bicyclo[1.1.0]butanes with methyleneindolinones has been developed. The reaction enables the construction of spirobicyclo[2.1.1]hexanes bearing an all-carbon quaternary center in moderate to good yields with excellent diastereoselectivities. This method features a broad substrate scope with good functional group compatibility. The practical utility of this protocol was further demonstrated by gram-scale synthesis and postsynthetic transformations of desired product.

Regio-, Enantio-Controlled Cascade Oxa-Michael Addition of Hydroxyl Amine: Synthesis of Dihydro-1,2-Oxazines.

Herein, we disclose a cinchona-alkaloid-based squaramide-catalyzed intermolecular oxa-Michael cascade addition cyclization of N-protected hydroxyl amine to formyl-tethered Michael acceptors toward the synthesis of enantioenriched 1,2-oxazine scaffolds. Generally, good yield (up to 78%), good to excellent enantiomeric ratio (up to 98:2 er), and excellent regioselectivity (>19:1) were observed. Furthermore, the scalability of this methodology and a successful demonstration of postsynthetic transformations have been accomplished.

A Regioselective, One-Pot, Transition-Metal-Free α-Alkylation of Quinone Monoacetals for Various Organic Transformations.

Regioselective reactions of biologically significant quinones are challenging. An unprecedented advancement in quinone monoacetal (QMA) chemistry is proposed for constructing regioselective and less explored α-alkylated QMAs through the Morita-Baylis-Hillman (MBH) reaction. Electrophilic QMAs were transformed to nucleophilic umpolung reagents for aldol-type condensation with several electrophiles. Mechanistic studies reveal that solvent (TFE:water (1:1)) and in situ-generated potassium acetate accelerate the reaction. The ensuing MBH adducts were scalable and underwent several post-synthetic transformations and late-stage functionalization.

Ag(I)-Mediated Site-Selective C(sp2)-H Chalcogenation of Tryptophan-Peptides with Dichalcogenides at Room Temperature.

This report presents a silver-mediated site-selective chalcogenation of tryptophan-containing peptides with various dichalcogenides (disulfides/diselenides) at room temperature in good to excellent yields. The significant features include broad substrate scope, functional group diversity, late-stage modification of drug molecules (Dopamine and Levodopa), and various valuable postsynthetic transformations under mild conditions.

High-Temperature Solid-State Post-Synthetic Modification of Highly Luminescent Cu(I) Metallacycles toward New Luminescent Thermic Tracers.

A new luminescent Cu(I) tetrametallic metallacycle B is reported that features very rare semi-bridging aqua ligands. When heated markedly above room temperature, this compound undergoes a post-synthetic transformation in the solid-state, affording the new luminescent metallacycle C. Thermogravimetric analysis, IR spectroscopy and single-crystal X-ray diffraction reveal that this alteration preserves the gross tetrametallic macrocycle structure, but is caused by the release of the coordinated water molecules with the concomitant formation of cuprophilic interactions. This transition induces a shift from eye-perceived green (B) to blue (C) room-temperature luminescence for these molecular solids. Photophysical measurements and time-dependent density-functional theory calculations have been conducted to identify the origins of the emission properties lying in these structurally related assemblies, and suggest that thermally activated delayed fluorescence dominates the radiative relaxation pathways. This study highlights the innovative feature of Cu(I) derivatives, offering access to stimuli-sensitive materials that can witness, a posteriori, the exceeding of critical temperatures in their environment.

Umpolung Reactivity of in Situ Derived Aryl Hydrazones: An Asymmetric Brønsted Acid Catalyzed Strategy to Access Fused Pyrazolidines.

Herein, we report an intriguing cascade strategy for synthesizing optically active fused pyrazolidines featuring three contiguous stereogenic centers. The formyl-tethered enones are templates for the developed umpolung reactivity, showcasing diverse substrate adaptability with various arylhydrazines. The chiral phosphoric acid catalyst offers stereochemical guidance, forming the fused pyrazolidines with commendable to excellent stereoselectivities. Additionally, the scalability, postsynthetic transformations, and instability of unacylated pyrazolidines have been successfully demonstrated.

A One-Pot Cascade Strategy toward Organocatalytic Enantioselective Construction of Fused Benzimidazoles.

Herein, we describe an asymmetric assembly of ortho-aromatic diamines and formyl tethered Michael acceptors forming chiral fused benzimidazoles. A cinchona-alkaloid-derived bifunctional squaramide catalyst enables the methodology through on-site dihydrobenzimidazole formation followed by an aza-Michael addition/oxidation cascade. This protocol stands out for its excellent catalytic efficiency over the background reaction and its mild conditions, making it more practical. Various Michael acceptors, including enones, ester, and thioester, were successful substrates in this study. Additionally, this methodology has demonstrated scalability and successfully showcased postsynthetic transformations.

Nanomaterials Research at a Primarily Undergraduate Institution: Transforming Nanorods, Undergraduate Research Communities, and Infrastructure.

Undergraduate research transforms student's conceptions of themselves as scientists and encourages participation and retention in science, technology, engineering, and mathematics (STEM) fields. Many barriers exist to carrying out scientifically impactful undergraduate research in nanomaterials at primarily undergraduate institutions (PUIs). Here, we share several practices and design principles that demonstrate pathways to overcome these barriers. Design of modular research projects with low entry barriers is essential. Postsynthetic transformation of nanoparticles is a field that enables such design and has been used successfully to advance nanoscience research while being achievable within undergraduate laboratories. Relatively large, inclusive research communities can be supported through the creation of opportunities with peer- and near-peer mentoring. We also share emerging strategies for enabling routine undergraduate access to transmission electron microscopy, which is one of the most mainstream characterization techniques in nanoscience yet is frequently absent from the infrastructure at undergraduate-focused institutions.

NHC-Catalyzed Formal [4 + 2] Annulation of o-Formyl-Tethered Michael Acceptors and Ynones to Access Highly Functionalized Naphthalene Derivatives.

Herein we demonstrate a novel organocatalytic method to access multifunctionalized naphthalenes via an NHC-catalyzed reaction of ynones and o-formyl-tethered Michael acceptors. The presented method proceeds through an intermolecular Stetter reaction-cyclization-aromatization cascade and represents a rare example of organocatalytic benzannulation for the synthesis of substituted arenes by using ynone as a two-carbon synthon. The current method has broad substrate scope; postsynthetic transformations and gram-scale syntheses highlight the practicality of the displayed methodology.

Base‐Promoted Structural Rearrangement of Ynamide and Simultaneous N‐Desulfonylation

AbstractHerein, we describe a base‐promoted regioselective and chemoselective cascade cyclization, ynamide N−Csp bond cleavage, selective intramolecular 1,3‐migration, and simultaneous N‐desulfonylation strategy for the synthesis of 2‐phenyl‐3‐(phenylethynyl)‐1H‐indole derivatives. We observed multiple bond breaking (−N−Ts, and Csp2−Ts, Csp2−I/Csp2−SePh) from (E)‐3‐(1‐iodo‐2‐phenyl‐2‐tosylvinyl)‐2‐phenyl‐1‐tosyl‐indole/(E)‐2‐phenyl‐3‐(2‐phenyl‐1‐(phenylselanyl)‐2‐tosylvinyl)‐1‐tosyl‐indole derivatives to prepare 2‐phenyl‐3‐(phenylethynyl)‐1H‐indole in 15–60 min using our standard reaction conditions. A gram‐scale experiment as well as postsynthetic transformations of the synthesized 2‐phenyl‐3‐(phenylethynyl)‐1H‐indole were performed to exhibit the advantages of this synthetic methodology.

Inherent directing group-enabled Co(III)-catalyzed C-H allylation/vinylation of isoquinolones.

Co(III)-catalysed site-selective C8-allylation and vinylation of isoquinolones with allyl acetate and vinyl acetates has been accomplished. The oxo group of isoquinolone has been utilised as an inherent directing group. Based on preliminary mechanistic studies, a plausible mechanism for the developed reaction has also been delineated. Broad substrate scope with good to excellent yields and post-synthetic transformations of allylated and vinylated isoquinolines highlight the importance of the reaction.

Temperature-Dependent Selection of Reaction Pathways, Reactive Species, and Products during Postsynthetic Selenization of Copper Sulfide Nanoparticles.

Rational design of elaborate, multicomponent nanomaterials is important for the development of many technologies such as optoelectronic devices, photocatalysts, and ion batteries. Combination of metal chalcogenides with different anions, such as in CdS/CdSe structures, is particularly effective for creating heterojunctions with valence band offsets. Seeded growth, often coupled with cation exchange, is commonly used to create various core/shell, dot-in-rod, or multipod geometries. To augment this library of multichalcogenide structures with new geometries, we have developed a method for postsynthetic transformation of copper sulfide nanorods into several different classes of nanoheterostructures containing both copper sulfide and copper selenide. Two distinct temperature-dependent pathways allow us to select from several outcomes-rectangular, faceted Cu2-xS/Cu2-xSe core/shell structures, nanorhombuses with a Cu2-xS core, and triangular deposits of Cu2-xSe or Cu2-x(S,Se) solid solutions. These different outcomes arise due to the evolution of the molecular components in solution. At lower temperatures, slow Cu2-xS dissolution leads to concerted morphology change and Cu2-xSe deposition, while Se-anion exchange dominates at higher temperatures. We present detailed characterization of these Cu2-xS-Cu2-xSe nanoheterostructures by transmission electron microscopy (TEM), powder X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning TEM-energy-dispersive spectroscopy. Furthermore, we correlate the selenium species present in solution with the roles they play in the temperature dependence of nanoheterostructure formation by comparing the outcomes of the established reaction conditions to use of didecyl diselenide as a transformation precursor.

Amine Chemistry of Porous CO2 Adsorbents.

ConspectusAs renewable energy and CO2 utilization technologies progress to make a more significant contribution to global emissions reduction, carbon capture remains a critical component of the mission. Current CO2 capture technologies involve operations at point sources such as fossil fuel-based power plants or source-agnostic like in direct air capture. Each strategy has its own advantages and limitations, but in common, they all employ sorption-based methods with the use of sorbents strongly adhering to CO2. Amine solutions are the most widely used absorbents for industrial operations due to the robust chemical bonds formed between amines and CO2 under both dry and humid conditions, rendering excellent selectivity. Such strong binding, however, causes problematic regeneration. In contrast, purely physisorptive porous materials with high surface areas allow for the confinement of CO2 inside narrow pores/channels and have a lower regeneration energy demand but with decreased selectivity and capacity. The most promising solution would then be the unification of both types of sorbents in one system, which could bring about a practical adsorption-desorption process. In other words, the development of porous solid materials with tunable amine content is necessary to leverage the high contact surface of porous sorbents with the added ability to manipulate amine incorporation toward lower CO2 binding strength.To answer the call to uncover the most feasible amine chemistry in carbon capture, our group has devoted intense effort to the study of amine-based CO2 adsorbents for the past decade. Oriented along practicality, we put forth a principle for the design of our materials to be produced in no more than three synthetic steps with economically viable starting materials. Porous organic polymers with amine functionalities of various substitutions, meaning primary, secondary, and tertiary amines, were synthesized and studied for CO2 adsorption. Direct synthesis proved to be feasibly applicable for secondary and tertiary amine-incorporated porous polymers whereas primary-amine-based sorbents would be conveniently obtained via postsynthetic modifications. Sorbents based on tertiary amines exhibit purely physical adsorption behavior if the nitrogen atoms are placed adjacent to aromatic cores due to the conjugation effect that reduces the electron density of the amine. However, when such conjugation is inhibited, chemisorptive activity is observed. Secondary amine adsorbents, in turn, express a higher binding strength than tertiary amine counterparts, but both types can merit a strengthened binding by the physical impregnation of small-molecule amines. Sorbents with primary-amine tethers can be obtained via postsynthetic transformation of precursor functionalities, and for them, chemical adsorption is mainly at work. We conclude that mixed-amine systems could exhibit unprecedented binding mechanisms, resulting in exceptionally specific interactions that would be useful for the development of highly selective sorbents for CO2.

Post-synthetic transformation of metal–organic frameworks revealing secondary coordination sites for incorporation of catalytic metal centres

Post-synthetic transformation of metal–organic frameworks revealing secondary coordination sites for incorporation of catalytic metal centres

Postsynthetic Transformation of Imine- into Nitrone-Linked Covalent Organic Frameworks for Atmospheric Water Harvesting at Decreased Humidity.

Herein, we report a facile postsynthetic linkage conversion method giving synthetic access to nitrone-linked covalent organic frameworks (COFs) from imine- and amine-linked COFs. The new two-dimensional (2D) nitrone-linked covalent organic frameworks, NO-PI-3-COF and NO-TTI-COF, are obtained with high crystallinity and large surface areas. Nitrone-modified pore channels induce condensation of water vapor at 20% lower humidity compared to their amine- or imine-linked precursor COFs. Thus, the topochemical transformation to nitrone linkages constitutes an attractive approach to postsynthetically fine-tune water adsorption properties in framework materials.

Non-solvent post-modifications with volatile reagents for remarkably porous ketone functionalized polymers of intrinsic microporosity

Chemical modifications of porous materials almost always result in loss of structural integrity, porosity, solubility, or stability. Previous attempts, so far, have not allowed any promising trend to unravel, perhaps because of the complexity of porous network frameworks. But the soluble porous polymers, the polymers of intrinsic microporosity, provide an excellent platform to develop a universal strategy for effective modification of functional groups for current demands in advanced applications. Here, we report complete transformation of PIM-1 nitriles into four previously inaccessible functional groups – ketones, alcohols, imines, and hydrazones – in a single step using volatile reagents and through a counter-intuitive non-solvent approach that enables surface area preservation. The modifications are simple, scalable, reproducible, and give record surface areas for modified PIM-1s despite at times having to pass up to two consecutive post-synthetic transformations. This unconventional dual-mode strategy offers valuable directions for chemical modification of porous materials.

Mn(OAc)3-Mediated Unexpected Cycloannulative Sulfonyl Migration Cascade using (E)-β-Iodovinyl Sulfones and ortho-Alkynylphenols for Direct Synthesis of Chromene-Derived Vinyl Sulfones.

Cycloannulative sulfonyl migration has received much attention; however, a carbon-to-carbon sulfonyl group shift still needs to be discovered. We hereby report a base-mediated oxa-Michael addition-elimination of (E)-β-iodovinyl sulfones with ortho-alkynylphenols, followed by cycloisomerization and unique stereoselective sulfonyl migration in one-pot, is realized under the influence of Mn(OAc)3·2H2O. A broad range of vinyl sulfone-tethered chromenes were readily accessed in moderate to high yields with good functional group compatibility. Notably, the reaction was robust at the gram scale, and postsynthetic transformations were successfully uncovered. Moreover, plausible mechanistic pathways were rationalized on the basis of existing experimental results.

Iodocycloisomerization/Nucleophile Addition Cascade Transformations of 1,2-Alkynediones

A general electrophilic iodocyclization/nucleophile addition cascade transformation for 1,2-alkynediones for the synthesis of various oxygen heterocycles and access to regioselective alkyne hydroxylation is reported. Furan-tethered ynediones resulted in the construction of exo-enol ethers via carbonyl-alkyne cyclization-initiated heteroarene dearomatization, whereas other (hetero)arene-, alkenyl-, and alkyl-tethered ynediones resulted in the formation of highly functionalized 3(2H)-furanones. Importantly, the developed domino protocols involve the construction of important heterocyclic scaffolds and installation of two functional groups in a single operation. Moreover, the use of water as a nucleophile resulted in regioselective alkyne hydroxylation via furanone ring opening. The developed protocols are characterized by a wide substrate scope, and their utility has been demonstrated by a number of postsynthetic transformations.

Multistep synthesis and X-ray structures of carboxyl-terminated hybrid iron(II) phthalocyaninatoclathrochelates and their postsynthetic transformation into polytopic carboranyl-containing derivatives.

A multistep general synthetic strategy towards polytopic carboranyl-containing (semi)clathrochelate metal complexes, based on the template synthesis, transmetallation, amide condensation and 1,3-dipolar cycloaddition reactions, is developed. Their mono(semi)clathrochelate precursors with a single reactive group were obtained using a transmetallation of the triethylantimony-capped macrobicyclic precursor. The thus obtained carboxyl-terminated iron(II) semiclathrochelate underwent a macrobicyclization with zirconium(IV) phthalocyaninate to form the corresponding phthalocyaninatoclathrochelate. The direct one-pot template condensation of the suitable chelating and cross-linking ligand synthons on the Fe2+ ion as a matrix was also used for its preparation. Further amide condensation of the aforementioned semiclathrochelate and hybrid complexes with propargylamine in the presence of carbonyldiimidazole gave the (pseudo)cage derivatives with a terminal CC bond. Their "click" reaction with an appropriate carboranylmethyl azide afforded the ditopic carboranosemiclathrochelates and the tritopic carboranyl-containing phthalocyaninatoclathrochelates with a flexible spacer fragment between their polyhedral entities. The obtained new complexes were characterized using elemental analysis, MALDI-TOF mass spectrometry, multinuclear NMR, and UV-vis spectroscopy, and by single crystal X-ray diffraction experiments. Their FeN6-coordination polyhedra show a truncated trigonal-pyramidal geometry, while the cross-linking heptacoordinate Zr4+ or Hf4+ cations in the hybrid compounds form the MIVN4O3-coordination polyhedra with the geometry of a capped trigonal prism.