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Metal–organic frameworks (MOFs) are important porous materials. Post-synthetic modification (PSM) of MOFs via the pendant groups or secondary functional groups of organic linkers has been widely used to introduce new or enhance existing properties of MOFs for various practical applications. In this work, we have constructed, for the first time, a novel platform for PSM of MOFs by introducing an anhydride functional group into a hierarchically porous MOF (MIL-121) as an effective anchor. We have demonstrated that the combination of the high reactivity of anhydride and hierarchical porosity makes this protocol particularly novel and important, as it led to excellent opportunities of incorporating not only a wide variety of organic molecules with different sizes and chemical nature but also the noble metal complexes in MOFs. Specifically, we show that the anhydride group decorated in the MOF exhibits a high reactivity toward covalently binding 10 different guest molecules including alcohols, amines, thiols, and noble metal (Pt(II)/Pt(IV)) complexes, whereas the hierarchical pores created in the MOF allow the incorporation of guest species varying in size from methanol to larger molecules such as polyaromatic amines. This novel approach provides the community with a new avenue to prepare MOF-based materials for targeted applications. To illustrate this point, we furnish an example of using this new platform to prepare a Pt-based electrocatalyst which shows excellent catalytic activity toward the oxygen reduction reaction (ORR), a pivotal half-reaction in hydrogen–oxygen fuel cells and other energy storage and conversion devices.

In this work, we present a clean one-step process for modifying headgroups of self-assembled monolayers (SAMs) on gold using photo-enabled click chemistry. A thiolated, cyclopropenone-caged strained alkyne precursor was first functionalized onto a flat gold substrate through self-assembly. Exposure of the cyclopropenone SAM to UVA light initiated the efficient photochemical decarbonylation of the cyclopropenone moiety, revealing the strained alkyne capable of undergoing the interfacial strain-promoted alkyne–azide cycloaddition (SPAAC). Irradiated SAMs were derivatized with a series of model azides with varied hydrophobicity to demonstrate the generality of this chemical system for the modification and fine-tuning of the surface chemistry on gold substrates. SAMs were characterized at each step with polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) to confirm the successful functionalization and reactivity. Furthermore, to showcase the compatibility of this approach with biochemical applications, cyclopropenone SAMs were irradiated and modified with azide-bearing cell adhesion peptides to promote human fibroblast cell adhesion, and then imaged by live-cell fluorescence microscopy. Thus, the “photoclick” methodology reported here represents an improved, versatile, catalyst-free protocol that allows for a high degree of control over the modification of material surfaces, with applicability in materials science as well as biochemistry.

Dialkynylborane complexes of N-donor ligands have received significant attention because of their application in biological imaging, as light-harvesting materials, and as the functional component of organic photovoltaics. Despite these advances, relatively few types of N-donor ligands have been explored in this context. To this end, we prepared a series of dialkynylborane complexes of formazanate ligands and explored their electronic properties and reactivity. In doing so, we demonstrated that (1) the nature of the alkynyl substituents has little influence over the UV–vis absorption properties of the title complexes, but does affect the potentials at which they are electrochemically oxidized and reduced, (2) dialkynylborane formazanate complexes can be converted to stable radical anions by chemical reduction with cobaltocene derivatives, and (3) copper-assisted alkyne–azide cycloaddition chemistry at the alkynyl substituents directly bound to boron can be used to elaborate structural diversity. These conclusions are likely to lead to the development of, and provide guiding principles for the design of, future examples of functional molecular materials based on boron complexes of N-donor ligands.

Ultrasmall atomically precise monolayer-protected gold thiolate nanoclusters are an intensely researched nanomaterial framework, but there is a lack of a system that can be directly synthesized and undergo interfacial surface chemistry. We report an [Au25(SCH2CH2-p-C6H4-N3)18]−nanocluster platform with azide moieties appended onto each surface ligand. The structure of this surface reactive cluster has been confirmed by single-crystal X-ray crystallography, mass spectrometry and ultraviolet visible, infrared and nuclear magnetic resonance spectroscopies. We show that all surface azide moieties are amenable to cluster-surface strain-promoted alkyne–azide cycloaddition chemistry with a strained cyclooctyne, opening this as a new platform to allow functional, postassembly surface modifications to this very prominent nanocluster.

Highly accelerated inverse-electron-demand strain-promoted alkyne-nitrone cycloaddition (IED SPANC) between a stable cyclooctyne (bicyclo[6.1.0]nonyne (BCN)) and nitrones delocalized into a Cα-pyridinium functionality is reported, with the most electron-deficient “pyridinium-nitrone” displaying among the most rapid cycloadditions to BCN that is currently reported. Density functional theory (DFT) and X-ray crystallography are explored to rationalize the effects of N- and Cα-substituent modifications at the nitrone on IED SPANC reaction kinetics and the overall rapid reactivity of pyridinium-delocalized nitrones.

The development of reactive moieties that enable molecular control of bond-forming and bond-breaking reactions within complex media is highly important in materials and biomaterials research as it provides opportunities to carefully manipulate small molecules and material surfaces in a reliable manner. Despite recent advances in the realization of new ligation strategies and “click-and-release” systems, there has been little development of multifunctional moieties that feature a broad range of chemical capabilities. To address this challenge, we designed a molecular tool that can utilize four well-defined bioorthogonal chemistries interchangeably for the attachment, replacement, and release of molecules within a system: the Staudinger–Bertozzi ligation (SBL), perfluoroaryl azide Staudinger reaction (PFAA-SR), strain-promoted alkyne–azide cycloaddition (SPAAC), and strain-promoted alkyne–nitrone cycloaddition (SPANC). We demonstrate “click-to-release” and “double-click” reactivity on small molecules and gold nanoparticles (AuNPs) as a model material substrate. As a proof of concept for material derivatization, we employed 5 nm AuNPs—functionalized with a Rhodamine B derivative and biotin through the double-click strategy—and showed their potential as a pretargeted delivery nanocarrier. This multifunctional molecular tool enables the design and production of molecular and material systems with unique, modular, and tunable dynamic properties that can be altered under mild and bioorthogonal conditions.

The reaction of N-heterocyclic carbene (NHC) Group 11 metal complexes, [(NHC)M–X] (X = chloride, acetate), with the new azide-modified arylthiol 1-HSCH2-2,5-Me2-4-N3CH2-C6H2, 1(for M = Au; X = Cl), or 1-Me3SiSCH2-2,5-Me2-4-N3CH2-C6H2, 2(for M = Cu, X = Cl; M = Ag, X = OAc), affords the “clickable” NHC-metal thiolates [(iPr2-bimy)Au-(1-SCH2-2,5-Me2-4-N3CH2-C6H2)], 5; [(IPr)Au-(1-SCH2-2,5-Me2-4-N3CH2-C6H2)], 6; [(IPr)Ag-(1-SCH2-2,5-Me2-4-N3CH2-C6H2)], 7; and [(IPr)Cu-(1-SCH2-2,5-Me2-4-N3CH2-C6H2)], 8(iPr2-bimy = 1,3-di-isopropylbenzimidazol-2-ylidene, IPr = 1,3-bis(2,6-di-iso-propylphenyl)imidazol-2-ylidene). Single-crystal X-ray analysis of all metal complexes show that they are two-coordinate, nearly linear, with a terminally bonded thiolate ligand possessing an accessible azide (−N3) moiety. The strain-promoted alkyne–azide cycloaddition (SPAAC) reaction of complex 6with bicyclo[6.1.0]non-4-yn-9-ylmethanol (BCN–OH) and dibenzocyclooctyne-amine (DBCO–NH2) illustrated the reactivity of the azide moiety toward strain-promoted cycloaddition. The rate of the SPAAC reaction between complex 6and BCN–OH was determined via 1H NMR spectroscopy under second order conditions, and was compared to that of BCN–OH with PhCH2N3.

Loading metal guests within metal–organic frameworks (MOFs) via secondary functional groups is a promising route for introducing or enhancing MOF performance in various applications. In this work, 14 metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Zn2+, Co2+, Mn2+, Ag+, Cd2+, La3+, In3+, and Pb2+) have been successfully introduced within the MIL-121 MOF using a cost-efficient route involving free carboxylic groups on the linker. The local and long-range structure of the metal-loaded MOFs is characterized using multinuclear solid-state NMR and X-ray diffraction methods. Li/Mg/Ca-loaded MIL-121 and Ag nanoparticle-loaded MIL-121 exhibit enhanced H2and CO2adsorption; Ag nanoparticle-loaded MIL-121 also demonstrates remarkable catalytic activity in the reduction of 4-nitrophenol.

Tip-enhanced Raman spectroscopy (TERS) is a highly sensitive spectroscopic technique that combines the spatial resolution of scanning near-field techniques with the chemical specificity of vibrational spectroscopy. TERS is based on the excitation of the localized surface plasmon resonance at the apex of an AFM metallized tip, producing a confined and enhanced electromagnetic field. Due to the inherent local nature of TERS and its confinement in the optical near-field of the object, TERS measurements can also be used to probe monolayers adsorbed onto surfaces providing better surface specificity in addition to higher spatial resolution. We implement here gap-mode TERS using gold nanoplates functionalized with thiolated reference molecules such as alkoxy substituted azobenzene thiol and 4-nitrothiophenol. The monolayer is probed with a silver coated AFM tip in order to obtain the largest electromagnetic field enhancement from the surface plasmon localized between the silver tip and the functionalized gold surface. More specifically, we have measured the TERS spectra of the self-assembled monolayer on gold using 532 nm excitation that is linearly (Gaussian–transverse TEM00) and radially polarized. We report the nature of the collected TERS spectra for the thiolated molecules (azobenzene thiol and nitrothiophenol) that appear to be dependent on the polarization of the excitation light at the tip/substrate interface.

The synthesis and characterization of several compounds representing a new class of multitask‐specific phosphonium ionic liquids that contain a maleimide functionality is reported. The maleimide moiety of the ionic liquid (IL) is shown to undergo Michael‐type additions with substrates containing either a thiol or amine moiety, thus, serving as a template to introduce wide structural diversity into the IL. Multitask‐specific ILs are accessible by reaction of the maleimide with Michael donors that are capable of serving some function. As a model example to illustrate this concept, a redox active ferrocenyl thiol was incorporated and examined by cyclic voltammetry. Because the maleimide moiety is highly reactive to additions, the task‐specific ionic liquids (TSILs) are prepared as the furan‐protected Diels–Alder maleimide. The maleimide moiety can then be liberated when required by simple heating.

A series of 3,3,6,6‐tetraaryl‐1,2‐dioxanes (TADs) have been investigated at an inert electrode by using cyclic voltammetry, constant potential electrolysis and digital simulations. The series consists of the phenyl‐substituted TAD (1 a), p‐methoxy‐aryl TADs (1 b, 1 c) and the p‐methoxy/nitro‐bearing TAD (1 d). The heterogeneous electron‐transfer (ET) reduction is dissociative, causing rupture of the oxygen–oxygen bond, which generates a distonic radical‐anion that reacts competitively either by β‐scission fragmentation or ET. Fragmentation of the distonic radical anion yields an alkene, a substituted benzophenone, and a benzophenone radical anion. The benzophenone radical‐anion propagates an efficient homogeneous ET–fragmentation chain reaction that accounts for the potential dependence of the product ratios and the low charge consumption observed in the controlled potential electrolysis experiments. Digital simulation of the experimental cyclic voltammograms allowed for estimates of the rate constants of the heterogeneous ET to the OO bond, and for the rate constants for the β‐scission fragmentation of the distonic radical‐anions. Density functional theory calculations corroborate the differences in the heterogeneous kinetics of the initial dissociative ET. The endoperoxides 1 a–1 creact predominantly by a concerted dissociative ET mechanism, although the data suggests a stepwise dissociative pathway is also competitive. Bearing a nitro‐aryl substituent, 1 dprovides a rare example of an endoperoxide that proceeds by a stepwise dissociative ET mechanism. Irrespective of the initial mechanistic details, we find a propagating radical‐anion cycle is a general mechanistic feature.

The electron‐transfer (ET) reduction of two diphenyl‐substituted bicyclic endoperoxides was studied in N,N‐dimethylformamide by heterogeneous electrochemical techniques. The study provides insight into the structural parameters that affect the reduction mechanism of the OO bond and dictate the reactivity of distonic radical anions, in addition to evaluating previously unknown thermochemical parameters. Notably, the standard reduction potentials and the bond dissociation energies (BDEs) were evaluated to be −0.55±0.15 V and 20±3 kcal mol−1, respectively, the last representing some of the lowest BDEs ever reported. The endoperoxides react by concerted dissociative electron transfer (DET) reduction of the OO bond yielding a distonic radical‐anion intermediate. The reduction of 1,4‐diphenyl‐2,3‐dioxabicyclo[2.2.2]oct‐5‐ene (1) results in the quantitative formation of 1,4‐diphenylcyclohex‐2‐ene‐cis‐1,4‐diol by an overall two‐electron mechanism. In contrast, ET to 1,4‐diphenyl‐2,3‐dioxabicyclo[2.2.2]octane (2) yields 1,4‐diphenylcyclohexane‐cis‐1,4‐diol as the major product; however, in competition with the second ET from the electrode, the distonic radical anion undergoes a β‐scission fragmentation yielding 1,4‐diphenyl‐1,4‐butanedione radical anion and ethylene in a mechanism involving less than one electron. These observations are rationalized by an unprecedented catalytic radical‐anion chain mechanism, the first ever reported for a bicyclic endoperoxide. The product ratios and the efficiency of the catalytic mechanism are dependent on the electrode potential and the concentration of weak non‐nucleophilic acid. A thermochemical cycle for calculating the driving force for β‐scission fragmentation is presented, and provides insight into why the fragmentation chemistry of distonic radical anions is different from analogous neutral biradicals.

The electron‐acceptor properties of series of related sulfides and disulfides were investigated in N,N‐dimethylformamide with homogeneous (redox catalysis) and/or heterogeneous (cyclic voltammetry and convolution analysis) electrochemical techniques. The electron‐transfer rate constants were determined as a function of the reaction free energy and the corresponding intrinsic barriers were determined. The dependence of relevant thermodynamic and kinetic parameters on substituents was assessed. The kinetic data were also analyzed in relation to corresponding data pertaining to reduction of diaryl disulfides. All investigated reductions take place by stepwise dissociative electron transfer (DET) which causes cleavage of the CalkylS or SS bond. A generalized picture of how the intrinsic electron‐transfer barrier depends on molecular features, ring substituents, and the presence of spacers between the frangible bond and aromatic groups was established. The reduction mechanism was found to undergo a progressive (and now predictable) transition between common stepwise DET and DET proceeding through formation of loose radical anions. The intrinsic barriers were compared with available results for ET to several classes of dissociative‐ and nondissociative‐type acceptors, and this led to verification that the heterogeneous and the homogeneous data correlate as predicted by the Hush theory.

The reduction of the bicyclic G‐factor endoperoxides G3 and G3Me was studied in N,N‐dimethylformamide using cyclic voltammetry and convolution analysis. Electron transfer leads to irreversible cleavage of the OO bond. Detailed analysis of the voltammetry curves reveals a non‐linear dependence on the transfer coefficient indicating a mechanistic transition from a stepwise mechanism to one with more concerted character with increasing potential. By using quantum calculations to estimate the OO bond dissociation energies, the experimental data was used to evaluate the standard reduction potentials and other pertinent thermochemical information.

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The homogeneous and heterogeneous electron transfer (ET) reduction of ascaridole (ASC) and dihydroascaridole (DASC), two bicyclic endoperoxides, chosen as convenient models of the bridged bicyclic endoperoxides found in biologically relevant systems, were studied in aprotic media by using electrochemical methods. ET is shown to follow a concerted dissociative mechanism that leads to the distonic radical anion, which is itself reduced in a second step by an overall two-electron process. The kinetics of homogeneous ET to these endoperoxides from an extensive series of radical anion electron donors were measured as a function of the driving force of electron transfer (ΔG$\rm{_{ET}^{\circ})}$. The kinetics of heterogeneous ET were also studied by convolution analysis. Together, the heterogeneous and homogeneous ET kinetic data provide the best example of the parabolic nature of the activation–driving force relationship for a concerted dissociative ET described by Savéant; the data is particularly illustrative due to the low bond-dissociation enthalpy (BDE) of the O−O bond and hence small intrinsic barriers. Analysis of the data allowed the dissociative reduction potentials (E$\rm{_{diss}^{\circ})}$ to be determined as −1.2 and −1.1 V against SCE for ASC and DASC, respectively. Unusually low pre-exponential factors measured in temperature-dependent kinetic studies suggest that ET to these O−O bonded systems is nonadiabatic. Analysis of ET kinetics for ASC and DASC by the Savéant model with a modification for nonadiabaticity allowed the intrinsic free energy for ET to be determined. The use of this approach and estimates for the BDE provide approximations of the reorganization energies. We suggest the methodology described herein can be used to evaluate the extent of ET to other endoperoxides of biological relevance and to provide thermochemical data not otherwise available. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2111/2001/f3008_s.pdf or from the author. A complete description of the temperature dependent rate studies, including plots of the data and tables of the experimental and calculated activation parameters.

The homogeneous and heterogeneous electron transfer (ET) reduction of ascaridole (ASC) and dihydroascaridole (DASC), two bicyclic endoperoxides, chosen as convenient models of the bridged bicyclic endoperoxides found in biologically relevant systems, were studied in aprotic media by using electrochemical methods. ET is shown to follow a concerted dissociative mechanism that leads to the distonic radical anion, which is itself reduced in a second step by an overall two‐electron process. The kinetics of homogeneous ET to these endoperoxides from an extensive series of radical anion electron donors were measured as a function of the driving force of electron transfer (ΔG$\rm{_{ET}^{\circ})}$. The kinetics of heterogeneous ET were also studied by convolution analysis. Together, the heterogeneous and homogeneous ET kinetic data provide the best example of the parabolic nature of the activation–driving force relationship for a concerted dissociative ET described by Savéant; the data is particularly illustrative due to the low bond‐dissociation enthalpy (BDE) of the O−O bond and hence small intrinsic barriers. Analysis of the data allowed the dissociative reduction potentials (E$\rm{_{diss}^{\circ})}$to be determined as −1.2 and −1.1 V against SCE for ASCand DASC, respectively. Unusually low pre‐exponential factors measured in temperature‐dependent kinetic studies suggest that ET to these O−O bonded systems is nonadiabatic. Analysis of ET kinetics for ASCand DASCby the Savéant model with a modification for nonadiabaticity allowed the intrinsic free energy for ET to be determined. The use of this approach and estimates for the BDE provide approximations of the reorganization energies. We suggest the methodology described herein can be used to evaluate the extent of ET to other endoperoxides of biological relevance and to provide thermochemical data not otherwise available.

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The photochemistry of β-phenyl-4-methoxypropiophenone (1) in the isotropic and liquid crystalline (nematic and smectic B) phases of trans, trans-4′-alkyl-(1,1′-bicyclohexyl)-4-carbonitrile (CCH-n) and trans-4-alkylcyclohexyl-trans-4′-alkylcyclohexylcarboxylate (OS-nm) mesogens has been investigated using nanosecond laser flash photolysis techniques. Solubility limits of 1as a function of temperature in the smectic phases have been rigorously determined by 2H NMR spectroscopy, using α-, methoxy-, and β-phenyl-deuterated analogs of the ketone. Triplet decay of 1in the smectic (Crystal B) phase of CCH-4 is multiexponential, suggesting that the ketone is solubilized in a distribution of conformations in the highly-ordered liquid crystalline lattice. The average triplet lifetime of 1at various temperatures throughout the smectic phase is about a factor of three longer than that in homologous nematic and isotropic phases at the same temperature. The differences in the Arrhenius parameters for triplet decay in the smectic and nematic/isotropic phases are very small, however. The present results for 1in the smectic phase of the CCH-nmesogens correct the interpretation of previously reported data obtained with higher concentration mixtures, and afford an accurate indication of the true effects of smectic B liquid crystalline order on the conformation-dependent triplet state behavior of this molecule. In OS-nmliquid crystals, triplet decay follows clean first order kinetics in all phases, but the variations in Arrhenius dependence with solvent phase are similar to those observed in the CCH-nliquid crystals. Keywords: smectic, liquid crystals, 2H NMR, nanosecond laser flash photolysis, intramolecular triplet quenching, photochemistry.

Der molekulare Nanocluster[Ag48(μ4‐S)6(μ2/3‐SCH2Fc)36] (1) (siehe Bild; Ag blau, S gelb, Fe orange, C grau; Fc=Ferrocenyl) wurde in guten Ausbeuten hergestellt und durch Einkristall‐Röntgenbeugung charakterisiert. Die 36 Ferrocenylmethylthiolat‐Liganden hüllen den Ag‐S‐Kern vollständig ein, und cyclovoltammetrische Messungen von 1ergeben eine einzelne reversible Oxidationswelle.

We describe the synthesis and kinetic evaluation of compounds from [4 2] alone and [4 2] followed by [2 2] cycloaddition reactions of electrochemically generated o-benzoquinone with 1,3-cyclopentadiene.

Trimethylsilylselenoferrocene 1has been prepared in good yield. The reactive silyl group on 1is used as a driving force for the synthesis Cl4Cd4μ2-SeC5H4FeC5H562−2, a Cd4Se6adamantoid cluster with six surface ferrocenyl groups.

Electron transfer to 3,3,6,6-tetraphenyl-1,2-dioxane results in the cleavage of the oxygen-oxygen bond, generating a distonic radical anion intermediate whose fragmentation initiates an unprecedented radical anion chain process in competition with a second electron transfer.

Electron transfer to 3,3,6,6-tetraphenyl-1,2-dioxane results in the cleavage of the oxygen-oxygen bond, generating a distonic radical anion intermediate whose fragmentation initiates an unprecedented radical anion chain process in competition with a second electron transfer.

Trimethylsilylselenoferrocene 1 has been prepared in good yield. The reactive silyl group on 1 is used as a driving force for the synthesis [Cl₄Cd₄{μ₂-Se(C₅H₄)Fe(C₅H₅)}₆]2− 2, a Cd₄Se₆ adamantoid cluster with six surface ferrocenyl groups.

For Abstract see ChemInform Abstract in Full Text.

For Abstract see ChemInform Abstract in Full Text.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.