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Ab initio structure solutions of two solvent containing potassium phenoxides using high-resolution powder x-ray diffraction methods are described. The new pseudoatom technique used in previous study of the structure solution of C6H5OK6 was also applied in the experiment. The compounds exhibited polymeric zigzag chains aligned along the c-axis. It was also observed that the coordination of the potassium was the same for both compounds. The resulting compounds can be used in the classification of the mechanism of Kolbe-Schmitt type reactions.

The geometric distortions imposed by the pyridinophane macrocycle on Cu(I) and Cu(II) is analyzed and the reactivity of the LCu(super +) fragment toward the dioxygen is reported. It is suggested that O(sub 2) oxidizes the Cu(II) species by an inner sphere mechanism through coordinated O(sub 2) and the impact of macrocycle is not much in reactant destabilization but it is occurs when copper reaches higher oxidation states.

The macrocycle [2.1.1]-(2,6)-pyridinophane (L) binds to CuCI to give a monomeric molecule with tridentate binding of the ligand but in a distorted tetrahedral "3 + 1" geometry, where one nitrogen forms a longer (by 0.12 Å) bond to Cu. In dichloromethane solvent this pyridine donor undergoes facile site exchange with a second pyridine in the macrocycle, to give time-averaged mirror symmetry. Both experimental and density functional theory studies of the product of chloride abstraction, using NaBArF2 in CH2CI2, show that the Cu+ binds in a trigonal pyramidal, not planar, arrangement in LCu+. This illustrates the ability of macrocyclic ligand constraint to impose an electronically unfavorable geometry on 3-coordinate Cu(I). LCuBArF4 and a triflate analogue LCuI(OTf)readily react with oxygen in dichloromethane to produce, in the latter case, a hydroxo-bridged dimer [LCuII(µ-OH)]2(OTf)2, of the intact (unoxidized) ligand L. Since the analogous LCuCI does not react as fast with O2 in CH2CI2, outer-sphere electron transfer is concluded to be ineffective for oxidation of cuprous ion here. [ABSTRACT FROM AUTHOR]

Focuses on the use of the high-resolution powder x-ray diffraction in reporting the ab initio structure solutions, relating to the solvent which contains potassium phenoxides. Industrial importance of the carboxylation of alkali phenolates, known as Kolbe-Schmitt synthesis; Sublimation of phenol; Similarity of coordination of the potassium ions for both compounds; Information on these structure solutions.

Despite their potential relevance as molecular models for industrial and biological catalysis, well-defined mononuclear iron carbide complexes are unknown, in part due to the limited number of appropriate C 1 synthons. Here, we show the ability of the cyaphide anion (C≡P - ) to serve as a C 1 source. The high spin ( S = 2) cyaphide complex PhB( t BuIm) 3 Fe-C≡P (PhB( t BuIm) 3 - = phenyl(tris(3- tert -butylimidazol-2-ylidene)borate) is readily accessed using the new cyaphide transfer reagent [Mg( Dipp NacNac)(CP)] 2 ( Dipp NacNac = CH{C(CH 3 )N(Dipp)} 2 and Dipp = 2,6-di(iso-propyl)phenyl). Phosphorus atom abstraction is effected by the three-coordinate Mo(III) complex Mo(N t BuAr) 3 (Ar = 3,5-Me 2 C 6 H 3 ), which produces the known phosphide ( t BuArN) 3 Mo≡P along with a transient iron carbide complex PhB( t BuIm) 3 Fe≡C. Electronic structure calculations reveal that PhB( t BuIm) 3 Fe≡C adopts a doublet ground state with nonzero spin density on the carbide ligand. While isolation of this complex is thwarted by rapid dimerization to afford the corresponding diiron ethynediyl complex, the carbide can be intercepted by styrene to provide an iron alkylidene.

The reaction of equimolar trimethylsilyldiazomethyllithium (LiTMSD) with high spin ( S = 2) PhB(AdIm) 3 FeCl (PhB(AdIm) 3 - = tris(3-adamantylimidazol-2-ylidene)phenylborate) affords the corresponding N- nitrilimido complex PhB(AdIm) 3 Fe-N═N═C(SiMe 3 ). This complex can be converted to the thermodynamically more favorable C -isocyanoamido isomer PhB(AdIm) 3 Fe-C═N═N(SiMe 3 ) by reaction with an additional equivalent of LiTMSD. While the iron(II) complexes are four-coordinate, the diazomethane is bound side-on in the iron(I) congener PhB(AdIm) 3 Fe( N , N '-κ 2 -N 2 C(H)Si(CH 3 ) 3 ). The latter complex adopts high spin ( S = 3/2) ground state and features an unusually weak C-H bond. Photolysis of the iron(II) complexes induces N═N bond cleavage, with the iron(II) cyanide PhB(AdIm) 3 Fe-C≡N and iron(IV) nitride PhB(AdIm) 3 Fe≡N complexes being the major products of the reaction. The same products are obtained when the iron(I) complex is photolyzed or treated with a fluoride source. The trimethylsilyldiazomethane-derived ligand disassembly reactions are contrasted with those observed for related tris(carbene)amine complexes.

We report a neutral high-spin diradical of chiral C 2 -symmetric bis[5]diazahelicene with Δ E ST ≈ 0.4 kcal mol -1 , as determined by EPR spectroscopy/SQUID magnetometry. The diradical is the most persistent among all high-spin aminyl radicals reported to date by a factor of 20, with a half-life of up to 6 days in 2-MeTHF at room temperature. Its triplet ground state and excellent persistence may be associated with the unique spin density distribution within the dihydrophenazine moiety, which characterizes two effective 3-electron C-N bonds analogous to the N-O bond of a nitroxide radical. The enantiomerically enriched (ee ≥ 94%) ( MM )- and ( PP )-enantiomers of the precursors to the diradicals are obtained by either preparative chiral supercritical fluid chromatography or resolution via functionalization with the chiral auxiliary of the C 2 -symmetric racemic tetraamine. The barrier for the racemization of the solid tetraamine is Δ G ‡ = 43 ± 0.01 kcal mol -1 in the 483-523 K range. The experimentally estimated lower limit of the barrier for the racemization of a diradical, Δ G ‡ ≥ 26 kcal mol -1 in 2-MeTHF at 293 K, is comparable to the DFT-determined barrier of Δ G ‡ = 31 kcal mol -1 in the gas phase at 298 K. While the enantiomerically pure tetraamine displays strong chiroptical properties, with anisotropy factor | g | = |Δε|/ε = 0.036 at 376 nm, | g | ≈ 0.005 at 548 nm of the high-spin diradical is comparable to that recently reported triplet ground-state diradical dication. Notably, the radical anion intermediate in the generation of diradical exhibits a large SOMO-HOMO inversion, SHI = 35 kcal mol -1 .

We report complex formation between the chloroacetamide 2,6-diazaadamantane nitroxide radical (ClA-DZD) and cucurbit[7]uril (CB-7), for which the association constant in water, K a M 6 M -1 , is at least 1 order of magnitude higher than the previously studied organic radicals. The radical is highly immobilized by CB-7, as indicated by the increase in the rotational correlation time, τ rot , by a factor of 36, relative to that in the buffer solution. The X-ray structure of ClA-DZD@CB-7 shows the encapsulated DZD guest inside the undistorted CB-7 host, with the pendant group protruding outside. Upon addition of CB-7 to T4 Lysozyme (T4L) doubly spin-labeled with the iodoacetamide derivative of DZD, we observe the increase in τ rot and electron spin coherence time, T m , along with the narrowing of interspin distance distributions. Sensitivity of the DEER measurements at 83 K increases by a factor 4-9, compared to the common spin label such as MTSL, which is not affected by CB-7. Interspin distances of 3 nm could be reliably measured in water/glycerol up to temperatures near the glass transition/melting temperature of the matrix at 200 K, thus bringing us closer to the goal of supramolecular recognition-enabled long-distance DEER measurements at near physiological temperatures. The X-ray structure of DZD-T4L 65 at 1.12 Å resolution allows for unambiguous modeling of the DZD label (0.88 occupancy), indicating an undisturbed structure and conformation of the protein.

Open-shell organic molecules, including S = 1/2 radicals, may provide enhanced properties for several emerging technologies; however, relatively few synthesized to date possess robust thermal stability and processability. We report the synthesis of S = 1/2 biphenylene-fused tetrazolinyl radicals 1 and 2 . Both radicals possess near-perfect planar structures based on their X-ray structures and density-functional theory (DFT) computations. Radical 1 possesses outstanding thermal stability as indicated by the onset of decomposition at 269 °C, based on thermogravimetric analysis (TGA) data. Both radicals possess very low oxidation potentials <0 V (vs. SCE) and their electrochemical energy gaps, E cell ≈ 0.9 eV, are rather low. Magnetic properties of polycrystalline 1 are characterized by superconducting quantum interference device (SQUID) magnetometry revealing a one-dimensional S = 1/2 antiferromagnetic Heisenberg chain with exchange coupling constant J '/ k ≈ -22.0 K. Radical 1 in toluene glass possesses a long electron spin coherence time, T m ≈ 7 μs in the 40-80 K temperature range, a property advantageous for potential applications as a molecular spin qubit. Radical 1 is evaporated under ultrahigh vacuum (UHV) forming assemblies of intact radicals on a silicon substrate, as confirmed by high-resolution X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) images indicate that the radical molecules form nanoneedles on the substrate. The nanoneedles are stable for at least 64 hours under air as monitored by using X-ray photoelectron spectroscopy. Electron paramagnetic resonance (EPR) studies of the thicker assemblies, prepared by UHV evaporation, indicate radical decay according to first-order kinetics with a long half-life of 50 ± 4 days at ambient conditions.

Two-coordinate silylamido complexes of nickel and copper rapidly react with CO 2 to selectively form a new cyanate ligand along with hexamethyldisiloxane byproducts. Mechanistic insight into these reactions was obtained from the synthesis of proposed intermediates, several silyl- and phenyl- substituted amido analogues, and their subsequent reactivity with CO 2 . These studies suggest that a unique intramolecular double silyl transfer step facilitates CO 2 deoxygenation, which likely contributes to the rapid rates of reaction. The deoxygenation reactions create a platform for a synthetic cycle in which copper amido complexes convert CO 2 to organic silylcarbamates.

The nitride ligand in the iron(IV) complex PhB( i Pr 2 Im) 3 Fe≡N reacts with boron hydrides to afford PhB( i Pr 2 Im) 3 FeN( B )H ( B = 9-BBN ( 1 ), Bpin ( 2 )) and with (Bpin) 2 to afford PhB( i Pr 2 Im) 3 FeN(Bpin) 2 ( 3 ). The iron(II) borylamido products have all been structurally and spectroscopically characterized, demonstrating facile insertion into B-H and B-B bonds by PhB( i Pr 2 Im) 3 Fe≡N. Density functional theory (DFT) calculations reveal that the quintet state ( S = 2) is significantly lower in energy than the singlet ( S = 0) and triplet ( S = 1) states for all products. Stoichiometric reaction with (Bpin) 2 does not produce the mono-borylated iron imido species PhB( i Pr 2 Im) 3 FeN(Bpin). DFT calculations suggest that this is because PhB( i Pr 2 Im) 3 FeN(Bpin) is unstable toward disproportionation to the starting iron(IV) nitride and PhB( i Pr 2 Im) 3 FeN(Bpin) 2 . Attempts at B-C bond insertion using phenyl- and benzyl-pinacol borane were unsuccessful, which we attribute to unfavorable kinetics.

Aspects of the proposed pathway combining chain-end and enantiomorphic site control for the stereospecific polymerization of lactide (LA) were investigated through studies of aluminum complexes supported by enantiopure and racemic bipyrrolidine-based salan ligands, Lig 1 AlOBn and Lig 2 AlOBn. Spectroscopic analysis of stoichiometric initiation reactions and the definition of the stereochemistry of the selective formation of the "match" single-insertion products by X-ray crystallography led to key conclusions about the observed stereocontrol. Notably, it was determined to rely heavily on the preference for the trio of stereocenters around the metal to have a "match" formation ( RR -ligand + S -polymer), which works synergistically with the enantiomorphic site preference of the catalyst to ring-open next to a stereocenter of a monomer of the same chirality as that of the ligand, resulting in highly heterotactic or syndiotactic PLA from rac - or meso -LA, respectively.

We report high-spin aminyl triradicals with near-planar triphenylene backbones. Near-planarity of the fused aminyl radicals and the 2,6,10-triphenylene ferromagnetic coupling unit (FCU), magnetically equivalent to three fused 3,4'-biphenyl FCUs, assures an effective 2p π -2p π overlap within the cross-conjugated π-system, leading to an S = 3/2 (quartet) ground state that is well separated from low-spin excited doublet states. Thermal populations of the low-spin ( S = 1/2) excited states are detectable both by SQUID magnetometry and electron paramagnetic resonance (EPR) spectroscopy, providing doublet-quartet energy gaps, Δ E DQ , corresponding to >85% population of the quartet ground states at room temperature. Notably, EPR-based determination of Δ E DQ relies on direct detection of the quartet ground state and doublet excited states. The Δ E DQ values are 1.0-1.1 kcal mol -1 , with the more sterically shielded triradical having the larger value. The half-life of the more sterically shielded triradical in 2-methyltetrahydrofuran (2-MeTHF) is about 6 h at room temperature. The less sterically shielded triradical in 2-MeTHF decomposes at 158 K with a half-life of about 4 h, while at 195 K, the half-life is still about 2 h. The dominant products of the decay of triradicals are the corresponding triamines, suggesting hydrogen atom abstraction from the solvent as the primary mechanism. This study expands the frontier of the open-shell PAHs/nanographenes, of which the unique electronic, nonlinear optical, and magnetic properties could be useful in the development of novel organic electronics, photonics, and spintronics.

Herein, we report the reactions of an Fe(II) imido complex [Ph 2 B( t BuIm) 2 Fe═NDipp] - ( 1 ) with internal alkynes and isobutyronitrile, affording the Fe amido allenyl complexes [Ph 2 B( t BuIm) 2 Fe(NHDipp)((R 1 )C═C═C(R 2 )(H))] - (R 1 = Et or n Pr; R 2 = Me or Et, 2-5 ) and the Fe amido keteniminate complex [Ph 2 B( t BuIm) 2 Fe(NHDipp)(N═C═CMe 2 )K(THF)] n ( 8-K ), respectively. These transformations represent the previously unknown ene-like reactivity of a metal-ligand multiple bond. Stoichiometric reactions of 2 and 8-K with DippNH 2 lead to the regeneration of 3-hexyne and isobutyronitrile, respectively, with concomitant formation of the bis(anilido) complex [Ph 2 B( t BuIm) 2 Fe(NHDipp) 2 ] - ( 9 ). These results provide the platform for 1 as an efficient catalyst for the selective α-deuteration of nitriles and alkynes by RND 2 . These results demonstrate a new reaction mode for metal imido complexes and suggest new avenues for using the imido ligand in catalysis.

Triplet ground-state organic molecules are of interest with respect to several emerging technologies but usually show limited stability, especially as thin films. We report an organic diradical, consisting of two Blatter radicals, that possesses a triplet ground state with a singlet-triplet energy gap, Δ E ST ≈ 0.4-0.5 kcal mol -1 (2 J / k ≈ 220-275 K). The diradical possesses robust thermal stability, with an onset of decomposition above 264 °C (TGA). In toluene/chloroform, glassy matrix, and fluid solution, an equilibrium between two conformations with Δ E ST ≈ 0.4 kcal mol -1 and Δ E ST ≈ -0.7 kcal mol -1 is observed, favoring the triplet ground state over the singlet ground-state conformation in the 110-330 K temperature range. The diradical with the triplet ground-state conformation is found exclusively in crystals and in a polystyrene matrix. The crystalline neutral diradical is a good electrical conductor with conductivity comparable to the thoroughly optimized bis(thiazolyl)-related monoradicals. This is surprising because the triplet ground state implies that the underlying π-system is cross-conjugated and thus is not compatible with either good conductance or electron delocalization. The diradical is evaporated under ultra-high vacuum to form thin films, which are stable in air for at least 18 h, as demonstrated by X-ray photoelectron and electron paramagnetic resonance (EPR) spectroscopies.

The presence of redox innocent metal ions has been proposed to modulate the reactivity of metal ligand multiple bonds; however, insight from structure/function relationships is limited. Here, alkali metal reduction of the Fe(III) imido complex [Ph 2 B( t BuIm) 2 Fe═NDipp] ( 1 ) provides the series of structurally characterized Fe(II) imido complexes [Ph 2 B( t BuIm) 2 Fe═NDippLi(THF) 2 ] ( 2 ), [Ph 2 B( t BuIm) 2 Fe═NDippNa(THF) 3 ] ( 3 ), and [Ph 2 B( t BuIm) 2 Fe═NDippK] 2 ( 4 ), in which the alkali metal cations coordinate the imido ligand. Structural investigations demonstrate that the alkali metal ions modestly lengthen the Fe═N bond distance from that in the charge separated complex [Ph 2 B( t BuIm) 2 Fe═NDipp][K(18-C-6)THF 2 ] ( 5 ), with the longest bond observed for the smallest alkali metal ion. In contrast to 5 , the imido ligands in 2 - 4 can be protonated and alkylated to afford Fe(II) amido complexes. Combined experimental and computational studies reveal that the alkali metal polarizes the Fe═N bond, and the basicity of imido ligand increases according to 5 < 4 ≈ 3 < 2 . The basicity of the imido ligands influences the relative rates of reaction with 1,4-cyclohexadiene, specifically by gating access to complex 5 , which is the species that is active for HAT. All complexes 2 - 4 react with benzophenone form metastable Fe(II) intermediates that subsequently eliminate the metathesis product Ph 2 C═NDipp, with relative rates dependent on the alkali metal ion. By contrast, the same reaction with 5 does not lead to the formation of Ph 2 C═NDipp. These results demonstrate that the coordination of alkali metal ions dictate both the structure and reactivity of the imido ligand and moreover can direct the reactivity of reaction intermediates.

There has been an increasing interest in chemistry involving nitrogen oxyanions, largely due to the environmental hazards associated with increased concentrations of these anions leading to eutrophication and aquatic "dead zones". Herein, we report the synthesis and characterization of a suite of MNO x complexes (M = Co, Zn: x = 2, 3). Reductive deoxygenation of cobalt bis(nitrite) complexes with bis(boryl)pyrazine is faster for cobalt than previously reported nickel, and pendant O-bound nitrito ligand is still readily deoxygenated, despite potential implication of an isonitrosyl primary product. Deoxygenation of zinc oxyanion complexes is also facile, despite zinc being unable to stabilize a nitrosyl ligand, with liberation of nitric oxide and nitrous oxide, indicating N-N bond formation. X-ray photoelectron spectroscopy is effective for discriminating the types of nitrogen in these molecules. ESI mass spectrometry of a suite of M(NO x ) y ( x = 2, 3 and y = 1, 2) shows that the primary form of ionization is loss of an oxyanion ligand, which can be alleviated via the addition of tetrabutylammonium (TBA) as a nonintuitive cation pair for the neutral oxyanion complexes. We have shown these complexes to be subject to deoxygenation, and there is evidence for nitrogen oxyanion reduction in several cases in the ESI plume. The attractive force between cation and neutral is explored experimentally and computationally and attributed to hydrogen bonding of the nitrogen oxyanion ligands with ammonium α-CH 2 protons. One example of ESI-induced reductive dimerization is mimicked by bulk solution synthesis, and that product is characterized by X-ray diffraction to contain two Co(NO) 2 + groups linked by a highly conjugated diazapolyene.

Synthesis of bis-spiro-oxetane and bis-spiro-tetrahydrofuran pyrroline nitroxide radicals relies on the Mitsunobu reaction-mediated double cyclizations of N -Boc protected pyrroline tetraols. Structures of the nitroxide radicals are supported by X-ray crystallography. In a trehalose/sucrose matrix at room temperature, the bis-spiro-oxetane nitroxide radical possesses electron spin coherence time, T m ≈ 0.7 μs. The observed enhanced T m is most likely associated with strong hydrogen bonding of oxetane moieties to the trehalose/sucrose matrix.

High-spin ( S = 3/2) organic triradicals may offer enhanced properties with respect to several emerging technologies, but those synthesized to date typically exhibit small doublet quartet energy gaps and/or possess limited thermal stability and processability. We report a quartet ground state triradical 3 , synthesized by a Pd(0)-catalyzed radical-radical cross-coupling reaction, which possesses two doublet-quartet energy gaps, Δ E DQ ≈ 0.2-0.3 kcal mol -1 and Δ E DQ 2 ≈ 1.2-1.8 kcal mol -1 . The triradical has a 70+% population of the quartet ground state at room temperature and good thermal stability with onset of decomposition at >160 °C under an inert atmosphere. Magnetic properties of 3 are characterized by SQUID magnetometry in polystyrene glass and by quantitative EPR spectroscopy. Triradical 3 is evaporated under ultrahigh vacuum to form thin films of intact triradicals on silicon substrate, as confirmed by high-resolution X-ray photoelectron spectroscopy. AFM and SEM images of the ∼1 nm thick films indicate that the triradical molecules form islands on the substrate. The films are stable under ultrahigh vacuum for at least 17 h but show onset of decomposition after 4 h at ambient conditions. The drop-cast films are less prone to degradation in air and have a longer lifetime.

Reduction of the three-coordinate iron(III) imido [Ph 2 B( t BuIm) 2 Fe═NDipp] ( 1 ) affords [Ph 2 B( t BuIm) 2 Fe═NDipp][K(18-C-6)THF 2 ] ( 2 ), a rare example of a high-spin ( S = 2) iron(II) imido complex. Unusually for a late metal imido complex, the imido ligand in 2 has nucleophilic character, as demonstrated by the reaction with DippNH 2 , which establishes an equilibrium with the bis(anilido) complex [Ph 2 B( t BuIm) 2 Fe(NHDipp) 2 ][K(18-C-6)THF 2 ] ( 3 ). In an unusual transformation, formal insertion of i PrN═C═N i Pr into the Fe═N(imido) bond yields the guanidinate [Ph 2 B( t BuIm) 2 Fe( i PrN) 2 CNDipp][K(18-C-6)THF 2 ] ( 4 ). Reaction of 4 with excess DippNH 2 provides 3 , along with the guanidine ( i PrNH) 2 C═NDipp. As suggested by these stoichiometric reactions, 2 is an efficient catalyst for the guanylation of carbodiimides, converting a wide range of aniline substrates under mild conditions.

Double deprotonation of the salt [Ph 2 B(PMe 3 ) 2 ][OTf] ( 1 ) provides access to a bis(ylide)diphenylborate ligand that is readily transferred in situ to iron(II). Depending on the reaction stoichiometry, both the "ate" complex [Ph 2 B(Me 2 PCH 2 ) 2 Fe(μ-Cl) 2 Li(THF) 2 ] ( 2 ) and the homoleptic complex [Ph 2 B(Me 2 PCH 2 ) 2 ] 2 Fe( 3 ) can be prepared from FeCl 2 (THF) 1.5 . Further reaction of 3 with FeCl 2 (THF) 1.5 produces the chloride-bridged dimer [Ph 2 B(Me 2 PCH 2 ) 2 Fe(μ-Cl) 2 Fe(CH 2 PMe 2 ) 2 BPh 2 ]( 4 ). Attempts to reduce or alkylate 4 provide 3 as the only isolable product, likely a consequence of the low steric hindrance of the bis(ylide)diphenylborate ligand. On the other hand, reaction of 4 with the strong field ligand CN t Bu provides the six-coordinate, diamagnetic complex [Ph 2 B(Me 2 PCH 2 ) 2 Fe(CN t Bu) 4 ][Cl]( 5 ). Electronic structure calculations for the bis(ylide)diphenylborate ligand and homoleptic complex 3 suggest that the C(ylide) atoms are strong σ-donors with little π-bonding character. These initial results suggest the potential for this bis(ylide)diphenylborate ligand in coordination chemistry.

Here, we report the structures and properties of biocatalysts based on glucose oxidase (GOx) macromolecules immobilized on the mesoporous zirconia surface with or without magnetic iron oxide nanoparticles (IONPs) in zirconia pores. Properties of these biocatalysts were studied in oxidation of d-glucose to d-gluconic acid at a wide range of pH and temperatures. We demonstrate that the calcination temperature (300, 400, or 600 °C) of zirconia determines its structure, with crystalline materials obtained at 400 and 600 °C. This, in turn, influences the catalytic behavior of immobilized GOx, which was tentatively assigned to the preservation of GOx conformation on the crystalline support surface. IONPs significantly enhance the biocatalyst activity due to synergy with the enzyme. At the same time, neither support porosity nor acidity/basicity shows correlations with the properties of this biocatalyst. The highest relative activity of 98% (of native GOx) at a pH 6-7 and temperature of 40-45 °C was achieved for the biocatalyst based on ZrO 2 calcined at 600 °C and containing IONPs. This process is green as it is characterized by a high atom economy due to the formation of a single product with high selectivity and conversion and minimization of waste due to magnetic separation of the catalyst from an aqueous solution. These and an exceptional stability of this catalyst in 10 consecutive reactions (7% relative activity loss) make it favorable for practical applications., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

We demonstrate a host-guest molecular recognition approach to advance double electron-electron resonance (DEER) distance measurements of spin-labeled proteins. We synthesized an iodoacetamide derivative of 2,6-diazaadamantane nitroxide (DZD) spin label that could be doubly incorporated into T4 Lysozyme (T4L) by site-directed spin labeling with efficiency up to 50% per cysteine. The rigidity of the fused ring structure and absence of mobile methyl groups increase the spin echo dephasing time ( T m ) at temperatures above 80 K. This enables DEER measurements of distances >4 nm in DZD-labeled T4L in glycerol/water at temperatures up to 150 K with increased sensitivity compared to that of a common spin label such as MTSL. Addition of β-cyclodextrin reduces the rotational correlation time of the label, slightly increases T m , and most importantly, narrows (and slightly lengthens) the interspin distance distributions. The distance distributions are in good agreement with simulated distance distributions obtained by rotamer libraries. These results provide a foundation for developing supramolecular recognition to facilitate long-distance DEER measurements at near physiological temperatures.

Sequence-controlled supramolecular polymers offer new design paradigms for generating stimuli-responsive macromolecules with enhanced functionalities. The dynamic character of supramolecular links present challenges to sequence definition in extended supramolecular macromolecules, and design principles remain nascent. Here, we demonstrate the first example of using stoichiometry-control to specify the monomer sequence in a linear supramolecular polymer by synthesizing both a homopolymer and an alternating copolymer from the same glycol-substituted cyanostar macrocycle and phenylene-linked diphosphate monomers. A 2:1 stoichiometry between macrocycle and diphosphate produces a supramolecular homopolymer of general formula ( A ) n comprised of repeating units of cyanostar-stabilized phosphate-phosphate dimers. Using a 1:1 stoichiometry, an alternating ( AB ) n structure is produced with half the phosphate dimers now stabilized by the additional counter cations that emerge hierarchically after forming the stronger cyanostar-stabilized phosphate dimers. These new polymer materials and binding motifs are sufficient to bear normal and shear stress to promote significant and tunable adhesive properties. The homopolymer ( A ) n , consisting of cyanostar-stabilized anti -electrostatic linkages, shows adhesion strength comparable to commercial superglue formulations based on polycyanoacrylate but is thermally reversible. Unexpectedly, and despite including traditional ionic linkages, the alternating copolymer ( AB ) n shows weaker adhesion strength more similar to commercial white glue based on poly(vinyl acetate). Thus, the adhesion properties can be tuned over a wide range by simply controlling the stoichiometric ratio of monomers. This study offers new insight into supramolecular polymers composed of custom-designed anion and receptor monomers and demonstrates the utility of emerging functional materials based on anion-anion linkages.

The paramagnetic cyano-bridged complex PhB( t BuIm) 3 Fe-NC-Mo(N t BuAr) 3 (Ar = 3,5-Me 2 C 6 H 3 ) is readily assembled from a new four-coordinate, high-spin ( S = 2) iron(II) monocyanide complex and the three-coordinate molybdenum(III) complex Mo(N t BuAr) 3 . X-ray diffraction and IR spectroscopy reveal that delocalization of unpaired electron density into the cyanide π* orbitals leads to a reduction of the C-N bond order. Direct current (dc) magnetic susceptibility measurements, supported by electronic structure calculations, demonstrate the presence of strong antiferromagnetic exchange between spin centers, with a coupling constant of J = -122(2) cm -1 . To our knowledge, this value represents the strongest magnetic exchange coupling ever to be observed through cyanide. These results demonstrate the ability of low-coordinate metal fragments to engender extremely strong magnetic exchange coupling through cyanide by virtue of significant π-backbonding into the cyanide ligand.

Structural and spectroscopic characterization of the dimeric iron hydride complex [Ph 2 B( t BuIm) 2 FeH] 2 reveals an unusual structure in which a tetrahedral iron(II) site ( S = 2) is connected to a square planar iron(II) site ( S = 1) by two bridging hydride ligands. Magnetic susceptibility reveals strong ferromagnetic coupling between iron centers, with a coupling constant of J = +110(12) cm -1 , to give an S = 3 ground state. High-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy confirms this model. A qualitative molecular orbital analysis of the electronic structure, as supported by electronic structure calculations, reveals that the observed spin configuration results from the orthogonal alignment of two geometrically distinct four-coordinate iron fragments held together by highly covalent hydride ligands.

A suite of lanthanoenediyne complexes of the form Ln(macrocycle)X 3 (Ln = La 3+ , Ce 3+ , Eu 3+ , Gd 3+ , Tb 3+ , Lu 3+ ; X = NO 3 - , Cl - , OTf - ) was prepared by utilizing an enediyne-containing [2 + 2] hexaaza-macrocycle ( 2 ). The solid-state Bergman cyclization temperatures, measured via DSC, decrease with the denticity of X (bidentate NO 3 - , T = 267-292 °C; monodentate Cl - , T = 238-262 °C; noncoordinating OTf - , T = 170-183 °C). 13 C NMR characterization shows that the chemical shifts of the acetylenic carbon atoms also rely on the anion identity. The alkyne carbon closest to the metal binding site, C A , exhibits a Δδ > 3 ppm downfield shift, while the more distal alkyne carbon, C B , displays a concomitant Δδ ≤ 2.5 ppm upfield shift, reflecting a depolarization of the alkyne on metal inclusion. For all metals studied, the degree of perturbation follows the trend 2 < NO 3 - < Cl - < OTf - . This belies a greater degree of electronic rearrangement in the coordinated macrocycle as the denticity of X and its accompanying shielding of the metal's Lewis acidity decrease. Computationally modeled structures of LnX 3 show a systematic increase in the lanthanide- 2 coordination number (CN La-mc = 2 (NO 3 - ), 4 (Cl - ), 5 (H 2 O, model for OTf - )) and a decrease in the mean Ln-N bond length (La-N average = 2.91 Å (NO 3 - ), 2.78 Å (Cl - ), 2.68 Å (H 2 O)), further suggesting that a decrease in the anion coordination number correlates with an increase in the metal-macrocycle interaction. Taken together, these data illustrate a Bergman cyclization landscape that is influenced by the bonding of metal to an enediyne ligand but whose reaction barrier is ultimately dominated by the coordinating ability of the accompanying anion.

Supramolecular polymers have enabled far-reaching fundamental science and the development of diverse macromolecular technologies owing to the reversible and noncovalent chemical connectivities that define their properties. Despite the unabated development of these materials using highly tailorable recognition elements, anion-based polymers remain rare as a result of the weak interactions they mediate. Here, we use design rules inspired by cation-driven polymers to demonstrate a new noncovalent link based on receptor-stabilized anion-anion interactions that enables the efficient linear polymerization of simple difunctional phosphonates. The linear main chain connectivity and molecular topology were confirmed by single crystal X-ray diffraction, which demonstrates the rare 2:2 stoichiometry between the anionic phosphonate end groups and a pair of π-stacked cyanostar macrocycles. The stability of these links enables rapid polymerization of difunctional phosphonates employing different aliphatic linkers (C 6 H 12 , C 8 H 16 , C 10 H 20 , C 12 H 24 ). Diphosphonates with greater chain flexibility (C 12 H 24 ) enable greater polymerization with an average degree of polymerization of nine emerging at 10 mM. Viscosity measurements show a transition from oligomers to polymers at the critical polymerization concentration of 5 mM. In a rare correlation, NMR spectroscopy shows a coincident molecular signature of the polymerization at 5 mM. These polymers are highly concentration dependent, reversibly polymerize with acid and base, and respond to competitive anions. They display the design simplicity of metallo-supramolecular polymers with transfer of the strong 2:2 recognition chemistry to macromolecules. The simplicity and understanding of this new class of supramolecular polymer is anticipated to open opportunities in tailoring anion-based functional materials.

High spin ( S = 1) organic diradicals may offer enhanced properties with respect to several emerging technologies, but typically exhibit low singlet triplet energy gaps and possess limited thermal stability. We report triplet ground state diradical 2 with a large singlet-triplet energy gap, Δ E ST ≥ 1.7 kcal mol -1 , leading to nearly exclusive population of triplet ground state at room temperature, and good thermal stability with onset of decomposition at ∼160 °C under inert atmosphere. Magnetic properties of 2 and the previously prepared diradical 1 are characterized by SQUID magnetometry of polycrystalline powders, in polystyrene glass, and in other matrices. Polycrystalline diradical 2 forms a novel one-dimensional (1D) spin-1 ( S = 1) chain of organic radicals with intrachain antiferromagnetic coupling of J'/ k = -14 K, which is associated with the N···N and N···O intermolecular contacts. The intrachain antiferromagnetic coupling in 2 is by far strongest among all studied 1D S = 1 chains of organic radicals, which also makes 1D S = 1 chains of 2 most isotropic, and therefore an excellent system for studies of low-dimensional magnetism. In polystyrene glass and in frozen benzene or dibutyl phthalate solution, both 1 and 2 are monomeric. Diradical 2 is thermally robust and is evaporated under ultrahigh vacuum to form thin films of intact diradicals on silicon substrate, as demonstrated by X-ray photoelectron spectroscopy. Based on C-K NEXAFS spectra and AFM images of the ∼1.5 nm thick films, the diradical molecules form islands on the substrate with molecules stacked approximately along the crystallographic a-axis. The films are stable under ultrahigh vacuum for at least 60 h but show signs of decomposition when exposed to ambient conditions for 7 h.

Ureas of chiral diamines are prominent features of therapeutics, chiral auxiliaries, and intermediates in complex molecule synthesis. Although many methods for diamine synthesis are available, metal-free enantioselective alkene functionalizations to make protected 1,2- and 1,3-diamines from simple achiral starting materials are rare, and a single reagent that accesses a cross-section of each congener with high enantiomeric excess is not available. We describe a method to synthesize enantioenriched cyclic 5- and 6-membered ureas from allylic amines and an isocyanate using a C2-symmetric BisAmidine (BAM) catalyst that delivers N-selectivity from an ambident sulfonyl imide intermediate, overcoming electronic and steric deactivation at nitrogen. The geometry of 1,2-disubstituted alkenes is correlated to 5-exo and 6-endo cyclizations without altering alkene face selectivity, which is unexpectedly opposite that observed with O-nucleophiles. Straightforward product manipulations to diamine and imidazolidinone derivatives are underscored by the synthesis of an NK1 antagonist., Competing Interests: Notes No competing financial interests have been declared.

Here, we report the development of monodisperse Zn-doped iron oxide nanoparticles (NPs) with different amounts of Zn (Zn x Fe 3- x O 4 , 0 < x < 0.43) by thermal decomposition of a mixture of zinc and iron oleates. The as-synthesized NPs show a considerable fraction of wüstite (FeO) which is transformed to spinel upon 2 h oxidation of the NP reaction solutions. At any Zn doping amounts, we observed the enrichment of the NP surface with Zn 2+ ions, which is enhanced at higher Zn loadings. Such a distribution of Zn 2+ ions is attributed to the different thermal decomposition profiles of Zn and Fe oleates, with Fe oleate decomposing at much lower temperature than that of Zn oleate. The decomposition of Zn oleate is, in turn, catalyzed by a forming iron oxide phase. The magnetic properties were found to be strongly dependent on the Zn doping amounts, showing the saturation magnetization to decrease by 9 and 20% for x = 0.05 and 0.1, respectively. On the other hand, X-ray photoelectron spectroscopy near the Fermi level demonstrates that the Zn 0.05 Fe 2.95 O 4 sample displays a more metallic character (a higher charge carrier density) than undoped iron oxide NPs, supporting its use as a spintronic material., Competing Interests: The authors declare no competing financial interest.

This paper reports the development of robust Pd- and Ru-containing magnetically recoverable catalysts in a one-pot procedure using commercially available, branched polyethyleneimine (PEI) as capping and reducing agent. For both catalytic metals, ∼3 nm nanoparticles (NPs) are stabilized in the PEI shell of magnetite NPs, whose aggregation allows for prompt magnetic separation. The catalyst properties were studied in a model reaction of 4-nitrophenol hydrogenation to 4-aminophenol with NaBH 4 . A similar catalytic NP size allowed us to decouple the NP size impact on the catalytic performance from other parameters and to follow the influence of the catalytic metal type and amount as well as the PEI amount on the catalytic activity. The best catalytic performances, the 1.2 min -1 rate constant and the 433.2 min -1 turnover frequency, are obtained for the Ru-containing catalyst. This is discussed in terms of stability of Ru hydride facilitating the surface-hydrogen transfer and the presence of Ru 4+ species on the Ru NP surface facilitating the nitro group adsorption, both leading to an increased catalyst efficiency. High catalytic activity as well as the high stability of the catalyst performance in five consecutive catalytic cycles after magnetic separation makes this catalyst promising for nitroarene hydrogenation reactions., Competing Interests: The authors declare no competing financial interest.

Reaction of the readily reduced pincer ligand bis-tetrazinylpyridine, btzp, with the zerovalent metal source M(CO) 3 (MeCN) 3 yields M(btzp) 2 for M = Cr, Mo. These diamagnetic molecules show intrapincer bond lengths consistent with major charge transfer from metal to ligand, a result which is further supported by X-ray photoelectron spectroscopy. These molecules show up to five reversible outer-sphere electron transfers by cyclic voltammetry. The electronic structure of neutral M(btzp) 2 is analyzed by DFT and CASSCF calculations, which reveal the degree of back-donation from the metal into pincer π* orbitals and also subtle differences in metal-ligand interaction for Mo vs Cr. Near-IR absorptions exhibited by both M(btzp) 2 species originate from charge transfer among differently reduced tetrazine rings, which thus further support pincer reduction in these species.

Here, we report transfer hydrogenation of nitroarenes to aminoarenes using 2-propanol as a hydrogen source and Ag-containing magnetically recoverable catalysts based on partially reduced graphene oxide (pRGO) sheets. X-ray diffraction and X-ray photoelectron spectroscopy data demonstrated that, during the one-pot catalyst synthesis, formation of magnetite nanoparticles (NPs) is accompanied by the reduction of graphene oxide (GO) to pRGO. The formation of Ag 0 NPs on top of magnetite nanoparticles does not change the pRGO structure. At the same time, the catalyst structure is further modified during the transfer hydrogenation, leading to a noticeable increase of sp 2 carbons. These carbons are responsible for the adsorption of substrate and intermediates, facilitating a hydrogen transfer from Ag NPs and creating synergy between the components of the catalyst. The nitroarenes with electron withdrawing and electron donating substituents allow for excellent yields of aniline derivatives with high regio and chemoselectivity, indicating that the reaction is not disfavored by these functionalities. The versatility of the catalyst synthetic protocol was demonstrated by a synthesis of an Ru-containing graphene derivative based catalyst, also allowing for efficient transfer hydrogenation. Easy magnetic separation and stable catalyst performance in the transfer hydrogenation make this catalyst promising for future applications.

A new rotamer-based strategy for negative allostery has been used to control host-host interactions and product yield upon anion complexation. Coassembly of anion dimers as guests inside two cyanostar macrocycles drives selection of one rotamer in which all ten steric groups get directed outward to destabilize triply stacked macrocycles. A large entropy penalty (Δ S) is quantified upon anion binding when the multiple dynamic rotamers collapse down to one.

The bis-pyrazolato pyridine complex LCo(PEt 3 ) 2 serves as a masked form of three-coordinate Co II and shows diverse reactivity in its reaction with several potential outer sphere oxidants and oxygen atom transfer reagents. N-Methylmorpholine N-oxide (NMO) oxidizes coordinated PEt 3 from LCo(PEt 3 ) 2 , but the final cobalt product is still divalent cobalt, in LCo(NMO) 2 . The thermodynamics of a variety of oxygen atom transfer reagents, including NMO, are calculated by density functional theory, to rank their oxidizing power. Oxidation of LCo(PEt 3 ) 2 with AgOTf in the presence of LiCl as a trapping nucleophile forms the unusual aggregate [LCo(PEt 3 ) 2 Cl(LiOTf) 2 ] 2 held together by Li + binding to very nucleophilic chloride on Co(III) and triflate binding to those Li + . In contrast, Cp 2 Fe + effects oxidation to trivalent cobalt, to form (HL)Co(PEt 3 ) 2 Cl + ; proton and the chloride originate from solvent in a rare example of CH 2 Cl 2 dehydrochlorination. An unexpected noncomplementary redox reaction is reported involving attack by 2e reductant PEt 3 nucleophile on carbon of the 1e oxidant radical Cp 2 Fe + , forming a P-C bond and H + ; this reaction competes in the reaction of LCo(PEt 3 ) 2 with Cp 2 Fe + .

The enantioselective desymmetrization of carboxylic acids by chiral Brønsted base catalysis is reported, leading to bridged bicyclic lactones with up to 94% ee. Crystallographic analysis of a substrate-catalyst complex suggests an origin of stereocontrol, reminiscent of functional Brønsted bases in biological settings, and enabled reaction optimization. The products contain an all-carbon quaternary stereocenter and can be derivatized to functionalized cyclopentanes.

Here, we present a controlled synthesis of Mn-doped ZnO nanoparticles (NPs) with predominantly nail-like shapes, whose formation occurs via tip-to-base-oriented attachment of initially formed nanopyramids, followed by leveling of sharp edges that lead to smooth single-crystalline "nails". This shape is prevalent in noncoordinating solvents such as octadecene and octadecane. Yet, the double bond in the former promotes oriented attachment. By contrast, Mn-doped ZnO NP synthesis in a weakly coordinating solvent, benzyl ether, results in dendritic structures because of random attachment of initial NPs. Mn-doped ZnO NPs possess a hexagonal wurtzite structure, and in the majority of cases, the NP surface is enriched with Mn, indicating a migration of Mn 2+ ions to the NP surface during the NP formation. When the NP formation is carried out without the addition of octadecyl alcohol, which serves as a surfactant and a reaction initiator, large, concave pyramid dimers are formed whose attachment takes place via basal planes. UV-vis and photoluminescence spectra of these NPs confirm the utility of controlling the NP shape to tune electro-optical properties.

A series of Mn(II) complexes of differently substituted pyridinophane ligands, (Py 2 NR 2 )MnCl 2 (R = i Pr, Cy) and [(Py 2 NR 2 )MnF 2 ](PF 6 ) (R = i Pr, Cy, t Bu) are synthesized and characterized. The electrochemical properties of these complexes are investigated by cyclic voltammetry, along with those of previously reported (Py 2 NMe 2 )MnCl 2 and the Mn(III) complex [(Py 2 NMe 2 )MnF 2 ](PF 6 ). The electronic structure of this and other Mn(III) complexes is probed experimentally and theoretically, via high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy ab initio quantum chemical theory (QCT), respectively. These studies show that the complexes contain relatively typical six-coordinate Mn(III). The catalytic activity of these complexes toward both H 2 O 2 disproportionation and H 2 O oxidation has also been investigated. The rate of H 2 O 2 disproportionation decreases with increasing substituent size. Some of these complexes are active for electrocatalytic H 2 O oxidation; however this activity cannot be rationalized in terms of simple electronic or steric effects.

A product of incomplete combustion of diesel fuel, 3-nitrobenzanthrone (3-NBA), has been classified as a cancer-causing substance. It first gained attention as a potential urinary bladder carcinogen due to the presence of its metabolite in urine and formation of DNA adducts. The aim of the present study was to characterize the dose-response relationship of 3-NBA in human urothelial cancer cell line (RT4) exposed to concentrations ranging from 0.0003 μM (environmentally relevant) to 80 μM by utilizing toxicological and metabolomic approaches. We observed that the RT4 cells were capable of bioactivation of 3-NBA within 30 min of exposure. Activity measurements of various enzymes involved in the conversion of 3-NBA in RT4 cells demonstrated NAD(P)H:quinone oxidoreductase (NQO1) as the main contributor for its bioactivation. Moreover, cytotoxicity assessment exhibited an initiation of adaptive mechanisms at low dosages, which diminished at higher doses, indicating that the capacity of these mechanisms no longer suffices, resulting in increased levels of intracellular reactive oxygen species, reduced proliferation, and hyperpolarisation of the mitochondrial membrane. To characterize the underlying mechanisms of this cellular response, the metabolism of 3-NBA and metabolomic changes in the cells were analyzed. The metabolomic analysis of the cells (0.0003, 0.01, 0.08, 10, and 80 μM 3-NBA) showed elevated levels of various antioxidants at low concentrations of 3-NBA. However, at higher exposure concentrations, it appeared that the cells reprogrammed their metabolism to maintain the cell homeostasis via activation of pentose phosphate pathway (PPP).

The new iron(IV) nitride complex PhB( i Pr 2 Im) 3 Fe≡N reacts with 2 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) to provide PhB( i Pr 2 Im) 3 Fe(CN)(N 2 )(BAC). This unusual example of a four-electron reaction involves carbon atom transfer from BAC to create a cyanide ligand along with the alkyne i Pr 2 N-C≡C-N i Pr 2 . The iron complex is in equilibrium with an N 2 -free species. Further reaction with CO leads to formation of a CO analogue, which can be independently prepared using NaCN as the cyanide source, while reaction with B(C 6 F 5 ) 3 provides the cyanoborane derivative.

Here, we report on the development of novel Zn-, Zn-Cr-, and Zn-Cu-containing catalysts using magnetic silica (Fe 3 O 4 -SiO 2 ) as the support. Transmission electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) showed that the iron oxide nanoparticles are located in mesoporous silica pores and the magnetite (spinel) structure remains virtually unchanged despite the incorporation of Zn and Cr. According to XPS data, the Zn and Cr species are intermixed within the magnetite structure. In the case of the Zn-Cu-containing catalysts, a separate Cu 2 O phase was also observed along with the spinel structure. The catalytic activity of these catalysts was tested in methanol synthesis from syngas (CO + H 2 ). The catalytic experiments showed an improved catalytic performance of Zn- and Zn-Cr-containing magnetic silicas compared to that of the ZnO-SiO 2 catalyst. The best catalytic activity was obtained for the Zn-Cr-containing magnetic catalyst prepared with 1 wt % Zn and Cr each. X-ray absorption spectroscopy demonstrated the presence of oxygen vacancies near Fe and Zn in Zn-containing, and even more in Zn-Cr-containing, magnetic silica (including oxygen vacancies near Cr ions), revealing a correlation between the catalytic properties and oxygen vacancies. The easy magnetic recovery, robust synthetic procedure, and high catalytic activity make these catalysts promising for practical applications.

The complex (PNP)Ti═CH t Bu(CH 2 t Bu) (PNP = N[2-P i Pr 2 -4-methylphenyl] 2 - ) dehydrogenates cyclohexane to cyclohexene by forming a transient low-valent titanium-alkyl species, [(PNP)Ti(CH 2 t Bu)], which reacts with 2 equiv of quinoline (Q) at room temperature to form H 3 C t Bu and a Ti(IV) species where the less hindered C 2 ═N 1 bond of Q is ruptured and coupled to another equivalent of Q. The product isolated from this reaction is an imide with a tethered cycloamide group, (PNP)Ti═N[C 18 H 13 N] (1). Under photolytic conditions, intramolecular C-H bond activation across the imide moiety in 1 occurs to form 2, and thermolysis reverses this process. The reaction of 2 equiv of isoquinoline (Iq) with intermediate [(PNP)Ti(CH 2 t Bu)] results in regioselective cleavage of the C 1 ═N 2 and C 1 -H bonds, which eventually couple to form complex 3, a constitutional isomer of 1. Akin to 1, the transient [(PNP)Ti(CH 2 t Bu)] complex can ring-open and couple two pyridine molecules, to produce a close analogue of 1, complex (PNP)Ti═N[C 10 H 9 N] (4). Multinuclear and multidimensional NMR spectra confirm structures for complexes 1-4, whereas solid-state structural analysis reveals the structures of 2, 3, and 4. DFT calculations suggest an unprecedented mechanism for ring-opening of Q where the reactive intermediate in the low-spin manifold crosses over to the high-spin surface to access a low-energy transition state but returns to the low-spin surface immediately. This double spin-crossover constitutes a rare example of a two-state reactivity, which is key for enabling the reaction at room temperature. The regioselective behavior of Iq ring-opening is found to be due to electronic effects, where the aromatic resonance of the bicycle is maintained during the key C-C coupling event.

The hierarchical assembly of colored cationic molecules with receptor-modified counteranions can be used to control optical properties in materials. However, our knowledge of when the optical properties emerge in the hierarchical organization and the variety of cation-anion salts that are available to create these materials is limited. In this work, we extend the salts from small halides to large inorganic anions and determine how the structure coevolves with the emission properties using solution assemblies. We study the chromogenic trioxatriangulenium (TOTA + ) cation and its coassembly with cyanostar (CS) macrocycles selected to modify tetrafluoroborate (BF 4 - ) counteranions through formation of 2:1 sandwich complexes. In the solid state, the TOTA + cation stacks in an alternating manner with the sandwich complexes producing new red-shifted emission and absorption bands. Critical to assigning the structural origin of the new optical features across the four levels of organization (1° → 4°) is the selection of specific solvents to produce and characterize different assemblies present in the hierarchical structure. A key species is the electrostatically stabilized ion pair between the TOTA + cation and sandwich complex. The red-shifted features only emerge when the ion pairs oligomerize together into larger (TOTA·[CS 2 BF 4 ]) n assemblies. New electronic states emerge as a result of multiple copies of the TOTA + making π-contact with cyanostar-anion complexes. Our findings and the ease with which the materials can be prepared as crystals and films by mixing the salt with a receptor provide a strong platform for the de novo design of new optical materials.

We report the design, synthesis, and electron spin relaxation properties of hydrophilic tetracarboxylate ester pyrroline nitroxides 1 and 2, which serve as models in the search for new spin labels for DEER distance measurement at room temperature. The nitroxides are designed to have the methyl groups further away from the N-O spin site to decrease the inequivalent couplings of the unpaired electron to the methyl protons that shorten T m at T > 70 K in currently used labels. The key step in the synthesis of 1 and 2 is the reaction of the dianion of pyrrole-1,2,5-tricarboxylic acid tert-butyl ester dimethyl ester with electrophiles such as methyl chloroformate and methyl bromoacetate. Structures of 1 and 2 are confirmed by X-ray crystallography. Studies of electron spin relaxation rates in rigid trehalose/sucrose matrices reveal approximately temperature independent values of 1/T m for 1 and 2 up to about 160 K and modest temperature dependence up to 295 K, demonstrating that increasing the distance between the nitroxide moiety and methyl groups is effective in lengthening T m at T > 70 K.

A new family of Ni-, Co-, and Cr-doped Zn-containing magnetic oxide nanoparticles (NPs) stabilized by polyphenylquinoxaline (PPQ) and hyperbranched pyridylphenylene polymer (PPP) has been developed. These NPs have been synthesized by thermal decomposition of Zn and doping metal acetylacetonates in the reaction solution of preformed magnetite NPs, resulting in single-crystal NPs with spinel structure. For the PPQ-capped NPs, it was demonstrated that all three types of metal species (Fe, Zn, and a doping metal) reside within the same NPs, the surface of which is enriched with Zn and a doping metal, while the deeper layers are enriched with Fe. The Cr-doped NPs at the high Cr loading are an exception due to favored deposition of Cr on magnetite located in the NP depth. The PPP-capped NPs exhibit similar morphology and crystallinity; however, the detailed study of the NP composition was barred due to the high PPP amount retained on the NP surface. The catalyst testing in syngas conversion to methanol demonstrated outstanding catalytic properties of doped Zn-containing magnetic oxides, whose activities are dependent on the doping metal content and on the stabilizing polymer. The PPP stabilization allows for better access to the catalytic species due to the open and rigid polymer architecture and most likely optimized distribution of doping species. Repeat experiments carried out after magnetic separation of catalysts from the reaction mixture showed excellent catalyst stability even after five consecutive catalytic runs.

Encapsulation of unstable guests is a powerful way to enhance their stability. The lifetimes of organic anions and their radicals produced by reduction are typically short on account of reactivity with oxygen while their larger sizes preclude use of traditional anion receptors. Here we demonstrate the encapsulation and noncovalent stabilization of organic radical anions by C-H hydrogen bonding in π-stacked pairs of cyanostar macrocycles having large cavities. Using electrogenerated tetrazine radical anions, we observe significant extension of their lifetimes, facile molecular switching, and extremely large stabilization energies. The guests form threaded pseudorotaxanes. Complexation extends the radical lifetimes from 2 h to over 20 days without altering its electronic structure. Electrochemical studies show tetrazines thread inside a pair of cyanostar macrocycles following voltage-driven reduction (+e - ) of the tetrazine at -1.00 V and that the complex disassembles after reoxidation (-e - ) at -0.05 V. This reoxidation is shifted 830 mV relative to the free tetrazine radical indicating it is stabilized by an unexpectedly large -80 kJ mol -1 . The stabilization is general as shown using a dithiadiazolyl anion. This finding opens up a new approach to capturing and studying unstable anions and a radical anions when encapsulated by size-complementary anion receptors.

Biomass processing to value-added chemicals and biofuels received considerable attention due to the renewable nature of the precursors. Here, we report the development of Ru-containing magnetically recoverable catalysts for cellulose hydrogenolysis to low alcohols, ethylene glycol (EG) and propylene glycol (PG). The catalysts are synthesized by incorporation of magnetite nanoparticles (NPs) in mesoporous silica pores followed by formation of 2 nm Ru NPs. The latter are obtained by thermal decomposition of ruthenium acetylacetonate in the pores. The catalysts showed excellent activities and selectivities at 100% cellulose conversion, exceeding those for the commercial Ru/C. High selectivities as well as activities are attributed to the influence of Fe3O4 on the Ru(0)/Ru(4+) NPs. A facile synthetic protocol, easy magnetic separation, and stability of the catalyst performance after magnetic recovery make these catalysts promising for industrial applications.

Triplet ground-state organic molecules are interesting with respect to several emerging technologies but typically exhibit limited stability. We report two organic diradicals, one of which possesses a triplet ground state (2J/kB = 234 ± 36 K) and robust stability at elevated temperatures. We are able to sublime this high-spin diradical under high vacuum at 140 °C with no significant decomposition.