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Porphyrins were identified some years ago as a promising, easily accessible, and tunable class of organic photoredox catalysts, but a systematic study on the effect of the electronic nature and of the position of the substituents on both the ground-state and the excited-state redox potentials of these compounds is still lacking. We prepared a set of known functionalized porphyrin derivatives containing different substituents either in one of the meso positions or at a β-pyrrole carbon, and we determined their ground- and (singlet) excited-state redox potentials. We found that while the estimated singlet excited-state energies are essentially unaffected by the introduction of substituents, the redox potentials (both in the ground- and in the singlet excited-state) depend on the electron-withdrawing or electron-donating nature of the substituents. Thus, the presence of groups with electron-withdrawing resonance effects results in an enhancement of the reduction facility of the photocatalyst, both in the ground and in the excited state. We next prepared a second set of four previously unknown meso-substituted porphyrins, having a benzoyl group at different positions. The reduction facility of the porphyrin increases with the proximity of the substituent to the porphine core, reaching a maximum when the benzoyl substituent is introduced at a meso position. [ABSTRACT FROM AUTHOR]

Comprehensive Summary Development of heterogeneous molecular photocatalysts for promising light‐driven hydrogen evolution reaction (HER) is highly demanding but still challenging. Here, we report the blue‐greenish emitting dinuclear metal–organic halides as photocatalyst by incorporating site‐specific single copper(I) atoms that exhibit an efficient carbon‐negative H2 production. Interestingly, the electronic properties, including the spin and charge density of central Cu(I) active site, can be triggered by substituent modulation in metal–organic halides, which greatly affect the exciton dissociation kinetics and thus the HER reactivity. The optimized spin density in these heterogeneous photocatalysts drastically boosts the hydrogen production rate from 1250 to 3130 μmol·g–1·h–1. Our molecular strategy provides a platform that rationally facilitates electronic modulation of copper(I) atoms, tunes the macroscopic optoelectronic properties of photocatalysts and boosts carbon‐negative HER activity, extending the boundaries of conventional molecular‐based photocatalysts. [ABSTRACT FROM AUTHOR]

Chalcogen bonds (ChB) are moderately strong, directional, and specific non‐covalent interactions that have garnered substantial interest over the last decades. Specifically, the presence of two σ‐holes offers great potential for crystal engineering, catalysis, biochemistry, and molecular sensing. However, ChB applications are currently hampered by a lack of methods to characterize and control chalcogen bonds. Here, we report on the influence of various substituents (halogens, cyano, and methyl groups) on the observed self‐complementary ChB networks of 2,1,3‐benzoselenadiazoles. From molecular electrostatic potential calculations, we show that the electrostatic surface potentials (ESP) of the σ‐holes on selenium are largely influenced by the electron‐withdrawing character of these substituents. Structural analyses via X‐ray diffraction reveal a variety of ChB geometries and binding modes that are rationalized via the computed ESP maps, although the structure of 5,6‐dimethyl‐2,1,3‐benzoselenadiazole also demonstrates the influence of steric interactions. 77Se solid‐state magic‐angle spinning NMR spectroscopy, in particular the analysis of the selenium chemical shift tensors, is found to be an effective probe able to characterize both structural and electrostatic features of these self‐complementary ChB systems. We find a positive correlation between the value of the ESP maxima at the σ‐holes and the experimentally measured 77Se isotropic chemical shift, while the skew of the chemical shift tensor is established as a metric which is reflective of the ChB binding motif. [ABSTRACT FROM AUTHOR]

Fluorescent aromatic urea compounds undergo excited-state intermolecular proton transfer (ESPT) in the presence of acetate anions to produce an excited state of the tautomer (T*) from the excited state of the complex (N*), resulting in dual fluorescence. Herein, we performed spectroscopic measurements of anthracen-1-yl-3-phenylurea derivatives with substituents, –CF3, –F, or –Cl, at the p-position of the phenyl group in the presence of acetate to investigate the substituent effects on the ESPT reaction and the deactivation processes of N* and T*. Kinetic analysis showed that the reverse ESPT rate constant (k−PT) depended on the respective substituents, suggesting that each substituent may influence the reverse ESPT process differently. In particular, since the electron-withdrawing properties of –F are estimated by the − I and + Iπ effects, it is plausible that –F has a slight electron-donating property and influences the reverse process from T* to N* in the excited state. This study shows that it is possible to control emission by selecting specific substituents in the ESPT system. [ABSTRACT FROM AUTHOR]

In this review, the principles of gas-phase proton basicity measurements and theoretical calculations are recalled as a reminder of how the basicity PA/GB scale, based on Brønsted–Lowry theory, was constructed in the gas-phase (PA—proton affinity and/or GB—gas-phase basicity in the enthalpy and Gibbs energy scale, respectively). The origins of exceptionally strong gas-phase basicity of some organic nitrogen bases containing N-sp3 (amines), N-sp2 (imines, amidines, guanidines, polyguanides, phosphazenes), and N-sp (nitriles) are rationalized. In particular, the role of push–pull nitrogen bases in the development of the gas-phase basicity in the superbasicity region is emphasized. Some reasons for the difficulties in measurements for poly-functional nitrogen bases are highlighted. Various structural phenomena being in relation with gas-phase acid–base equilibria that should be considered in quantum-chemical calculations of PA/GB parameters are discussed. The preparation methods for strong organic push–pull bases containing a N-sp2 site of protonation are briefly reviewed. Finally, recent trends in research on neutral organic superbases, leaning toward catalytic and other remarkable applications, are underlined. [ABSTRACT FROM AUTHOR]

A series of chemically and biologically relevant N‐(arylthio)phthalimides is synthesized and its electrochemical reduction investigated. The results of the electrochemical study are analysed through application of Savéant's dissociative electron transfer theory and with the assistance of theoretical calculations. Reduction of all investigated N‐(arylthio)phthalimides leads to the corresponding radical anions, followed by the ejection of the phthalimide anion resulting from the dissociation of the N−S chemical bond. This stepwise electron transfer mechanism is evidenced by the electrochemical data which allow determination of the standard reduction potentials of all compounds. In the formation of the N‐(arylthio)phthalimide radical anions, the theoretical calculations show that the incoming electron, is hosted by the phthalimidyl group indicating a homolytic dissociation mechanism. The dissociation rate constants of the radical anions are deduced and show that upon changing the substituent from the MeO, to Me, H, F, Cl and Br the dissociation becomes faster. A good correlation with the Hammett substituent constants is also obtained. Application of Savéant's theory through determination of the associated driving force and the intrinsic barrier energies help rationalize the observed results and show that the change in the dissociation rate constant depends mainly on the standard reduction potential of the parent compounds. [ABSTRACT FROM AUTHOR]

The aromatic Cope rearrangement is an elusive transformation that has been the subject of a limited number of investigations compared to those seemingly close analogues, namely the Cope and aromatic Claisen rearrangement. Herein we report our investigations inspired by moderate success observed in the course of pioneering works. By careful experimental and theoretical investigations, we demonstrate that key substitutions on 1,5‐hexadiene scaffold allow fruitful transformations. Especially, efficient functionalisation of the heteroaromatic rings results from the aromatic Cope rearrangement, while highly stereoselective interrupted aromatic Cope rearrangements highlight the formation of chiral compounds through a dearomative process. [ABSTRACT FROM AUTHOR]

The effects of backbone amine functionalization in three new homoleptic C^N^C type ruthenium(II) complexes bearing a tridentate bis‐imidazole‐2‐ylidene pyridine ligand framework are characterized and studied by single crystal diffraction, electrochemistry, optical spectroscopy and transient absorption spectroscopy in combination with ab initio DFT calculations. Functionalization by dimethylamine groups in 4‐position of the pyridine backbone significantly influences the properties of the complexes as revealed by comparison with the unfunctionalized references. As a result of the amine functionalization, a higher molar absorption coefficient of the MLCT bands, a decreased photoluminescence quantum yield at room temperature together with a shortened excited state lifetime but an improved photostability is observed. Introduction of electron donating and withdrawing groups at the NHC unit modifies the electronic and optical properties, such as the oxidation potential, absorption and emission properties, and the lifetimes of the excited states. [ABSTRACT FROM AUTHOR]

The concatenation of Suzuki coupling and two‐fold Buchwald‐Hartwig amination in sequentially palladium‐catalyzed consecutive multicomponent syntheses paves a concise, convergent route to diversely functionalized para‐biaryl‐substituted triarylamines (p‐bTAAs) from simple, readily available starting materials. An extensive library of p‐bTAAs permits comprehensive investigations of their electronic properties by absorption and emission spectroscopy, cyclic voltammetry, and quantum chemical calculations, which contribute to a deep understanding of their electronic structure. The synthesized p‐bTAAs exhibit tunable fluorescence from blue to yellow upon photonic excitation with quantum yields up to 98 % in solution and 92 % in the solid state. Furthermore, a pronounced bathochromic shift of the emission maxima by increasing solvent polarity indicates positive emission solvatochromism. Aggregation‐induced enhanced emission (AIEE) in dimethyl sulfoxide (DMSO)/water mixtures causes the formation of intensely blue fluorescent aggregates. Cyclic voltammetry shows reversible first and second oxidations of p‐bTAAs at low potentials, which are tunable by variation of the introduced para substituents. 3D Hammett plots resulting from the correlation of oxidation potentials and emission maxima with electronic substituent parameters emphasize the rational design of tailored p‐bTAAs with predictable electrochemical and photophysical properties. [ABSTRACT FROM AUTHOR]

Several ortho‐carboranes bearing a phenoxy or a phenylamino group in the B9 position were prepared employing various protection and deprotection strategies. Following established protocols, dendritic compounds were synthesized from a hexachlorocyclotriphosphazene or thiophosphoryl chloride core, and possible anchoring options for the B9‐substituted ortho‐carboranes were investigated experimentally and theoretically (DFT). Furthermore, 1‐ or 1,2‐phosphanyl‐substituted carborane derivatives were obtained. The resulting diethyl‐, diisopropyl‐, di‐tert‐butyl‐, diphenyl‐ or diethoxyphosphines bearing a tunable ortho‐carborane moiety are intriguing ligands for future applications in homogeneous catalysis or the medicinal sector. [ABSTRACT FROM AUTHOR]

Tetradecyltrimethylammonium (TTA+) benzoate surfactants have a range of CMC values dependent on the substituent effects of the benzoate counterions. Twenty‐three TTA+/X‐benzoate CMC values were determined by conductivity and surface tension. The 12 TTA+/para‐ and meta‐benzoate and the unsubstituted benzoate CMC values yield a correlation to the hydrophobicity parameter (log P) of the benzoic acid, as the counterion. The logarithm of conductivity CMCs correlated to the log P value of the benzoic acid yields a slope of—0.4399. All 10 of the TTA+/ortho‐benzoate CMC values do not yield a correlation with hydrophobicity yet the TTA+/ortho‐halogenated benzoates give a strong correlation to hydrophobicity (log P). For this subset, the correlation was nearly identical to one of the TTA+/para‐ and meta‐benzoates. The slope of the logarithm of TTA+/ortho‐halogenated benzoate CMC values to the log P of benzoic acid is—0.413. Another subset is the TTA+/ortho‐hydrogen bond donating benzoates which clearly show micelle formation is favored in addition to the hydrophobic effect. The surface tension data CMCs yield a similar correlation to the conductivity data. This combined data yields further insight on the structural features of the counterion contribution to micelle formation. Specifically, the benzoates show both hydrophobicity effects and when ortho‐hydrogen bond donating substituents are present, micelle formation is strongly enhanced in addition to the hydrophobic effect of the anion. [ABSTRACT FROM AUTHOR]

Photo‐induced charge transfer (CT) states are pivotal in many technological and biological processes. A deeper knowledge of such states is mandatory for modeling the charge migration dynamics. Real‐time time‐dependent density functional theory (RT‐TD‐DFT) electronic dynamics simulations are employed to explicitly observe the electronic density time‐evolution upon photo‐excitation. Asymmetrically substituted indenotetracene molecules, given their potential application as n‐type semiconductors in organic photovoltaic materials, are here investigated. Effects of substituents with different electron‐donating characters are analyzed in terms of the overall electronic energy spacing and resulting ultrafast CT dynamics through linear response (LR‐)TD‐DFT and RT‐TD‐DFT based approaches. The combination of the computational techniques here employed provided direct access to the electronic density reorganization in time and to its spatial and rational representation in terms of molecular orbital occupation time evolution. Such results can be exploited to design peculiar directional charge dynamics, crucial when photoactive materials are used for light‐harvesting applications. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Palladium‐catalyzed Mizoroki‐Heck reaction is a powerful and efficient method for construction of Csp2–Csp2 bonds. Herein, four palladium complexes (I—IV) with N,O‐bidentate ligands (L1—L4) based on N‐oxide units from cyclic secondary amines were easily synthesized and successfully applied in Mizoroki‐Heck reaction of aryl bromides with electron‐deficient olefins. X‐ray diffraction analyses indicated the palladium(II) atom of II took the distorted square planar geometry and was four‐coordinated by nitrogen and oxygen atoms from two ligands (L2). Two free chloride ions were presented as counter anions in complex II. But the palladium(II) center of IV was coordinated by nitrogen and oxygen atoms from one ligand (L4) as well as two chlorine atoms, which exhibited the nearly square‐planar geometry. The study on catalytic properties of palladium complexes revealed that complex II exhibited high activity superior to the other complexes. The coupling reactions of a series of aryl bromides and olefin derivatives proceeded in the presence of 2—5 mol% palladium complex II, giving the desired products in good to excellent yields. The advantages of this method such as good compatibility of functional groups, high yields, and short reaction times made it more attractive for constructing Csp2–Csp2 bonds in the synthesis of functional molecules and materials. [ABSTRACT FROM AUTHOR]

The influence of phosphorus substitution of nitrogen in heterocyclic compounds on the vibrational spectroscopy as well as frontier molecular orbitals are analyzed. Nicotine with two nitrogen atoms in its structure is taken as the sample system to be studied computationally. By replacing the nitrogen atom in one or both rings of this molecule with phosphorus, three nicotine derivatives are created. The vibrational circular dichroism and infrared spectra of these four molecules in their monomer state, as well as the assemblies up to trimers are determined. The aforementioned spectra are calculated using static quantum chemical calculations employing a cluster‐weighted approach. The calculated gas phase spectra of nicotine are compared to their respective experimental spectra. It is observed that the nicotine derivatives with phosphorus in the methylpyrrolidine ring have considerably different gas phase and bulk phase vibrational circular dichroism spectra when compared to nicotine. The phosphorus substitution reduces the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital as well as altering the polarizability and reactivity of the investigated molecules. [ABSTRACT FROM AUTHOR]

A series of substituted 2‐pyrazolines were synthesized, and the steric and electronic effects of substituents on the C3‐ and C5‐positions of the heterocyclic ring on their fluorescent ability were investigated. Two different conjugative intramolecular charge transfer (ICT) and intramolecular charge transfer through space (spiro‐conjugation) affect the fluorescence intensity of these compounds. The extent of the ICT process and spiro‐conjugation depends on the electronic nature of the additional substitution and its position on the attached aryl rings. In addition, the effects of the concentration and the solvent polarity on the fluorescence emission were studied. Density functional theory (DFT) calculations were carried out to gain insight into the geometric, electronic, and spectroscopic properties of the pyrazoline derivatives. The results of both experimental and computational studies explain the effects of the geometrical orientation of the C3‐ and C5‐aryl rings toward the heterocyclic ring and also the electronic nature of their additional substitutions on the fluorescence intensity. [ABSTRACT FROM AUTHOR]

The total synthesis of Laetevirenol A, a natural product with antioxidant activity, has been achieved. A gold‐catalyzed cycloisomerization of an o‐alkenyl‐o'‐alkynylbiphenyl has been used as the key step for the construction of the phenanthrene moiety present in Laetevirenol A. Several studies in model substrates have been carried out to unveil the effect of substituents in different locations in the outcome of this cyclization, which allowed the design of an appropriate precursor for the fundamental gold‐catalyzed cycloisomerization. The suitably functionalized phenanthrene intermediate obtained in this key step could be further transformed into Laetevirenol A via a Friedel‐Crafts cyclization, which also turned out to be dependent on the nature of the substituents. Finally, Laetevirenol A was obtained in 10 steps from commercially available substrates, with a 20% global yield. [ABSTRACT FROM AUTHOR]

Three series of palladium(II) complexes supported by a phosphine‐iminophosphorane ligand built upon an ortho‐phenylene core were investigated to study the influence of the iminophosphorane N substituent. Cis‐dichloride palladium(II) complexes 1 in which the N atom bears an isopropyl (iPr, 1 a), a phenyl (Ph, 1 b), a trimethylsilyl (TMS, 1 c) group or an H atom (1 d) were synthesized in high yield. They were characterized by NMR, IR spectroscopy, HR‐mass spectrometry, elemental analysis, and X‐ray diffraction. A substantial bond length difference between the Pd−Cl bonds was observed in 1. Complexes 1 a–d were converted into [Pd(LR)Cl(CNtBu)](OTf)] 2 a–d whose isocyanide is located trans to the iminophosphorane. The corresponding dicationic complexes [Pd(LR)(CNtBu)2](OTf)23 a–d were also synthesized, however they exhibited lower stability in solution than 2, the isopropyl derivative 3 a being the most stable of the series. Molecular modeling was performed to rationalize the regioselectivity of the substitution of the single chloride by isocyanide (from 1 to 2) and to study the electronic distribution in the complexes. In particular differences between the TMS and H containing complexes vs. the iPr and Ph ones were found. This suggests that the nature of the N substituent is far from innocent and can help tune the reactivity of iminophosphorane complexes. [ABSTRACT FROM AUTHOR]

Substituent effects (SEs) are fundamental for predicting molecular reactivity, while polyene, polyyne and acene derivatives are precursors to compounds with diverse applications. Computations were performed for Y‐R‐X systems, where reaction sites Y=NO2 and O−, substituents X=NO2, CN, Cl, H, OH, NH2, and spacers R=polyene, polyyne (n=1‐5, 10 repeating units) and acene (up to tetracene). The cSAR (charge of the substituent active region) approach allowed to present, for the first time, quantitative relations describing the spacer's electron‐donating and withdrawing properties as a function of n and the spacer type. The electronic properties of the X substituents depend on the type of spacer, its length and the Y group, which is an example of the reverse SE. To describe how the SE between Y and X weakens with n, two approaches were compared: cSAR and SESE (SE stabilization energy). The EDDB (electron density of delocalized bonds) characterize changes in electron delocalization in spacers due to the SE. A new approach – EDDB differential maps – allow to extract the effect of X substitution on the electron delocalization. The charges at spacer's C atoms correlate with cSAR; changes in the slopes confirm the charge transfer by resonance. [ABSTRACT FROM AUTHOR]

Direct excitation of aromatic compounds grants access to high‐energy intermediates that can be utilised in organic synthesis. Understanding and predicting the substituent effects at the excited state for aromatic molecules remains challenging for the synthetic photochemist. In this work, we present an experimental and computational investigation of the excited state of the isomeric chloroanilines, which promptly react by losing the chloride when the amino group is in para position, but are non‐reactive and non‐emissive in the meta and ortho isomers. XMS‐CASPT2//CASSCF computations explain this apparent contradiction of the meta‐ortho selectivity rule of Zimmerman, which originates from the substituent effects lowering to a different extent the barrier to populate the prefulvenic conical intersection that deactivates non‐radiatively the singlet excited state of the chloroanilines. [ABSTRACT FROM AUTHOR]

Abstract A series of chemically and biologically relevant N‐(arylthio)phthalimides is synthesized and its electrochemical reduction investigated. The results of the electrochemical study are analysed through application of Savéant's dissociative electron transfer theory and with the assistance of theoretical calculations. Reduction of all investigated N‐(arylthio)phthalimides leads to the corresponding radical anions, followed by the ejection of the phthalimide anion resulting from the dissociation of the N−S chemical bond. This stepwise electron transfer mechanism is evidenced by the electrochemical data which allow determination of the standard reduction potentials of all compounds. In the formation of the N‐(arylthio)phthalimide radical anions, the theoretical calculations show that the incoming electron, is hosted by the phthalimidyl group indicating a homolytic dissociation mechanism. The dissociation rate constants of the radical anions are deduced and show that upon changing the substituent from the MeO, to Me, H, F, Cl and Br the dissociation becomes faster. A good correlation with the Hammett substituent constants is also obtained. Application of Savéant's theory through determination of the associated driving force and the intrinsic barrier energies help rationalize the observed results and show that the change in the dissociation rate constant depends mainly on the standard reduction potential of the parent compounds.

Porphyrins were identified some years ago as a promising, easily accessible, and tunable class of organic photoredox catalysts, but a systematic study on the effect of the electronic nature and of the position of the substituents on both the ground-state and the excited-state redox potentials of these compounds is still lacking. We prepared a set of known functionalized porphyrin derivatives containing different substituents either in one of the meso positions or at a β-pyrrole carbon, and we determined their ground- and (singlet) excited-state redox potentials. We found that while the estimated singlet excited-state energies are essentially unaffected by the introduction of substituents, the redox potentials (both in the ground- and in the singlet excited-state) depend on the electron-withdrawing or electron-donating nature of the substituents. Thus, the presence of groups with electron-withdrawing resonance effects results in an enhancement of the reduction facility of the photocatalyst, both in the ground and in the excited state. We next prepared a second set of four previously unknown meso-substituted porphyrins, having a benzoyl group at different positions. The reduction facility of the porphyrin increases with the proximity of the substituent to the porphine core, reaching a maximum when the benzoyl substituent is introduced at a meso position.

Comprehensive Summary: An unprecedented copper nitrate‐mediated bond cleavage of alkynes was developed for the modular synthesis of isoxazoles, where either C—S bond or C≡C triple bond was cleaved selectively. Substituents attached to the C≡C triple bonds could differentiate the chemical bonds cleavage and reaction pathways disparately. Various transformations of products illustrate promising applications of the given protocols. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: An unprecedented copper nitrate‐mediated bond cleavage of alkynes was developed for the modular synthesis of isoxazoles, where either C—S bond or C≡C triple bond was cleaved selectively. Substituents attached to the C≡C triple bonds could differentiate the chemical bonds cleavage and reaction pathways disparately. Various transformations of products illustrate promising applications of the given protocols. [ABSTRACT FROM AUTHOR]

Diketopyrrolopyrrole (DPP) systems have promising applications in different organic electronic devices. In this work, we investigated the effect of 20 different substituent groups on the optoelectronic properties of DPP‐based derivatives as the donor (D)‐material in an organic photovoltaic (OPV) device. For this purpose, we employed Hammett's theory (HT), which quantifies the electron‐donating or ‐withdrawing properties of a given substituent group. Machine learning (ML)‐based σm, σp, σm0, σp0, σp+, σp−, σI, and σR Hammett's constants previously determined were used. Mono‐ (DPP‐X1) and di‐functionalized (DPP‐X2) DPPs, where X is a substituent group, were investigated using density functional theory (DFT), time‐dependent DFT (TDDFT), and ab initio methods. Several properties were computed using CAM‐B3LYP and the second‐order algebraic diagrammatic construction, ADC(2), an ab initio wave function method, including the adiabatic ionization potential (IPA), the electron affinity (EAA), the HOMO‐LUMO gaps (Eg), and the maximum absorption wavelengths (λmax), the first excited state transition 1S0→ 1S1 energies (∆E) (the optical gap), and exciton binding energies. From the optoelectronic properties and employing typical acceptor systems, the power conversion efficiency (PCE), open‐circuit voltage (VOC), and fill factor (FF) were predicted for a DPP‐based OPV device. These photovoltaic properties were also correlated with the machine learning (ML)‐based Hammett's constants. Overall, good correlations between all properties and the different types of σ constants were obtained, except for the σI constants, which are related to inductive effects. This scenario suggests that resonance is the main factor controlling electron donation and withdrawal effects. We found that substituent groups with large σ values can produce higher photovoltaic efficiencies. It was also found that electron‐withdrawing groups (EWGs) reduced Eg and ∆E considerably compared to the unsubstituted DPP‐H. Moreover, for every decrease (increase) in the values of a given optoelectronic property of DPP‐X1 systems, a more significant decrease (increase) in the same values was observed for the DPP‐X2, thus showing that the addition of the second substituent results in a more extensive influence on all electronic properties. For the exciton binding energies, an unsupervised machine learning algorithm identified groups of substituents characterized by average values (centroids) of Hammett's constants that can drive the search for new DDP‐derived materials. Our work presents a promising approach by applying HT on molecular engineering DPP‐based molecules and other conjugated molecules for applications on organic optoelectronic devices. [ABSTRACT FROM AUTHOR]

Unsymmetrical 11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-dione, incorporating a para-phenyl substituted pyridine unit fused by both 6- and 7-membered carbocyclic rings, has been prepared on the gram-scale via a multi-step procedure involving cyclization, hydrogenation and oxidation. Templating this diketone, in the presence of cobalt(II) chloride hexahydrate, with the corresponding aniline afforded in good yield five examples of doubly fused bis(arylimino)pyridine-cobalt(II) chlorides, Co1 (aryl = 2,6-dimethylphenyl), Co2 (2,6-diethylphenyl), Co3 (2,6-diisopropylphenyl), Co4 (2,4,6-trimethylphenyl) and Co5 (2,6-diethyl-4-methylphenyl). Structural characterization of Co1, Co2 and Co3 highlights the flexible nature of the inequivalent fused rings on the NNN'-ligand and the skewed disposition of the para-phenyl group. On activation with MAO, Co1–Co5 exhibited high activity for ethylene polymerization at 30 °C (up to 5.66 × 106 g (PE) mol−1 (Co) h−1) with the relative order being as follows: Co4 > Co1 > Co5 > Co3 > Co2. All polyethylenes were strictly linear, while their molecular weights and dispersities showed some notable variations. For Co1, Co2, Co4 and Co5, all polymerizations were well controlled as evidenced by the narrow dispersities of their polymers (Mw/Mn range: 1.8–2.7), while their molecular weights (Mw range: 2.9–10.9 kg mol−1) steadily increased in line with the greater steric properties of the N-aryl ortho-substituents. By contrast, the most hindered 2,6-diisopropyl counterpart Co3 displayed a broad distribution with bimodal characteristics (Mw/Mn = 10.3) and gave noticeably higher molecular weight polymer (Mw = 75.5 kg mol−1). By comparison, the MMAO-activated catalysts were generally less active, but showed similar trends in molecular weight and polymer dispersity. End group analysis of selected polymers via 13C and 1H NMR spectroscopy revealed the presence of both saturated and unsaturated polyethylenes in accordance with competing chain transfer pathways. Notably, when comparing Co3/MAO with its non-phenyl substituted analogue (E2,6-iPr2Ph)CoCl2/MAO, the former, though less controlled, displayed higher activity and molecular weight, a finding that points towards a role played by the remote para-phenyl group. [ABSTRACT FROM AUTHOR]

We previously studied the effect of 4' substitution in iron(II)-bis-terpyridine complexes, showing that the photoexcited high-spin quintetstate is stabilized by electron-donating substituents. In this paper we explore the effects of electron-donating ( X = NH2, Cl) and withdrawing (X = NO2) substituents in the 5,5" positions on the stability and lifetime of the quintet-state. We used a simple densitiy-functional theory (DFT) based method that had been proven fairly accurate in the case of 4' substitution to estimate the energy barrier of the quintet-singlet transition and thereby predict the quintet state lifetime. We synthetized the complexes and used ultrafast transient optical absorption spectroscopy to experimentally determine the quintet lifetimes, in order to test the applicability of these quantum-chemistry based predictive methods for these side-ring substitution cases. UV-Visible spectra of the complexes have shown that the metal-to-li gand charge transfer (MLCT) and ligand-localized transitions of these complexes change according to the previous observations. We have shown that in the 5,5" positions, electron withdrawing groups stabilize the quintet state, while donating groups destabilize it. This is in stark contrast to the effects previously observed for the 4' case, and indicates that unlike the latter case, the simple concept of inductive and mesomeric effects may not be adequate to describe the changes due to 5,5" substitution, warranting further study of the area. [ABSTRACT FROM AUTHOR]

In this review, the principles of gas-phase proton basicity measurements and theoretical calculations are recalled as a reminder of how the basicity PA/GB scale, based on Brønsted–Lowry theory, was constructed in the gas-phase (PA—proton affinity and/or GB—gas-phase basicity in the enthalpy and Gibbs energy scale, respectively). The origins of exceptionally strong gas-phase basicity of some organic nitrogen bases containing N-sp3 (amines), N-sp2 (imines, amidines, guanidines, polyguanides, phosphazenes), and N-sp (nitriles) are rationalized. In particular, the role of push–pull nitrogen bases in the development of the gas-phase basicity in the superbasicity region is emphasized. Some reasons for the difficulties in measurements for poly-functional nitrogen bases are highlighted. Various structural phenomena being in relation with gas-phase acid–base equilibria that should be considered in quantum-chemical calculations of PA/GB parameters are discussed. The preparation methods for strong organic push–pull bases containing a N-sp2 site of protonation are briefly reviewed. Finally, recent trends in research on neutral organic superbases, leaning toward catalytic and other remarkable applications, are underlined.

This work examines theoretically the problem of the migration of borane groups between the nitrogen atoms of pyrazolyl rings. We have studied as a model the BH2 pyrazol‐1‐yl derivatives to determine the effects of substituents on the pyrazole ring; also 1‐(9‐borabicyclo[3.3.1]nonan‐9‐yl)‐1H‐pyrazoles to compare the calculated barriers with the experimental ones as well as to determine steric effects, i. e., how the buttressing effect increases the rate. The interacting quantum atoms methodology has been used for partitioning the energy of the systems in their stationary points into the contribution of pyrazole and BH2 group and their mutual interaction. [ABSTRACT FROM AUTHOR]

The propulsion of photocatalytic hydrogen (H2) production is limited by the rational design and regulation of catalysts with precise structures and excellent activities. In this work, the [MoOS3]2− unit is introduced into the CuI clusters to form a series of atomically‐precise MoVI−CuI bimetallic clusters of [Cu6(MoOS3)2(C6H5(CH2)S)2(P(C6H4−R)3)4] ⋅ xCH3CN (R=H, CH3, or F), which show high photocatalytic H2 evolution activities and excellent stability. By electron push‐pull effects of the surface ligand, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of these MoVI−CuI clusters can be finely tuned, promoting the resultant visible‐light‐driven H2 evolution performance. Furthermore, MoVI−CuI clusters loaded onto the surface of magnetic Fe3O4 carriers significantly reduced the loss of catalysts in the collection process, efficiently addressing the recycling issues of such small cluster‐based catalyst. This work not only highlights a competitively universal approach on the design of high‐efficiency cluster photocatalysts for energy conversion, but also makes it feasible to manipulate the catalytic performance of clusters through a rational substituent strategy. [ABSTRACT FROM AUTHOR]

We present a comprehensive host‐guest study of four substituted and unsubstituted [10]cycloparaphenylenes with the fullerenes C60 and C70. Within this study, the influence on the complexation behavior was investigated experimentally and computationally. Due to the increased steric demand the substitution on the nanohoop results in an energetic penalty, which could be partially compensated by additional substituent‐fullerene interactions. These attractive interactions are intensified in the C70 complexes and with an increased degree of substitution. For the computational investigation conformer ensembles were taken into account, providing reliable structures with Boltzmann weighted energies. An analysis of the noncovalent interactions elucidated the origin of the enhanced substituent‐C70 interaction. The ellipsoid fullerene C70 can be considered as a π‐extended version of C60, which is able to increase the attractive van der Waals interactions within these supramolecular complexes. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: In this work, we adopt a "heteroatom side‐chains" modification strategy to modify the thiophene units in A‐DA'D‐A (acceptor‐donor‐acceptor'‐donor‐acceptor) type pentacyclic SMAs (small molecule acceptors), that is, introducing branched alkyl chain at the β‐position of thiophene instead of straight alkyl chain, and then introducing oxygen atom at the third‐position on the basis of branched chain. Two new pentacyclic SMAs (BZ4F‐EH and BZ4F‐OEH) were synthesized, and the influence of the heteroatom side‐chains on photoelectric properties of A‐DA'D‐A type pentacyclic SMAs was systematically studied. Compared with our previously reported BZ4F (Y26), BZ4F‐EH shows slightly blue‐shifted absorption, while BZ4F‐OEH has obvious red‐shifted absorption. As a result, BZ4F‐OEH‐based binary device achieved a high power conversion efficiency (PCE) of 16.56% with a fill factor (FF) of 79.3%, which is the highest efficiency of pentacyclic SMAs to date. The results indicated that the modification of hetero‐atomization on the β‐position of thiophene is a simple and efficient way to improve the PCE of A‐DA'D‐A type SMAs, and this work provides an important guideline for future molecular design. [ABSTRACT FROM AUTHOR]

Halide‐triel bonds between halosilane donors and alane/borane/gallane acceptors are investigated considering 24 model complexes using quantum chemical calculations. Nature and strength of Si−X....Tr interactions (X=F, Cl, Br and Tr=Al, B, Ga) binding these complexes has been studied using Electrostatic Potential (ESP), Quantum Theory of Atoms in Molecules (QTAIM), Natural Bond Orbital (NBO), and Energy Decomposition Analysis (EDA) techniques. Basis Set Superposition Error (BSSE) corrected binding energy of the complexes ranges from −3.19 to −29.40 kcal mol−1. QTAIM parameters Laplacian and the total electron density at the Bond Critical Points (BCPs) indicate that the halide‐triel bonds studied here are largely electrostatic in nature (closed‐shell interactions); this has also been revealed through ESP analysis and EDA scheme. In addition, role of charge transfer in these halide‐triel bonds has also been established through NBO analysis. Two charge transfer orbital interactions are responsible for the primary interaction Si−X....Tr: n(F/Cl/Br)→n*(Al/Ga/B) ${n(F/Cl/Br)\to {n}^{^{\ast}}(Al/Ga/B){\rm \ }}$ and σ(Si−X)→n*(Al/Ga) ${\to {\rm \ }{n}^{^{\ast}}(Al/Ga)}$. EDA analysis identifies electrostatic term as the biggest contributor towards the binding of the complexes followed by the polarisation and dispersion terms in most of the complexes. Results of this study have relevance in the Si−F bond activation methodology in organic synthesis. [ABSTRACT FROM AUTHOR]

Strained cyclic allenes, first discovered in 1966 by Wittig and co-workers, have recently emerged as valuable synthetic building blocks. Previous experimental investigations, and computations reported here, demonstrate that the Diels-Alder reactions of furans and pyrroles with 1,2-cyclohexadiene and oxa- and azaheterocyclic analogs proceed with endo selectivity. This endo selectivity gives the adduct with the allylic saturated carbon of the cyclic allene endo to the diene carbons. The selectivity is very general and useful in synthetic applications. Our computational study establishes the origins of this endo selectivity. We analyze the helical frontier molecular orbitals of strained cyclic allenes and show how secondary orbital and electrostatic effects influence stereoselectivity. The LUMO of carbon-3 of the allene (C-3 is not involved in primary orbital interactions) interacts in a stabilizing fashion with the HOMO of the diene in such a way that the carbon of the cyclic allene attached to C-1 favors the endo position in the transition state. The furan LUMO, allene HOMO interaction reinforces this preference. These mechanistic studies are expected to prompt the further use of long-avoided strained cyclic allenes in chemical synthesis.

Metalloporphyrins have been regarded as one of the most promising electrocatalysts for oxygen reduction reactions (ORRs) due to their ease of structure modification and the robust coordinated M−N4 environment. However, the electrocatalytic activity, selectivity and stability of the metalloporphyrin‐based composite catalysts are often reported to be much poorer than those of the Pt‐based materials, arousing researchers to devote to exploring a thorough understanding of the relationship between the catalyst structures and ORR performance/mechanisms. Here we will review the design of meso‐positioned porphyrin structures from the aspects of selection of central metal ion species in both monometallic and bimetallic molecules, and modulation of peripheral functional substituents to introduce beneficial effects, including electron affinity, steric effects, interfacial charge states and proton management. Influences from different carbon materials as the support for composite catalysts as well as the electrolytes on oxygen reduction properties will be briefly illustrated before presenting the perspectives and insights for future works in conclusion remarks. We hope that this Review will serve as a roadmap for advancing the insights of the molecular structural and substrate morphological factors impacting ORR properties with the ultimate goal of developing and improving novel metalloporphyrins as efficient and durable electrocatalysts to champion the precious Pt/C. [ABSTRACT FROM AUTHOR]

The roles of substituent and solvent effects in promoting the 4π electrocyclization of N‐alkenylnitrones to give azetidine nitrones have been investigated by experimental examination of relative rates, activation energies, and linear free energy relationships. These transformations are synthetically important because they favor the formation of a strained heterocyclic ring with imbedded functionality and stereochemical information for versatile derivatization. Mechanistic investigations, including Hammett studies, solvent‐dependent Eyring studies, and solvent isotope effects, provide insight into the steric and electronic factors that control these electrocyclizations and identify trends that can be used to advance this approach towards the rapid synthesis of complex azetidines. [ABSTRACT FROM AUTHOR]

The synthesis of novel mono‐, di‐, tri‐, tetra‐, and hexafluorinated hexa‐peri‐hexabenzocoronenes (HBCs) and their conversion into their thioether‐substituted analogs is reported. The substitution reaction with the corresponding thiolates was performed microwave‐assisted to significantly reduce the reaction time. With increasing amount of fluorination or thioether‐substituents, a decreasing extinction coefficient can be observed for the HBCs. Successive addition of thioether‐moieties leads to a bathochromic shift of the absorption and emission bands, whereas the nature of the attached thioether does not affect the optoelectronical properties. To further tune the electronic environment of the HBC core, a successive oxidation to the corresponding sulfone as well as the formation of the sulfonium salts were performed. With that, the electron‐donating thioethers were transformed into electron‐withdrawing substituents, resulting in an inversed electron demand in the periphery of the core. The so obtained compounds showed decreased extinction coefficients and a broadening of the absorption and emission bands. [ABSTRACT FROM AUTHOR]

A self‐promoted glycosylation method for the stereoselective formation of β‐glucosides from a substrate library of glycosyl trichloroacetimidate glycosyl donors and glycosyl acceptors is presented. The simple two‐component reaction takes place at elevated temperatures, without the addition of any additives or catalysts. After a simple basic workup, N‐glycosides were obtained in good yields and with high β‐selectivity and hence this method allows for easy access to glycoconjugates under very mild conditions. The influences of neighboring group participation and substituents, in both the glycosyl donor and acceptor, were studied. Kinetic data were obtained from in situ IR and these were used for a Hammett study. A connection between the pKa of the acceptor and reaction rate was found and new mechanistic insight in self‐promoted glycosylations gained. [ABSTRACT FROM AUTHOR]

Non‐benzenoid acenes containing heptagons have received increasing attention. We herein report a heptacene analogue containing a quinoidal benzodi[7]annulene core. Derivatives of this new non‐benzenoid acene were obtained through an efficient synthetic strategy involving an Aldol condensation and a Diels–Alder reaction as key steps. The configuration of this heptacene analogue can be modulated from a wavy to a curved one by just varying the substituents from a (triisopropylsilyl)ethynyl group to a 2,4,6‐triisopropylphenyl (Trip) group. When mesityl (Mes) groups are linked to the heptagons, the resulting non‐benzenoid acene displays polymorphism with a tunable configuration from a curved to a wavy one upon varying the crystallization conditions. In addition, this new non‐benzenoid acene can be oxidized or reduced by NOSbF6 or KC8 to the respective radical cation or radical anion. Compared with the neutral acene, the radical anion shows a wavy configuration and the central hexagon becomes aromatic. [ABSTRACT FROM AUTHOR]

Regioselectivity in electrophilic aromatic substitution (EAS) is partly governed by how well a preexisting substituent stabilizes or destabilizes the cationic intermediate formed by addition of an electrophile. Such intermediates were modeled computationally (G4) by adding a proton ortho, meta, or para to an existing substituent on a benzene ring. The effect of a meta substituent depends on the electronic character, as measured by the Hammett substituent constant σm or, better yet, σ+m. Similarly, the effect of a para or ortho substituent correlates with σ+p (= σ+). However, the influence of a substituent at the para position is 10% stronger than at the ortho position. Frontier molecular orbital arguments rationalize this observation. Consequently, the ortho:para product ratio in EAS is expected to depend, at least in part, on σ+p, with greater electron‐donating character associated with a greater preference for para over ortho. The ortho‐substituted cationic intermediate can even be favored over both meta and para if the electron‐withdrawing character is sufficient to favor ortho over para but insufficient to favor meta over either. This phenomenon is observed to occur in at least some cases when the quantity σ+p–σm falls between –0.5 and 0. [ABSTRACT FROM AUTHOR]

In this manuscript substituent effects in several silicon tetrel bonding (TtB) complexes were investigated at the RI-MP2/def2-TZVP level of theory. Particularly, we have analysed how the interaction energy is influenced by the electronic nature of the substituent in both donor and acceptor moieties. To achieve that, several tetrafluorophenyl silane derivatives have been substituted at the meta and para positions by several electron donating and electron withdrawing groups (EDG and EWG, respectively), such as –NH2, –OCH3, –CH3, –H, –CF3 and –CN substituents. As electron donor molecules, we have used a series of hydrogen cyanide derivatives using the same EDGs and EWGs. We have obtained the Hammett's plots for different combinations of donors and acceptors and in all cases we have obtained good regression plots (interaction energies vs. Hammet's σ parameter). In addition, we have used the electrostatic potential (ESP) surface analysis as well as the Bader's theory of atoms in molecules (AIM) and noncovalent interaction plot (NCI plot) techniques to further characterize the TtBs studied herein. Finally, a Cambridge Structural Database (CSD) inspection was carried out, retrieving several structures where halogenated aromatic silanes participate in tetrel bonding interactions, being an additional stabilization force of their supramolecular architectures. [ABSTRACT FROM AUTHOR]

The in forms of molecular iron maidens are known for their unique ultrashort interaction between the apical hydrogen atom or its small substituent and the surface of the benzene ring. It is generally believed that this forced ultrashort X ⋯ π contact is associated with high steric hindrance, which is responsible for specific properties of iron maiden molecules. The main aim of this article is to investigate the influence of significant charge enrichment or depletion of the benzene ring on the characteristics of the ultrashort C-X ⋯ π contact in iron maiden molecules. For this purpose, three strongly electron-donating (-NH 2 ) or strongly electron-withdrawing (-CN) groups were inserted into the benzene ring of in-[3 4 , 10 ][7]metacyclophane and its halogenated (X = F, Cl, Br) derivatives. It is shown that, despite such extremely electron-donating or electron-accepting properties, the considered iron maiden molecules surprisingly reveal quite high resistance to changes in electronic properties. [ABSTRACT FROM AUTHOR]

A new series of mono‐ and bis‐alkynyl CoIII(TIM) complexes (TIM=2,3,9,10‐tetramethyl‐1,4,8,11‐tetraazacyclotetradeca‐1,3,8,10‐tetraene) is reported herein. The trans‐[Co(TIM)(C2R)Cl]+ complexes were prepared from the reaction between trans‐[Co(TIM)Cl2]PF6 and HC2R (R=tri(isopropyl)silyl or TIPS (1), ‐C6H4‐4‐tBu (2), ‐C6H4‐4‐NO2 (3 a), and N‐mesityl‐1,8‐naphthalimide or NAPMes (4 a)) in the presence of Et3N. The intermediate complexes of the type trans‐[Co(TIM)(C2R)(NCMe)](PF6)(OTf), 3 b and 4 b, were obtained by treating 3 a and 4 a, respectively, with AgOTf in CH3CN. Furthermore, bis‐alkynyl trans‐[Co(TIM)(C2R)2]PF6 complexes, 3 c and 4 c, were generated following a second dehydrohalogenation reaction between 3 b and 4 b, respectively, and the appropriate HC2R in the presence of Et3N. These new complexes have been characterized using X‐ray diffraction (2, 3 a, 4 a, and 4 c), IR, 1H NMR, UV/Vis spectroscopy, fluorescent spectroscopy (4 c), and cyclic voltammetry. [ABSTRACT FROM AUTHOR]

The regioselective lithiation of 1,2,3‐triazoles provides an opportunity to introduce additional functionality, however this simple functionalisation strategy using triazoles bearing electron‐withdrawing N‐substituents has not been investigated until now. Herein, we demonstrate that the lithiated triazole intermediates can readily decompose, even at −78 °C. In addition, lithiation‐deuteration studies reveal lithiation can take place competitively on both the triazole and the electron‐withdrawn aryl ring. Careful control of reaction conditions is therefore required to i) minimise decomposition pathways; and ii) facilitate regioselective functionalisation of the triazole. [ABSTRACT FROM AUTHOR]

To explore the substituent effects on the stretching vibration frequencies νC=C of C=C bridge bond in 1‐furyl/thienyl‐2‐aryl ethylene XCH=CHArYs, 60 samples of XCH=CHArYs were synthesized, and their infrared absorption spectra were recorded. The regression analyses between the νC=C values of XCH=CHArYs and the substituent parameters of X and Y were made in detail. Finally, an optimality equation (shown as Equation 3) quantifying the νC=C values of XCH=CHArYs was obtained. It shows that the substituent effects on the νC=C values of XCH=CHArYs mainly reflect in Hammett constant of X and the excited‐state substituent constants of X and Y. Among the parameters in Equation (3), the excited‐state substituent constant of X contributes the most to the νC=C values of XCH=CHArYs as seen from the fraction contributions. On the whole, the contribution of X to the νC=C values of XCH=CHArYs is larger than that of Y. [ABSTRACT FROM AUTHOR]

Hydrodenitrogenation (HDN) experiments and density functional theory (DFT) calculations were combined herein to study the substituent effects of the nitrogen heterocycle on the HDN behaviors of indole and quinoline. Indole (IND), 2-methyl-indole (2-M-IND), 3-methyl-indole (3-M-IND), quinoline (QL), 2-methyl-quinoline (2-M-QL) and 3-methyl-quinoline (3-M-QL) were used as the HDN reactant on the NiMo/γ-Al2O3 catalyst. Some key elementary reactions in the HDN process of these nitrogen compounds on the Ni-Mo-S active nanocluster were calculated. The notable difference between IND and QL in the HDN is that dihydro-indole (DHI) can directly convert to O-ethyl aniline via the C–N bond cleavage, whereas tetrahydro-quinoline (THQ) can only break the C–N single bond via the full hydrogenation saturation of the aromatic ring. The reason for this is that the –NH and C=C groups of DHI can be coplanar and well adsorbed on the Ni-Mo-edge simultaneously during the C–N bond cleavage. In comparison, those of THQ cannot stably simultaneously adsorb on the Ni-Mo-edge because of the non-coplanarity. Whenever the methyl group locates on the α-C or the β-C atom of indole, the hydrogenation ability of the nitrogen heterocycle will be evidently weakened because the methyl group increases the space requirement of the sp3 carbon, and the impaction of the C=C groups on the Ni-S-edge cannot provide enough space. When the methyl groups are located on the α-C of quinoline, the self-HDN behavior of 2-M-QL is similar to quinoline, whereas the competitive HDN ability of 2-M-QL in the homologs is evidently weakened because the methyl group on the α-C hinders the contact between the N atom of 2-M-QL and the exposed metal atom of the coordinatively unsaturated active sites (CUS). When the methyl group locates on the β-C of quinoline, the C–N bond cleavage of 3-methyl-quinoline becomes more difficult because the methyl group on the β-C increases the steric hindrance of the C=C group. However, the competitive HDN ability of 3-M-QL is not evidently influenced because the methyl group on the β-C does not evidently hinder the adsorption of 3-M-QL on the active sites. [ABSTRACT FROM AUTHOR]

In this work we explored the excited state reactivity of triplet chlorobenzenes with density functional theory and a cluster‐continuum approach. We modeled two competing reactions: a direct abstraction of hydrogen from a solvent molecule and solvolysis via photo‐SN2Ar. Electron donating (–OMe, –CH2SiMe3, –SiMe3) and withdrawing (–CN) substituents not only have distinct effects on the triplet geometries, inducing structural distortions due to the relief of excited state antiaromaticity, but also affect the reactivity of the system. Therefore, electron‐rich chlorobenzenes favor the radical reduction, while electron deficiency opens the possibility for solvolysis. Both reactions are energetically comparable to or more favorable then the dissociation of the C‐Cl bond to form triplet or singlet aryl cations, the intermediates considered responsible for these reactivities. Our findings can be correlated with experimental results on similar systems available from the literature, deeming the proposed pathways as viable alternatives to established mechanisms involving aryl cations. [ABSTRACT FROM AUTHOR]

Unsymmetrical 11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-dione, incorporating a para-phenyl substituted pyridine unit fused by both 6- and 7-membered carbocyclic rings, has been prepared on the gram-scale via a multi-step procedure involving cyclization, hydrogenation and oxidation. Templating this diketone, in the presence of cobalt(II) chloride hexahydrate, with the corresponding aniline afforded in good yield five examples of doubly fused bis(arylimino)pyridine-cobalt(II) chlorides, Co1 (aryl = 2,6-dimethylphenyl), Co2 (2,6-diethylphenyl), Co3 (2,6-diisopropylphenyl), Co4 (2,4,6-trimethylphenyl) and Co5 (2,6-diethyl-4-methylphenyl). Structural characterization of Co1, Co2 and Co3 highlights the flexible nature of the inequivalent fused rings on the NNN’-ligand and the skewed disposition of the para-phenyl group. On activation with MAO, Co1–Co5 exhibited high activity for ethylene polymerization at 30 °C (up to 5.66 × 106 g (PE) mol−1 (Co) h−1) with the relative order being as follows: Co4 > Co1 > Co5 > Co3 > Co2. All polyethylenes were strictly linear, while their molecular weights and dispersities showed some notable variations. For Co1, Co2, Co4 and Co5, all polymerizations were well controlled as evidenced by the narrow dispersities of their polymers (Mw/Mn range: 1.8–2.7), while their molecular weights (Mw range: 2.9–10.9 kg mol−1) steadily increased in line with the greater steric properties of the N-aryl ortho-substituents. By contrast, the most hindered 2,6-diisopropyl counterpart Co3 displayed a broad distribution with bimodal characteristics (Mw/Mn = 10.3) and gave noticeably higher molecular weight polymer (Mw = 75.5 kg mol−1). By comparison, the MMAO-activated catalysts were generally less active, but showed similar trends in molecular weight and polymer dispersity. End group analysis of selected polymers via 13C and 1H NMR spectroscopy revealed the presence of both saturated and unsaturated polyethylenes in accordance with competing chain transfer pathways. Notably, when comparing Co3/MAO with its non-phenyl substituted analogue (E2,6-iPr2Ph)CoCl2/MAO, the former, though less controlled, displayed higher activity and molecular weight, a finding that points towards a role played by the remote para-phenyl group.

Substituent effects on the ultraviolet absorption properties of 2,4-dihydroxy dibenzophenone were investigated experimentally. Nine compounds of 2,4-dihydroxy dibenzophenone with different substituents were prepared by a solvent-free reaction of benzoyl chloride. The maximum absorption wavelength (λmax) of these samples was measured, and their UV resistance properties in cotton fabric as well as in polyester were determined. The results show that the λmax is dependent on the substituents at the benzylidene ring, and both electron donating substituents and electron withdrawing substituents cause a bathochromic shift. The UV resistance of fabric increases with the increase in compound concentration. The dyeing rate of each compound on polyester was higher than that of cotton. On cotton fabric, the dyeing rate of 2,4-dihydroxybenzophenone was the highest, 77.8%. On polyester, that of 2,4-dihydroxy-4′-ethyl dibenzophenone was the highest, 84.1%. The study provides new insights into the effect of substituents on the properties of 2,4-dihydroxy dibenzophenone that are related to the whitening of cotton and polyester materials. [ABSTRACT FROM AUTHOR]

HNO has broad chemical and biomedical properties. Metal complexes and derivatives are widely used to make excellent HNO sensors. However, their favorable mechanistic origins are largely unknown. Cu cyclam is a useful platform to make excellent HNO sensors including imaging agents. A quantum chemical study of Cu cyclams with various substitutions was performed, which reproduced diverse experimental reactivities. Structural, electronic, and energetic profiles along reaction pathways show the importance of HNO binding and a proton‐coupled electron transfer mechanism for HNO reaction. Results reveal that steric effect is primary and electronic factor is secondary (if the redox potential is sufficient), but their interwoven effects can lead to unexpected reactivity, which looks mysterious experimentally but can be explained computationally. This work suggests rational substituent design ideas and recommends a theoretical study of a new design to save time and cost due to its subtle effect. [ABSTRACT FROM AUTHOR]

In this series of articles, the Board Members of ChemSusChem review recent research articles that they consider of exceptional quality and importance for sustainability. This entry features Prof. Rui Cao, who discusses how tuning the second‐sphere environments of Fe porphyrins can improve the activity and selectivity for CO2 reduction. Substituents with proton relay capability, hydrogen‐bonding, and electrostatic features have significant impact on the efficiency of Fe porphyrins for the electrocatalytic CO2 reduction reaction [ABSTRACT FROM AUTHOR]