2,8'-disubstituted-1,1'-binaphthyls: a new pattern in chiral ligands

Impact of Anion Exchange Ionomers on the Electrocatalytic Performance for the Oxygen Reduction Reaction of B-N Co-doped Carbon Quantum Dots on Activated Carbon

Composite electrocatalytic electrodes made from B-N co-doped carbon quantum dots (CQD) and various anion exchange ionomers (AEI) are studied for the oxygen reduction reaction (ORR) in alkaline solutions. The quantity and positions of dopants in CQD, prepared by hydrothermal synthesis, are analyzed by various spectroscopies, including ¹¹B NMR spectroscopy that evidenced boronic acid at edge sites. The AEI are synthesized with various backbones, including more hydrophilic polysulfone, hydrophobic poly(alkylene biphenyl), and poly(2,6-dimethyl-1,4-phenylene oxide) with intermediate hydrophilicity; the functional groups are trimethylammonium moieties grafted on long (LC) or short (SC) side chains. The CQD/AEI ink is drop-casted on activated carbon paper, and the samples are fixed on a rotating disk electrode and studied in three-electrode configuration in oxygen-saturated 0.1 M KOH. The onset potentials are among the best in the literature (E_onset ≈ 0.94 V vs RHE). The highest electrocatalytic activity is observed for electrodes containing AEI with long side chains; the sample containing PPO LC attains excellent ORR currents approaching that of benchmark Pt/C cloth. The electrocatalytic performances are discussed in view of the many relevant AEI parameters, including hydrophilicity, oxygen permeability, catalyst dispersivity, and ionic conductivity.

Aggregation-Induced Polarization (AIP): Optical Rotation Amplification and Adjustment of Chiral Aggregates of Folding Oligomers and Polymers

The phenomenon of aggregation-induced polarization (AIP) was observed showing optical rotation amplification and adjustment. The relationship between optical rotations of chiral aggregates of multilayered chiral folding oligomers and polymers with water% in THF (f_w) has been established accordingly. New multilayered chiral oligomers were synthesized under the asymmetric catalytic systems established by our laboratory recently. These products were well-characterized by UV-vis, NMR, and MALDI-TOF spectra. Absolute stereochemistry (enantio- and diastereochemistry) was assigned by comparison with similar asymmetric induction by the same catalyst in our previous reactions. The present AIP work can serve as a new tool to determine chiral aggregates, especially for those that cannot display emission. AIP would also complement AIE-based CPL since AIP serves as a new tool providing enhanced right- or left-hand polarized lights with individual wavelengths. It will find many applications in chemical and materials science in the future.

1-Substituted Perylene Derivatives by Anionic Cyclodehydrogenation: Analysis of the Reaction Mechanism

Perylene derivatives constitute a promising class of compounds with technological applications mainly due to their optoelectronic properties. One mechanism proposed to synthesize them, starting from binaphthyl derivatives, is anionic cyclodehydrogenation (under reductive conditions). However, the scope of this reaction is limited. In the present study, we report a theoretical and experimental analysis of this particular reaction mechanism for its use in the synthesis of 1-substituted perylenes. Different substituents at position 2 of 1,1'-binaphthalene were evaluated: -OCH₃, -OSi(CH₃)₂C(CH₃)₃, and -N(CH₃)₂. Based on density functional theory (DFT) calculations on the proposed mechanism, we suggest that the cyclization takes place from binaphthyl dianion instead of its radical anion. This dianion has an open-shell diradical nature, and this could be the species that was detected by EPR in previous studies. The O-substituted derivatives could not afford the perylene derivatives since their radical anions fragment and the necessary binaphthyl dianion could not be formed. On the other hand, 49% of N,N-dimethylperylen-1-amine was obtained starting from the N-substituted 2-binapthyl derivative as a substrate, employing a simpler experimental methodology.

Asymmetric Catalytic Assembly of Triple-Columned and Multiple-Layered Chiral Folding Polymers Showing Aggregation-Induced Emission (AIE)

The first chiral multi-layer 3D folding polymers have been assembled and regulated by both uniformed and differentiated aromatic chromophoric units between naphthyl piers. Screening catalysts, catalytic systems and monomers was proven to be crucial for asymmetric catalytic Suzuki-Miyaura poly-couplings for this assembly. X-ray crystallography of corresponding dimers and trimers revealed the absolute stereochemistry and the intermolecular packing pattern. Up to 61,960 M w /41,900 M n and m / z = 4317 for polymers and oligomers as confirmed by GPC and MALDI-TOF MS indicated that the present frameworks were composed of multiple layers stacked. The resulting multiple π-assemblies exhibited remarkable optical properties in aggregated states (PL in solids and AIE in solutions), as well as reversible redox properties in electrochemical performance.

Reductive Amination Revisited: Reduction of Aldimines with Trichlorosilane Catalyzed by Dimethylformamide─Functional Group Tolerance, Scope, and Limitations

Aldimines, generated in situ from aliphatic, aromatic, and heteroaromatic aldehydes and aliphatic, aromatic, and heteroaromatic primary or secondary amines, can be reduced with trichlorosilane in the presence of dimethylformamide (DMF) as an organocatalyst (≤10 mol %) in toluene or CH₂Cl₂ at room temperature. The reduction tolerates ketone carbonyls, esters, amides, nitriles, sulfones, sulfonamides, NO₂, SF₅, and CF₃ groups, boronic esters, azides, phosphine oxides, C═C and C≡C bonds, and ferrocenyl nucleus, but sulfoxides and N-oxides are reduced. α,β-Unsaturated aldimines undergo 1,2-reduction only, leaving the C═C bond intact. N-Monoalkylation of primary amines is attained with a 1:1 aldehyde to amine ratio, whereas excess of the aldehyde (≥2:1) allows second alkylation, giving rise to tertiary amines. Reductive N-alkylation of α-amino acids proceeds without racemization; the resulting products, containing a C≡C bond or N₃ group, are suitable for click chemistry. This reaction thus offers advantages over the traditional methods (borohydride reduction or catalytic hydrogenation) in terms of efficiency and chemoselectivity. Solubility of some of the reacting partners appears to be the only limitation. The byproducts generated by the workup with aqueous NaHCO₃ (i.e., NaCl and silica) are environmentally benign. As a greener alternative, DMA can be employed as a catalyst instead of DMF.

Lewis pairing and frustration of group 13/15 elements geometrically enforced by (ace)naphthalene, biphenylene and (thio)xanthene backbones

The synthesis, structure, and reactivity of mixed group 13/group 15 compounds (E¹³ = B, Al, Ga, In, Tl; E¹⁵ = N, P, Sb, Bi) featuring a rigid (ace)naphthalene or (thio)xanthene backbone are discussed in this review. The backbone may either enforce or prevent E¹⁵→E¹³ interactions, resulting in Lewis pairing or frustration. The formation of strong E¹⁵→E¹³ interactions is possible upon peri-substitution of (ace)naphthalenes. This gives the opportunity to access and study highly reactive species, as exemplified by P-stabilised borenium salts and boryl radicals. In turn, rigid expanded spacers such as biphenylenes, (thio)xanthenes and dibenzofurans impose long distances and geometrically prevent E¹⁵→E¹³ interactions. Such P-B derivatives display ambiphilic coordination properties and frustrated Lewis pair behaviour towards small molecules, their preorganised structure favouring reversible interaction/activation. Throughout the review, the importance of the scaffold in enforcing or preventing E¹⁵→E¹³ interactions is highlighted and discussed based on experimental data and theoretical calculations.

Asymmetric Catalytic Approach to Multilayer 3D Chirality

The first asymmetric catalytic approach to multilayer 3D chirality has been achieved by using Suzuki-Miyaura cross-couplings. New chiral catalysts were designed and screened under various catalytic systems that proved chiral amide-phosphines to be more efficient ligands than other candidates. The multilayer 3D framework was unambiguously determined by X-ray structural analysis showing a parallel pattern of three layers consisting of top, middle and bottom aromatic rings. The X-ray structure of a catalyst complex, dichloride complex of Pd-phosphine amide, was obtained revealing an interesting asymmetric environment nearby the Pd metal center. Three rings of multilayer 3D products can be readily changed by varying aromatic ring-anchored starting materials. The resulting multilayer products displayed strong luminescence under UV irradiation and strong aggregation-induced emission (AIE). In the future, this work would benefit not only the field of asymmetric synthesis but also materials science, in particular polarized organic electronics, optoelectronics and photovoltaics.

Triple-Columned and Multiple-Layered 3D Polymers: Design, Synthesis, Aggregation-Induced Emission (AIE), and Computational Study

Conjugated polymers and oligomers have great potentials in various fields, especially in materials and biological sciences because of their intriguing electronic and optoelectronic properties. In recent years, the through-space conjugation system has emerged as a new assembled pattern of multidimensional polymers. Here, a novel series of structurally condensed multicolumn/multilayer 3D polymers and oligomers have been designed and synthesized through one-pot Suzuki polycondensation (SPC). The intramolecularly stacked arrangement of polymers can be supported by either X-ray structural analysis or computational analysis. In all cases, polymers were obtained with modest to good yields, as determined by GPC and ¹H-NMR. MALDI-TOF analysis has proven the speculation of the step-growth process of this polymerization. The computational study of ab initio and DFT calculations based on trimer and pentamer models gives details of the structures and the electronic transition. Experimental results of optical and AIE research confirmed by calculation indicates that the present work would facilitate the research and applications in materials.

Copper-Catalyzed Selective Arylation of Nitriles with Cyclic Diaryl Iodonium Salts: Direct Access to Structurally Diversified Diarylmethane Amides with Potential Neuroprotective and Anticancer Activities

A novel, simple, and high-yielding approach for the preparation of diarylmethane amide derivatives has been developed by reacting cyclic diaryl iodonium salts with nitriles using CuCl as a catalyst. The procedure is efficient with high atom economy and a wide substrate range. Importantly, selective arylation of nitriles was obtained without affecting the phenyl amino/hydroxyl groups. Furthermore, two of the diarylmethane amides (3k, 3s) displayed excellent neuroprotective and anticancer activities.

Multilayer 3D Chirality and Its Synthetic Assembly

3D chirality of sandwich type of organic molecules has been discovered. The key element of this chirality is characterized by three layers of structures that are arranged nearly in parallel fashion with one on top and one down from the center plane. Individual enantiomers of these molecules have been fully characterized by spectroscopies with their enantiomeric purity measured by chiral HPLC. The absolute configuration was unambiguously assigned by X-ray diffraction analysis. This is the first multilayer 3D chirality reported and is anticipated to lead to a new research area of asymmetric synthesis and catalysis and to have a broad impact on chemical, medicinal, and material sciences in future.

Nitrogen-doped heptazethrene and octazethrene diradicaloids

Nitrogen-doped heptazethrene and octazethrene diradicaloids were synthesized. The N-aryl dications show larger diradical character and enhanced stability than the parent ones.

Source Function applied to experimental densities reveals subtle electron-delocalization effects and appraises their transferability properties in crystals

The Source Function (SF), introduced in 1998 by Richard Bader and Carlo Gatti, is succinctly reviewed and a number of paradigmatic applications to in vacuo and crystal systems are illustrated to exemplify how the SF may be used to discuss chemical bonding in both conventional and highly challenging cases. The SF enables the electron density to be seen at a point determined by source contributions from the atoms or a group of atoms of a system, and it is therefore well linked to the chemist's awareness that any local property and chemical behaviour is to some degree influenced by all the remaining parts of a system. The key and captivating feature of the SF is that its evaluation requires only knowledge of the electron density (ED) of a system, thereby enabling a comparison of ab initio and X-ray diffraction derived electron density properties on a common and rigorous basis. The capability of the SF to detect electron-delocalization effects and to quantify their degree of transferability is systematically explored in this paper through the analysis and comparison of experimentally X-ray derived Source Function patterns in benzene, naphthalene and (±)-8'-benzhydrylideneamino-1,1'-binaphthyl-2-ol (BAB) molecular crystals. It is shown that the SF tool recovers the characteristic SF percentage patterns caused by π-electron conjugation in the first two paradigmatic aromatic molecules in almost perfect quantitative agreement with those obtained from ab initio periodic calculations. Moreover, the effect of chemical substitution on the degree of transferability of such patterns to the benzene- and naphthalene-like moieties of BAB is neatly shown and quantified by the observed systematic deviations, relative to benzene and naphthalene, of only those SF contributions from the substituted C atoms. Finally, the capability of the SF to reveal electron-delocalization effects is challenged by using a promolecule density, rather than the proper quantum mechanical density, to determine the changes in SF patterns along the cyclohexene, 1,3-cyclohexadiene and benzene molecule series. It is shown that, differently from the proper quantum density, the promolecular density is unable to reproduce the SF trends anticipated by the increase of electron delocalization along the series, therefore ruling out the geometrical effect as being the only cause for the observed SF patterns changes.

Straightforward access to mono- and bis-cycloplatinated helicenes that display circularly polarized phosphorescence using crystallization resolution methods

Enantiopure mono-cycloplatinated-[8]helicene and bis-cycloplatinated-[6]helicene derivatives were prepared through column chromatography combined with crystallization of diastereomeric complexes using a chiral ancillary sulfoxide ligand. The UV-visible spectra, circular dichroism, molar rotations, and (circularly polarized) luminescence activity of these new helical complexes have been examined in detail and analysed with the help of first-principles quantum-chemical calculations.

Regioselective functionalization of iminophosphoranes through Pd-mediated C-H bond activation: C-C and C-X bond formation

The orthopalladation of iminophosphoranes [R(3)P=N-C(10)H(7)-1] (R(3) = Ph(3) 1, p-Tol(3) 2, PhMe(2) 3, Ph(2)Me 4, N-C(10)H(7)-1 = 1-naphthyl) has been studied. It occurs regioselectively at the aryl ring bonded to the P atom in 1 and 2, giving endo-[Pd(μ-Cl)(C(6)H(4)-(PPh(2=N-1-C(10)H(7))-2)-κ-C,N](2) (5) or endo-[Pd(μ-Cl)(C(6)H(3)-(P(p-Tol)(2)=N-C(10)H(7)-1)-2-Me-5)-κ-C,N](2) (6), while in 3 the 1-naphthyl group is metallated instead, giving exo-[Pd(μ-Cl)(C(10)H(6)-(N=PPhMe(2))-8)-κ-C,N](2) (7). In the case of 4, orthopalladation at room temperature affords the kinetic exo isomer [Pd(μ-Cl)(C(10)H(6)-(N=PPh(2)Me)-8)-κ-C,N](2) (11exo), while a mixture of 11exo and the thermodynamic endo isomer [Pd(μ-Cl)(C(6)H(4)-(PPhMe=N-C(10)H(7)-1)-2)-κ-C,N](2) (11endo) is obtained in refluxing toluene. The heating in toluene of the acetate bridge dimer [Pd(μ-OAc)(C(10)H(6)-(N=PPh(2)Me)-8)-κ-C,N](2) (13exo) promotes the facile transformation of the exo isomer into the endo isomer [Pd(μ-OAc)(C(6)H(4)-(PPhMe=N-C(10)H(7)-1)-2)-κ-C,N](2) (13endo), confirming that the exo isomers are formed under kinetic control. Reactions of the orthometallated complexes have led to functionalized molecules. The stoichiometric reactions of the orthometallated complexes [Pd(μ-Cl)(C(10)H(6)-(N=PPhMe(2))-8)-κ-C,N](2) (7), [Pd(μ-Cl)(C(6)H(4)-(PPh(2)[=NPh)-2)](2) (17) and [Pd(μ-Cl)(C(6)H(3)-(C(O)N=PPh(3))-2-OMe-4)](2) (18) with I(2) or with CO results in the synthesis of the ortho-halogenated compounds [PhMe(2)P=N-C(10)H(6)-I-8] (19), [I-C(6)H(4)-(PPh(2)=NPh)-2] (21) and [Ph(3)P=NC(O)C(6)H(3)-I-2-OMe-5] (23) or the heterocycles [C(10)H(6)-(N=PPhMe(2))-1-(C(O))-8]Cl (20), [C(6)H(5)-(N=PPh(2)-C(6)H(4)-C(O)-2]ClO(4) (22) and [C(6)H(3)-(C(O)-1,2-N-PPh(3))-OMe-4]Cl (24).

Organotrifluoroborates and monocoordinated palladium complexes as catalysts--a perfect combination for Suzuki-Miyaura coupling

Monocoordinated palladium catalysts derived from sterically hindered, electron-rich phosphines or N-heterocyclic carbenes have revolutionized the Suzuki-Miyaura coupling reaction. The emergence of organotrifluoroborates has provided important new perspectives for the organoboron component of these reactions. In combination, these two components prove to be extraordinarily powerful partners for cross-coupling reactions.

Cellulose tris(3,5-dimethylphenylcarbamate)-based chiral stationary phases as effective tools for enantioselective HPLC separation of structurally different disubstituted binaphthyls

Cellulose tris(3,5-dimethylphenylcarbamate)-based chiral stationary phases (CSPs) were used for a study of the HPLC retention and enantioseparation behavior of 2,2'-disubstituted or 3,2,2'-trisubstituted 1,1'-binaphthyls and 8,3'-disubstituted 1,2'-binaphthyls. The effects of the mobile phase composition in normal- (NP) and reversed-phase (RP) separation modes were investigated. The NP mobile phases contained n-hexane and propane-2-ol at various volume ratios, the RP ones were obtained by mixing acetonitrile with water or a 20 mM phosphate buffer of pH 6.0 or 3.0. The RP separation mode has been found more suitable for enantioresolution of most of the analytes. The best enantioseparation of 2,2'-diacetyl-1,1'-binaphthyl, 2-hydroxy-2'-(phenylamino)-1,1'-binaphthyl-3-carboxylic acid and 2-amino-2'-hydroxy-1,1'-binaphthyl-3-carboxylic acid was obtained in the mobile phase of ACN/20 mM phosphate buffer, pH 3.0, 40/60 (v/v), whereas N-(2'-hydroxy-1,1'-binaphthyl-2-yl)acetamide, N-(3'-methoxy-1,2'-binaphthyl-8-yl)acetamide, and N-(3'-hydroxy-1,2'-binaphthyl-8-yl)acetamide yielded better results in ACN/water at the same v/v ratio. The analyte-CSP interaction mechanism was found to be temperature independent but the enantioresolution improved at an elevated temperature. The mechanism of the enantioselective discrimination is discussed on the basis of the thermodynamic parameters obtained. Semi-preparative separation conditions have been proposed for 2-amino-2'-hydroxy-1,1'-binaphthyl-3-carboxylic acid, N-(3'-methoxy-1,2'-binaphthyl-8-yl)acetamide, and N-(3'-hydroxy-1,2'-binaphthyl-8-yl)acetamide.

Ultralong carbon-carbon bonds in dispirobis(10-methylacridan) derivatives with an acenaphthene, pyracene, or dihydropyracylene skeleton

Acenapthalene, pyracene, and dihydropyracylene attached to two units of spiroacridan are a novel class of hexaphenylethane (HPE) derivatives that have an ultralong Csp3-Csp3 bond (1.77-1.70 A). These sterically challenged molecules were cleanly prepared by C-C bond formation through two-electron reduction from the less-hindered dications. These ultralong bonds were realized based on several molecular-design concepts including enhanced "front strain" through "multiclamping" by means of fusing or bridging aryl groups in the HPE molecule. The lengths of these ultralong bonds and their relation to the conformation (torsional angle) were also validated by means of theoretical calculations. Bond-fission experiments revealed that the bonds are more easily cleaved than standard covalent bonds to produce the corresponding dication upon oxidation with an increase in the length of the C-C bond.

On the mechanism of asymmetric allylation of aldehydes with allyltrichlorosilanes catalyzed by QUINOX, a chiral isoquinoline N-oxide

Allylation of aromatic aldehydes 1a-m with allyl- and crotyl-trichlorosilanes 2- 4, catalyzed by the chiral N-oxide QUINOX (9), has been found to exhibit a significant dependence on the electronics of the aldehyde, with p-(trifluoromethyl)benzaldehyde 1g and its p-methoxy counterpart 1h affording the corresponding homoallylic alcohols 6g, h in 96 and 16% ee, respectively, at -40 degrees C. The kinetic and computational data indicate that the reaction is likely to proceed via an associative pathway involving neutral, octahedral silicon complex 22 with only one molecule of the catalyst involved in the rate- and selectivity-determining step. The crotylation with (E) and (Z)-crotyltrichlorosilanes 3 and 4 is highly diastereoselective, suggesting the chairlike transition state 5, which is supported by computational data. High-level quantum chemical calculations further suggest that attractive aromatic interactions between the catalyst 9 and the aldehyde 1 contribute to the enantiodifferentiation and that the dramatic drop in enantioselectivity, observed with the electron-rich aldehyde 1h, originates from narrowing the energy gap between the (R)- and (S)-reaction channels in the associative mechanism (22). Overall, a good agreement between the theoretically predicted enantioselectivities for 1a and 1h and the experimental data allowed to understand the specific aspects of the reaction mechanism.

Intramolecular triarylmethane-triarylmethylium complexes with a naphthalene-1,8-diyl skeleton: isolation, structure, and reactivities of the C--H-bridged carbocations

Isolation and low-temperature X-ray analyses of intramolecular triarylmethane-triarylmethylium complexes with a naphthalene-1,8-diyl-type skeleton have been achieved. These bridged cations prefer a C--H localized structure both in solution and in the solid state. The bridging hydrogen undergoes a facile intramolecular 1,5-hydride shift from one carbon to another in solution. The C--H delocalized geometry is suggested to be the transition-state structure of the degenerate rearrangement. Charge-transfer interaction from the triarylmethane to the triarylmethylium units is evident in the electronic spectra. This interaction stabilizes the present cations. Low reactivity toward Brønsted acids indicates that these species are not the reaction intermediates in the acid-assisted long-bond cleavage of 1,1,2,2-tetraarylacenaphthene derivatives.