Showing papers on "Substituent published in 2014"
Abstract: Low bandgap and two-dimensional (2D)-conjugated copolymers based on benzo[1,2-b:4,5-b′]dithiophene with conjugated thiophene side chains (BDTT) and thieno[3,4-b]thiophene with electron-withdrawing substituents (TT) are attractive high efficiency polymer donor materials in polymer solar cells (PSCs). In this work, we introduced an alkylthio substituent on the thiophene side chain in the polymer and synthesized a new low bandgap 2D-conjugated polymer PBDTT-S-TT. The alkylthio substituent increased the hole mobility of the polymer to 4.08 × 10−3 cm2 V−1 s−1 and down-shifted the HOMO energy level of the polymer by 0.11 eV with absorption of the polymer film red-shifted slightly. The PSCs based on PBDTT-S-TT as a donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) as an acceptor without solvent additive treatment demonstrated a high open-circuit voltage (Voc) of 0.84 V, leading to a high power conversion efficiency (PCE) of 8.42%, under the illumination of AM 1.5 G 100 mW cm−2. For comparison, the Voc and PCE of the devices based on the corresponding parent polymer PBDTT-TT with the device optimization of 3% DIO additive treatment are 0.77 V and 7.38%, respectively. The enhanced Voc value of 0.84 V for the PSC based on PBDTT-S-TT should be benefited from the down-shifted HOMO energy level of the polymer. The results indicate that the alkylthio substitution is an effective way to further improve the photovoltaic performance of the 2D-conjugated polymer donor materials in PSCs.
484 citations
TL;DR: The experiments suggest that the major product distribution is similar for all model compounds, but a stable phenyl-dihydrobenzofuran species is observed in the acidolysis of two of the γ-carbinol containing model compounds.
Abstract: Acid catalysis has long been used to depolymerize plant cell wall polysaccharides, and the mechanisms by which acid affects carbohydrates have been extensively studied. Lignin depolymerization, however, is not as well understood, primarily due to the heterogeneity and reactivity of lignin. We present an experimental and theoretical study of acid-catalyzed cleavage of two non-phenolic and two phenolic dimers that exhibit the β-O-4 ether linkage, the most common intermonomer bond in lignin. This work demonstrates that the rate of acid-catalyzed β-O-4 cleavage in dimers exhibiting a phenolic hydroxyl group is 2 orders of magnitude faster than in non-phenolic dimers. The experiments suggest that the major product distribution is similar for all model compounds, but a stable phenyl-dihydrobenzofuran species is observed in the acidolysis of two of the γ-carbinol containing model compounds. The presence of a methoxy substituent, commonly found in native lignin, prevents the formation of this intermediate. Reacti...
297 citations
TL;DR: The difunctionalization of alkenes by a tandem process that involves radical addition, 1,4-aryl migration, and desulfonylation generates α-aryl-β-heterofunctionalized amides bearing a quaternary stereocenter when the substituent on the nitrogen atom is an aryl group.
Abstract: Two radical-mediated processes of activated alkenes, namely arylphosphonylation and arylazidation, are described. The difunctionalization of alkenes by a tandem process that involves radical addition, 1,4-aryl migration, and desulfonylation generates α-aryl-β-heterofunctionalized amides bearing a quaternary stereocenter when the substituent on the nitrogen atom is an aryl group. Alternatively, heterooxindoles or spirobicycles can be obtained with excellent regioselectivity in the presence of an alkyl substituent on the nitrogen atom.
213 citations
TL;DR: Increasing the electron density in BF2-coodinated azo compounds through para-substitution leads to a bathochromic shift in their activation wavelength, which controls the hydrolysis half-life of the switch in aqueous solution, which is drastically longer for the cis isomer, while the BF2 -coodination prevents reduction by glutathione.
Abstract: Increasing the electron density in BF2-coodinated azo compounds through para-substitution leads to a bathochromic shift in their activation wavelength. When the substituent is dimethyl amine, or the like, the trans/cis isomerization process can be efficiently modulated using near infrared light. The electron donating capability of the substituent also controls the hydrolysis half-life of the switch in aqueous solution, which is drastically longer for the cis isomer, while the BF2-coodination prevents reduction by glutathione.
160 citations
TL;DR: In this article, the authors investigated the stability of benzyl trimethylammonium (BTMA)-functionalized polyaromatic membranes and computed the barrier heights of aryl-aryl cleavage.
Abstract: Alkaline stability of benzyl trimethylammonium (BTMA)-functionalized polyaromatic membranes was investigated by computational modeling and experimental methods. The barrier height of hydroxide initiated aryl-ether cleavage in the polymer backbone was computed to be 85.8 kJ/mol, a value lower than the nucleophilic substitution of the α-carbons on the benzylic position of BTMA cationic functional group, computed to be 90.8 kJ/mol. The barrier heights of aryl–aryl cleavage (polymer backbone) are 223.8–246.0 kJ/mol. The computational modeling study suggests that the facile aryl–ether cleavage is not only due to the electron deficiency of the aryl group but also due to the low bond dissociation energy arising from the ether substituent. Ex situ degradation studies using Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR) spectroscopy indicated that 61% of the aryl–ether groups degraded after 2 h of treatment in 0.5 M NaOH at 80 °C. BTMA cationic groups degraded slowly over 48 h under the ...
140 citations
TL;DR: The reaction of enals with β-diketones, β-ketoesters, and malonates bearing a β-oxyalkyl substituent at the α-position by oxidative NHC catalysis to provide highly substituted β-lactones is described.
Abstract: The reaction of enals with β-diketones, β-ketoesters, and malonates bearing a β-oxyalkyl substituent at the α-position by oxidative NHC catalysis to provide highly substituted β-lactones is described. Reactions occur with excellent diastereo- and enantioselectivity. The organo cascade comprises two CC bond formations and one CO bond formation. Up to four contiguous stereogenic centers including two fully substituted stereocenters are formed in the cascade.
130 citations
TL;DR: Electronic structure investigation of ((Ph2PPr)PDI)Mn revealed that this complex possesses an unpaired electron on the metal center, rendering it likely that catalysis takes place following electron transfer to the incoming carbonyl substituent.
Abstract: The reduction of (Ph2PPrPDI)MnCl2 allowed the preparation of the formally zerovalent complex, (Ph2PPrPDI)Mn, which features a pentadentate bis(imino)pyridine chelate. This complex is a highly active precatalyst for the hydrosilylation of ketones, exhibiting TOFs of up to 76,800 h–1 in the absence of solvent. Loadings as low as 0.01 mol % were employed, and (Ph2PPrPDI)Mn was found to mediate the atom-efficient utilization of Si–H bonds to form quaternary silane products. (Ph2PPrPDI)Mn was also shown to catalyze the dihydrosilylation of esters following cleavage of the substrate acyl C–O bond. Electronic structure investigation of (Ph2PPrPDI)Mn revealed that this complex possesses an unpaired electron on the metal center, rendering it likely that catalysis takes place following electron transfer to the incoming carbonyl substituent.
123 citations
TL;DR: Electrochemical investigations of the radical suggest the possibility to generate a stable formal boryl anion species, both in solution and in the solid state.
Abstract: Utilizing a cyclic (alkyl)(amino)carbene (CAAC) as a ligand, neutral CAAC-stabilized radicals containing a boryl functionality could be prepared by reduction of the corresponding haloborane adducts. The radical species with a duryl substituent was fully characterized by single-crystal X-ray structural analysis, EPR spectroscopy, and DFT calculations. Compared to known neutral boryl radicals, the isolated radical species showed larger spin density on the boron atom. Furthermore, the compound that was isolated is extraordinarily stable to high temperatures under inert conditions, both in solution and in the solid state. Electrochemical investigations of the radical suggest the possibility to generate a stable formal boryl anion species.
116 citations
TL;DR: In this article, 1,2,3-Triazolium-based poly(ionic liquid)s containing a triethylene glycol spacer were synthesized from the polyaddition of an α-azide-ω-alkyne monomer by copper-catalyzed azide-alkne cycloaddition (CuAAC) followed by quaternization reactions with alkyl halides and subsequent anion exchanges with different fluorinated salts.
Abstract: 1,2,3-Triazolium-based poly(ionic liquid)s containing a triethylene glycol spacer were synthesized from the polyaddition of an α-azide-ω-alkyne monomer by copper-catalyzed azide–alkyne cycloaddition (CuAAC) followed by quaternization reactions with alkyl halides and subsequent anion exchanges with different fluorinated salts. A detailed structure–property relationship for solubility, thermal stability, and ionic conductivity was investigated by means of 1H NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and broadband dielectric spectroscopy (BDS). One of these poly(ionic liquid)s with a methyl substituent and bis(trifluoromethylsulfonyl)imide anion exhibits an ionic conductivity of 2 × 10–5 S cm–1 at 30 °C, which is on par with the best PILs with side-chain charge carriers reported so far and is much higher than any previously reported ionenes. The straightforward synthesis along with the broad structural design and enhanced properties of this new class of poly...
114 citations
TL;DR: A copper-mediated C6-selective dehydrogenative heteroarylation of 2-pyridones with 1,3-azoles has been developed and the reaction proceeded smoothly by twofold C-H cleavage even in the absence of noble-metal catalysts.
Abstract: A copper-mediated C6-selective dehydrogenative heteroarylation of 2-pyridones with 1,3-azoles has been developed. The reaction proceeded smoothly by twofold CH cleavage even in the absence of noble-metal catalysts. The observed site selectivity was directed by a pyridyl substituent on the nitrogen atom of the pyridone ring. This directing group was readily removed after the coupling event, thus leading to 2-pyridone derivatives with a free NH group. Moreover, in some cases, catalytic turnover of the Cu salt was also possible with the ideal terminal oxidant: molecular oxygen in air.
111 citations
TL;DR: The hypothesis is that for systems of this type the fluorescence may be tuned and even predicted by changing the substituent on the adjacent Cc, comparable to that observed for previously reported styrene-containing carboranes.
Abstract: Two sets of o-carborane derivatives incorporating fluorene and anthracene fragments as fluorophore groups have been successfully synthesized and characterized, and their photophysical properties studied. The first set, comprising fluorene-containing carboranes 6-9, was prepared by catalyzed hydrosilylation reactions of ethynylfluorene with appropriate carboranylsilanes. The compound 1-[(9,9-dioctyl-fluorene-2-yl)ethynyl]carborane (11) was synthesized by the reaction of 9,9-dioctyl-2-ethynylfluorene and decaborane (B10H14). Furthermore, reactions of the lithium salt of 11 with 1 equivalent of 4-(chloromethyl)styrene or 9-(chloromethyl)anthracene yielded compounds 12 and 13. Members of the second set of derivatives, comprising anthracene-containing carboranes, were synthesized by reactions of monolithium or dilithium salts of 1-Me-1,2-C2B10H 11, 1-Ph-1,2-C2B10H11, and 1,2-C2B10H12 with 1 or 2 equivalents of 9-(chloromethyl)anthracene, respectively, to produce compounds 14-16. In addition, 2 equivalents of the monolithium salts of 1-Me-1,2-C2B 10H11 (Me-o-carborane) and 1-Ph-1,2-C2B 10H11 (Ph-o-carborane) were reacted with 9,10-bis(chloromethyl)anthracene to produce compounds 17 and 18, respectively. Fluorene derivatives 6-9 exhibit moderate fluorescence quantum yields (32-44 %), whereas 11-13, in which the fluorophore is bonded to the Ccluster (Cc), show very low emission intensity (6 %) or complete fluorescence quenching. The anthracenyl derivatives containing the Me-o-carborane moiety exhibit notably high fluorescence emissions, with φF=82 and 94 %, whereas their Ph-o-carborane analogues are not fluorescent at all. For these compounds, we have observed a correlation between the Cc - C c bond length and the fluorescence intensity in CH2Cl 2 solution, comparable to that observed for previously reported styrene-containing carboranes. Thus, our hypothesis is that for systems of this type the fluorescence may be tuned and even predicted by changing the substituent on the adjacent Cc. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
TL;DR: Density functional theory calculations (B3LYP and M06) have been utilized to study a newly reported Heck-type reaction that uses an allylic or alkenyl alcohol as substrate and palladium as catalyst in the form of a chelate with a chiral pyridine oxazoline (PyrOx) ligand to reveal the C═C bond migratory insertion step determines both the regioselectivity and the enantioselectivities of arylation.
Abstract: Density functional theory (DFT) calculations (B3LYP and M06) have been utilized to study a newly reported Heck-type reaction that uses an allylic or alkenyl alcohol as substrate and palladium as catalyst in the form of a chelate with a chiral pyridine oxazoline (PyrOx) ligand. The reaction not only controls the regio- and enantioselectivities of arylation of the C═C bond, but also forms the carbonyl functionality up to four bonds away from the aryl substituent via tandem C═C bond migration and enol-to-keto conversion. Computations performed on representative reaction systems allow us to propose a detailed mechanism with several key steps. Initial oxidation of palladium(0) by aryldiazonium generates active arylpalladium(II) species that bind the C═C bond of an allylic or alkenyl alcohol. The activated C═C bond inserts into the palladium-aryl moiety to attain aryl substitution and a chiral carbon center, and the resulting complex undergoes β-hydride elimination to give a new C═C bond that can repeat the insertion/elimination process to move down the carbon chain to form an enol that tautomerizes to a highly stable carbonyl final product. The calculations reveal that the C═C bond migratory insertion step determines both the regioselectivity and the enantioselectivity of arylation, with the former arising mainly from the electronic effect of the hydroxyl group on the charge distribution over the C═C bond and the latter originating from a combination of steric repulsion, trans influence, and C-H/π dispersion interactions.
TL;DR: A novel and efficient Cu(OAc)2-catalyzed oxyazidation of unactivated alkenes was developed and the reactions are easy to conduct, occur under mild conditions, and form azido-substituted isoxazolines in good yields.
TL;DR: In this article, a novel N-doped carbon (CN) was prepared by the hydrothermal method using glucosamine hydrochloride as both carbon and nitrogen precursor, followed by a postsynthesis heat treatment.
Abstract: A novel N-doped carbon (CN) was prepared by the hydrothermal method using glucosamine hydrochloride as both carbon and nitrogen precursor, followed by a postsynthesis heat treatment. Pd@CN exhibited 9 times higher activity compared to that of commercial Pd@AC on hydrogenation of benzoic acid to cyclohexanecarboxylic acid. The influence of solvent and substituent were also investigated. Besides, the hydrogenations of various benzoic acids have been carried out over Pd@CN.
TL;DR: A mild, versatile, and convenient method for efficient intramolecular oxytrifluoromethylthiolation of unactivated alkenes catalyzed by Cu(OAc)2 has been developed.
TL;DR: The N,N,N-trimethyl chitosan with 100% quaternization showed the highest antibacterial activity with moderate cytotoxicity, while increasing the spacer length reduced the activity.
Abstract: A series of water-soluble cationic chitosan derivatives were prepared by chemoselective functionalization at the amino group of five different parent chitosans having varying degrees of acetylation and molecular weight. The quaternary moieties were introduced at different alkyl spacer lengths from the polymer backbone (C-0, C-2 and C-6) with the aid of 3,6-di-O-tert-butyldimethylsilyl protection of the chitosan backbone, thus allowing full (100%) substitution of the free amino groups. All of the derivatives were characterized using 1H-NMR, 1H-1H COSY and FT-IR spectroscopy, while molecular weight was determined by GPC. Antibacterial activity was investigated against Gram positive S. aureus and Gram negative E. coli. The relationship between structure and activity/toxicity was defined, considering the effect of the cationic group’s structure and its distance from the polymer backbone, as well as the degree of acetylation within a molecular weight range of 7–23 kDa for the final compounds. The N,N,N-trimethyl chitosan with 100% quaternization showed the highest antibacterial activity with moderate cytotoxicity, while increasing the spacer length reduced the activity. Trimethylammoniumyl quaternary ammonium moieties contributed more to activity than 1-pyridiniumyl moieties. In general, no trend in the antibacterial activity of the compounds with increasing molecular weight or degree of acetylation up to 34% was observed.
TL;DR: In this article, the formal potentials of carbonyl-based organic molecules (C-bOMs) have been analyzed and a wide range of chemical variations/modifications can be performed to modify their electrochemical behavior via synthesis, such as increasing the number of electrons transferred while minimizing the molecular weight of the compound, thus maximizing their gravimetric energy density.
Abstract: Organic compounds represent an attractive choice for cathode materials in rechargeable lithium batteries. Among all the organic functionalities, carbonyl-based organic molecules (C-bOMs) exhibit rapid and generally chemically reversible electrochemical behavior, and their reduced forms (enolates) can have strong ionic interactions with small radii cations (such as Li+). Furthermore, a wide range of chemical variations/modifications can be performed on C-bOM structures via synthesis. We have systematically investigated how to modify their electrochemical behavior by shifting the formal potential, maximizing the interaction of the various redox forms with lithium ions, and maximizing the number of electrons transferred while minimizing the molecular weight of the compound, thus maximizing their gravimetric energy density. We have performed density-functional calculations to predict the formal potentials of the C-bOMs materials (E = 2.0–4.0 V) and identify the most promising candidates. We have determined ho...
TL;DR: The first asymmetric intermolecular addition of non-acidic C–H bonds to imines is reported and the activating N-perfluorobutanesulfinyl imine substituent provides outstanding diastereoselectivity.
Abstract: The first asymmetric intermolecular addition of non-acidic C–H bonds to imines is reported. The use of the activating N-perfluorobutanesulfinyl imine substituent is essential for achieving sufficient reactivity and provides outstanding diastereoselectivity (>98:2 dr). Straightforward removal of the sulfinyl group with HCl yields the highly enantiomerically enriched amine hydrochlorides.
TL;DR: A new modular approach to the smallest substituted cycloparaphenylenes (CPPs) is presented, which permits access to substituted CPPs, choosing the substituent at a late stage of the synthesis.
TL;DR: Ab initio MP2/aug'-cc-pVTZ calculations have been carried out in search of equilibrium structures with P···Cl pnicogen bonds or halogen bonds on the potential energy surfaces H2FP, finding three different types of halogen-bonded complexes with traditional, chlorine-shared, and ion-pair bonds.
Abstract: Ab initio MP2/aug′-cc-pVTZ calculations have been carried out in search of equilibrium structures with P···Cl pnicogen bonds or halogen bonds on the potential energy surfaces H2FP:ClY for Y = F, NC, Cl, CN, CCH, CH3, and H. Three different types of halogen-bonded complexes with traditional, chlorine-shared, and ion-pair bonds have been identified. Two different pnicogen-bonded complexes have also been found on these surfaces. The most electronegative substituents F and NC form only halogen-bonded complexes, while the most electropositive substituents CH3 and H form only pnicogen-bonded complexes. The halogen-bonded complexes involving the less electronegative groups Cl and CN are more stable than the corresponding pnicogen-bonded complexes, while the pnicogen-bonded complexes with CCH are more stable than the corresponding halogen-bonded complex. Traditional halogen-bonded complexes are stabilized by charge transfer from the P lone pair to the Cl–A σ* orbital, where A is the atom of Y directly bonded to C...
TL;DR: The straightforward synthesis and detailed characterization of nine substituted triarylformazanate boron difluoride complexes is reported, showing substituent-dependent absorption and emission properties, accompanied by significant Stokes shifts, with the aryl substituents at the 1,5-positions of the formazanates backbone having a greater influence on these properties than aryal substituented at the 3-position.
Abstract: The straightforward synthesis and detailed characterization of nine substituted triarylformazanate boron difluoride complexes is reported. The effect of electron-donating (p-anisole) and electron-withdrawing (p-benzonitrile) substituents on optical and electrochemical properties, relative to phenyl substituents, was studied at two different positions within the formazanate ligand framework. Each of the BF2 complexes was characterized by 1H, 13C, 11B, and 19F NMR spectroscopy, cyclic voltammetry, infrared spectroscopy, UV–vis absorption and emission spectroscopy, mass spectrometry, and elemental analysis. Select examples were studied by X-ray crystallography, revealing highly delocalized structures in the solid state. The complexes were reversibly reduced in two steps electrochemically to their radical anion and dianion forms. The complexes also exhibited substituent-dependent absorption and emission properties, accompanied by significant Stokes shifts, with the aryl substituents at the 1,5-positions of th...
TL;DR: A method for the synthesis of amide-containing molecules was developed using vinyl azides as an enamine-type nucleophile towards carbon electrophiles, such as imines, aldehydes, and carbocations that were generated from alcohols in the presence of BF3 ⋅OEt2.
Abstract: A method for the synthesis of amide-containing molecules was developed using vinyl azides as an enamine-type nucleophile towards carbon electrophiles, such as imines, aldehydes, and carbocations that were generated from alcohols in the presence of BF3 ⋅OEt2 . After nucleophilic attack of the vinyl azide, a substituent of the resulting iminodiazonium ion intermediate migrates to form a nitrilium ion, which is hydrolyzed to afford the corresponding amide.
TL;DR: In this article, the crystal structure of a (R)-ω-transaminase from Aspergillus terreus determined by X-ray crystallography at a resolution of 1.6 A. The structure of the protein is a homodimer that displays the typical class IV fold of PLPdependent aminotransferases.
Abstract: Chiral amines are important building blocks for the synthesis of pharmaceutical products, fine chemicals, and agrochemicals. ω-Transaminases are able to directly synthesize enantiopure chiral amines by catalysing the transfer of an amino group from a primary amino donor to a carbonyl acceptor with pyridoxal 5′-phosphate (PLP) as cofactor. In nature, (S)-selective amine transaminases are more abundant than the (R)-selective enzymes, and therefore more information concerning their structures is available. Here, we present the crystal structure of an (R)-ω-transaminase from Aspergillus terreus determined by X-ray crystallography at a resolution of 1.6 A. The structure of the protein is a homodimer that displays the typical class IV fold of PLP-dependent aminotransferases. The PLP-cofactor observed in the structure is present in two states (i) covalently bound to the active site lysine (the internal aldimine form) and (ii) as substrate/product adduct (the external aldimine form) and free lysine. Docking studies revealed that (R)-transaminases follow a dual binding mode, in which the large binding pocket can harbour the bulky substituent of the amine or ketone substrate and the α-carboxylate of pyruvate or amino acids, and the small binding pocket accommodates the smaller substituent.
TL;DR: Various parameters of these systems have been investigated, including homodesmotic reactions in terms of the substituent effect stabilization energy (SESE), the π and σ electron donor-acceptor indexes (pEDA and sEDA, respectively), the charge on the substitution active region (cSAR), and bond lengths, which have been regressed against Hammett constants, resulting mostly in an accurate correspondence.
Abstract: The application of ab initio and DFT computational methods at six different levels of theory (MP2/cc-pVDZ, MP2/aug-cc-pVTZ, B3LYP/cc-pVDZ, B3LYP/aug-cc-pVTZ, M06/cc-pVDZ, and M06/aug-cc-pVTZ) to meta- and para-substituted fluoro- and trifluoromethylbenzene derivatives and to 1-fluoro- and 1-trifluoromethyl-2-substituted trans-ethenes allowed the study of changes in the electronic and geometric properties of F- and CF3-substituted systems under the impact of other substituents (BeH, BF2, BH2, Br, CFO, CHO, Cl, CN, F, Li, NH2, NMe2, NO, NO2, OH, H, CF3, and CH3). Various parameters of these systems have been investigated, including homodesmotic reactions in terms of the substituent effect stabilization energy (SESE), the π and σ electron donor–acceptor indexes (pEDA and sEDA, respectively), the charge on the substituent active region (cSAR, known earlier as qSAR), and bond lengths, which have been regressed against Hammett constants, resulting mostly in an accurate correspondence except in the case of p-flu...
TL;DR: A series of acylthiourea anion transporters were synthesised and their anion binding and transport properties in POPC bilayers have been investigated.
Abstract: Small molecule synthetic anion transporters may have potential application as therapeutic agents for the treatment of diseases including cystic fibrosis and cancer. Understanding the factors that can dictate the anion transport activity of such transporters is a crucial step towards their application in biological systems. In this study a series of acylthiourea anion transporters were synthesised and their anion binding and transport properties in POPC bilayers have been investigated. The transport activity of these receptors is dominated by their lipophilicity, which is in turn dependent on both substituent effects and the formation and strength of an intramolecular hydrogen bond as inferred from DFT calculations. This is in contrast to simpler thiourea systems, in which the lipophilicity depends predominantly on substituent effects alone.
TL;DR: A new activation principle in organocatalysis is presented: halide binding through Coulombic interactions, which was realized by using 3,5-di(carbomethoxy)pyridinium ions that carry an additional electron-withdrawing substituent on the nitrogen atom, for example, pentafluorobenzyl or cyanomethyl.
Abstract: A new activation principle in organocatalysis is presented: halide binding through Coulombic interactions. This mode of catalysis was realized by using 3,5-di(carbomethoxy)pyridinium ions that carry an additional electron-withdrawing substituent on the nitrogen atom, for example, pentafluorobenzyl or cyanomethyl. For the N-pentafluorobenzyl derivative, Coulombic interaction with the pyridinium moiety is complemented in the solid state by anion–π interactions with the perfluorophenyl ring. Bromide and chloride are bound by these cations in a 1:1 stoichiometry. Catalysis of the CC coupling between 1-chloroisochroman (and related electrophiles) with silyl ketene acetals occurs at −78 °C and at low catalyst loading (2 mol %).
TL;DR: In this article, the adsorption behavior as well as the influence of bromine substituents on the formation of highly-ordered two-dimensional structures of pyrene derivatives on Au(111) were studied by a combination of scanning tunnelling microscopy (STM) and density functional theory (DFT) calculations.
TL;DR: TD-DFT calculations suggest that the low-energy electronic transition is attributed to the intramolecular "through-space" charge transfer between the appended aryl group (HOMO) and the central phenylene ring (LUMO), and the greater change in the HOMO level by the substituent than that in the LUMO is responsible for the emission color tuning.
Abstract: 1,4-Di-(1-Ar-o-carboran-2-yl)benzene (Ar = 3,5-bis(trifluoromethyl)phenyl (1), phenyl (2), 4-n-butylphenyl (3), 4-N,N-dimethylaniline (4)) compounds that are electronically modulated at the C1-position of o-carborane with the electron-withdrawing or -donating aryl groups were prepared and characterized The X-ray crystal structures of 1, 3, and 4 reveal that the two aryl groups on the C1-carborane carbon atoms are oppositely positioned, featuring overall C2-symmetry, and the C1–C2 bond length of carborane increases with the increasing order of electron-donating effect of an aryl group UV-vis absorption spectra exhibit small low-energy absorption bands at around 275–300 nm for 1–3 while 4 shows a broad absorption tail at 350–400 nm Although 1–4 show virtually no emission in solution, an intense aggregation-induced emission over the region ranging from 400–700 nm is observed in the solid state Importantly, the emission wavelengths of 1–4 exhibit an apparent red-shift upon changing the aryl substituent from the CF3 to the NMe2 group (from 1 to 4) TD-DFT calculations suggest that the low-energy electronic transition is attributed to the intramolecular “through-space” charge transfer between the appended aryl group (HOMO) and the central phenylene ring (LUMO), and the greater change in the HOMO level by the substituent than that in the LUMO is responsible for the emission color tuning
TL;DR: Ni(PCy3)2Cl2 was demonstrated to effectively catalyze cross-coupling of aryl fluorides and organozinc reagents and a wide range of substituents and functional groups are tolerated.
Abstract: Ni(PCy3)2Cl2 was demonstrated to effectively catalyze cross-coupling of aryl fluorides and organozinc reagents. Both electron-poor and -rich aryl fluorides can react effectively with nucleophiles including aryl-, methyl-, and benzylzinc chlorides. A wide range of substituents and functional groups are tolerated. In the presence of a directing group, PhC(O), the reaction is selective for cleavage of the C–F bond ortho to the carbonyl substituent in a difluoroarene.
TL;DR: The design, synthesis, and mechanistic studies of the half-sandwich ruthenium complex 12 are reported, which are established as the most active and practical catalyst for anti-Markovnikov reductive hydration discovered to date and define the structural parameters of 12 underlying its activity and stability and delineate design strategies for synthesis of other multifunctional catalysts.
Abstract: The conversion of terminal alkynes to functionalized products by the direct addition of heteroatom-based nucleophiles is an important aim in catalysis. We report the design, synthesis, and mechanistic studies of the half-sandwich ruthenium complex 12, which is a highly active catalyst for the anti-Markovnikov reductive hydration of alkynes. The key design element of 12 involves a tridentate nitrogen-based ligand that contains a hemilabile 3-(dimethylamino)propyl substituent. Under neutral conditions, the dimethylamino substituent coordinates to the ruthenium center to generate an air-stable, 18-electron, κ3-complex. Mechanistic studies show that the dimethylamino substituent is partially dissociated from the ruthenium center (by protonation) in the reaction media, thereby generating a vacant coordination site for catalysis. These studies also show that this substituent increases hydrogenation activity by promoting activation of the reductant. At least three catalytic cycles, involving the decarboxylation ...