Showing papers on "Steric effects published in 2023"
TL;DR: In this paper , two Y-type non-fullerene acceptors of BTP-Cy•4F and BTP•Cy−4Cl were designed and synthesized by adopting outer branched side chains and inner cyclohexane side chains.
Abstract: Raising the lowest unoccupied molecular orbital (LUMO) energy level of Y‐type non‐fullerene acceptors can increase the open‐circuit voltage (Voc) and thus the photovoltaic performance of the current top performing polymer solar cells (PSCs). One of the viable routes is demonstrated by the successful Y6 derivative of L8‐BO with the branched alkyl chains at the outer side. This will introduce steric hindrance and reduce intermolecular aggregation, thus open up the bandgap and raise the LUMO energy level. To take further advantages of the steric hindrance influence on optoelectronic properties of Y6 derivatives, two Y‐type non‐fullerene acceptors of BTP‐Cy‐4F and BTP‐Cy‐4Cl are designed and synthesized by adopting outer branched side chains and inner cyclohexane side chains. An outstanding Voc of 0.937 V is achieved in the D18:BTP‐Cy‐4F binary blend devices along with a power conversion efficiency (PCE) of 18.52%. With the addition of BTP‐eC9 to extend the absorption spectral coverage, a remarkable PCE of 19.36% is realized finally in the related ternary blend devices, which is one of the highest values for single‐junction PSCs at present. The results illustrate the great potential of cyclohexane side chains in constructing high‐performance non‐fullerene acceptors and their PSCs.
20 citations
TL;DR: In this paper , the authors present the successful development of stereodivergent allylic C(sp3)-H bond arylations through a systematic investigation of the direction and degree of stereoselectivity in the cross-coupling process.
Abstract: While significant progress has been made in developing selective C-H bond cross-couplings in the field of radical chemistry, the site and stereoselectivity remain a long-standing challenge. Here, we present the successful development of stereodivergent allylic C(sp3)-H bond arylations through a systematic investigation of the direction and degree of stereoselectivity in the cross-coupling process. In contrast to the signature photosensitized geometrical isomerization of alkenes, the catalytic reaction demonstrates the feasibility of switching the C-C double bond stereoselectivity by means of ligand control as well as steric and electronic effects. Computational studies explain the stereochemical outcome and indicate that excitation of a Ni-allyl complex from singlet to a triplet state results in a spontaneous change of the allyl group coordination and that the subsequent isomerization can be directed by the choice of the ligand to achieve E/Z selectivity.
8 citations
TL;DR: The authors used 19F nuclear magnetic resonance spectroscopy to follow the reversible, two-state unfolding thermodynamics of the N−terminal Src homology 3 domain of the Drosophila signal transduction protein drk in the presence of polyethylene glycols (PEGs) of various molecular weights and concentrations.
Abstract: Proteins in the cellular milieu reside in environments crowded by macromolecules and other solutes. Although crowding can significantly impact the protein folded state stability, most experiments are conducted in dilute buffered solutions. To resolve the effect of crowding on protein stability, we use 19F nuclear magnetic resonance spectroscopy to follow the reversible, two‐state unfolding thermodynamics of the N‐terminal Src homology 3 domain of the Drosophila signal transduction protein drk in the presence of polyethylene glycols (PEGs) of various molecular weights and concentrations. Contrary to most current theories of crowding that emphasize steric protein–crowder interactions as the main driving force for entropically favored stabilization, our experiments show that PEG stabilization is accompanied by significant heat release, and entropy disfavors folding. Using our newly developed model, we find that stabilization by ethylene glycol and small PEGs is driven by favorable binding to the folded state. In contrast, for larger PEGs, chemical or soft PEG–protein interactions do not play a significant role. Instead, folding is favored by excluded volume PEG–protein interactions and an exothermic nonideal mixing contribution from release of confined PEG and water upon folding. Our results indicate that crowding acts through molecular interactions subtler than previously assumed and that interactions between solution components with both the folded and unfolded states must be carefully considered.
7 citations
TL;DR: In this paper , an efficient gold-catalyzed C-O cross-coupling reaction of (hetero)aryl iodides with primary and secondary alcohols via an AuI-AuIII catalytic cycle was developed.
Abstract: We have developed an efficient gold-catalyzed C–O cross-coupling reaction of (hetero)aryl iodides with primary and secondary alcohols via an AuI–AuIII catalytic cycle. This protocol featured moisture/air insensitivity, simple operation, and excellent functional group tolerance. Good yields were obtained regardless of steric hindrance and electronic factor (electron-rich or poor) of substrates, and the chirality of chiral alcohol starting materials could be preserved. Our protocol worked well for both intermolecular and intramolecular couplings. In addition, the RuPhos ligand was applied to gold-catalyzed cross-couplings. An unbalanced ion pair promoter and hydrogen bond donor solvent might be crucial in this transformation.
6 citations
TL;DR: Wang et al. as mentioned in this paper presented a proactive fouling prevention mechanism that endows superhydrophilic membranes with antifouling capability against migratory viscous crude oil fouling.
Abstract: Here, we present a proactive fouling prevention mechanism that endows superhydrophilic membranes with antifouling capability against migratory viscous crude oil fouling. By simulating the hierarchical architecture/chemical composition of a dahlia leaf, a membrane surface is decorated with wrinkled-pattern microparticles, exhibiting a unique proactive fouling prevention mechanism based on a synergistic hydration layer/steric hindrance. The density functional theory and physicochemical characterizations demonstrate that the main chains of the microparticles are bent towards Fe3+ through coordination interactions to create nanoscale wrinkled patterns on smooth microparticle surfaces. Nanoscale wrinkled patterns reduce the surface roughness and increase the contact area between the membrane surface and water molecules, expanding the steric hindrance between the oil molecules and membrane surface. Molecular dynamic simulations reveal that the water-molecule densities and strengths of the hydrogen bonds are higher near the resultant membrane surface. With this concept, we can successfully inhibit the initial adhesion, migration, and deposition of oil, regardless of the viscosity, on the membrane surface and achieve migratory viscous crude oil antifouling. This research on the PFP mechanism opens pathways to realize superwettable materials for diverse applications in fields related to the environment, energy, health, and beyond.
6 citations
TL;DR: In this article , the authors investigated the catalytic performance of picket fence cobalt porphyrin and its atropisomer for ORR by density functional theory methods.
5 citations
TL;DR: In this paper , a sterically hindered unit (Nphenylcarbazole) at the para and meta positions of boron/nitrogen (B/N) framework was introduced to separate adjacent multiple-resonance thermally activated delayed fluorescence (TADF) skeletons and suppress self-quenching and spectral broadening.
Abstract: Multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters with highly planar and rigid skeleton tend toward self‐quenching and spectral broadening caused by strong inter‐chromophore interactions at high doping ratios. Herein, by introducing the sterically hindered unit (N‐phenylcarbazole) at the para‐ and meta‐positions of boron/nitrogen (B/N) framework (p−1‐PCzBN and m−1‐PCzBN), the face‐to‐face steric modulation between the non‐conjugated benzene ring and B/N skeleton is achieved to separate adjacent MR‐TADF skeletons and to suppress self‐quenching and spectral broadening. Consequently, the p−1‐PCzBN and m−1‐PCzBN emitters based organic light‐emitting diodes (OLEDs) show the maximum external quantum efficiency (EQEmax) values of up to 33.6% and 32.6% with full width at half maximum (FWHM) bands of 26 and 30 nm for electroluminescence (EL), respectively. Remarkably, the doped concentration has little effect on the device efficiency and FWHM of the EL, and this phenomenon is seldom reported for OLEDs based on MR‐TADF materials. Even at doping ratio of 30 wt%, the EQEs are still retained to be 28.5% and 25.6% with nearly unchanged electroluminescence spectra. These results manifest an effective strategy for constructing efficient doping concentration independent OLEDs through face‐to‐face steric modulation.
5 citations
TL;DR: In this paper , aryl sulfonium salts, a versatile electrophilic linchpin for carbon-carbon and carbon-heteroatom bond formation reactions, were synthesized via a novel Cu-mediated thianthrenation and phenoxathiination.
Abstract: Great success in synthetic chemistry is motivated by the development of novel and reactive linchpins for carbon-carbon and carbon-heteroatom bond formation reactions, which has dramatically altered chemists' approach to building molecules. Herein, we report the ready synthesis of aryl sulfonium salts, a versatile electrophilic linchpin, via a novel Cu-mediated thianthrenation and phenoxathiination of commercially available arylborons with thianthrene and phenoxathiine, providing a series of aryl sulfonium salts in high efficiency. More importantly, by leveraging the sequential Ir-catalyzed C-H borylation and Cu-mediated thianthrenation of arylborons, the formal thianthrenation of arenes is also achieved. The Ir-catalyzed C-H borylation with undirected arenes normally occurred at the less steric hindrance position, thus providing a complementary method for thianthrenation of arenes in comparison with electrophilic thianthrenation. This process is capable of late-stage functionalization of a series of pharmaceuticals, which might find wide synthetic applications in both industry and academic sectors.
4 citations
TL;DR: In this article , a method for C3-selective cyanation of pyridines by a tandem process with the reaction of an in situ generated dihydropyridine with a cyano electrophile was reported.
Abstract: Methods for C-H cyanation of pyridines are rare. Here, we report a method for C3-selective cyanation of pyridines by a tandem process with the reaction of an in situ generated dihydropyridine with a cyano electrophile as the key step. The method is suitable for late-stage functionalization of pyridine drugs. The low reduction potential of the electrophile and effective transfer of the nitrile group were found to be essential for the success of this method. We studied the reaction mechanism in detail by means of control experiments and theoretical calculations and found that a combination of electronic and steric factors determined the regioselectivity of reactions involving C2-substituted pyridines.
4 citations
TL;DR: In this article , the Pd/Cu-catalyzed dynamic kinetic asymmetric alkylation of racemic allenylic esters was used to synthesize allene compounds bearing α,β-adjacent central chiralities.
Abstract: The stereodivergent synthesis of allene compounds bearing α,β-adjacent central chiralities has been realized via the Pd/Cu-catalyzed dynamic kinetic asymmetric alkylation of racemic allenylic esters. The matched reactivity of bimetallic catalytic system enables the challenging reaction of racemic aryl-substituted allenylic acetates with sterically crowded aldimine esters smoothly under mild reaction conditions. Various chiral non-natural amino acids bearing a terminal allenyl group are easily synthesized in high yields and with excellent diastereo- and enantioselectivities (up to >20:1 dr, >99% ee). Importantly, all four stereoisomers of the product can be readily accessed by switching the configurations of the two chiral metal catalysts. Furthermore, the easy interconversion between the uncommon η3-butadienyl palladium intermediate featuring a weak C=C/Pd coordination bond and a stable Csp2-Pd bond is beneficial for the dynamic kinetic asymmetric transformation process (DyKAT).
4 citations
TL;DR: In this paper , the synthesis and characterization of a neutral monosubstituted Sn(I) radical (2) supported by a sterically hindered hydrindacene ligand is presented.
Abstract: Due to their intrinsic high reactivity, isolation of heavier analogues of carbynes remains a great challenge. Here, we report the synthesis and characterization of a neutral monosubstituted Sn(I) radical (2) supported by a sterically hindered hydrindacene ligand, which represents the first tin analogue of a free carbyne. Different from all Sn(I/III) species reported thus far, the presence of a sole Sn-C σ bond in 2 renders the remaining two Sn 5p orbitals energetically almost degenerate, of which one is singly occupied and the other is empty. Consequently, its S = 1/2 ground state possesses two-fold orbital pseudo-degeneracy and substantial unquenched orbital angular momentum, as evidenced by one component of its g matrix (1.957, 1.896, and 1.578) being considerably less than 2. Consistent with this unique electronic structure, 2 can bind to an N-heterocyclic carbene to afford a neutral two-coordinate Sn(I) radical and initiate a one-electron transfer to benzophenone to furnish a Sn(II)-ketyl radical anion adduct. As a manifestation of its Sn-centered radical nature, 2 reacts with diphenyl diselenide and p-benzoquinone to form Sn-S and Sn-O bonds, respectively.
TL;DR: In this paper , an asymmetrical blue emitter with TADF, aggregation-enhanced emission (AEE) and weak intermolecular electron exchange interactions behaviors is demonstrated.
TL;DR: In this paper , a system for remote hydroamination of disubstituted alkenes to functionalize an alkyl chain selectively at the subterminal, unactivated, methylene position is presented.
Abstract: Remote hydrofunctionalizations of alkenes incorporate functional groups distal to existing carbon-carbon double bonds. While remote carbonylations are well-known, remote hydrofunctionalizations are most common for addition of relatively nonpolar B-H, Si-H, and C-H bonds with alkenes. We report a system for the remote hydroamination of disubstituted alkenes to functionalize an alkyl chain selectively at the subterminal, unactivated, methylene position. Critical to the high regioselectivity and reaction rates are the electronic properties of the substituent on the amine and the development of the ligand DIP-Ad-SEGPHOS by evaluating the steric and electronic effects of ligand modules on reactivity and selectivity. The remote hydroamination is compatible with a broad scope of alkenes and aminopyridines and enables the regioconvergent synthesis of amines from an isomeric mixture of alkenes. The products can be derivatized by nucleophilic aromatic substitution on the amino substituent with a variety of nucleophiles.
TL;DR: In this paper , a Pd-catalysed enantioselective C-H arylation in the presence of a unique bifunctional phosphine-carboxylate ligand provides a simple and general access to these lower carbo[ n ]helicenes.
Abstract: Abstract The three-dimensional structure of carbohelicenes has fascinated generations of molecular chemists and has been exploited in a wide range of applications. Their strong circularly polarized luminescence has attracted considerable attention in recent years due to promising applications in new optical materials. Although the enantioselective synthesis of fused carbo- and heterohelicenes has been achieved, a direct catalytic enantioselective method allowing the synthesis of lower, non-fused carbo[ n ]helicenes ( n = 4–6) is still lacking. We report here that Pd-catalysed enantioselective C–H arylation in the presence of a unique bifunctional phosphine-carboxylate ligand provides a simple and general access to these lower carbo[ n ]helicenes. Computational mechanistic studies indicate that both the C–H activation and reductive elimination steps contribute to the overall enantioselectivity. The observed enantio-induction seems to arise from a combination of non-covalent interactions and steric repulsion between the substrate and ligand during the two key reductive elimination steps. The photophysical and chiroptical properties of the synthesized scalemic [ n ]helicenes have been systematically studied.
TL;DR: In this article , the symmetry-breaking self-assembly of a defined C1-symmetric supramolecular structure from an Oh-smmetric hydrogen-bonded resorcin[4]arene capsule and cationic bis-cyclometalated Ir complexes is reported.
Abstract: Bio-inspired self-assembly is invaluable to create well-defined giant structures from small molecular units. Owing to a large entropy loss in the self-assembly process, highly symmetric structures are typically obtained as thermodynamic products while formation of low symmetric assemblies is still challenging. In this study, we report the symmetry-breaking self-assembly of a defined C1-symmetric supramolecular structure from an Oh-symmetric hydrogen-bonded resorcin[4]arene capsule and C2-symmetric cationic bis-cyclometalated Ir complexes, carrying sterically demanding tertiary butyl (tBu) groups, on the basis of synergistic effects of weak binding forces. The flexible capsule framework shows a large structural change upon guest binding to form a distorted resorcin[4]arene hexameric capsule, providing an asymmetric cavity. Location of the chiral guest inside the anisotropic environment leads to modulation of its Electric Dipole (ED) and Magnetic Dipole (MD) transition moments in the excited state, causing an increased emission quantum yield, longer emission lifetime, and enhancement of the dissymmetry factor (glum) in the circularly polarized luminescence.
TL;DR: In this article , a systematic investigation of photocatalytic oxidative coupling of methane (OCM) over transition-metal-loaded ZnO photocatsalysts was conducted, and the results indicated that the d-σ center may be a suitable descriptor for predicting product selectivity during OCM over metal/ZnO copatalysts.
Abstract: Methane conversion to higher hydrocarbons requires harsh reaction conditions due to high energy barriers associated with C-H bond activation. Herein, we report a systematic investigation of photocatalytic oxidative coupling of methane (OCM) over transition-metal-loaded ZnO photocatalysts. A 1 wt.% Au/ZnO delivered a remarkable C2-C4 hydrocarbon production rate of 683 μmol g-1 h-1 (83% C2-C4 selectivity) under light irradiation with excellent photostability over two days. The metal type and its interaction with ZnO strongly influence the selectivity toward C-C coupling products. Photogenerated Zn+-O- sites enable CH4 activation to methyl intermediates (*CH3) migrating onto adjacent metal nanoparticles. The nature of the *CH3-metal interaction controls the OCM products. In the case of Au, strong d-σ orbital hybridization reduces metal-C-H bond angles and steric hindrance, thereby enabling efficient methyl coupling. Findings indicate the d-σ center may be a suitable descriptor for predicting product selectivity during OCM over metal/ZnO photocatalysts.
TL;DR: In this article , a visible-light-induced enantioselective free carbene transfer reaction of α-diazoesters with 1,3-diketones is established by utilizing a chiral bifunctional guanidine-amide organocatalyst.
Abstract: A visible-light-induced enantioselective free carbene transfer reaction of α-diazoesters with 1,3-diketones is established by utilizing a chiral bifunctional guanidine-amide organocatalyst. Selective insertion of free carbene into the C–C or C–H bonds of 1,3-diketone could be achieved with α-diazoesters bearing different steric hindrances. The transformations enable the preparation of a series of 1,4-diketones with a quaternary carbon chiral center or chiral 2-substituted-1,3-diketones in good enantioselectivities. On the basis of the control experiments and DFT calculation, a stepwise triplet free carbene coupling pathway is suggested. A possible reaction mechanism is proposed to explain the origin of high enantioselectivities via hydrogen-bonds and electrostatic interactions of the catalyst.
TL;DR: In this article , a new class of NFA-based organic photovoltaics with local isomerized conjugated side-groups is developed and the impact of local isomers on their geometries and device performance/stability are systematically investigated.
Abstract: Organic photovoltaics (OPVs) have achieved great progress in recent years due to delicately designed non-fullerene acceptors (NFAs). Compared with tailoring of the aromatic heterocycles on the NFA backbone, the incorporation of conjugated side-groups is a cost-effective way to improve the photoelectrical properties of NFAs. However, the modifications of side-groups also need to consider their effects on device stability since the molecular planarity changes induced by side-groups are related to the NFA aggregation and the evolution of the blend morphology under stresses. Herein, a new class of NFAs with local-isomerized conjugated side-groups are developed and the impact of local isomerization on their geometries and device performance/stability are systematically investigated. The device based on one of the isomers with balanced side- and terminal-group torsion angles can deliver an impressive power conversion efficiency (PCE) of 18.5%, with a low energy loss (0.528 V) and an excellent photo- and thermal stability. A similar approach can also be applied to another polymer donor to achieve an even higher PCE of 18.8%, which is among the highest efficiencies obtained for binary OPVs. This work demonstrates the effectiveness of applying local isomerization to fine-tune the side-group steric effect and non-covalent interactions between side-group and backbone, therefore improving both photovoltaic performance and stability of fused ring NFA-based OPVs.
TL;DR: In this paper , a polysiloxane with isobornyl acrylate and thiol groups as side groups was further used in the preparation of poly(thiourethane-urethane) materials.
TL;DR: In this article , an easy-to-perform approach to assess and quantify steric properties of Lewis acids with differently substituted Lewis acidic centers is reported, which applies the concept of the percent buried volume (%VBur) to fluoride adducts.
Abstract: Steric and electronic effects play a very important role in chemistry, as these effects influence the shape and reactivity of molecules. Herein, an easy-to-perform approach to assess and quantify steric properties of Lewis acids with differently substituted Lewis acidic centers is reported. This model applies the concept of the percent buried volume (%VBur) to fluoride adducts of Lewis acids, as many fluoride adducts are crystallographically characterized and are frequently calculated to judge fluoride ion affinities (FIAs). Thus, data such as cartesian coordinates are often easily available. A list of 240 Lewis acids together with topographic steric maps and cartesian coordinates of an oriented molecule suitable for the SambVca 2.1 web application is provided, together with different FIA values taken from the literature. Diagrams of %VBur as a scale for steric demand vs. FIA as a scale for Lewis acidity provide valuable information about stereo-electronic properties of Lewis acids and an excellent evaluation of steric and electronic features of the Lewis acid under consideration. Furthermore, a novel LAB-Rep model (Lewis acid/base repulsion model) is introduced, which judges steric repulsion in Lewis acid/base pairs and helps to predict if an arbitrary pair of Lewis acid and Lewis base can form an adduct with respect to their steric properties. The reliability of this model was evaluated in four selected case studies, which demonstrate the versatility of this model. For this purpose, a user-friendly Excel spreadsheet was developed and is provided in the ESI, which works with listed buried volumes of Lewis acids %VBur_LA and of Lewis bases %VBur_LB, and no results from experimental crystal structures or quantum chemical calculations are necessary to evaluate steric repulsion in these Lewis acid/base pairs.
TL;DR: In this article , a catalytic system, based on cobalt(0) complex and bulky N-heterocyclic carbene (NHC) ligands, permitting the highly effective hydrosilylation of a broad scope of alkynes and silanes is described.
Abstract: The hydrosilylation of alkynes is one of the most attractive and, at the same time, most challenging catalytic transformations, usually demanding the use of noble transition metals. We describe a catalytic system, based on cobalt(0) complex and bulky N-heterocyclic carbene (NHC) ligands, permitting the highly effective hydrosilylation of a broad scope of alkynes and silanes. The application of bulky NHC ligands allowed a decrease in the amount of cobalt necessary for an effective reaction run to 2.5 mol% and provided excellent selectivity towards challenging α-vinylsilanes. The developed method tolerates a number of substituted aryl, alkyl, and silyl acetylenes. Moreover, it is suitable for both tertiary and secondary silanes. Our findings confirm that steric hindrance around the metal center can effectively increase the activity of a catalyst and ensure better selectivity than those of analogous complexes bearing smaller ligands.
TL;DR: In this paper , a mesoporous carbon nitride-supported ruthenium single-atom photocatalyst (Ru1/MCN) is reported for efficient oxidative CC bonds scissoring towards lignin β-O-4 model compounds with high activity and selectivity under visible-light irradiation and room temperature.
TL;DR: In this paper , a plausible reaction mechanism that has an overall free energy span of 22.4 kcal/mol (for N-methylindole borylation), consistent with experimental observations, is presented.
Abstract: [(NacNac)Zn(DMT)][B(C6F5)4], 1, (NacNac = {(2,6-iPr2H3C6)N(CH3)C}2CH), DMT = N,N-dimethyl-4-toluidine), was synthesized via two routes starting from either (NacNac)ZnEt or (NacNac)ZnH. Complex 1 is an effective (pre)catalyst for the C–H borylation of (hetero)arenes using catecholborane (CatBH) with H2 the only byproduct. The scope included weakly activated substrates such as 2-bromothiophene and benzothiophene. Computational studies elucidated a plausible reaction mechanism that has an overall free energy span of 22.4 kcal/mol (for N-methylindole borylation), consistent with experimental observations. The calculated mechanism starting from 1 proceeds via the displacement of DMT by CatBH to form [(NacNac)Zn(CatBH)]+, D, in which CatBH binds via an oxygen to zinc which makes the boron center much more electrophilic based on the energy of the CatB-based LUMO. Combinations of D and DMT act as a frustrated Lewis pair (FLP) to effect C–H borylation in a stepwise process via an arenium cation that is deprotonated by DMT. Subsequent B–H/[H-DMT]+ dehydrocoupling and displacement from the coordination sphere of zinc of CatBAr by CatBH closes the cycle. The calculations also revealed a possible catalyst decomposition pathway involving hydride transfer from boron to zinc to form (NacNac)ZnH which reacts with CatBH to ultimately form Zn(0). In addition, the key rate-limiting transition states all involve the base, thus fine-tuning of the steric and electronic parameters of the base enabled a further minor enhancement in the C–H borylation activity of the system. Outlining the mechanism for all steps of this FLP-mediated process will facilitate the development of other main group FLP catalysts for C–H borylation and other transformations.
TL;DR: In this article , a cyclic (alkyl)(amino) carbene ligand that contains a phosphino anchor enables the hydrogenation of alkynes in a trans-addition manner, selectively forming E-olefins.
Abstract: The hydrogenation of alkynes allows the synthesis of olefins, which are important feedstock for the materials, pharmaceutical, and petrochemical industry. Thus, methods that enable this transformation via low-cost metal catalysis are desirable. However, achieving stereochemical control in this reaction is a long-standing challenge. Here, we report on the chromium-catalyzed E- and Z-selective olefin synthesis via hydrogenation of alkynes, controlled by two carbene ligands. A cyclic (alkyl)(amino)carbene ligand that contains a phosphino anchor enables the hydrogenation of alkynes in a trans-addition manner, selectively forming E-olefins. With an imino anchor-incorporated carbene ligand, the stereoselectivity can be switched, giving mainly Z-isomers. This ligand-enabled geometrical stereoinversion strategy by one metal catalysis overrides common methods in control of the E- and Z-selectivity with two different metal catalysis, allowing for highly efficient and on-demand access to both E- and Z-olefins in a stereo-complementary fashion. Mechanistic studies indicate that the different steric effect between these two carbene ligands may mainly dominate the selective forming E- or Z-olefins in control of the stereochemistry.
TL;DR: In this paper , 4-Biphenyle-4′-alkyloxybenzenamines were synthesized as a homologous series of liquid crystals based on the biphenyl moiety.
Abstract: In this study, 4-Biphenyle-4′-alkyloxybenzenamines were synthesized as a homologous series of liquid crystals based on the biphenyl moiety. Their mesomorphic and optical properties were examined for both pure and mixed components. Elemental analysis, NMR, and FT-IR spectroscopy were used to determine the molecular structures of the developed materials. Using differential scanning calorimetry (DSC), the mesophase transitions were studied, and polarized optical microscopy was used to identify the textures of the mesophases (POM). The obtained results showed that all compounds are dimorphic and only have smectic B (SmB) and smectic A (SmA) phases for all terminal side chains, which are enantiotropic. With variably proportionated terminal side chains and a focus on the mesomorphic temperature range, binary phase diagrams were constructed and an induced smectic C phase was achieved (SmC). It was found that terminal chain length affects both conformation and steric impact in the mixed states. The absorption and fluorescence emission spectra of pure as well as their binary mixtures liquid crystalline films were recorded to investigate the optical and photophysical properties. It was noted that, with the increase in alkyl chain length, the energy bandgap increases from 3.24 eV (for C6H13) to 3.37 eV (for C16H33) and charge carrier lifetime decreases, ascribing to the increase in stearic hindrance causing, consequently, the faster decay of charge carriers.
TL;DR: In this paper , the authors report the direct synthesis of a wide range of sterically demanding secondary amines, including several important active pharmaceutical ingredients and pharmaceutical intermediates, via reductive amination of carbonyl substrates and bulky amine nucleophiles employing imine reductases.
Abstract: The synthesis of structurally diverse amines is of fundamental significance in the pharmaceutical industry due to the ubiquitous presence of amine motifs in biologically active molecules. Biocatalytic reductive amination for amine production has attracted great interest owing to its synthetic advantages. Herein, we report the direct synthesis of a wide range of sterically demanding secondary amines, including several important active pharmaceutical ingredients and pharmaceutical intermediates, via reductive amination of carbonyl substrates and bulky amine nucleophiles employing imine reductases. Key to success for this route is the identification of an imine reductase from Penicillium camemberti with unusual substrate specificity and its further engineering, which empowered the accommodation of a broad range of sterically demanding amine nucleophiles encompassing linear alkyl and (hetero)aromatic (oxy)alkyl substituents and the formation of final amine products with up to >99% conversion. The practical utility of the biocatalytic route has been demonstrated by its application in the preparative synthesis of the anti-hyperparathyroidism drug cinacalcet.
TL;DR: In this paper , new isatin-based sulphonamides were designed and synthesised as potential dual VEGFR-2 and carbonic anhydrase inhibitors with anticancer activities.
Abstract: Abstract In this work, new isatin-based sulphonamides (6a-i, 11a-c, 12a-c) were designed and synthesised as potential dual VEGFR-2 and carbonic anhydrase inhibitors with anticancer activities. Firstly, all target isatins were examined for in vitro antitumor action on NCI-USA panel (58 tumour cell lines). Then, the most potent derivatives were examined for the potential CA inhibitory action towards the physiologically relevant hCA isoforms I, II, and tumour-linked hCA IX isoform, in addition, the VEGFR-2 inhibitory activity was evaluated. The target sulphonamides failed to inhibit the CA isoforms that could be attributable to the steric effect of the neighbouring methoxy group, whereas they displayed potent VEGFR-2 inhibitory effect. Following that, isatins 11b and 12b were tested for their influence on the cell cycle disturbance, and towards the apoptotic potential. Finally, detailed molecular modelling analyses, including docking and molecular dynamics, were carried out to assess the binding mode and stability of target isatins.
TL;DR: In this paper , a copper-catalyzed enanti-convergent radical C-N cross-coupling of alkyl halides with sulfoximines (as ammonia surrogates) under mild conditions by employing a chiral anionic N,N,N-ligand with a long spreading side arm was reported.
Abstract: Transition-metal catalyzed enantioconvergent cross-coupling of tertiary alkyl halides with ammonia offers a rapid avenue to chiral unnatural α,α-disubstituted amino acids. However, the construction of chiral C-N bonds between tertiary-carbon electrophiles and nitrogen nucleophiles presented a great challenge owing to steric congestion. We report a copper-catalyzed enantioconvergent radical C-N cross-coupling of alkyl halides with sulfoximines (as ammonia surrogates) under mild conditions by employing a chiral anionic N,N,N-ligand with a long spreading side arm. An array of α,α-disubstituted amino acid derivatives were obtained with good efficiency and enantioselectivity. The synthetic utility of the strategy has been showcased by the elaboration of the coupling products into different chiral α-quaternary amine building blocks.
TL;DR: In this paper , a general approach for the synthesis of disilanes as well as linear and cyclic oligosilanes via the reductive activation of readily available chlorosilane was developed.
Abstract: Silanes are important compounds in industrial and synthetic chemistry. Here, we develop a general approach for the synthesis of disilanes as well as linear and cyclic oligosilanes via the reductive activation of readily available chlorosilanes. The efficient and selective generation of silyl anion intermediates, which are arduous to achieve by other means, allows for the synthesis of various novel oligosilanes by heterocoupling. In particular, this work presents a modular synthesis for a variety of functionalized cyclosilanes, which may give rise to materials with distinct properties from linear silanes but remain challenging synthetic targets. In comparison to the traditional Wurtz coupling, our method features milder conditions and improved chemoselectivity, broadening the functional groups that are compatible in oligosilane preparation. Computational studies support a mechanism whereby differential activation of sterically and electronically distinct chlorosilanes are achieved in an electrochemically driven radical-polar crossover mechanism.
TL;DR: In this article , the experimental data of dynamic viscosity (η) and ultrasonic speed (u) for 2-amino-2-methylpropan-1-ol (AMP) (1) + alkanol (C1-C3) (2) at T = (298.15-318.15) K and 0.1 MPa pressure were derived through Redlich-Kister polynomial equation.