The effect of donor atoms on the complexation of alkali cations with spherands: A density functional investigation

Spherands are highly preorganized hosts composed of methoxy 1, fluoro 2, and cyano 3 benzene units attached to one another at their 2,6‐positions. Density functional theory calculations were used to investigate the complexation between these spherands and alkali metal ions (Li⁺, Na⁺, and K⁺) to understand the intrinsic factors affecting cation complexation. A comparison of binding energies for these spherands shows that, this order O? Me ? F ? CN. Although anisyl units are basically poor ligands for metal ions, the rigid placements of their oxygen during synthesis rather than during complexation are undoubtedly responsible for the enhanced binding and selectivity of the spherand. The ion–dipolar moiety interactions are found to be the main factors affecting the preference of external binding in the CN‐spherands. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

The role of Zn in enhancing the rate and stereoselectivity of the aldol reactions catalyzed by the simple prolinamide model

The aldol reaction between acetone and 4-nitrobenzaldehyde catalyzed by single l-prolinamide and its zinc complexes has been studied. An increase in the rate and the stereoselectivity of the reaction has been shown by using zinc derivatives. A mechanistic proposal, based on NMR and ESI studies, has been put forward to explain the experimental data: zinc-prolinamide complexes catalyze the reaction following the general mechanism of stereoselective enamine nucleophilic addition to the acceptor aldehyde. Zn²⁺ prevents the nonspecific base-catalyzed reaction by diminishing the basicity of the amine nitrogen of prolinamide.     

Preparation and application of microparticles prepared via the primary amine‐catalyzed michael addition of a trithiol to a triacrylate

We report a novel approach to prepare microparticles via a dispersion polymerization using the amine‐catalyzed addition of a trithiol to a triacrylate. Microparticles loaded with various core materials were produced and applied in various systems to improve the desired characteristics of the given system. We determined that this type of microparticle could be used as either a stimulated release or controlled release system for certain desired core materials. These microparticles were able to prevent the interaction between a Lewis acid initiator and fumed silica, improving the rheological properties of an epoxy system containing the initiator. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

DFT study of the full catalytic cycle for the propene hydroformylation catalyzed by a heterobimetallic HPt(SnCl3)(PH3)2 model catalyst

DFT calculations were carried out to study the full catalytic cycle for the hydroformylation of propene, catalyzed by the heterobimetallic model catalyst trans‐Pt(H)(PH₃)₂(SnCl₃). Before the study of the full catalytic cycle, the performance of six pure GGA, one GGA with inclusion of dispersion corrections, four hybrid‐GGA, and three meta‐GGA exchange correlation functional to describe a model reaction promoted by Pt‐Sn catalyst were assessed. It is shown that the BP86 and GPW91 functionals, using extended basis set, provides reliable energetic results when compared with the CCSD(T) calculations. All intermediates and transition states along the elementary steps of the entire catalytic cycle were located and the energies involved in the catalytic cycle calculated using BP86 functional. The solvent effects along the entire catalytic cycle were evaluated using the polarizable continuum model. In contrast with the rhodium catalysts, the regioselectivity of the hydroformylation is set at the carbonylation step. The hydrogenolysis is the rate determining step of the entire cycle, with the activation energy of ～21 kcal mol^?1 in agreement with the experimental value of ～25 kcal mol^?1. The trans effect of the SnCl ligand seems to be pronounced only in the first step of the catalytic cycle, facilitating the insertion of the olefin into the Pt? H bond trans to it. The analysis of the stationary points obtained along each elementary step of the catalytic cycle is carried out separately and discussed. The BP86/cc‐pVTZ/SBKJC results shows that the pathway leading to the linear aldehyde is preferred, being in agreement with the experimental findings. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

The influence of electron donor and electron acceptor groups on the electronic structure of the anti‐inflammatory tripeptide Cys‐Asn‐Ser

It has been discussed in the literature that electron delocalization along the peptide backbone and side chain modulates the physical and chemical features of peptides and proteins. The structure and properties of peptides are determined by their charge‐density distribution, such that the modification of its side chain plays an important role on its electronic structure and physicochemical properties. Research on Entamoeba histolytica soluble factors led to the identification of the pentapeptide Met‐Gln‐Cys‐Asn‐Ser, with anti‐inflammatory in vivo and in vitro effects. A synthetic pentapeptide, Met‐Pro‐Cys‐Asn‐Ser, maintained the same anti‐inflammatory actions in experimental assays. A previous theoretical study allowed proposing the Cys‐Asn‐Ser tripeptide (CNS tripeptide) as the pharmacophore group of both molecules. This theoretical hypothesis was recently confirmed experimentally. The objective of this work was to study the influence of the electron donor and electron withdrawing substituent groups on the electronic structure and physicochemical properties of the CNS tripeptide derivatives through a theoretical study at the density functional theory level of theory. Our results in deprotonation energies showed that the relative acidity of hydrogen atom (H2) of the serine‐amide group increases with the electron withdrawing groups. This result was confirmed by means of a study of bond order. The proton affinities illustrated that the electron donor groups favored the basicity of the amino group of the cysteine amino acid. Atomic charges, Frontier molecular orbitals (HOMO–LUMO), and electrostatic potential isosurface and its geometric parameters permitted to analyze the effect that provoked the electron donor and electron attractor groups on its electronic structure and physicochemical features and to identify some reactive sites that could be associated with the anti‐inflammatory activity of tripeptide CNS derivatives. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2398–2410, 2010     

Synthesis and Characterization of the Lewis Acid‐Base Complexes SbCl5 · LB (LB = ICN,BrCN, ClCN, 1/2(CN)2, NH2CN,Pyridine) – a Combined Theoretical and Experimental Investigation. The Crystal Structures of SbCl5 · NCCl and SbCl5 · NCCN · SbCl5

The Lewis acid‐base complexes SbCl₅ · LB (LB = ICN, BrCN, ClCN, ¹/₂(CN)₂, NH₂CN, pyridine) were prepared. The products formed were characterized by Raman and NMR spectroscopy. Density functional theory (B3LYP) was applied to calculate structural and vibrational data. Vibrational assignments of the normal modes for these Lewis acid‐base adducts was made on the basis of their Raman spectra in comparison with computational results. The stability of the complexes was investigated by calculating the bond dissociation enthalpy. SbCl₅ · NCCl and SbCl₅ · NCCN · SbCl₅ were characterized by X‐ray structural analysis. NBO analyses were performed on the crystallographic data.     

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.     

Tin(II) Chloride Dihydrate Catalyzed Groebke Condensation: An Efficient Protocol for the Synthesis of 3-Aminoimidazo[1,2-a]pyridines

The ability of tin(II) chloride dihydrate as a catalyst to promote the three-component condensation reaction from a diversity of aromatic aldehydes, 2-aminopyridines and isonitriles at room temperature is described. This methodology affords a number of 3-aminoimidazo[1,2-a]pyridines in the presence of tin(II) chloride dihydrate as a new and mild Lewis acid catalyst in the multi-component reaction in reasonable yields and short reaction time without any significant optimization of the reaction conditions.     

Effects of two benzenedicarboxylic acids on the construction of CdII coordination polymers incorporating a flexible N‐donor ligand

Compared with the monomorphic type of ligand, combining mixed ligands in one coordination polymer offers greater tunability of the structural framework. Employment of N‐heterocyclic ligands and aromatic polycarboxylates is an effective approach for the construction of metal–organic frameworks (MOFs). Two new coordination polymers incorporating both 2‐[(1H‐imidazol‐1‐yl)methyl]‐1H‐benzimidazole (imb) and benzenedicarboxylic acid isomers, namely, catena‐poly[[[di‐μ‐chlorido‐bis[(2‐carboxybenzoato‐κ²O¹,O^1′)cadmium(II)]]‐bis{μ‐2‐[(1H‐imidazol‐1‐yl)methyl]‐1H‐benzimidazole‐κ²N:N′}] dihydrate], {[Cd(C₈H₅O₄)Cl(C₁₁H₁₀N₄)]·H₂O}_n, (I), and poly[[aqua(μ₂‐benzene‐1,3‐dicarboxylato‐κ³O¹,O^1′:O³){μ₂‐2‐[(1H‐imidazol‐1‐yl)methyl]‐1H‐benzimidazole‐κ²N:N′}cadmium(II)] dihydrate], {[Cd(C₈H₄O₄)(C₁₁H₁₀N₄)(H₂O)]·2H₂O}_n, (II), have been prepared and structurally characterized by single‐crystal X‐ray diffraction. In polymer (I), imb ligands bridge Cd^II ions, forming a one‐dimensional chain, and 2‐carboxybenzoate anions coordinate to the Cd^II ions in a terminal fashion. Polymer (II) exhibits a two‐dimensional network structure in which imb ligands and the benzene‐1,3‐dicarboxylate anions join Cd^II ions co‐operatively. This indicates that changing of the aromatic dicarboxylic acids can result in polymers with different compositions and architectures. Moreover, their IR spectra, PXRD (powder X‐ray diffraction) patterns, thermogravimetric analyses and fluorescence properties were also investigated.     

How the choice of a computational model could rule the chemical interpretation: The Ni(II) catalyzed ethylene dimerization as a case study

In this article, we present a critical study of the theoretical protocol used for the determination of the nickel(II) catalyzed ethylene dimerization mechanism, considered as a representative example of the various problems related to the modeling a catalytic cycle. The choice of an appropriate computational procedure is indeed crucial for the validity of the conclusions that will be drawn from the computational process. The influence of the exchange‐correlation functional on energetic profiles and geometries, the role of the basis set describing the metal atom, as well as the importance of the chosen molecular model, have been thus examined in details. From the obtained results, some general conclusions and guidelines are presented, which could constitute useful warnings in modeling homogenous catalysis. Besides, the database constituted by our high‐level calculations can be used within benchmarking procedures to assess the performances of new computational methods based on density functional theory. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Understanding the nature of the molecular mechanisms associated with the competitive Lewis acid catalyzed [4+2] and [4+3] cycloadditions between arylidenoxazolone systems and cyclopentadiene: a DFT analysis

The molecular mechanisms of the reactions between aryliden-5(4H)-oxazolone 1, and cyclopentadiene (Cp), in presence of Lewis acid (LA) catalyst to obtain the corresponding [4+2] and [4+3] cycloadducts are examined through density functional theory (DFT) calculations at the B3LYP/6-31G* level. The activation effect of LA catalyst can be reached by two ways, that is, interaction of LA either with carbonyl or carboxyl oxygen atoms of 1 to render [4+2] or [4+3] cycloadducts. The endo and exo [4+2] cycloadducts are formed through a highly asynchronous concerted mechanism associated to a Michael-type addition of Cp to the beta-conjugated position of alpha,beta-unsaturated carbonyl framework of 1. Coordination of LA catalyst to the carboxyl oxygen yields a highly functionalized compound, 3, through a domino reaction. For this process, the first reaction is a stepwise [4+3] cycloaddition which is initiated by a Friedel-Crafts-type addition of the electrophilically activated carbonyl group of 1 to Cp and subsequent cyclization of the corresponding zwitterionic intermediate to yield the corresponding [4+3] cycloadduct. The next rearrangement is the nucleophilic trapping of this cycloadduct by a second molecule of Cp to yield the final adduct 3. A new reaction pathway for the [4+3] cycloadditions emerges from the present study.     

The role of benzoic acid in proline‐catalyzed asymmetric michael addition: A density functional theory study

In asymmetric Michael addition between ketones and nitroolefins catalyzed by L ‐proline, we observed that it was benzoic acid or its derivatives rather than other proton acid that could accelerate the reaction greatly, and different benzoic acid derivatives brought different yields. To explain the experimental phenomena, a density functional theory study was performed to elucidate the mechanism of proline‐catalyzed asymmetric Michael addition with benzoic acid. The results of the theoretical calculation at the level of B3LYP/6‐311+G(2df,p)//B3LYP/6‐31G(d) demonstrated that benzoic acid played two major roles in the formation of nitroalkane: assisting proton transfer and activating the nitro group. In the stage of enamine formation from imine, the energy profiles of benzoic acid derivatives were also calculated to investigate the reasons why different benzoic acid derivatives caused different yields. The results demonstrated that the pK_a value was the major factor for p‐substituted benzoic acid derivatives to improve the yields, whereas for m/o‐substituted benzoic acid derivatives, both pK_a value and electronic and steric effects could significantly increase the yields. The calculated results would be very helpful for understanding the reaction mechanism of Michael addition and provide some insights into the selection of efficient additives for similar experiments. © 2012 Wiley Periodicals, Inc.     

Lewis acid catalyzed intramolecular [3+2] cross-cycloaddition of donor-acceptor cyclopropanes with carbonyls: a general strategy for the construction of acetal[n.2.1] skeletons

Build a bridge: The first catalytic intramolecular [3+2] cycloaddition of monodonor-monoacceptor cyclopropanes (see scheme) provides a general and efficient strategy for construction of structurally diverse acetal[n.2.1] and 1,4-dioxygen-substituted cyclic skeletons, which are widely distributed in biologically important natural products.     

DielsAlder Cyclization of a Dihydropyridine: NMR Spectroscopy,X‐Ray Crystallography,and DFT Computations. Bent Aromatic Dimeric Clusters in the Solid Phase

Structural studies of the N‐(2,4‐dinitrophenyl) derivative of a Diels? Alder‐cyclized 1,2‐dihydropyridine both unequivocally established the polycyclic framework and revealed interesting distortions of aromatic structure and unique dimeric clustering of the aromatic entities in the solid state.     

Aldol additions of dihydroxyacetone phosphate to N-Cbz-amino aldehydes catalyzed by L-fuculose-1-phosphate aldolase in emulsion systems: inversion of stereoselectivity as a function of the acceptor aldehyde

The potential of L-fuculose-1-phosphate aldolase (FucA) as a catalyst for the asymmetric aldol addition of dihydroxyacetone phosphate (DHAP) to N-protected amino aldehydes has been investigated. First, the reaction was studied in both emulsion systems and conventional dimethylformamide (DMF)/H2O (1:4 v/v) mixtures. At 100 mM DHAP, compared with the reactions in the DMF/H2O (1:4) mixture, the use of emulsion systems led to two- to three-fold improvements in the conversions of the FucA-catalyzed reactions. The N-protected aminopolyols thus obtained were converted to iminocyclitols by reductive amination with Pd/C. This reaction was highly diastereoselective with the exception of the reaction of the aldol adduct formed from (S)-N-Cbz-alaninal, which gave a 55:45 mixture of both epimers. From the stereochemical analysis of the resulting iminocyclitols, it was concluded that the stereoselectivity of the FucA-catalyzed reaction depended upon the structure of the N-Cbz-amino aldehyde acceptor. Whereas the enzymatic aldol reaction with both enantiomers of N-Cbz-alaninal exclusively gave the expected 3R,4R configuration, the stereochemistry at the C-4 position of the major aldol adducts produced in the reactions with N-Cbz-glycinal and N-Cbz-3-aminopropanal was inverted to the 3R,4S configuration. The study of the FucA-catalyzed addition of DHAP to phenylacetaldehyde and benzyloxyacetaldehyde revealed that the 4R product was kinetically favored, but rapidly disappeared in favor of the 4S diastereoisomer. Computational models were generated for the situations before and after C-C bond formation in the active site of FucA. Moreover, the lowest-energy conformations of each pair of the resulting epimeric adducts were determined. The data show that the products with a 3R,4S configuration were thermodynamically more stable and, therefore, the major products formed, in agreement with the experimental results.     

Understanding the role of the Lewis acid catalyst on the 1,3-dipolar cycloaddition of N-benzylideneaniline N-oxide with acrolein: a DFT study

The Lewis acid (LA) catalyzed 1,3-dipolar cycloaddition of N-benzylideneaniline N-oxide with acrolein has been studied using DFT calculations. Coordination of AlCl₃ to the acrolein oxygen atom produces a drastic change in the mechanism along the more favorable meta reactive channel. The process is characterized by a strong nucleophile/electrophile interaction allowing the formation of a zwitterionic intermediate, a Michael-type addition. The subsequent ring closure constitutes the rate-determining step. The energies obtained with the inclusion of solvent effect by means of the polarizable continuum model are in good agreement with experimental findings. Analysis of the global and local electrophilicity allows to explain correctly the reactivity and regioselectivity of the LA catalyzed cycloaddition.     

Formic acid catalyzed gas-phase reaction of H2O with SO3 and the reverse reaction: a theoretical study

The formic acid catalyzed gas‐phase reaction between H₂O and SO₃ and its reverse reaction are respectively investigated by means of quantum chemical calculations at the CCSD(T)//B3LYP/cc‐pv(T+d)z and CCSD(T)//MP2/aug‐cc‐pv(T+d)z levels of theory. Remarkably, the activation energy relative to the reactants for the reaction of H₂O with SO₃ is lowered through formic acid catalysis from 15.97 kcal mol^?1 to ?15.12 and ?14.83 kcal mol^?1 for the formed H₂O ??? SO₃ complex plus HCOOH and the formed H₂O ??? HCOOH complex plus SO₃, respectively, at the CCSD(T)//MP2/aug‐cc‐pv(T+d)z level. For the reverse reaction, the energy barrier for decomposition of sulfuric acid is reduced to ?3.07 kcal mol^?1 from 35.82 kcal mol^?1 with the aid of formic acid. The results show that formic acid plays a strong catalytic role in facilitating the formation and decomposition of sulfuric acid. The rate constant of the SO₃+H₂O reaction with formic acid is 10⁵ times greater than that of the corresponding reaction with water dimer. The calculated rate constant for the HCOOH+H₂SO₄ reaction is about 10^?13 cm³ molecule^?1 s^?1 in the temperature range 200–280 K. The results of the present investigation show that formic acid plays a crucial role in the cycle between SO₃ and H₂SO₄ in atmospheric chemistry.     

Simultaneous construction of the polymer backbone and side chains by three‐component polycondensation: The synthesis of polyurethanes with allyl side chains from dialdehydes,alkylene N,N′‐bis(trimethylsilyl) carbamates,and allyltrimethylsilane

Polyurethanes with allyl side chains were synthesized by the simultaneous acid‐catalyzed reaction of dialdehydes ( 1 ), alkylene N,N′‐bis(trimethylsilyl) carbamates ( 4 ), and allyltrimethylsilane ( 5 ). When 5 was added to a mixture of 1 , 4 , and the catalyst, a low molecular weight polymer was formed, as well as a large amount of an insoluble gel. However, when a mixture of 1 , 4 , and 5 was added to the catalyst, the formation of gel was depressed, and the desired polyurethanes, consisting of 1 , 4 , and 5 in a molar ratio of 1/1/2, were obtained in good yields. This polyurethane synthesis is unusual in that it concurrently constructs both the polymer backbone and the functional side chains from three starting compounds. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1236–1242, 2002     

Lewis acid catalyzed intramolecular halo-arylation of tethered alkenes using N-halosuccinimide (NXS) as the halogen source: a general method for the synthesis of chromanones, chromans, quinolones, tetrahydroquinolines and tetralins

Lewis acid catalyzed intramolecular halo-arylation of tethered alkenes was performed using N-halosuccinimide (NXS) as the halogen source. Among the Lewis acids investigated, Sm(OTf)₃ was found to be the best catalyst. This catalytic process provides a general method for the regio- and stereoselective synthesis of annulated arene heterocycles and carbocycles such as 2-chromanones, chromans, 2-quinolones, tetrahydroquinolines and tetralins possessing a halo-functionality.     

Time‐resolved spectroscopy study of donor–acceptor‐type copolymers in a monodisperse system: The effect of ratio between the acceptor and the donor

The photoexcitation processes of two donor–acceptor‐type copolymers PCFBT with different ratios between the donor and the acceptor ( PCFBT_0.5 and PCFBT_0.1 ) in the solution system are systematically studied. If the number of the donor is equal to that of the acceptor in one repeat unit (such as PCFBT_0.5 ), intrachain charge transfer (ICT) can occur and participate in the relaxation of the excited state after photoexcitation. When the number of donors is much larger than that of acceptors (such as PCFBT_0.1 ) in one repeat unit, the ICT character can disappear, and the localized exciton decay process is dominant in the relaxation of the copolymer, which also involves an excitation intensity‐independent vibrational thermal relaxation process at the initial time. The results further the understanding of the basic structure‐property relationship. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 992–996