How computational methods and relativistic effects influence the study of chemical reactions involving Ru‐NO complexes?

Two treatments of relativistic effects, namely effective core potentials (ECP) and all‐electron scalar relativistic effects (DKH2), are used to obtain geometries and chemical reaction energies for a series of ruthenium complexes in B3LYP/def2‐TZVP calculations. Specifically, the reaction energies of reduction ( A ‐ F ), isomerization ( G‐I ), and Cl⁻ negative trans influence in relation to NH₃ ( J ‐ L ) are considered. The ECP and DKH2 approaches provided geometric parameters close to experimental data and the same ordering for energy changes of reactions A ‐ L . From geometries optimized with ECP, the electronic energies are also determined by means of the same ECP and basis set combined with the computational methods: MP2, M06, BP86, and its derivatives, so as B2PLYP, LC‐wPBE, and CCSD(T) (reference method). For reactions A ‐ I , B2PLYP provides the best agreement with CCSD(T) results. Additionally, B3LYP gave the smallest error for the energies of reactions J ‐ L . © 2017 Wiley Periodicals, Inc.     

What factors influence the catalytic activity of iron-salan complexes for aerobic oxidative coupling of 2-naphthols?

A few Fe-salan dimer complexes serve as catalysts for aerobic oxidative coupling (AOC) of 2-naphthols, but some others do not. X-Ray and cyclic voltammetry studies of various Fe-salan complexes revealed that the absence or the presence of double hydrogen bonding in Fe-salan dimers, the oxidation potential of monomeric Fe-salan species and the location of the resulting radical cation are critical factors for the catalytic activity of iron-salan complexes for the AOC.     

Can B3LYP be improved by optimization of the proportions of exchange and correlation functionals?

B3LYP is the most famous hybrid density functional theory model, which includes Hartree–Fock exchange, local exchange, gradient exchange correction, local correlation, and gradient correlation correction. Historically, the relative weight of each component in B3LYP, which is controlled by three empirical parameters (a₀, a_x, a_c), has not been optimized. In this work, we perform global optimization against accurate experimental reference, optimal empirical parameters, and the better version of B3LYP are obtained and denoted as OpB3LYP. The performance of OpB3LYP is widely tested over many species and chemical properties, the results show that the computational accuracy is significantly improved as compared to original B3LYP and the serious size dependence of B3LYP is remarkably overcome by the employment of OpB3LYP. The comparative assessment of OpB3LYP and other prevalent functionals indicates that OpB3LYP is a promising functional for large molecules. © 2015 Wiley Periodicals, Inc.     

Synthesis and characterization of aluminum and zinc complexes supported by pyrrole-based ligands and catalysis of the aluminum complexes toward the ring-opening polymerization of ?-caprolactone

Reaction of quinolin-8-amine with 1H-pyrrole-2-carbaldehyde or 5-tert-butyl-1H-pyrrole-2-carbaldehyde catalyzed by HCO₂H forms N-((1H-pyrrol-2-yl)methylene)quinolin-8-amine (≡ HL, 3a) or N-((5-tert-butyl-1H-pyrrol-2-yl)methylene)quinolin-8-amine (≡ HL′, 3b). Treatment of 3a and 3b respectively with AlMe₃ or AlEt₃ in toluene affords corresponding aluminum complexes LAlMe₂ (4a), L′AlMe₂ (4b) and LAlEt₂ (4c). Reaction of 3a and 3b with an equivalent of ZnEt₂ in toluene generates L₂Zn and L′₂Zn, respectively. A related compound N-((1H-pyrrol-2-yl)methylene)-2-(3,5-dimethyl-1H-pyrazol-1-yl)benzenamine (≡ HL″, 7) was prepared by reaction of 2-(3,5-dimethyl-1H-pyrazol-1-yl)benzenamine with 1H-pyrrole-2-carbaldehyde in the presence of HCO₂H. Reaction of 7 with AlMe₃ gives L″₂AlMe (8), and with ZnEt₂ yields L″₂Zn (9). All new compounds were characterized by NMR spectroscopy and elemental analysis. The structures of complexes 4b, 5b and 8 were additionally characterized by single crystal X-ray diffraction analyses. Complexes 4a-4c, and 8 were proved to be active catalysts for the ring-opening polymerization (ROP) of ?-caprolactone (?-CL) in the presence of BnOH. The kinetic study of the polymerization reactions catalyzed by 4a and 8 was performed.     

Is the μ‐Oxo‐μ‐Peroxodiiron Intermediate of a Ribonucleotide Reductase Biomimetic a Possible Oxidant of Epoxidation Reactions?

Density functional calculations on a mu-oxo-mu-peroxodiiron complex (1) with a tetrapodal ligand BPP (BPP=N,N-bis(2-pyridylmethyl)-3-aminopropionate) are presented that is a biomimetic of the active site region of ribonucleotide reductase (RNR). We have studied all low-lying electronic states and show that it has close-lying broken-shell singlet and undecaplet (S=0, 5) ground states with essentially two sextet spin iron atoms. In strongly distorted electronic systems in which the two iron atoms have different spin states, the peroxo group moves considerably out of the plane of the mu-oxodiiron group due to orbital rearrangements. The calculated absorption spectra of (1,11)1 are in good agreement with experimental studies on biomimetics and RNR enzyme systems. Moreover, vibrational shifts in the spectrum due to (18)O(2) substitution of the oxygen atoms in the peroxo group follow similar trends as experimental observations. To identify whether the mu-oxo-mu-1,2-peroxodiiron or the mu-oxo-mu-1,1-peroxodiiron complexes are able to epoxidize substrates, we studied the reactivity patterns versus propene. Generally, the reactions are stepwise via radical intermediates and proceed by two-state reactivity patterns on competing singlet and undecaplet spin state surfaces. However, both the mu-oxo-mu-1,2-peroxodiiron and mu-oxo-mu-1,1-peroxodiiron complex are sluggish oxidants with high epoxidation barriers. The epoxidation barriers for the mu-oxo-mu-1,1-peroxodiiron complex are significantly lower than the ones for the mu-oxo-mu-1,2-peroxodiiron complex but still are too high to be considered for catalytic properties. Thus, theory has ruled out two possible peroxodiiron catalysts as oxidants in RNR enzymes and biomimetics and the quest to find the actual oxidant in the enzyme mechanism continues.     

Theoretical study of the structure and properties of complexes formed by lithium and a boron α sheet

The ability of lithium to form complexes with a boron α sheet and the occurrence of ionic conduction in the compounds formed were evaluated using quantum-chemical methods. The obtained materials were established to be stable, and the weight fraction of lithium can reach 0.32. It was concluded that a low potential barrier for migration of lithium ions over the surface indicates the presence of ionic conduction.     

Direct C?C Cross‐Coupling of Secondary and Primary Alcohols Catalyzed by a γ‐Alumina‐Supported Silver Subnanocluster

Let's drink to that! Two alcohols (one primary and one secondary) can be coupled in an atom‐efficient process by a hydrogen‐autotransfer catalytic system in the form of silver subnanoclusters supported on γ‐Al₂O₃. The recyclable heterogeneous catalyst promoted the one‐pot C? C cross‐coupling in the presence of a catalytic amount of the weak base Cs₂CO₃ (see reaction mechanism).

     

DFT study of the mechanism of hydroamination of ethylene with ammonia catalyzed by diplatinum(II) complexes: Inner‐ or outer‐sphere?

A detailed analysis of the reaction profiles of the hydroamination reaction between ethylene and ammonia catalyzed by the diplatinum(II) [{Pt(NH₂)(μ‐H)(PPh₃)}₂] complex is presented herein using density functional theory computational techniques. The coordinatively unsaturated 14e T‐shaped [Pt(NH₂)(PPh₃)H] species resulted from the dissociation of the diplatinum [{Pt(NH₂)(μ‐H)(PPh₃)}₂] precatalyst are identified as the active catalytic species. All possible reaction pathways that constitute the entire catalytic cycle have exhaustively been investigated. Overall, the rate‐determining step of all catalytic cycles constructed was found to be the oxidative addition of ammonia that leads to the regeneration of the catalyst. According to the energy span model, the outer‐sphere mechanism for the hydroamination of ethylene with ammonia catalyzed by the diplatinum complexes is favored over the inner‐sphere one, whereas TOF values are in favor of the inner‐sphere mechanism. © 2012 Wiley Periodicals, Inc.     

On the optimization of a vertical twisted tape arrangement in a channel subjected to MWCNT–water nanofluid by coupling numerical simulation and genetic algorithm

Journal of Thermal Analysis and Calorimetry - Heat transfer and fluid flow are optimized in a three-dimensional channel under the constant heat flux boundary condition employing a genetic algorithm...     

What factors influence the ratio of C-H hydroxylation versus C=C epoxidation by a nonheme cytochrome P450 biomimetic?

Density functional calculations on a nonheme biomimetic (Fe=O(TMCS+) have been performed and its catalytic properties versus propene investigated. Our studies show that this catalyst is able to chemoselectively hydroxylate C=H bonds even in the presence of C=C double bonds. This phenomenon has been analyzed and found to occur due to Pauli repusions between protons on the TMCS ligand with protons attached to the approaching substrate. The geometries of the rate determining transition states indicate that the steric hindrance is larger in the epoxidation transition states than in the hydroxylation ones with much shorter distances; hence the hydroxylation pathway is favored over the epoxidation. Although, the reactant experiences close lying triplet and quintet spin states, the dominant reaction mechanism takes place on the quintet spin state surface; i.e., Fe=O(TMCS)+ reacts via single-state reactivity. Our calculations show that this spin state selectivity is the result of geometric orientation of the transition state structures, whereby the triplet ones are destabilized by electrostatic repulsions between the substrate and the ligand while the quintet spin transition states are aligned along the ideal axis. The reactivity patterns and geometries are compared with oxoiron species of dioxygenase and monoxygenase enzymes. Thus, Fe=O(TMCS)+ shows some similarities with P450 enzyme reactivity: it chemoselectively hydroxylates C=H bonds even in the presence of a C=C double bond and therefore is an acceptable P450 biomimetic. However, the absolute barriers of substrate oxidation by Fe=O(TMCS)+ are higher than the ones obtained with heme enzymes, but the chemoselectivity is lesser affected by external perturbations such as hydrogen bonding of a methanol molecule toward the thiolate sulfur or a dielectric constant. This is the first oxoiron complex whereby we calculated a chemoselective hydroxylation over epoxidation in the gas phase.     

The influence of structural factors on the solvation and coordination unsaturation of metal complexes of several structurally related alkyl substituted dipyrrolylmethenes-2,2′ and porphin

The literature data and new results of calorimetric studies of the solution of copper(II), cobalt(II), zinc(II), nickel(II), and mercury(II) complexes with 3,3′,4,4′,5,5′-hexamethyldipyrrolylmethene-2,2′; 3,3′,5,5′-tetramethyl-4,4′-diethyldipyrrolylmethene-2,2′; 3,3′,5,5′-tetramethyl-4,4′-dibutyldipyrrolylmethene-2,2′ (A), and 2,8,12,18-tetramethyl-3,7,13,17-tetrabutylporphin in various organic solvents were used to calculate the enthalpies of transfer Δ_tr H ^o from benzene and estimate the contribution of specific solvation caused by the additional coordination (Δ_c H ^o) of electron donor solvent molecules (pyridine and dimethylformamide). The greatest degree of coordination unsaturation and ability to extracoordination was characteristic of copper(II) and mercury(II) complexes with ligand A. The influence of the nature of the complex-forming metal, differences in the alkylation of the ligands, solvent properties, and the macrocyclization effect on the solvation and coordination unsaturation of metal complexes was discussed.     

Redox‐Triggered C?C Coupling of Diols and Alkynes: Synthesis of β,γ‐Unsaturated α‐Hydroxyketones and Furans by Ruthenium‐Catalyzed Hydrohydroxyalkylation

Direct ruthenium‐catalyzed C C coupling of alkynes and vicinal diols to form β,γ‐unsaturated ketones occurs with complete levels of regioselectivity and good to complete control over the alkene geometry. Exposure of the reaction products to substoichiometric quantities of p‐toluenesulfonic acid induces cyclodehydration to form tetrasubstituted furans. These alkyne‐diol hydrohydroxyalkylations contribute to a growing body of merged redox‐construction events that bypass the use of premetalated reagents and, hence, stoichiometric quantities of metallic by‐products.     

Correction to: On the optimization of a vertical twisted tape arrangement in a channel subjected to MWCNT–water nanofluid by coupling numerical simulation and genetic algorithm

Journal of Thermal Analysis and Calorimetry - Lignin-based polycaprolactone (PCL) graft copolymers with various graft ratios were prepared by ring-opening reaction in order to design new lignin...     

Does the Surface Matter? Hydrogen‐Bonded Chain Formation of an Oxalic Amide Derivative in a Two‐ and Three‐Dimensional Environment

We report on a multi‐technique investigation of the supramolecular organisation of N,N‐diphenyl oxalic amide under differently dimensioned environments, namely three‐dimensional (3D) in the bulk crystal, and in two dimensions on the Ag(111) surface as well as on the reconstructed Au(111) surface. With the help of X‐ray structure analysis and scanning tunneling microscopy (STM) we find that the molecules organize in hydrogen‐bonded chains with the bonding motif qualitatively changed by the surface confinement. In two dimensions, the chains exhibit enantiomorphic order even though they consist of a racemic mixture of chiral entities. By a combination of the STM data with near‐edge X‐ray absorption fine‐structure spectroscopy, we show that the conformation of the molecule adapts such that the local registry of the functional group with the substrate is optimized while avoiding steric hindrance of the phenyl groups. In the low coverage case, the length of the chains is limited by the Au(111) reconstruction lines restricting the molecules into fcc stacked areas. A kinetic Monte Carlo simulated annealing is used to explain the selective assembly in the fcc stacked regions.