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A new mechanism is proposed for the Ni-catalyzed carboxylation of organoboronates with CO2. DFT investigations at the PBE0-D3 level have shown that direct CO2 addition to the catalysts [Ni(NHC)(Allyl)Cl] ( 1NHC, NHC=IMe, IPr, SIPr and IPr*) is kinetically disfavored and formation of the Aresta-type intermediate is unlikely to occur. According to the mechanism proposed here, the carboxylation process starts with addition of the borate species to 1NHC, followed by transmetalation, CO2 cycloaddition and carboxylation. The rate-determining step was identified as being the transmetalation process, with computed relative free energy barriers of 34.8, 36.8, and 33.5 kcal mol−1 for 1IPr, 1SIPr and 1IPr*, respectively. [ABSTRACT FROM AUTHOR]

Adsorption of CO2 on MCM-41 functionalised with [3-(2-aminoethylamino)propyl]trimethoxysilane (MCM-41-N2), N1-(3-trimethoxysilylpropyl)diethylenetriamine (MCM-41-N3), 4-aminopyridine (MCM-41-aminopyridine), 4-(methylamino)pyridine (MCM-41-methylaminopyridine) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (MCM-41-guanidine) was investigated. The amine-functionalised materials were characterised by 29Si and 13C solid-state nuclear magnetic resonance, N2 adsorption/desorption isotherms, X-ray diffraction and transmission electron microscopy. CO2 adsorption at 1.0 bar and 30 °C showed that the amount of CO2 (nads/mmol g−1) adsorbed on MCM-41-N2 and MCM-41-N3 is approximately twice the amount adsorbed on MCM-41. For MCM-41-aminopyridine, MCM-41-methylaminopyridine and MCM-41-guanidine, the CO2 adsorption capacity was smaller than that of MCM-41 at the same conditions. The proton affinity (computed with wB97x-D/6-311++G(d,p)) of the secondary amino groups is higher than that of the primary amino groups; however, the relative stabilities of the primary and secondary carbamates are similar. The differential heat of adsorption decreases as the number of secondary amino groups increases. [ABSTRACT FROM AUTHOR]

Density Functional Theory (UB3LYP/6-311++G(d,p)) calculations of the affinity of the pentaaqua nickel(II) complex for a set of phosphoryl [OP(H)(CH3)(PhR)], imino [HNC(CH3)(PhR)], thiocarbonyl [SC(CH3)(PhR)] and carbonyl [OC(CH3)(PhR)] ligands were performed, where RNH2, OCH3, OH, CH3, H, Cl, CN, and NO2 is a substituent at the para-position of a phenyl ring.The affinity of the pentaaqua nickel(II) complex for these ligands was analized and quantified in terms of interaction enthalpy (Δ H), Gibbs free energy (Δ G298), geometric and electronic parameters of the resultant octahedral complexes. The Δ H and Δ G298 results show that the ligand coordination strength increases in the following order: carbonyl < thiocarbonyl < imino < phosphoryl. This coordination strength order is also observed in the analysis of the metal-ligand distances and charges on the ligand atom that interacts with the Ni(II) cation. The electronic character of the substituent R is the main parameter that affects the strength of the metal-ligand coordination. Ligands containing electron-donating groups (NH2, OCH3, OH) have more exothermic Δ H and Δ G298 than ligands with electron-withdrawing groups (Cl, CN, NO2). The metal-ligand interaction decomposed by means of the energy decomposition analysis (EDA) method shows that the electronic character of the ligand modulates all the components of the metal-ligand interaction. The absolute softness of the free ligands is correlated with the covalent contribution to the instantaneous interaction energy calculated using the EDA method. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The article presents a study which describes the relationship between nostoclide derivatives' structure and their ability to interfere with electron transport. The study involves the use of molecular modeling, biological assays, and careful analysis of the structure. The study indicates the effectivity of polarity as the most relevant molecular property which determines photosynthetic inhibitory activity.

Systematic investigations of conformational effects of the hydroxyl group on carbon or hydrogen chemical shifts of different types of alcohols reveal that, besides stereoelectronic effects, hyperconjugation with lone pairs may have a strong influence. In view of the growing use of chemical shifts in probing the structure of biologic molecules, we employed DFT/GIAO/NBO calculations at the B3LYP level for conformers obtained from partial optimization of structures resulting from 30° variations of the C—C—X—H (X=O, N) dihedral angles to verify if nitrogen responded in a fashion similar to oxygen. Although the hybridization and geometry of hydroxyl and amine groups are distinct, the lone pair on nitrogen reveals hyperconjugation with suitably positioned orbitals on alkyl groups. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 322–328, 2003 [ABSTRACT FROM AUTHOR]

In this work we describe a systematic and comparative study of the 17O NMR and related parameters of 17 polycyclic compounds: bicyclic, tricyclic, tetracyclic (endo–endo and endo–exo fusion), pentacyclic compounds (ketone; endo and exo-alcohols), hexacyclic alcohol. Concentration, temperature and solvent effects on the 17O NMR chemical shifts and the relaxation rate are also described. We compare all experimental 17O NMR chemical shifts with chemical shifts calculated from gauge-independent atomic orbitals within density functional theory (GIAO-DFT). Correlations between calculated and experimental 17O NMR chemical shifts for respective functional groups were carried out and linear equations for chemical shift predictions were generated. [Copyright &y& Elsevier]

The conversion of CO 2 into dimethyl carbonate (DMC) is an environmental and industrial appealing topic because it contributes to reduce the emissions of CO 2 and to increase its use as raw material. In the present study we employed the CAM-B3LYP/def2-SVP DFT approach to evaluate the thermodynamic and kinetic parameters for the catalytic conversion of CO 2 and methanol into DMC. Starting with the activation of four methanol molecules by the [Me 2 SnO] 2 dimer, we computed all the stationary points along the pathway to convert CO 2 and methanol into the DMC. The capture of two CO 2 molecules is promoted by an alkoxitin intermediate, in an exothermic process, with low activation energy. Formation of a first DMC occurs after an intramolecular rerrangement involving a tetrahedral intermediate. The formation of a second DMC may occur either in a process similar to the first one or by dimerization of the hemicarbonate formed after releasing the first DMC. In this pathway, the [Me 2 (OH)SnO(OMe)SnMe 2 ] 2 complex is formed. This complex is less reactive than [Me 2 Sn(OMe) 2 ] 2 but still conserves the catalytic activity. Identification of this mechanism suggests that the catalytic action of Me 2 SnO can be improved by modulating the formation of the final [Me 2 (OH)SnO(OMe)SnMe 2 ] 2 complex.

A new mechanism is proposed for the Ni-catalyzed carboxylation of organoboronates with CO 2 . DFT investigations at the PBE0-D3 level have shown that direct CO 2 addition to the catalysts [Ni(NHC)(Allyl)Cl] (1 NHC , NHC=IMe, IPr, SIPr and IPr*) is kinetically disfavored and formation of the Aresta-type intermediate is unlikely to occur. According to the mechanism proposed here, the carboxylation process starts with addition of the borate species to 1 NHC , followed by transmetalation, CO 2 cycloaddition and carboxylation. The rate-determining step was identified as being the transmetalation process, with computed relative free energy barriers of 34.8, 36.8, and 33.5 kcal mol -1 for 1 IPr , 1 SIPr and 1 IPr* , respectively., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)