1,721,035 research outputs found
Disentanglement of orthogonal hydrogen and halogen bonds via natural orbital for chemical valence: A charge displacement analysis
Full text linkAs known, the electron density of covalently bound halogen atoms is anisotropically distributed, making them potentially able to establish many weak interactions, acting at the same time as halogen bond donors and hydrogen bond acceptors. Indeed, there are many examples in which the halogen and hydrogen bond coexist in the same structure and, if a correct bond analysis is required, their separation is mandatory. Here, the advantages and limitations of coupling the charge displacement analysis with natural orbital for chemical valence method (NOCV-CD) to separately analyze orthogonal weak interactions are shown, for both symmetric and asymmetric adducts. The methodology gives optimal results with intermolecular adducts but, in the presence of an organometallic complex, also intramolecular interactions can be correctly analyzed. Beyond the methodological aspects, it is shown that correctly separate and quantify the interactions can give interesting chemical insights about the systems
Charge Displacement Analysis-A Tool to Theoretically Characterize the Charge Transfer Contribution of Halogen Bonds
Full text linkTheoretical bonding analysis is of prime importance for the deep understanding of the various chemical interactions, covalent or not. Among the various methods that have been developed in the last decades, the analysis of the Charge Displacement function (CD) demonstrated to be useful to reveal the charge transfer effects in many contexts, from weak hydrogen bonds, to the characterization of σ hole interactions, as halogen, chalcogen and pnictogen bonding or even in the decomposition of the metal-ligand bond. Quite often, the CD analysis has also been coupled with experimental techniques, in order to give a complete description of the system under study. In this review, we focus on the use of CD analysis on halogen bonded systems, describing the most relevant literature examples about gas phase and condensed phase systems. Chemical insights will be drawn about the nature of halogen bond, its cooperativity and its influence on metal-ligand bond components
Influence of halogen bonding on gold(i)-ligand bond components and DFT characterization of a gold-iodine halogen bond
No full textA gold(i) complex bearing nitrogen acyclic carbene (NAC) and selenourea (SeU) has been used to verify whether the second-sphere Se⋯I halogen bond (XB) is able to modify the Dewar-Chatt-Duncanson components of the Au-C and Au-Se bonds. The chosen system was found to be thermically unstable but it allowed an in-depth theoretical study by means of Energy Decomposition Analysis, Natural Bond Orbital and Natural Orbitals for Chemical Valence methods, coupled with Charge Displacement analysis. Indeed, in the presence of iodoperfluoroalkanes as XB donors, iodine interacts with the lone pair of the coordinated selenium, enhancing the Au ← C σ donation and depressing the Au → C π back-donation, as demonstrated also by the increase of the rotational barrier of the C-N bond of the NAC (see G. Ciancaleoni and others, Chem.-Eur. J., 2015, 21, 2467). On the other hand, in the presence of N-iodosuccinimide (NIS), the gold directly establishes a XB with the iodine by using its d lone pairs. This Au⋯I XB is favored by the low steric hindrance of the ligands coordinated to the gold and the presence of the amino protons of SeU, which establish additional hydrogen bonds with the NIS. Also in this case, the effect is to increase the σ acidity and decrease the π basicity of the metal
Theoretical insights into the reversible CO2 absorption by ethylene glycol/KOH/boric acid low temperature transition mixture
No full textThe Low Temperature Transition Mixture (LTTM) formed by ethylene glycol, potassium hydroxide and boric acid experimentally demonstrated to reversibly absorb carbon dioxide (see J. Mol. Liq. 340 (2021) 117180). In this paper, we study the speciation of the components and the absorption/desorption mechanism by Density Functional Theory, providing reasonable hypotheses to explain all the experimental facts for which it was not possible to provide a satisfactory explanation. In addition, we used the recently developed Extended Transition StateNatural Orbitals for Chemical Valence (ETS-NOCV) analysis of concerted transition states (cTS), in order to isolate and quantitatively evaluate the relative importance and asynchrony of all the concurrent molecular events embedded in the cTS
Construction of Two-Faced (Hetero)hydrocarbyl Diiron Complexes Mediated by the Interplay of Ligands
Full text linkThe functionalized allylidene complex [Fe2Cp2(CO)(mu-CO){mu-eta 1:eta 3-C gamma(Fc)-C beta HC alpha(CN)NMe2}], 1 [Cp = eta 5-C5H5; Fc = CpFe(eta 5-C5H4)], reacted with isocyanides (CNR), in isopropanol solution at ca. 100 degrees C, to give the CO-substitution products [Fe2Cp2(CO)(mu- CNR){mu-eta 1:eta 3-C gamma(Fc)C beta HC alpha(CN)NMe2}] [R = CH2P(O)(OEt)2, 2a; R = 2-naphthyl, 2b; R = CH2C(O)(OEt), 2c], which were isolated in 61-84% yields. The bridging coordination of CNR in 2a-c is forced by a stabilizing electrostatic interaction between the nitrogen lone pair belonging to the {NMe2} group and the terminal CO ligand. Isocyanide methylation with methyl triflate proceeded with the inversion of stereochemistry at the C alpha carbon and led to [Fe2Cp2(CO){mu- CN(Me)R}{mu-eta 1:eta 3-C gamma(Fc)C beta HC alpha(CN)NMe2}]CF3SO3 (R = CH2P(O)(OEt)2), ([3a]CF3SO3; R = 2-naphthyl, [3b]CF3SO3), containing bridging allylidene and aminocarbyne ligands (68-74% yields). All products were fully characterized by IR and multinuclear NMR spectroscopy, and the structures of 2a and [3a]CF3SO3 were elucidated by X-ray diffraction studies. Density functional theory (DFT) calculations were extensively carried out to shed light on structural, mechanistic, and thermodynamic features
Carbonyl-isocyanide mono-substitution in [Fe2Cp2(CO)4]: A re-visitation
Full text linkThe reactions of [Fe2Cp2(CO)4] with a series of isocyanides, CNR, were conducted in acetonitrile and afforded, after a thermal treatment, the mono-isocyanide derivatives [Fe2Cp2(CO)3(CNR)] [R = 1H-indol-5-yl, 1; CH2P(O)(OEt)2, 2; Cy = C6H11, 3; 4-C6H4OMe, 4; Xyl = 2,6-C6H3Me2, 5; Me, 6; 2-naphthyl, 7; Bn = CH2Ph, 8]. In order to avoid multiple substitution, the diiron reactant was used in a molar excess with respect to the isocyanide (1.6 equivalents; 1.1 for the synthesis of 8). The products were separated from unreacted [Fe2Cp2(CO)4] by chromatography or via reversible protonation, and finally isolated in 50–83% yields. IR and NMR spectroscopy indicate that the isocyanide ligand is bridging coordinated in 2 and 7, terminal in 3 and 5, while in the remaining cases a mixture of terminal- and bridging-CNR isomers is obtained. The molecular structure of 5 was ascertained by X-ray diffraction. In general, the coordination mode of the isocyanide is scarcely influenced by the environment (solvents with different polarities, solid state). Sluggish partial isocyanide migration from terminal to bridging position was recognized for 3 and 5 upon heating in refluxing toluene, a process which was reproduced by DFT calculations
Aggregazione in soluzione di precatalizzatori neutri "half-sandwich”, basati sul Ru(II), usati nella reazione di idrogenazione per trasferimento di idrogeno
No full textAggregation in solution of neutral half-sandwich Ru(II) precatalysts for transfer hydrogenation
No full textSintesi e caratterizzazione di nuovi complessi cationici di Ru (II) contenenti leganti chinali
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