Disentanglement of orthogonal hydrogen and halogen bonds via natural orbital for chemical valence: A charge displacement analysis

As 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

Diiron bis-cyclopentadienyl complexes as transfer hydrogenation catalysts: The key role of the bridging aminocarbyne ligand

The catalytic activity of a series of diiron complexes based on the {Fe2Cp2(CO)(x)} core (x = 2-3) and containing a bridging aminocarbyne ligand was screened in transfer hydrogenation reaction of cyclohexanone from isopropanol. The series includes cationic tricarbonyl complexes, [1a-d]CF3SO3, and neutral derivatives obtained by substitution of one carbonyl with hydride (2a-c), cyanide (3a-d) or chloride (4a) ligands. The novel compounds 2a-b, 3a-b and 4a were characterized by analytical and spectroscopic techniques, and the single crystal X-ray structure of one isomer of 4a was determined. In general, diiron complexes exhibited a moderate activity in combination with potassium hydroxide; [Fe2Cp2(CN)(CO)(mu-CO){mu-CN (Me)(4-C6H4OMe)}], 3a, emerged as the best catalyst, and the study of its activity was extended to a range of other ketones. DFT calculations suggest an unusual carbyne-centred mechanism, and the better performance displayed by 3a is ascribable to the stabilizing effect provided by the cyanide co-ligand, which is experimentally supported by IR analyses

Bypassing the Inertness of Aziridine/CO2 Systems to Access 5-Aryl-2-Oxazolidinones: Catalyst-Free Synthesis Under Ambient Conditions

The development of sustainable synthetic routes to access valuable oxazolidinones via CO2 fixation is an active research area, and the aziridine/carbon dioxide coupling has aroused a considerable interest. This reaction features a high activation barrier and thus requires a catalytic system, and may present some other critical issues. Here, the straightforward gram-scale synthesis of a series of 5-aryl-2-oxazolidinones was developed at ambient temperature and atmospheric CO2 pressure, in the absence of any catalyst/co-catalyst. The key to this innovative procedure consists in the direct transfer of the pre-formed amine/CO2 adduct (carbamate) to common aziridine precursors (dimethylsulfonium salts), replacing the classical sequential addition of amine (intermediate isolation of aziridine) and then CO2. The reaction mechanism was investigated by NMR spectroscopy and DFT calculations applied to model cases

Drafting a prioritized checklist of Crop Wild Relatives and Wild Harvested Plants of Italy: problems and solutions

The National checklists of Crop Wild Relatives (CWR) and Wild Harvested Plants (WHP) are the basic tools for the development of in situ and ex situ conservation strategies of plant genetic resources. Here we discuss the methodologies and the prioritization process we previously used in the preparation of the prioritized checklist of CWR and WHP for Italy. The starting point were the most up-to-date Italian checklists of native and alien flora with their updates used as a nomenclatural and distributive source of data. Sardinia and Sicily were kept separate from peninsular Italy to perform detailed analyses focused on the taxa of the two major islands. The origin, the endemic status, cultivation, economic importance, uses, gene pool or taxon group, and the Red List status information were added. The WHP status was attributed to all the taxa with known direct uses. A qualitative approach was adopted in the prioritization process, the main criteria used were: 1) the inclusion of wild relative taxa of crops listed in Annex I of the International Treaty on Plant Genetic Resources for Food and Agriculture (ITPGRFA) and/or by the Italian Institute of Statistics (ISTAT) for cultivated areas and yield in the last 5 years; 2) the threatened taxa occurring in national or global Red lists; 3) the endemism. This prioritization process generated 102 taxa as most in need of specific protection and /or monitoring measures, 57 taxa requiring monitoring because of their restricted distribution although not requiring specific protection measures and 735 taxa not requiring any specific protection. However, different prioritization processes could have been applied to the Italian checklists yielding different results. Here we discuss the matter

Ruthenium(II) Tris-Pyrazolylmethane Complexes in Transfer Hydrogenation Reactions

While ruthenium(II) arene complexes have been widely investigated for their potential in catalytic transfer hydrogenation, studies on homologous compounds replacing the arene ligand with the six-electron donor tris(1-pyrazolyl)methane (tpm) are almost absent in the literature. The reactions of [RuCl(κ3-tpm)(PPh3)2]Cl, 1, with a series of nitrogen ligands (L) proceeded with selective PPh3 mono-substitution, affording the novel complexes [RuCl(κ3-tpm)(PPh3)(L)]Cl (L=NCMe, 2; NCPh, 3; imidazole, 4) in almost quantitative yields. Products 2–4 were fully characterized by IR and multinuclear NMR spectroscopy, moreover the molecular structure of 4 was ascertained by single crystal X-ray diffraction. Compounds 2–4 were evaluated as catalytic precursors in the transfer hydrogenation of a series of ketones with isopropanol as the hydrogen source, and 2 exhibited the highest activity. Extensive NMR experiments and DFT calculations allowed to elucidate the mechanism of the transfer hydrogenation process, suggesting the crucial role played by the tpm ligand, reversibly switching from tri- to bidentate coordination during the catalytic cycle

Post-Modification of the Electronic Properties by Addition of π-Stacking Additives in N-Heterocyclic Carbene Complexes with Extended Polyaromatic Systems

A series of iridium complexes containing phenanthro[4,5-abc]phenazino[11,12-d]imidazol-2-ylidene and acetonaphtho[1,2-b]quinoxaline[11,12-d]imidazol-2-ylidene ligands have been obtained and fully characterized. These complexes display highly extended polyaromatic systems attached to the backbone of the N-heterocyclic carbene. The presence of this extended polyaromatic system makes the electron-donating character of these ligands sensitive to the presence of π-stacking additives, such as pyrene and hexafluorobenzene. The computational studies predict that the addition of pyrene affords an increase of the electron-donating character of the polyaromatic ligand (TEP decreases), while the addition of hexafluorobenzene has the opposite effect (TEP increases). This prediction is experimentally corroborated by IR spectroscopy, by measuring the shift of the CO stretching bands of a series of IrCl(NHC)(CO)2 complexes, where NHC is the N-heterocyclic carbene ligand with the polyaromatic system. Finally, the energy of the π-stacking interaction of one of the key Ir(I) complexes with pyrene and hexafluorobenzene has been estimated by using the Benesi-Hildebrand treat-ment, based on the δ-shifts observed by 1H NMR spectroscopy.MEC of Spain (CTQ2011-24055/BQU

4-Aryl-2-Imino-1,3-Dithiolanes from the Room Temperature Coupling of Sodium Dithiocarbamates with Sulfonium Salts

A series of 4-aryl-2-imino-1,3-dithiolanes was synthesized by means of a straightforward strategy starting from readily available precursors: reactions of dithiocarbamates and arylsulfonium salts, at room temperature in water/CH2Cl2 as biphasic medium, afforded the five-membered cyclic products in good yields. The reaction mechanism was investigated by DFT calculations

Charge Displacement Analysis-A Tool to Theoretically Characterize the Charge Transfer Contribution of Halogen Bonds

Theoretical 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

A 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