Aleksandra Pazio

The Doping Effect of Fluorinated Aromatic Solvents on the Rate of Ruthenium‐Catalysed Olefin Metathesis

A study concerning the effect of using a fluorinated aromatic solvent as the medium for olefin metathesis reactions catalysed by ruthenium complexes bearing N-heterocyclic carbene ligands is presented. The use of fluorinated aromatic hydrocarbons (FAH) as solvents for olefin metathesis reactions catalysed by standard commercially available ruthenium pre-catalysts allows substantially higher yields of the desired products to be obtained, especially in the case of demanding polyfunctional molecules, including natural and biologically active compounds. Interactions between the FAH and the second-generation ruthenium catalysts, which apparently improve the efficiency of the olefin metathesis transformation, have been studied by X-ray structure analysis and computations, as well as by carrying out a number of metathesis experiments. The optimisation of reaction conditions by using an FAH can be regarded as a complementary approach for the design of new improved ruthenium catalysts. Fluorinated aromatic solvents are an attractive alternative medium for promoting challenging olefin metathesis reactions.

Ruthenium-amido complexes: synthesis, structure, and catalytic activity in olefin metathesis.

Olefin metathesis has become a powerful reaction for the formation of carbon–carbon bonds in organic and polymer chemistry. Availability of well-defined ruthenium-based catalysts (e.g., 1–3) tolerant of moisture, oxygen, various functional groups and normal organic or polymer processing conditions has greatly expanded the scope and applications of this process and has made it widely used in synthesis.

Consequences of the electronic tuning of latent ruthenium-based olefin metathesis catalysts on their reactivity

Summary Two ruthenium olefin metathesis initiators featuring electronically modified quinoline-based chelating carbene ligands are introduced. Their reactivity in RCM and ROMP reactions was tested and the results were compared to those obtained with the parent unsubstituted compound. The studied complexes are very stable at high temperatures up to 140 °C. The placement of an electron-withdrawing functionality translates into an enhanced activity in RCM. While electronically modified precatalysts, which exist predominantly in the trans-dichloro configuration, gave mostly the RCM and a minor amount of the cycloisomerization product, the unmodified congener, which preferentially exists as its cis-dichloro isomer, shows a switched reactivity. The position of the equilibrium between the cis- and the trans-dichloro species was found to be the crucial factor governing the reactivity of the complexes.

Bis(l-serinium) oxalate dihydrate: polymorph II.

A corrected and improved structure of the polymorph II of 2C3H8NO3 +·C2O4 2−·2H2O, based on single-crystal data, is presented. The structure is refined with anisotropic displacement parameters for all non-H atoms and all H atoms are located. Due to the charged moieties, the structure is classified as a molecular salt. Intermolecular O—H⋯O−, O—H⋯O and N+—H⋯O−hydrogen bonds link the components of the structure. The l-serinium cations and oxalate anions form a network of channels in [100] direction, filled with the water molecules of crystallization. The dihedral angle between the CO2 units of the oxalate dianion is 10.2 (3)°

Protonated nucleobases are not fully ionized in their chloride salt crystals and form metastable base pairs further stabilized by the surrounding anions

Charge-density studies of cytosinium chloride, adeninium chloride hemihydrate and guaninium dichloride crystals based on ultra-high-resolution X-ray diffraction data and extensive theoretical calculations are presented. The studies confirm the importance of electrostatic interactions in ionic crystals and show how counterintuitive they can be for protonated nucleobases of like charge.

High resolution X-ray diffraction datasets of guanine dichloride

High-resolution single crystal X-ray measurement was carried out on a Bruker APEX II ULTRA single-crystal diffractometer with a TXS rotating anode (Mo K\u03b1, radiation \u03bb = 0.71073 \xc5) equipped with a CCD-type area detector, multilayer optics and an Oxford Cryostream low temperature attachment set to 100 K. A total of 12412 frames were collected in 44 runs to obtain the high redundancy data. Diffraction data was collected using the \u03c9 and \u03c6 scan method with a rotation width of 0.5\xb0 and the exposure time in the range of 20 - 60 seconds.\r\n

Experimental charge densities of nucleobase chlorides from intermolecular interaction perspective

Nucleobases are one of the basic building blocks of nucleic acids, the most important molecules for every living organism. The richness of possibilities of how nucleobases may interact with themselves and with other molecules, yet still maintaining specificity of an interaction, makes them a key contributor to the 3D structure and function of DNA, and even more of RNA. The presented work contributes to our understanding of intermolecular interactions among protonated nucleobases and surrounding them chloride counter ions in the solid state. For cytosinium chloride, adeninium chloride hemihydrate and guaninediium dichloride we collected high-resolution X-ray diffraction data to determine crystal charge densities. Experimental results we further supported by extensive theoretical calculations: UBDB charge density modelling, EPMM electrostatic interaction energy calculations, QTAIM analysis, dimer interaction energy from perturbation theory (PIXEL, DFTSAPT) and periodic quantum mechanics based on variational principle. We found that cohesive energies of studied systems are dominated by electrostatic interaction energy (Ees) contributions as expected for ionic crystals. Ees contributions from pairs of neighboring ions are big in magnitude, much bigger than for pairs of neutral molecules of the same type. However, Ees computed from experimental charge densities are not as big in magnitude as theoretical calculations based on perturbation theory suggest. This is because studied molecules are not fully ionized in crystal state according to experiment and periodic quantum calculations. Because of that and because of charge density polarization, some pairs of single protonated bases exhibit attractive interactions (negative Ees) despite same molecular charge. In addition, these pairs, but also other pairs of ions show that the values of Ees cannot be predicted only from interactions between monopole moments (point charges) of studied molecules. The higher electric moments and the overlap of molecular charge densities matters. On the other hand we found, that despite their overall repulsive character of interactions, there are bond critical points (BCP) and bonding lines between many nucleobases in studied crystals according to QTAIM analysis of crystal electron densities (experimental, UBDB derived and from periodic quantum mechanics). Moreover, interaction energies computed from electron density and its Laplacian at BCPs according to Espinosa-Lecomte-Molins approach are negative pointing to attractive interaction. Although there is no correlation between the sum of these energies for particular pair of ions (regardless their charge) and Ees of this pair, there is strong correlation of these energies with charge penetration contribution to the Ees. We found it to be one of the most significant results of the presented work. Indeed, BCPs are very important single point descriptors of interactions between the whole molecules as they bear the information about molecular charge densities overlap and its contribution to interaction energy.

Charge densities of three polymorphs of glycine

The experimental charge densities of three polymorphs of glycine are presented. Two polymorphs crystallize in the monoclinic system: α-glycine in P21/c and β-glycine in P21 space groups, whereas γ-glycine grows as merohedral twins composed of two trigonal lattices (space groups P31 and P32) combined by applying the [0 1 0 1 0 0 0 0 -1] twin matrix. The TAAM model of electron density (UBDB databank [1]) is used as a starting point in all refinements of experimental electron density. Different models of thermal motion were tested for all polymorphs (from the SHADE [2] server and theoretical calculations in Crystal09 [3]) and detailed results are discussed. The role of the anisotropic model of thermal motion of hydrogen atoms is emphasized.