12 research outputs found
The trans influence in unsymmetrical pincer palladacycles: an experimental and computational study
A library of unsymmetrical SCN pincer palladacycles, [ClPd{2-pyr-6-(RSCH2)C6H3}], R = Et, Pr, Ph, p-MePh, and p-MeOPh, pyr = pyridine, has been synthesized via CâH bond activation, and used, along with PCN and NâCN unsymmetrical pincer palladacycles previously synthesized by the authors, to determine the extent to which the trans influence is exhibited in unsymmetrical pincer palladacycles. The trans influence is quantified by analysis of structural changes in the X-ray crystal and density functional theory (DFT) optimized structures and a topological analysis of the electron density using quantum theory of atoms in molecules (QTAIM) to determine the strength of the Pd-donor atom interaction. It is found that the trans influence is controlled by the nature of the donor atom and although the substituents on the donor-ligand affect the Pd-donor atom interaction through the varied electronic and steric constraints, they do not influence the bonding of the ligand trans to it. The data indicate that the strength of the trans influence is P > S > N. Furthermore, the synthetic route to the family of SCN pincer palladacycles presented demonstrates the potential of late stage derivitization for the effective synthesis of ligands towards unsymmetrical pincer palladacycles
Bismuth coordination networks containing deferiprone: synthesis, characterisation, stability and antibacterial activity
A series of bismuthâdicarboxylateâdeferiprone coordination networks have been prepared and structurally characterised. The new compounds have been demonstrated to release the iron overload drug deferiprone on treatment with PBS and have also been shown to have antibacterial activity against H. pylori
Inclusion and release of ant alarm pheromones from metalâorganic frameworks
Zinc(II) and zirconium(IV) metalâorganic frameworks show uptake and slow release of the ant alarm pheromones 3-octanone and 4-methyl-3-heptanone. Inclusion of N-propyl groups on the MOFs allows for enhanced uptake and release over several months. In preliminary field trials, leaf cutting ants show normal behavioural responses to the released pheromones
The nature of the bonding in symmetrical pincer palladacycles
The accuracy of DFT-optimised geometries of the symmetrical pincer palladacycles PdNCN and PdSCS, [ClPd{2,6- Me2NCH2)2C6H3}] and [ClPd{2,6-(MeSCH2)2C6H3}] respectively, has been evaluated by investigating the performance of eight commonly used density functionals with four combinations of basis set, in reproducing their X-ray crystal structures. It was found that whilst the ÏB97XD functional performed best over all, the PBE and TPSS functionals performed best when considering the palladium coordination geometry. The role of the donor atom in the stability and reactivity of the symmetric palladacycles, PdYCY, Y = N, S, or P, has been determined using Baderâs Atoms in Molecules method to elucidate the nature of the bonding, and using a model formation reaction, which involves the CâH activation of the pincer ligand YCY by PdCl2. The calculations reveal distinct differences in the bond strength and nature of the interaction of Pd with the donor atoms Y, which support differences in the thermodynamic stability of the palladacycles
Rationalization of the mechanism of in situ Pd(0) formation for cross-coupling reactions from novel unsymmetrical pincer palladacycles using DFT calculations
Density functional theory (DFT) is used to determine the mechanism for Pd(0) generation from pincer palladacycle pre-catalysts. The elucidated mechanisms comprise two key steps, transmetallation and reductive elimination. It is found that the presence of a base in the pre-catalyst activation step serves to significantly lower the Gibbs free energy barrier of the transmetallation step and the Gibbs free energy of the overall pre-catalyst activation. The DFT results are used to rationalize the catalytic activity of a number of pincer palladacycles in the Suzuki-Miyaura coupling of sterically demanding and electronically deactivated aryl bromides with 2-tolyboronic acid. A strong correlation exists between the Gibbs free energy barrier of the transmetallation step and/or overall pre-catalyst activation energy and the percentage conversions of the Suzuki- Miyaura coupling in the presence of the novel pre-catalysts. The data presented suggest that the slow, controlled release of the âtrue, active catalyst,â Pd(0), from the pincer palladacycle pre-catalysts provides the optimum reaction conditions and may be achieved by a high transmetallation energy barrier or overall pre-catalyst activation energy or both
Computational study of the coordination of methane to first row transition metal dication complexes
The coordination of methane, the first step in methane activation, to coordinately unsaturated first row transition metal dication complexes has been studied computationally to determine the most stable metal-methane interaction. The geometries and the vibrational frequencies of the encounter complexes [M(pyridine)2(CH4)]2+ have been determined using density functional theory with the ÏB97XD hybrid functional and triple-ζ basis sets. The structure is dependent on the metal center; for the early transition metals η3 coordination is favored, whereas η2 is more favorable for the later transition metals. The periodic trend in methane binding energies in the [M(pyridine)2(CH4)]2+ complexes follows the trend in electron affinity until the Mn complex but then exhibits decreasing energies from Fe to Zn. This is attributed to increasing Pauli repulsion and ligandâligand repulsion. For the most stable complex, [Cr(pyridine)2(CH4)]2+, the structures, energies, and spin states of the key intermediates and products in the oxidative addition/reductive elimination pathway have been investigated. It is found that the reaction is thermodynamically favorable and indicates that two-state reactivity may play an important role in lowering the energy of the hydridomethyl intermediate
Computational Study of the Coordination of Methane to First Row Transition Metal Dication Complexes
The coordination of methane, the
first step in methane activation,
to coordinately unsaturated first row transition metal dication complexes
has been studied computationally to determine the most stable metal-methane
interaction. The geometries and the vibrational frequencies of the
encounter complexes [MÂ(pyridine)<sub>2</sub>(CH<sub>4</sub>)]<sup>2+</sup> have been determined using density functional theory with
the ÏB97XD hybrid functional and triple-ζ basis sets.
The structure is dependent on the metal center; for the early transition
metals η<sup>3</sup> coordination is favored, whereas η<sup>2</sup> is more favorable for the later transition metals. The periodic
trend in methane binding energies in the [MÂ(pyridine)<sub>2</sub>(CH<sub>4</sub>)]<sup>2+</sup> complexes follows the trend in electron affinity
until the Mn complex but then exhibits decreasing energies from Fe
to Zn. This is attributed to increasing Pauli repulsion and ligandâligand
repulsion. For the most stable complex, [CrÂ(pyridine)<sub>2</sub>(CH<sub>4</sub>)]<sup>2+</sup>, the structures, energies, and spin states
of the key intermediates and products in the oxidative addition/reductive
elimination pathway have been investigated. It is found that the reaction
is thermodynamically favorable and indicates that two-state reactivity
may play an important role in lowering the energy of the hydridomethyl
intermediate
Bismuth coordination networks containing deferiprone:synthesis, characterisation, stability and antibacterial activity
A series of bismuth-dicarboxylate-deferiprone coordination networks have been prepared and structurally characterised. The new compounds have been demonstrated to release the iron overload drug deferiprone on treatment with PBS and have also been shown to have antibacterial activity against H. pylori.</p
VĂœzkum sedimentĆŻ pĆehradâ nĂĄdrĆŸĂ a jezer - zhodnocenĂ rizik a nĂĄvrhy opatĆenĂ:Ć lichovĂĄ charakteristika okolĂ nĂĄdrĆŸe Vrchlice
PĆĂprava podkladĆŻ a regionĂĄlnĂ zhodnocenĂ geochemickĂœch (ĆĄlichovĂœch) dat v oblasti VN Vrchlice. Svazek obsahuje jeĆĄtÄ tyto zprĂĄvy: ShrnutĂ hlavnĂch principĆŻ vytvĂĄĆenĂ eroznĂch a transportnĂch procesĆŻ z povodĂ nĂĄdrĆŸĂ (Aplikace v povodĂ VN Vrchlice). NĂĄdrĆŸnĂ sedimenty a jejich role v procesech eutrofizace