Catalysis based on nanoparticles is very rapidly evolving. As a result of our cooperation in COST, we reported here a method for the generation and entrapment of rhodium nanoparticles in simple solid ammonium salts, starting from quaternary ammonium salts, rhodium compounds, hydrogen and CO2. Nanoparticles thus obtained were used as selective catalysts for the hydrogenation of simple substrates and also for more complex, that cannot be easily hydrogenated. Prof. Leitner received Wöhler Prize for 2009 for the presented results (See: Angew. Chem. Int. Ed., 2009, 48, 6587).
COBISS.SI-ID: 30100997
Heteroaromatics (furan, thiophene, isoxazole, thiazole) bearing hydroxyalkyl group were directly arylated using low-loading ligand-free Pd(OAc)2 (0.01-0.5 mol%) as precatalyst without any protection of hydroxy group. Reaction proceeded via activation of C-H bond of heteroaromate which was further functionalized with (hetero)aryl bromides thus selectively leading to 5-arylated products. Our methodology represents a more environmentally and economically attractive access to such arylated products in comparison with classical cross-coupling reactions. 55 independent SCI citations.
COBISS.SI-ID: 33849861
A series of analogs of FDDNP, a well established molecular probe for the detection of changes in the CNS of Alzheimer disease patients, has been synthesized and characterized using spectroscopic and computational methods. The binding affinities of these molecules have been measured experimentally and explained through the use of a computational model. The analogs were created by systematically modifying the donor and the acceptor sides of FDDNP to learn the structural requirements for optimal binding to Aβ aggregates. FDDNP and its analogs are neutral, environmentally sensitive, fluorescent molecules with high dipole moments, as evidenced by their spectroscopic properties and dipole moment calculations. The preferred solution-state conformation of these compounds is directly related to the binding affinities. The extreme cases were a nonplanar analog tert-butyl-FDDNP, which shows low binding affinity for Aβ aggregates (520 nM Ki) in vitro and a nearly planar tricyclic analog cDDNP, which displayed the highest binding affinity (10 pM Ki). Using a previously published X-ray crystallographic model of DDNP bound to an amyloidogenic Aβ peptide model, we show that the binding affinity is inversely related to the distortion energy necessary to avoid steric clashes along the internal surface of the binding channel.
COBISS.SI-ID: 36232965
This account deals with recent advances in the chemistry of hydrogen trioxide, HOOOH, the simplest member of the family of polyoxides of the general formula ROnR, where R stands for hydrogen or other atoms or groups and n ≥ 3. These species, which may be regarded as higher homologues of hydrogen peroxide, are believed to be key intermediates in the low-temperature oxidations, atmospheric and environmental chemistry, chemistry of combustion and in biochemical oxidations. Various chemical methods were used for the preparation of relatively highly concentrated solutions of HOOOH, thus enabling unambiguous identification (1H and 17O NMR, IR (matrix and solution) and microwave spectroscopy, and state-of-the-art ab initio calculations). Theoretical and NMR spectroscopic evidence indicates that (HOOOH)n (n = 2, 3, 4, ...) assemblies are the characteristic structural feature of the polyoxide in the gas phase and in inert (nonpolar) solvents. Organic oxygen bases (B) as solvents are capable of disrupting these assemblies by forming intermolecularly hydrogen-bonded complexes, HOOOH−B. Water plays a crucial role in the decomposition of this polyoxide by acting as a bifunctional catalyst and accelerates the decomposition of HOOOH () 1000 times) to produce water and singlet oxygen. Hydrogen trioxide is more lipophilic than water and hydrogen peroxide, and a stronger acid than HOOH as well. Protonation of terminal oxygen atoms (the most basic sites in HOOOH) gives HOOO(H)H+, a short-lived intermediate, which rapidly decomposes to produce H3O+ and singlet oxygen. HOOOH (together with the HOOO• radical and the HOOO— anion) may be regarded as an effective reactive oxygen species involved in the “peroxone process” and in the atmosphere. This polyoxide can also seriously damage different important biomolecules including DNA, lipids, and proteins (atherosclerosis, cancer, neurodegenerative disorders).
COBISS.SI-ID: 1615407
Since the discovery of copper catalyzed cycloaddition of organic azides and alkynes into Click triazoles (1,2,3-triazoles), the corresponding triazolylidenes (1,2,3-triazol-5-ylidenes) have emerged as a powerful subclass of N-heterocyclic carbene ligands possessing unique complexation ability to transition metals. Especially attractive are the ligands of advanced architecture such as pyridyl-triazolylidenes, which can through a variety of bi- and multidentate coordination fine-tune the catalytic, spectroscopic and electrochemical properties of the metal centre. Despite the tremendous potential of pyridyl-triazolylidenes their preparation, even starting from easily derived Click triazoles, remains a significant challenge due to some serious selectivity issues that are connected to the existing methods. In this communication we reported on highly selective and efficient protocol to easily access a variety of isomeric and homologous pyridyl-triazolium salts. It is based on a simple, yet carefully selected, reliable and selective protection of pyridine functionalized Click triazoles through the pyridine N-oxidation with subsequent triazole ring alkylation and deprotection. Our methodology offers a platform for the preparation of structurally diverse pyridyl-triazolylidenes almost at will. The concept and the applicability was demonstrated on in situ generated palladium N-heterocyclic carbene complex of this type and its use in Suzuki–Miyaura catalysis. Turnover of 9000 was achieved in selected C–C coupling reactions at room temperature in the environmentally benign water as a solvent, with as low as 0.01 mol% loading of the in situ generated catalyst. This article was highlighted in Chemistry & Industry 2013, 77 (12), p. 57), DOI: 10.1002/cind.7712_19.x (http://onlinelibrary.wiley.com/doi/10.1002/cind.7712_18.x/abstract).
COBISS.SI-ID: 1623855