Some spectroscopic and freezing point depression measurements on the homogeneous hydrogenation catalyst CoH3(PPh3)3

NMR, EPR and freezing point depression (FPD) experiments were performed on solutions of the homogeneous hydrogenation catalyst CoH₃(PPh₃)₃. The results of these measurements show that the compound has a dynamic structure on the NMR time scale at room temperature and that it is slightly dissociated into bisphosphine species and free phosphine. FPD and¹H-NMR measurements indicate that one Et₂O molecule is present per catalyst molecule.

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, () CoH₃(PPh₃)₃. , , . H¹- , Et₂O.

     

Surface morphologies—Equilibria and transient states

The relationship between the orientation dependent surface free energy and the surface morphology of crystalline materials is the main subject of this study. Small particles under equilibrium conditions as well as periodic profiles in transient states are considered. A second relationship of interest is that between step energy, step interaction energy and the orientation dependent surface free energy. Periodic surface profiles as transient states offer the possibility of measuring kinetic changes that provide information on the products mobility × energy while the shape alone may also be used to extract energy parameters. The rate of kinetic changes of profiles on vicinal surfaces depends sensitively on the orientation of the profile relative to the miscut direction. This has recently been demonstrated for vicinal Au crystals.     

Nucleophilic 18F-fluorination of heteroaromatic iodonium salts with no-carrier-added [18F]fluoride

Diaryliodonium salts containing the 2-thienyl group as an example of an electron-rich heteroaromatic moiety proved to be very potent precursors for the nucleophilic, regioselective no-carrier-added (nca) radiofluorination of various arenes. It even allowed the nucleophilic introduction of nca [18F]fluoride into electron-rich arene compounds in one step. The influences of the substitution pattern, of counteranions, and of different reaction conditions were studied. Effects of counterions could be explained by the influence of solvent on ion pair separation of precursor salts. Different aryl(2-thienyl)iodonium salts were used as precursors, where the homoaromatic group systematically varied from bearing electron-deficient to electron-rich substituents. Relative rates of exchange kinetics correlated linearly with Hammett constants of the appropriate substituents confirming a nucleophilic aromatic substitution reaction of high reactivity and low selectivity.