The combination of parahydrogen induced polarization (PHIP), kinetics and NMR spectroscopy yields a powerful analytical tool: quantitative in situ NMR spectroscopy. Two versions of PHIP NMR experiments are presented to investigate the kinetics of homogeneously catalyzed hydrogenations. The first method, an experimental variation of the ROCHESTER experiment (ROCHESTER = rates of catalytic hydrogenation estimated spectroscopically through enhanced resonances), allows one to determine the hydrogenation rate independently of relaxation and other sources of decay, e.g., subsequent chemical reaction steps. The second method named DYPAS (dynamic PASADENA spectroscopy) uses a variable delay between the end of the hydrogen-addition period and the detection pulse. In principle, all processes during this delay can be described by a set of coupled differential equations. Their solutions can be fitted to the experimental data by a least-squares optimization of the involved kinetic parameters. The DYPAS method can be used to determine the rates of formation as well as the rates of decomposition of stable intermediates and has been applied to the case of freshly hydrogenated and still catalyst-attached product molecules. We provide kinetic data for the formation and decomposition of these unusual product-catalyst complexes during the hydrogenation of different styrene derivatives with a cationic RhI catalyst containing a chelating diphosphine ligand. The kinetic measurements indicate that the rate of formation of the catalyst-attached product increases whereas the rate constant of its decomposition diminishes if the para position of the arene ring of styrene carries an electron-donating substituent. In the case of p-aminostyrene as the substrate, the detachment step turned out to be rate limiting for the catalytic cycle. With certain substituted styrenes and cationic RhI complexes containing chiral chelating diphosphine ligands, two geometrically different (diastereomeric) product-catalyst adducts can be discriminated via PHIP NMR spectroscopy. The associated alternative reaction pathways have been analyzed by applying the DYPAS method, which can also be used to investigate the mechanism of an asymmetric hydrogenation

The attenuated total reflectance Fourier transform infrared dialysis technique is introduced for the time-resolved investigation of the binding processes of Ca2+ to polyacrylates dissolved in water. We observed transient formation of intermediates in water with various types of coordination of the carboxylate group to Ca2+ throughout the complexation steps. Time-resolved changes in the spectra were analyzed with principal component analysis, from which the spectral species were obtained as well as their formation kinetics. We propose a model for the mechanisms of Ca2+ coordination to polyacrylates. The polymer chain length plays an important role in Ca2+ binding.

Nuclear magnetic resonance (NMR) is well-suited to implement quantum algorithms experimentally. However, there are serious problems associated with the noisy mixed initial state that is described by the thermal equilibrium density operator of NMR spectroscopy. Here we present a new strategy to dramatically increase the sensitivity of a NMR quantum computing experiment. Para hydrogen can be used to prepare a density operator in a suitable molecule that is very close to a pure state, an improvement on the order of 104 compared to “conventional” NMR quantum computing. Our strategy is demonstrated experimentally solving the Deutsch–Jozsa problem based on para hydrogen and Vaska’s complex.

Fast scan voltammetry gives kinetic evidence for the reversible dimerization of the radical cations of thianthrene (T) and 2,3,7,8-tetramethoxythianthrene (TMOT) in acetonitrile. At 256 K an equilibrium constant KD~,,, ~9 0 0 for TMOT ( K D i m 'z I . 1. lo4 for T) and rate constants k+ 1.10' and k,,= l.2.104 were determined. Using the semiempirical PM3 method, the formation of o-bonded dimers is indicated. For the dimerization reaction in acetonitrile, enthalpy values of -79 kJ/mol for T and -56 kJlmol for TMOT respectively were calculated. Despite the folded structure of the neutral T and TMOT systems and their planarization during the radical cation formation, the heterogeneous electron transfer kinetics was found to be very fast in both cases (1.6 cmls; 298 K). The activation enthalpy was determined to be 14 kJ/mol in the case of TMOT. Calculations of the inner-sphere reorganization energy using the Marcus theory produced Aff'(s0) = 4.6 kJ/mol for TMOT and 3.9 kJlmol for T respectively at infinite temperatures. This explains the fast electron transfer kinetics and their low activation enthalpies.

A new in situ NMR method for the structural characterization of hydrogenation intermediates based on the PHIP effect (PHIP=parahydrogen‐induced polarization): by means of a nuclear Overhauser effect (NOE) the intermediate bonding of hydrogenated [D8]styrene to cationic RhI–diphosphane catalyst complexes could be detected (see picture).