Intermediäre Produktanbindung bei der homogenen Hydrierung von Styrolderivaten mit Parawasserstoff und kationischen RhI-Katalysatoren

A new synthetic route to ligands of the general composition R2PCH2ER′2 (E = P, As) and some rhodium complexes derived thereof

“…In this respect, our results complement recent work by Bargon et al which illustrates that the cleavage of the ring-to-metal bond in cationic species [(η 6 -C 6 H 5 R)Rh-{κ 2 P,PЈ-Ph 2 P(CH 2 ) 4 PPh 2 }] ϩ , formed as intermediates in the rhodium-catalyzed hydrogenation of styrene, is less favored than previously assumed. 34…”

In situ Transfer of Parahydrogen-Induced Nuclear Spin Polarization—Structural Characterization of Hydrogenation Intermediates

“…Again, phase cycling is used to eliminate all magnetization that has not been produced by the selective excitation sequence. Under the same experimental conditions as chosen for the experiments in Figure 2 but using the pulse sequence PH-1D-ROESY, very similar spectra are obtained Hexaaryltetragermabuta-1,3-diene: A Molecule with Conjugated Ge À Ge Double Bonds** Helmut Schäfer, Wolfgang Saak, and Manfred Weidenbruch* With the recent isolation of the first diplumbenes, [1,2] molecules containing a short lead ± lead double bond, homonuclear double bonds of the type R 2 EER 2 (E C, Si, Ge, Sn, Pb) are now known between all elements of Group 14. [3] The strong decrease in bond dissociation energies of these double bonds from silicon to lead is reflected in the distinctly different behavior in the crystalline state and in solution.…”

“…[1,2] The detection of these hydrogenation intermediates present in very low concentrations was possible using PHIP NMR spectroscopy (PHIP parahydrogen-induced polarization), which takes advantage of the large signal enhancement produced by the (pairwise) transfer of para-enriched hydrogen. [3,4] The intermediate product ± catalyst complexes have a life time of a few seconds at room temperature.…”

“…[2] Several facts indirectly lead to the conclusion that the arene ring of the product molecule, for a short time, remains h 6 -coordinated to the Rh I center. [1] However, no direct proof for the intermediate bonding between the catalyst and the product molecule could so far be obtained. Based on the PHIP effect, we present the first NMR experiments that detect intra-and intermolecular cross relaxation (NOE) [5] within the life time of a hydrogenation intermediate.…”

PHIP NMR Spectroscopy in Ionic Liquids: Influence of Salts on the Intensity of Polarization Signals

“…PHIP NMR spectroscopy (parahydrogen-induced polarization) is a powerful method for studying homogeneous hydrogenation reactions. − It is conducted by hydrogenating inside the NMR magnet using para-enriched hydrogen. In this way, polarization signals arise, given that the hydrogen molecule is transferred to the substrate in a pairwise fashion.…”