Homogeneous Gold Catalysis through Relativistic Effects: Addition of Water to Propyne

In the catalytic addition of water to propyne the Au(III) catalyst is not stable under non-relativistic conditions and dissociates into a Au(I) compound and Cl2. This implies that one link in the chain of events in the catalytic cycle is broken and relativity may well be seen as the reason why Au(III) compounds are effective catalysts.Comment: 12 pages, 3 figures, 1 tabl

Solvation of copper(II) sulfate in binary water/N,N-dimethylformamide mixtures: From the solution to the gas phase

The solvation of copper(II) sulfate in binary mixtures of water and N,N-dimethylformamide (DMF) is studied by a combined approach using electrochemical studies in solution and a mass spectrometric assay of the solvated ions formed from these solutions upon electrospray ionization (ESI). In the condensed phase, the limiting transference numbers (t±°) and the apparent ion association constants (KA'S) of CuSO4 have been determined in water/DMF solutions at 20 °C. The t+° values decrease with increasing DMF content, demonstrating a gradual solvation of Cu2+ by DMF molecules. The association constants indicate that aggregation becomes more pronounced as the DMF content increases. In order to achieve complementary insight, the intrinsic interactions among the ions and solvent molecules are investigated in gas-phase experiments of the CuSO 4/water/DMF system using ESI mass spectrometry. Under the conditions used, the dications [Cu(DMF)n]2+ (n = 3-6), [Cu 2(DMF)nSO4]2+ (n = 2-7), and [Cu3(DMF)n(SO4)2]2+ (n = 2-7), and the monocations [Cu(OH)(DMF)n]+, [Cu(DMF) n(HSO4)]+ (both, n = 1-3), and [Cu(DMF) n]+ (n = 1, 2), are formed as the leading copper-containing cations. Likewise, polynuclear copper clusters observed in the anion ESI spectra support partial aggregation occurring in solution. The gas-phase studies clearly support the conclusions that (i) DMF is a highly preferred ligand for CuII in comparison to water and that (ii) DMF supports ion association for which the mass spectrometric data suggest the formation of polynuclear copper clusters. © 2008 American Chemical Society

Monitoring Reaction Intermediates to Predict Enantioselectivity Using Mass Spectrometry**

Enantioselective reactions are at the core of chemical synthesis. Their development mostly relies on prior knowledge, laborious product analysis and post-rationalization by theoretical methods. Here, we introduce a simple and fast method to determine enantioselectivities based on mass spectrometry. The method is based on ion mobility separation of diastereomeric intermediates, formed from a chiral catalyst and prochiral reactants, and delayed reactant labeling experiments to link the mass spectra with the reaction kinetics in solution. The data provide rate constants along the reaction paths for the individual diastereomeric intermediates, revealing the origins of enantioselectivity. Using the derived kinetics, the enantioselectivity of the overall reaction can be predicted. Hence, this method can offer a rapid discovery and optimization of enantioselective reactions in the future. We illustrate the method for the addition of cyclopentadiene (CP) to an α,β-unsaturated aldehyde catalyzed by a diarylprolinol silyl ether