Observation of binuclear palladium clusters upon ESI-MS monitoring of the Suzuki–Miyaura cross-coupling catalyzed by a dichloro-bis(aminophosphine) complex of palladium

Electrospray ionization mass spectrometry (ESI-MS) is used for monitoring the progress of the Suzuki–Miyaura cross-coupling reaction between bromobenzene and arylboronic acids using a palladium dichloro-bis(aminophosphine) complex as a precatalyst. The ESI-MS studies demonstrate that initiation of the catalytic reaction requires the presence of a base and that the selectivity for cross-coupling is favorable at elevated temperatures. Interestingly, after completion of the coupling reaction, the palladium is present as a dinuclear Pd0/PdII cluster, which still acts as an active catalyst when a new aliquot of reactants is added to the reaction mixture

Deprotonation of <i>p-</i>Hydroxybenzoic Acid: Does Electrospray Ionization Sample Solution or Gas-Phase Structures?

Despite the simplicity of the molecule, the site of single deprotonation of <i>p-</i>hydroxybenzoic acid upon electrospray ionization (ESI) has recently formed a subject of debate in this journal. By means of NMR experiments in solution and gas-phase studies employing ion-mobility mass spectrometry (IM-MS), the apparent controversy is resolved. It is shown that irrespective of the solvent the carboxylate tautomer is preferred in solution, while the opposite holds true for isolated ions in the gas phase. The tautomer distribution sampled in the gas phase very much depends on the actual solvent used in ESI, the pH value, as well as the total concentration. Moreover, the occurrence of gas-phase reactions in the course of the ESI process influences the tautomer ratio. Implications for correlations between ESI mass spectra and solution-phase chemistry are discussed

Electrospray Ionization Mass Spectrometry Reveals an Unexpected Coupling Product in the Copper-Promoted Synthesis of Pyrazoles

The reaction mechanism of the intermolecular oxidative formation of pyrazole <b>2</b> via a C–C/N–N bond-formation cascade of the enaminone <b>1</b> is investigated by means of ESI-MS. No direct reaction intermediates are observed; however, the formation of an unexpected imidazolid-3-one derivative <b>X</b> is observed that involves an oxidative dimerization of <b>1</b> in the presence of dioxygen. The derivative <b>X</b> is isolated and characterized by means of multidimensional ¹H and ¹³C NMR spectroscopy