Substitution reactions of gaseous ions in a three‐dimensional quadrupole ion trap

Abstract

Substitution reactions between gaseous ions and neutral substrate molecules are of ongoing high interest. To investigate these processes in a qualitative and quantitative manner, we have constructed a device, with which a defined amount of a volatile substrate can be mixed with a defined amount of helium gas and added into a three‐dimensional quadrupole ion trap. From the known inner volume of the device, the known ratio nsubstrate:nHe of the mixture, and the determined absolute partial pressure of helium in the ion trap, we can derive the partial pressure of the substrate in the ion trap and, thus, convert the directly observable pseudo–first‐order rate constants of the substitution reactions into absolute bimolecular rate constants. We have tested the device by investigating a series of SN2 reactions of Br− and CF3CH2O− anions as well as ligand exchange reactions of ligated Na+ cations. As the obtained results suggest, the described device makes it possible to determine the bimolecular rate constants of substitution reactions as well as other ion‐molecule reactions with satisfactory accuracy and reliability.

Second Comes First: Switching Elementary Steps in Palladium‐Catalyzed Cross‐Coupling Reactions

“…Defined mixtures of neutral reactants and helium were prepared and introduced into the three-dimensional quadrupole ion trap using am ixing device, which has been described in detail previously. [36] Scheme3. Alternative catalytic cycle of aP d-catalyzedc ross-coupling reaction:formation of an organopalladate(0) intermediateb yt ransmetalation with an organometallic reagent R-M, subsequent oxidative addition of an organyl halide R'X, and reductive elimination of the cross-coupling product from the resultingn eutralintermediate or after afurthertransmetalation.…”

“…Ion‐molecule reactions in the gas phase were analyzed by means of an HCT quadrupole‐ion trap mass spectrometer (Bruker Daltonik). Defined mixtures of neutral reactants and helium were prepared and introduced into the three‐dimensional quadrupole ion trap using a mixing device, which has been described in detail previously …”

Towards Higher Sensitivity of Mass Spectrometry: A Perspective From the Mass Analyzers

“…The ion trap mass analyzer has played an important role in expanding the field of proteomics (Mayya et al, 2005;Blackler et al, 2006). It is also used to investigate the chemical reaction of gas phase ions (Guo et al, 2015;Parchomyk and Koszinowski, 2019). But there are strong Coulomb interactions among the large number of ions trapped in the ion trap, resulting in space charge effects.…”

Constitution and Reactivity of Palladium Ate Complexes in Cross-Coupling Reactions

“…An alternative method which avoids these difficulties is the preparation of a well-defined mixture of the substrate gas with helium, which is then added to the reaction chamber at a constant flow rate. [69] Massselected ions of interest can then be kept inside the reaction chamber for defined storage times and their reaction with the substrate gas can be monitored based on the relative signal intensites of precursor and product ions.…”

“…However, Absolute bimolecular rate constants k 2 can be calculated from k 1 by dividing it by the number density of the substrate N S inside the ion trap (equation (4.44)). [69] The number density N S is derived from the absolute helium pressure inside the ion trap p He and the amounts of helium and substrate gas in the ion trap, n He and n S . Both amounts are accessible by the amounts of substrate gas and helium introduced into the gas mixing chamber, n He,GMC and n S,GMC (equations (4.45) and (4.46) with M He and M S representing the molar mass of helium and the substrate gas).…”